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s m i t h s o n i a n c o n t r i b u t i o n s t o z o o l o g y • n u m b e r 6 2 7

The Therian Skull

A Lexicon with

Emphasis on the Odontocetes

J. G. Mead and R. E. Fordyce
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s m i t h s o n i a n c o n t r i b u t i o n s t o z o o l o g y • n u m b e r 6 2 7

The Therian Skull

A Lexicon with

Emphasis on the Odontocetes

J. G. Mead and R. E. Fordyce

washington d.c.

2009
ABSTRACT

Mead, J. G., and R. E. Fordyce. The Therian Skull: A Lexicon with Emphasis on the Odontocetes. Smithsonian Contributions to Zoology, number 627, 248 pages, frontispiece, 2 diagrams, 

32 figures, 9 tables, 2009. — Cetaceans form one of the most unique groups in the evolutionary 

history of mammals. They have returned to the sea and modified their tail as an efficient means of 

locomotion. As they adapted to the limited visibility in the aquatic environment, the odontocetes 

developed a system of echolocation that resulted in extensive modifications to the skull bones. 

This made descriptive comparisons very difficult and early anatomists unwittingly composed new 

terms for anatomical structures that had already been named in other taxa. This made anatomical 

comparisons, based on the literature, extremely tenuous.

This lexicon is an attempt to remedy that situation in that it provides headwords and definitions for all the terms that have been used in describing the mammal skull and notes the synonymous terms. The lexicon includes the human nomenclature (Nomina Anatomica), the veterinary 

nomenclature (Nomina Anatomica Veterinaria) and the nomenclature that is used in descriptive 

comparative anatomy. The lexicon covers not only extant but extinct mammalian groups and is 

extensively indexed.

Cover: Detail from Frontispiece, illustration of a dolphin skull (cf. Delphinus sp.) presented by 

Gesner (1560). 

Published by Smithsonian Institution Scholarly Press

P.O. Box 37012, MRC 957

Washington, D.C. 20013-7012

www.scholarlypress.si.edu

Library of Congress Cataloging-in-Publication Data

Mead, James G.

The therian skull : a lexicon with emphasis on the odontocetes / J. G. Mead and R. E. Fordyce.

 p. cm. — (Smithsonian contributions to zoology, ISSN 0081-0282 ; no. 627)

Includes bibliographical references and index.

1. Skull—Dictionaries. 2. Mammals—Anatomy. 3. Cetacea—Anatomy. 4. Anatomy, 

Comparative. I. Fordyce, R. Ewan. II. Title. 

QL822M43 2009

571.3'195—dc22

2007045891

∞ The paper used in this publication meets the minimum requirements of the American National 

Standard for Permanence of Paper for Printed Library Materials Z39.48–1992.
Dedication

The authors dedicate this work to the memory of 

Dr. John E. Heyning (6 January 1957–17 February 2007), 

who was a colleague in anatomy, a fellow museum curator, 

and a valued friend.
Frontispiece. Dolphin skull (cf. Delphinus spp.) with the caption “Delphini Calvaria è libro Bellonij” presented by Gesner (1560:162).
Contents

LIST OF ILLUSTRATIONS vii

LIST OF TABLES ix

INTRODUCTION 1

History 1

Evolutionary Changes 2

MATERIALS AND METHODS 3

Protocol for Terms in the Lexicon 3

 Priority 4

 Embryological Terms 4

 Orientation Terms and Terms that Imply Size, Shape,

 and Proportion 4

 Eponymous Terms 5

 Usage of Terms 5

 Absence of Landmarks 5

 Illustrations 5

 Separate Treatment of Bones Associated with the Ear 5

Craniometric Landmarks 5

Specimens Used 5

OSTEOLOGICAL RELATIONSHIPS OF THE SKULL BONES 6

Types of Features 6

Topographic Relationships of the Bones 6

Cranial Nerves 6

GUIDE TO LEXICON ENTRIES 10

LEXICON 11

Basioccipital Bone 11

Ethmoid Bone 13

Exoccipital Bone 17

Frontal Bone 24

Hyoid Apparatus 32

Interparietal Bone 33

Jugal Bone 35

Lacrimal Bone 38

Mandible 42
v i • smithsonian contributions to zoolog y

Maxilla 48

Nasal Bone 68

Palatine Bone 70

Parietal Bone 76

Premaxilla 79

Pterygoid Bone 82

Septomaxilla 90

Sphenoid Bone 90

Squamosal Bone 102

Supraoccipital Bone 108

Tympanoperiotic Complex 111

 Periotic Bone 111

 Tympanic Bulla 133

Auditory Ossicles 149

 Malleus 149

 Incus 151

 Stapes 151

Vomer 151

MULTI-ELEMENT COMPLEXES: STRUCTURES SHARED BY

ADJACENT BONES 154

Topographic Features 154

 The Rostrum 154

 Antorbital Region 154

 Facial Region 154

 The Palate and Pterygopalatine Fossa 154

 The Cranium 154

 Vertex 155

 Occipital Area 155

 Zygomatic Arch and Temporal Fossa 155

 Orbit and Orbital Fissure 155

 Basicranium 155

 Tympanoperiotic 155

 Cranial Hiatus 155

 Pterygoid Sinus Complex 156

 Venous Sinus System 156

 Mandible and Mandibular Foramen 156

Transmission of Vessels, Nerves, and Passages 156

 Infraorbital Complex 156

 Nasal Passages 156

 Nares 156

 Nasal Cavity 157

 Basipharyngeal Canal 157

 Paranasal Sinuses 157

 Arterial Circulation and Basicranial Foramina 157

FIGURES 159

ACKNOWLEDGMENTS 201

APPENDIX A. Historical Terminology of the Cranial

Nerves 203

APPENDIX B. Skull Measurements for Delphinids 205

REFERENCES 207

INDEX 217
Illustrations

Cover. Detail from Frontispiece.

Frontispiece. Dolphin skull (cf. Delphinus spp.) presented by Gesner 

(1560). iv

Diagram 1. Schematic cross section of the rostrum and antorbital fossa. 50

Diagram 2. Schematic dorsal view around the antorbital notch in 

Odontoceti. 51

Figure 1. Intact skull of adult specimen, dorsal view. 160

Figure 2. Intact skull of adult specimen, ventral view. 161

Figure 3. Intact skull of adult specimen, lateral view. 162

Figure 4. Intact skull of adult specimen, anterior view. 162

Figure 5. Intact skull of adult specimen, posterior view. 163

Figure 6a–f. Intact neonatal skull. 164

Figure 6g–i. Disarticulated neonatal skull (g) and anterodorsal views of 

young (h) and adult (i) specimens. 165

Figure 7. Disarticulated neonatal skull, basioccipital. 166

Figure 8. Disarticulated neonatal skull, ethmoid. 167

Figure 9. Disarticulated neonatal skull, exoccipital. 168

Figure 10. Disarticulated neonatal skull, frontal. 169

Figure 11. Disarticulated neonatal skull, hyoid. 170

Figure 12. Disarticulated neonatal skull, interparietal. 171

Figure 13. Disarticulated neonatal skull, jugal. 172

Figure 14. Disarticulated neonatal skull, lacrimal. 173

Figure 15. Disarticulated neonatal skull, mandible. 174

Figure 16. Disarticulated neonatal skull, maxilla. 175

Figure 17. Disarticulated neonatal skull, nasal. 176

Figure 18. Disarticulated neonatal skull, palatine. 177

Figure 19. Disarticulated neonatal skull, parietal. 178

Figure 20. Disarticulated neonatal skull, premaxilla. 179

Figure 21. Disarticulated neonatal skull, pterygoid. 180

Figure 22. Disarticulated neonatal skull, sphenoid. 181

Figure 23. Disarticulated neonatal skull, squamosal. 182

Figure 24. Disarticulated neonatal skull, supraoccipital. 183
v i i i • smithsonian contributions to zoolog y

Figure 25a–c. Disarticulated neonatal skull, tympanoperiotic. 184

Figure 25d,e. Disarticulated neonatal skull, tympanic, right. 185

Figure 25f–k. Adult skull, tympanic, right. 186

Figure 25l–q. Adult skull, periotic, right. 187

Figure 25r,s. Adult skull, tympanic and malleus, left. 188

Figure 25t–v. Adult skull, periotic, left. 189

Figure 25w,x. Adult skull, sectioned tympanoperiotic, right. 190

Figure 25y. Disarticulated neonatal skull, tympanoperiotic, left. 191

Figure 26a–f. Skull of juvenile specimen, malleus, right. 192

Figure 26g–l. Skull of juvenile specimen, incus, right. 193

Figure 26m–r. Skull of juvenile specimen, stapes, right. 194

Figure 27. Disarticulated neonatal skull, vomer. 195

Figure 28. Disarticulated neonatal skull, basicranium, right, 

dorsal view. 196

Figure 29. Disarticulated neonatal skull, bulla, right, 

ventrolateral view. 197

Figure 30. Skull of adult specimen, basicranium, right, 

ventrolateral view. 198

Figure 31. Skull of adult specimen, cranium, left, interior view. 199

Figure 32. Skull of adult specimen, orbit, left, lateral view. 200
Tables

1. Craniometric points and the bones under which they are discussed. 5

2. Specimens of the bottlenose dolphin Tursiops truncatus in the 

collection of the United States National of Museum Natural 

History. 6

3. Topographic relationships between bony skull elements for two 

mammals. 7

4. Terms applied to the mammalian skull region that includes 

the cranial hiatus. 23

5. Terms used by selected authors to designate landmarks in 

vicinity of the antorbital notch. 52

6. Terms used by selected authors for antorbital canal and its 

distal and proximal openings. 60

7. Components of the pterygoid sinus complex in odontocetes. 84

8. Summary of homologies of some bullar and associated 

structures in Tursiops and Odocoileus. 144

9. Terminology for narial openings used by selected authors. 157

The Therian Skull: A Lexicon 

with Emphasis on the Odontocetes

Because of the perfected adaptation to a completely aquatic life, with all its attendant conditions of respiration, circulation, 

dentition, locomotion, etc., the cetaceans are on the whole the most peculiar and aberrant of mammals.

—G. G. Simpson (1945:213)

INTRODUCTION

Cetaceans are a highly specialized order of mammals. Anatomists have long 

been interested in them because they are radically different from other aquatic 

orders and from terrestrial mammals. Early systematists attempted to describe 

the differences using terms that were readily available from existing anatomical vocabulary or by creating new terms. Over the years, a literature developed full of 

vaguely defined or mistaken terminology.

The authors have undertaken this project in an attempt to develop a dictionary that 

defines terms used to describe osteological landmarks on the skulls of one family of cetaceans, the delphinid odontocetes (dolphins).

One failing of current published anatomical literature dealing with animals other 

than humans and nondomesticated mammals is an emphasis on the unusual. Detailed 

descriptions exist for the rare species and nothing for commonplace animals. Thus, little 

exists for truly comparative analysis. It was with this in mind that the authors set out to 

create this dictionary. We have attempted to treat every term that pertains to landmarks 

in the mammalian skull.

The following classic works were used as primary sources: Owen (1866a) on the 

dwarf sperm whale (Kogia sima), Anderson (1879) on the Ganges river dolphin (Platanista gangetica) and the Irawaddy river dolphin (Orcaella brevirostris), Schulte (1917) on 

the pygmy sperm whale (Kogia breviceps), and Kernan (1918) on the goosebeaked whale 

(Ziphius cavirostris). Other heavily used sources were those of Boenninghaus (1904) on 

the ear region of odontocetes, Fraser and Purves (1960) on hearing in whales, and van 

der Klaauw (1931) on the tympanic bulla in fossil mammals.

Several contributions on noncetacean mammals, both living and extinct, were particularly useful to elucidate the origin of cetacean terms, or to identify terms that might be 

applied to the cetacean skull. Of note are Evans and Christensen (1979) on the domestic 

dog (see also Evans, 1993), MacPhee (1981) on the primate and insectivore basicranium, 

Novacek (1986) on leptictid insectivores, and Wible and Gaudin (2004) on armadillos.

History

As long as humans have been in contact with the sea, there has been an interest in Cetacea. Aristotle, a Greek naturalist philosopher (384–322 bc), was the first author to treat 

cetaceans biologically. He was familiar with both great whales and dolphins, although it is 

now impossible to tell how much he knew from first-hand observation and how much was 

based on conversations with fishermen. Nonetheless, he clearly understood that cetaceans 

were mammals and that they suckled their young, breathed air, and had hair.

Pliny the Elder, the Roman philosopher and scholar (ad 23–79), was a prolific compiler of natural history. In the preface to his main work, Naturalis Istoria, he claimed to 

James G. Mead, Division of Mammals, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20013-7012, 

USA; R. Ewan Fordyce, Research Associate, 

Division of Mammals, Department of Geology, University of Otago, Post Office Box 56, 

Dunedin, New Zealand. Manuscript received 

6 June 2007; accepted 22 August 2007.
2 • smithsonian contributions to zoolog y the therian skull

have assembled 20,000 facts from 2,000 books written by 100 

authors. Most of the works that Pliny cited have disappeared, but 

the information extracted has persisted. In the sixteenth century, 

libraries began to include anatomical works by authors who had 

first-hand experience with cetacean anatomy. Two ichthyologists, Pierre Belon (1551, 1553) and Guilliame Rondelet (1554), 

wrote monographs on fish anatomy in which they included cetaceans. Belon (1553:14) illustrated a skull of a dolphin that might 

have been the specimen that Craigie (1831:45) said Belon found 

on the shore of the “Cimmerian Bosphorus.” Conrad Gesner 

(1560:162), whom many people style the father of natural history, presented a figure of a dolphin skull with the caption “Delphini Calvaria è libro Bellonij” that looks like the skull that Belon 

(1553:14) illustrated but in a better state of preparation. We have 

reproduced Gesner’s illustration as the frontispiece of this work. 

Gesner obtained most, if not all of his information concerning 

cetaceans from Belon and Rondelet. Edward Tyson (1680) was 

the first to treat the anatomy of a cetacean in a work devoted 

solely to that purpose. In 1787 John Hunter presented a paper, 

“Observations on the Structure and Oeconomy of Whales,” to 

the Royal Society of London. These works dealt primarily with 

soft-part anatomy, as did others of their time. Hunter and others 

of his generation had medical training and used terms that were 

oriented toward human anatomy.

It was not until the classic studies of Georges Cuvier (1769–

1832) that scientific interest in the skeleton became widespread. 

His Recherches sur les Ossemens Fossiles de Quadrupèdes

(1821–1823) and Leçons d’Anatomie Comparée (1835–1846) 

are seminal academic works.

As more studies were done on a variety of animals, it became 

apparent that structures were present in nonhuman mammals 

that were not present in humans, and the body of comparative 

anatomical terms began to expand. It was with the works of 

Richard Owen (1804–1892) and William Henry Flower (1831–

1899) that comparative studies reached a peak. Flower was the 

first person to take an evolutionary approach, in the Darwinian 

sense, to cetacean anatomy. Two works have become classical 

references: Owen’s (1866b–1868) On the Anatomy of Vertebrates and Flower’s (1885) An Introduction to the Osteology of 

the Mammalia.

When comparative anatomy became a recognized academic 

field, the vocabulary increased exponentially. Many terms were 

coined to document diversity of form and to avoid confusion 

with terms used for human descriptive anatomy. In addition, veterinary anatomy produced terminology that hybridized human 

and nonhuman mammalian terms. Studies on cetaceans were 

performed as material became available. Anatomists were dealing with anatomical structures of uncertain origin and function, 

and studies were not always performed on the freshest of specimens. Some workers, frustrated with the uncertain definitions 

and homologies of past works, contributed terms that seemed 

more appropriately descriptive. As a result, cetacean terminology 

did not develop consistent anatomical standards.

Evolutionary Changes

Cetacean skulls have radically diverged from the skulls of 

terrestrial mammals. In both suborders of living cetaceans, the 

skull has been extremely modified in terms of location of external 

nares, structural modification of middle and inner ear, changes 

in feeding apparatus, and elimination or reduction of structures. 

Homology and analogy have always been of concern to evolutionary biologists, and problems have been compounded by differences in terminology. The basic problem is the difficulty in 

recognizing structures that have a common evolutionary origin.

The topographic changes of cetaceans are obviously the result of aquatic adaptation. Changes in cetacean skulls are best 

viewed in terms of functional complexes. These complexes include feeding, breathing, sound production, sound reception, 

and locomotion. Individual changes usually overlap two or more 

functional areas.

In the head, the rostrum has elongated and the position of 

the external nares has shifted to a more dorsal position, altering the relationship of the nose to the eye and ear. The ear has 

become highly modified in response to the aquatic environment. 

The external ear has disappeared and is represented by vestigial 

cartilage. The middle and inner ears have become isolated from 

the surrounding skull bones and have changed their morphology 

drastically, reducing bony conduction of sound.

In odontocetes, the soft tissue between the mouth and the 

nose—the upper lip—has become hypertrophied in association 

with development of the melon and associated musculature and 

nasal diverticula or epicranial sinuses. The melon is a subdermal structure composed of layers of lipids of differing composition that function in acoustic transmission. Correlated with this 

change is the differentiation of a number of lipid bodies associated with the lower jaw and ear. The shape of the melon body 

differs from the external profile of the head, which could reflect 

sexual or other modes of selection. The melon makes possible the 

development of impressive foreheads seen in such species as pilot 

whales, belugas, bottlenose whales, and finless porpoises. The 

spermaceti organ in sperm whales is derived from different anatomical origins but is possibly functionally similar to the melon. 

In addition to the melon, the muscles and nasal diverticula associated with the complicated external nasal passage have an effect 

on the morphology of the underlying bones (Mead, 1975).

The pterygoid bones surrounding the internal nares have 

become modified to form pterygoid sinuses. The pterygoids have 

joined ventrally to form the posterior margin of the hard palate. 

The lamina of the pterygoid has split into lateral and medial portions and has been invaded by an air sinus that is an extension 

of the middle ear cavity. This sinus system is commonly referred 

to as the pterygoid sinus system. It consists of a number of basicranial sinuses and bony fossae that may or may not be directly 

related to the pterygoid sinus. This system has been thoroughly 

described in a monograph by Fraser and Purves (1960).

The external nares of cetaceans began their posterodorsal 

migration shortly after they diverged from terrestrial mammals, 

resulting in changes to the relative positions of the skull bones in 

both mysticetes and odontocetes. Breathing and, possibly, sound 

production were two of the factors driving the changes. The 

rapid exchange of air that is necessary in an active, air breathing, 

aquatic organism was responsible for simplification of the bony 

nasal passage, formation of a palatal sphincter, and elimination 

of nasal turbinates and olfaction in odontocetes.

A new term introduced by Winge (1918) to explain the overall result of the changes was sammenskudt, translated by Miller as 

“telescoping.” Subsequently, Miller (1923) used “telescoping” in 
a l e x i c o n n u m b e r 6 2 7 • 3

a paper describing the structural relationships of the skull elements 

in archaeocetes, mysticetes, and odontocetes. Although neither 

Winge (1921) nor Miller (1923) defined it, the term “telescoping” 

has been applied in comparing relationships of bony elements in 

cetaceans to the overlapping tubes of a telescope. The Century 

Dictionary (Whitney, 1989–1910:[vol. 8]6218) provided this definition: “telescope, v. to drive into one another like the movable 

joints or slides of a spy glass; as ‘in the collision the forward cars 

were telescoped’; to shut up or protrude like a jointed telescope.”

All these adaptations result in extensive changes in the 

skulls. Cladistic analysis shows that there are four styles of telescoping: (a) facial telescoping in odontocetes, (b) facial telescoping in mysticetes, (c) supraoccipital telescoping in odontocetes, 

and (d) supraoccipital telescoping in mysticetes. Widening, flattening, and thickening of the occipital bones at the rear of the 

skull allows for stronger attachment of more muscles associated 

with locomotion without limb involvement. Facial telescoping in 

(a) and (b) also involves movement of the nares independent of 

changes in the maxilla and premaxilla.

Changes in both odontocetes and mysticetes are most dramatic in non-braincase structures. In odontocetes the rostral elements (maxilla and premaxilla) move dorsally and posteriorly 

over the cranium to form elements of the facial region. In mysticetes the rostrum is expanded anteriorly and the rostral elements 

do not move back over the cranium. In extant odontocetes the 

occipital elements move slightly anteriorly so that the parietal 

is excluded from the dorsal midline by the interparietal and the 

supraoccipital bones. In mysticetes the external borders of the 

occipital elements move radically farther anteriorly and the supraoccipital lies far forward of the braincase. The braincase does 

change, but in more subtle ways. The sum total of changes results in odontocete skulls that are strikingly asymmetrical.

The rostrum or snout is extremely plastic in mammals, with 

marked evolutionary changes in length and width. Once cetacean 

teeth had simplified, it was a relatively simple matter to increase 

the length of the rostrum and number of teeth to form impressive 

specializations for use in manipulation and feeding.

The entire paranasal sinus complex (frontal, maxillary, and 

sphenoid sinuses) is lost in living cetaceans, involving the maxilla, 

frontal, ethmoid, and sphenoid bones. Some of the paranasal sinuses are still present in some archaeocetes (Kellogg, 1936), and 

it is possible that some cranial foramina in living Cetacea are vestigial and once associated with the paranasal sinuses.

The throat of cetaceans has been modified to form a more 

efficient food passage for mammals that swallow their food 

whole. The balaenopterid mysticetes have developed a specialization, the cavum ventrale, that permits expansion of the mouth 

to accommodate the schools of fish and crustaceans on which 

they feed. The odontocete nasopharynx became modified into a 

sphincter that holds the larynx and provides a relatively strong 

continuous air passage between the lungs and the nasal diverticula or epicranial sinuses. This modification is important in 

providing a mechanism by which feeding and echolocation can 

take place simultaneously.

In the axial and appendicular elements of cetaceans, there 

has been considerable change. There has been a tendency to fuse 

anterior cervical vertebrae. The sacral region has been lost in 

all living whales and the caudal region has retained the usual 

mammalian variation in both living and fossil species. Only the 

thoracic and lumbar series have remained relatively stable in 

number. The other axial elements associated with the vertebral 

column (ribs and sternal elements) have varied in number depending on the variation in thoracic count.

Multiplication or reduction has occurred in areas where 

there are serial elements that are functionally similar. These areas 

in mammals include the digits of the limbs, the teeth, and the vertebrae and ribs. Cetaceans have not increased the primitive number of digits, but hyperphalangy is widespread. Once the teeth 

began to simplify, they either increased or decreased beyond the 

primitive mammalian count of 11 per jaw (total of 44). Mysticetes lost all adult teeth but still have a number of tooth buds 

in utero. In all odontocete males there is at least one erupted 

tooth. Females and young of some species remain edentulous, 

although teeth are present as vestiges. When the number of teeth 

increased, they became morphologically similar and conical in 

shape. The La Plata River dolphin (Pontoporia blainvillei) represents the most extreme increase, with a total of 242 teeth.

MATERIALS AND METHODS

Protocol for Terms in the Lexicon

The course of cetacean evolution has resulted in skulls in 

which the homologies with terrestrial mammals and humans are 

sometimes uncertain. For one cetacean species, the bottlenose 

dolphin (Tursiops truncatus), we have attempted to homologize 

the osteological landmarks we found with features recognized in 

Nomina Anatomica Veterinaria (3rd edition, ICGVAN, 1983), 

Nomina Anatomica (5th edition, IANC, 1983), and current 

comparative anatomical usage. That is, we attempted to treat 

every term that pertains to landmarks in the mammalian skull. 

We used Schaller (1992) extensively because this work included 

all the terms that the Nomina Anatomica Veterinaria recognized, and we used Feneis (1994) because it did the same for 

Nomina Anatomica. In citing these works we used the following 

format: publication year:page number.reference number used by 

the author for the structure in the author’s figure (e.g., Schaller, 

1992:14.9 for canalis nasolacrimalis). We used the 1918 edition 

of Gray’s Anatomy of the Human Body in preference to more 

recent editions because we felt there was a tendency in later editions to reduce the anatomical detail.

In dealing with an anatomical system that has become so 

changed by evolution as the cetacean skull, we continually found 

structures that were radically modified morphologically but were 

homologous with structures in other mammals. If the structure 

in cetaceans could be satisfactorily derived from another structure in terrestrial mammals, we considered the structures to be 

homologous.

We generally restricted our observations to the bottlenose 

dolphin, but wherever enough data were available, we extended 

the observations to the family level (Delphinidae) or to the suborder (Odontoceti) or order (Cetacea).

We realize that our conclusions will have importance beyond 

the bottlenose dolphin and should be applicable to the entire 

order, both fossil and recent. Thus, we took pains to not “paint 

ourselves into a corner” and considered the situation, where appropriate, in mysticetes and fossil taxa, including archaeocetes.
4 • smithsonian contributions to zoolog y the therian skull

By “Cetacea” we mean the living Odontoceti and Mysticeti 

and their close fossil relatives. These represent the crown-group 

Cetacea or Neoceti—living odontocetes and mysticetes, plus all 

fossil descendants of their most recent common ancestor. We 

give only occasional mention of stem-Cetacea, the wholly extinct 

Archaeoceti.

In the Lexicon, we differentiated the formal Latin terms in 

the heading by putting them in parentheses. We then used the 

English term as the preferred term in the text. If there did not 

appear to be an English term for the structure, we translated the 

Latin term and put the English term in the heading. We realized 

that some Latin terms have become universally used (e.g., sella 

turcica) and the English translation (Turk’s saddle) would not 

be an appropriate preferred term, so we have used the Latin. 

Other Latin terms that we retained as preferred include the foramen magnum and foramina ovale and rotundum.

Priority

In deciding which term to use, we have weighed the earliest usage of a term for a feature, the number of authors who 

have used the term, the etymological correctness of the term, 

conflicting and/or ambiguous usage, and whether the term was 

used in the anatomical standards (Nomina Anatomica, Nomina 

Anatomica Veterinaria). Some historical terms were never used 

after their proposal and have been forgotten, and new synonymous terms were published much later. In such cases, the older 

terms might be viewed as nomina oblita and not worthy of being 

resurrected. 

For Cetacea it is desirable to use terms that are applied in 

other mammals unless the feature in Cetacea is so highly modified 

that the normal mammalian term is misleading; in such cases, we 

indicate the homology (see, e.g., tegmen tympani). We have not 

adhered strictly to one system or another, nor used strict priority 

rules, but have provided cross-references and an extensive index.

Where the arguments for and against using a term were 

equal, we have used Flower’s (1885) introduction to the osteology of the Mammalia, which was the first osteological work 

based on evolutionary thought.

We have not imposed a strict chronological priority system 

but returned to what most people consider the foundation of 

modern anatomy, Vesalius’ 1543 Fabrica, and considered the 

terms that Vesalius used in the figures for the skull (liber I, capita 

6–12). Our research was made easier by Richardson and Carman’s translation of Vesalius (Vesalius et al., 1998), particularly 

the table compiled by Richardson and Carman listing all the 

identifiable foramina of the head and upper jaw. 

In our definitions of the foramina, we have inserted the 

Latin terms that Vesalius used in his 1543 edition. We felt that it 

would be valuable as a temporal landmark to demonstrate either 

the name or phrase that Vesalius used in speaking of the foramina. We also consulted a later edition of Vesalius’ osteological 

work (Vesalius and Sandifort, 1782), and examined Lancisius’ 

publication of Eustachius’ plates (Eustachius and Lancisius, 

1714). The nomenclature of those plates was supplied by Lancisius and was in vogue at the beginning eighteenth century, not 

during Eustachius’ lifetime (1520–1574). Although Eustachius 

was a contemporary of Vesalius and did equally detailed work, 

his results were not published until 1714.

One significant anatomical author antedates Vesalius­—

Galen. Charles Singer (Galen and Singer, 1956:xviii), in his translation of Galen’s work of ad 177, said:

The Greeks, unlike ourselves, had no classical language from which to draw scientific terms. These they 

made either by combinations of words, or by giving 

ordinary words a special meaning, or by using short 

descriptive clauses. Taking examples from our text, 

one illustrative of the first method is PERIKRANION, 

“around the cranium”; of the second is KONARION, 

“cone-shaped thing,” pineal gland; of the third is O 

TOU BRACHIONOS PROSTHIOS MYS, “the anterior muscle of the arm,” biceps. Manifestly these terms 

were far less distinctive for Greek speakers than are 

their equivalents for English speakers. It is especially 

for the description of muscles, vessels, and nerves that 

the text presents difficulties to the translator. The obstacles to understanding for those ancient readers who 

did not dissect and had no anatomical figures were 

insuperable. Until modern times, and until the revival 

of the practice of dissection and the introduction of 

representational art, the anatomical works of Galen 

were almost incomprehensible.

Embryological Terms

Terms included in the Lexicon generally do not include embryological terms unless such names have also been applied to 

adult cetaceans and other placental mammals considered in our 

main sources of literature.

Orientation Terms and Terms that Imply 

Size, Shape, and Proportion

Many orientation terms have become incorporated into 

names of bony features. For example, terms for the ear include anterior process (of periotic), posterior process (of tympanic bulla), 

lateral tuberosity (of periotic), and dorsal surface of pars cochlearis (of periotic). Some of these terms reflect the orientation of a 

part as seen in a particular species of cetacean, which could be an 

extinct species, or the orientation as seen in other placental mammals. Because of evolutionary changes in the orientation of parts 

of the cetacean skull, a particular structure may no longer face the 

direction that its name suggests. This is particularly the case for 

the ear region. Thus, the long axis of the tympanoperiotic complex 

in many living odontocetes commonly faces somewhat anteromedially rather than anteroposteriorly and, in the extreme case of 

pygmy sperm whales, Kogia spp., the long axis faces markedly anteromedially. In Kogia spp., also, the periotic is rotated so that the 

cerebral surface, which is homologous with the dorsal surface in 

some other living and many extinct Cetacea, faces dorsomedially.

To aid comparison, and circumvent problems created by 

variable orientations among species, we used anatomical terms 

that have an orientation component (e.g., anterior process, posterior process) as if the structures are actually oriented as their 

name suggests. Such use requires that we separately describe the 

actual orientation of the part in the broader context of the skull.

The terms “major” and “minor” are preferred over “greater” 

and “lesser”; we consider that the latter do not create synonyms.
a l e x i c o n n u m b e r 6 2 7 • 5

Many names as used originally were hyphenated. In general, 

we have stripped hyphens except where quoting in the original 

context.

Descriptive terms such as “angle” and “tubercle” may convey to different readers quite different concepts of profile or 

degree of development. Where a skull feature consistently has 

a shape or size that suits such terms as angle or tubercle, we retained the particular term, but in general we prefer to use more 

generic terms such as “process.”

Eponymous Terms

Where they have been in wide use, or are less contentious 

than certain descriptive terms that do not always apply across a 

range of species, we accepted eponymous anatomical terms, such 

as Eustachian tube and Meckel’s cartilage.

Usage of Terms

We have gone to more effort in researching the usage of 

these terms than is obvious from the citations we provided for 

the terms, but we felt that to give a blow-by-blow account of 

each term would not be useful.

As an example, the case of the foramina and canals on the 

maxilla that contain the branches of the infraorbital nerve and 

vessels deserves some mention. In researching the terms that had 

been used for the openings, we found antorbital, infraorbital, 

maxillary, suborbital, and supraorbital, and the canal also had 

been referred to as antorbital and infraorbital. There was no unambiguous way to refer to these structures, so we felt obliged 

to coin new terms. We chose the “internal maxillary foramen” 

for the proximal opening, “external maxillary foramen” for the 

distal opening, and “infraorbital canal” for the canal. A detailed 

discussion of our reasoning is provided in the section on the infraorbital canal under “Maxilla.”

We use “jugal” because of the confusion with the multiple 

features that are termed zygomatic; we prefer to use “zygomatic” 

to refer to the arch rather than the bone.

Absence of Landmarks

It can be difficult to deal with some structures that cetaceans 

supposedly lack, such as the lacrimal gland and paranasal sinuses. 

If we were able to locate the osteological features that define the 

structure in other mammals, we named the feature. A good example of this is the anterior lacrimal crest on the maxilla. In dealing 

with these cases, we still need studies of the soft anatomy, including histology, to be absolutely certain of the correct term.

Illustrations

One outstanding requirement for a work such as this is adequate illustrations. We have illustrated an intact neonate skull 

and adult bottlenose dolphin skulls from the standard anatomical views (dorsal, ventral, anterior, posterior, and lateral). We 

have also provided oblique views in areas where the orthogonal 

views did not portray a feature adequately. We then illustrated 

the individual bones in a disarticulated skull of a newborn bottlenose dolphin from all five anatomical viewpoints.

Separate Treatment of Bones Associated with the Ear

As anyone who has looked into the systematic importance 

of the skull bones realizes, the bones associated with the ear are 

very important. The importance that we attached to them will be 

evident by the number of pages in the text and the number of illustrations devoted to them. We felt that these bones constituted 

an important subsystem and deserved to be treated accordingly.

Craniometric Landmarks

We have treated all the craniometric terms included in Nomina Anatomica, although many of them involved points that 

could not be found on a delphinid skull. We illustrated those that 

could be located, and the others are discussed under the bones on 

which they were located (Table 1).

Specimens Used

We were greatly assisted in this project by having access to 

an outstanding collection of bottlenose dolphin skulls. We were 

able to take individual and ontogenetic variation into account 

when considering the identity of structures. Table 2 gives data 

on the specimens on which we relied.

For comparative purposes we also used the following specimens from the collections of the National Museum of Natural History: the skull of an adult white-tailed deer (Odocoileus 

virginianus) from Maryland that had been sectioned along the 

sagittal plane (from the comparative collection, Division of 

Vertebrate Paleontology); three adult skulls of un-cataloged 

Table 1. Craniometric points and the bone sections under 

which they are discussed.

Craniometric Term used in 

point this work Bone

Asterion Mastoid angle Parietal

Basion Basion Exoccipital

Bregma Frontal angle Parietal

Clivus Clivus Basioccipital

Frons Frons Frontal

Gnathion Gnathion Mandible

Gonion Gonion Mandible

Inion External occipital protuberance Interparietal

Lambda Occipital angle Parietal

Nasion Occipital angle, sphenoidal angle Parietal

Occiput Occiput Supraoccipital

Ophryon Frontal angle Parietal

Opisthion Opisthion Supraoccipital

Opisthion Occipital angle Parietal

Pogonion Pogonion Mandible

Prosthion Prosthion Premaxilla

Pterion Sphenoidal angle Parietal

Sinciput Sinciput Frontal

Vertex Vertex Frontal
6 • smithsonian contributions to zoolog y the therian skull

potential dog/red wolf/coyote hybrids, (1) broken skull #1299, 

(2) sagittally sectioned female skull #1221, and (3) intact skull 

#1266 (from the National Biological Service, U.S. Department 

of the Interior collections at the USNM); and a human skull (sex 

unknown) from the Division of Mammals, USNM 301622.

OSTEOLOGICAL RELATIONSHIPS

OF THE SKULL BONES

Types of Features

Osteological features found on the bones of the skull consist 

of either protuberances or lack of bone.

Features Involving a Lack of Bone

alveoli fossae pores

aperturae fossulae sellae

aqueducti foveae semicanales

canales hiates sinuses

canaliculi impressiones sulci

cavitas incisura vestibuli

fissura infundibula

foramina labyrinthi

Protuberances

alae crura rami

anguli eminentia rostra

anuli facies septa

apices hamuli spinae

arci juga squamata

bases laminae suturae

bullae linea symphyses

capita lingula tegmina

choanae marginis tori

colla meatuses tuber

condyles partes tubercula

corpora plana tuberositas

cristae processes

Topographic Relationships of the Bones

Table 3 lists the relationships between the skull bones of 

a generalized terrestrial mammal (Canis lupis) and a delphinid 

(Tursiops truncatus). There is some degree of subjectivity in the 

relationships because the bony elements are not perfect squares 

and do not bear purely orthogonal relationships with other elements. When (in our opinion) one element bears an anterolateral relationship to another element, the first element is listed as 

both an anterior and lateral relationship of the second. When 

an element bears primarily an anterior relationship to another 

element, but has a slight lateral relationship, the first element is 

listed as only an anterior relationship of the second.

Where elements bear only an occasional relationship to one 

another, the second (relational) element is followed by a question mark (?). When an element does not have any bony relationship in a particular direction x, “x element” is entered where “x” 

is the direction concerned. For example, the premaxilla does not 

have any anterior relationships because it is at the most anterior 

extremity of the skull, hence “anterior element” is entered in 

the anterior relationship space for the premaxilla. “Midline element” is used where the medial relationships of an element are 

its opposite half.

We used some soft anatomical structures in this section 

when we wanted to be certain that there was no osteological 

contact in that direction. For example “peribullary sinus” is used 

as one of the lateral relationships of the basioccipital in delphinids to demonstrate that the basioccipital does not contact any 

components of the temporal.

It soon became clear that orientation is one of our primary problems. Some orientation terms are used as the proper 

names of structures and, because of the shift of osteological 

orientation in the cetacean skull, these terms may be misleading. We have dealt with that problem on a case-by-case basis 

(Table 3).

Cranial Nerves

The cranial nerves form an important part of the anatomy 

of the skull. Their nomenclature differs, depending primarily on 

which animal is the subject of study. The following list presents 

the cranial nerves in order of their exit from the skull. We used 

Table 2. Data on specimens of the bottlenose dolphin, Tursiops 

truncatus, in the collection of the United States National Museum of Natural History; CBL = condylobasal length; ? = data 

not available.

 Total

Catalog length CBL

number (cm) (cm) Sex Comments

241288 ? ? ? Isolated periotic, no data

241289 ? ? ? Isolated periotic, no data

500851 113 28.2 M Calf, intact

501197 ? 52.6 ? Extremely mature, lacerate

 foramina filled

504144 106 27.5 F Vomer

504420 163 37.3 M Skull, earbones in place

504560 126 31 F Calf, disarticulated (drawn)

504567 174 37.7 M Earbones, partially 

 disarticulated skull

550403 202 44.9 M Good skull (drawn)

550835 106 26.9 F Calf, intact

550836 ? 47.0 ? Sectioned tympanoperiotic

571017 264 50.3 M Sectioned tympanoperiotic

571036 160 39.3 ? Sectioned tympanoperiotic

571471 203 42.3 M Good complete skull, 

 disarticulated lacrimal

571622 119 28.9 ? Calf, calvarium removed, 

 occiput good

571643 115 28.4 M Calf, intact

571695 ? 45.7 ? Sagittally sectioned adult 

 skull
a l e x i c o n n u m b e r 6 2 7 • 7

Table 3. Topographic relationships between the bony elements of the skull for two mammals. A question mark (?) indicates a bone 

that sometimes was present in the orientation described and sometimes was absent; orientation for free-standing bones is marked “n/a” 

(not applicable).

Element and relationship Relational elements for skull type

of other elements Non-cetacean (Canis) Delphinid (Tursiops)

Basioccipital Bone

Anterior Sphenoid Sphenoid, pterygoid

Posterior Exoccipital Exoccipital

Dorsal Cranial cavity Cranial cavity

Ventral Pharynx Pharynx

Lateral Temporal (bulla, petrosal) Peribullary sinus (parietal)

Medial Midline element Midline element

Ethmoid Bone

Anterior Nasal cavity Vomer, pterygoid, palatine?, mesorostral cartilage

Posterior Sphenoid, cranial Sphenoid, cranial cavity, nasal cavity (adults)

Dorsal Frontal, nasal Frontal (adult), maxilla?

Ventral Vomer, palatine Vomer, pterygoid

Lateral Maxilla, frontal, Frontal, lacrimal

Medial Midline element Midline element

Exoccipital Bone

Anterior Temporal Parietal, squamosal, basioccipital, peribullary sinus

Posterior Atlas Atlas

Dorsal Supraoccipital Supraoccipital

Ventral Pharynx Basioccipital, squamosal

Lateral Temporal Parietal, squamosal

Medial Basioccipital Basioccipital, contralateral exoccipital

Frontal Bone

Anterior Maxilla, nasal, lacrimal, palatine Maxilla, nasal, lacrimal, palatine

Posterior Parietal, sphenoid Interparietal, parietal, sphenoid

Dorsal Dorsal element Nasal, contralateral frontal

Ventral Palatine, sphenoid Pterygoid, sphenoid

Lateral Lacrimal, maxilla Lacrimal

Medial Contralateral frontal sphenoid Contralateral frontal, sphenoid

Hyoid Apparatusa

Thyrohyoid Most distal Fuses with basihyoid with age

Basihyoid Midline element, articulates with thyrohyoid distally, Articulates via a cartilage (ceratohyoid) with

ceratohyoid proximally stylohyoid

Ceratohyoid Paired, articulates with epihyoid proximally Reduced to cartilage in cetaceans

Epihyoid Paired, articulates with stylohyoid proximally Lost or fused with ceratohyal

Stylohyoid Paired, articulates with tympanohyoid cartilage Articulates with ceratohyoid distally and

proximally paroccipital process proximally

Tympanohyoid Cartilaginous, articulates with mastoid process of Fused with posterior process of periotic, lost direct

petrosal (periotic) bony connection with rest of hyoid apparatus.

Interparietal Bone

Anterior Parietal Frontal

Posterior Supraoccipital Supraoccipital

Dorsal Dorsal element Dorsal element

Ventral Cranial cavity Cranial cavity

Lateral Parietal Parietal, frontal

Medial Midline element Midline element

Jugal Bone (Malar)

Anterior Maxilla Maxilla

Posterior Squamosal Squamosal

Dorsal Squamosal, lacrimal Maxilla, lacrimal, squamosal

Ventral Maxilla Maxilla

Lateral Lateral element Lacrimal

Medial Squamosal, maxilla, lacrimal Maxilla, squamosal?

(continued)
8 • smithsonian contributions to zoolog y the therian skull

Table 3. (Continued)

Element and relationship Relational elements for skull type

of other elements Non-cetacean (Canis) Delphinid (Tursiops)

Lacrimal Bone

Anterior Maxilla Maxilla, jugal

Posterior Frontal, palatine Frontal

Dorsal Frontal, maxilla? Maxilla, frontal

Ventral Palatine Jugal

Lateral Jugal Lateral element

Medial Ethmoid Maxilla, jugal

Mandible

Anterior Anterior element Anterior element

Posterior Squamosal Squamosal

Dorsal Squamosal Squamosal

Ventral Ventral element Ventral element

Lateral Lateral element Lateral element

Medial Contralateral mandible Contralateral mandible

Maxilla

Anterior Premaxilla Premaxilla

Posterior Frontal, lacrimal, jugal Frontal

Dorsal Palatine, lacrimal Premaxilla

Ventral Ventral element Palatine, lacrimal, jugal, vomer

Lateral Jugal Lacrimal, jugal, frontal

Medial Nasal, frontal, ethmoid, premaxilla, palatine Premaxilla, nasal, vomer, contralateral maxilla

Nasal Bone

Anterior Anterior element Anterior element

Posterior Frontal Frontal

Dorsal Dorsal element Dorsal element

Ventral Ethmoid Frontal, ethmoid

Lateral Frontal, maxilla, premaxilla Frontal, maxilla

Medial Contralateral nasal Contralateral nasal

Palatine Bone

Anterior Maxilla, ethmoid Maxilla

Posterior Sphenoid, pterygoid Pterygoid,

Dorsal Vomer, frontal, lacrimal Maxilla

Ventral Ventral element Pterygoid

Lateral Frontal, lacrimal Lateral element

Medial Palatine, sphenoid, vomer Pterygoid, vomer, maxilla

Parietal Bone

Anterior Frontal, alisphenoid Frontal, interparietal

Posterior Interparietal, supraoccipital, temporal Supraoccipital, exoccipital

Dorsal Interparietal Interparietal, supraoccipital

Ventral Alisphenoid, temporal Alisphenoid, squamosal, exoccipital

Lateral Temporal Squamosal

Medial Interparietal Alisphenoid (basioccipital)

Premaxilla

Anterior Anterior element Anterior element

Posterior Maxilla Maxilla

Dorsal Nasal Dorsal element

Ventral Maxilla Maxilla

Lateral Maxilla Maxilla

Medial Contralateral premaxilla Vomer, contralateral premaxilla, mesorostral 

cartilage

Pterygoid Bone

Anterior Palatine Palatine

Posterior Basisphenoid Basisphenoid, basioccipital, ethmoid

Dorsal Palatine, basisphenoid, ethmoid Palatine, presphenoid

Ventral Ventral element Ventral element

Lateral Palatine, basisphenoid Palatine, frontal?

Medial Basisphenoid, presphenoid Vomer, palatine, contralateral pterygoid

(continued)
a l e x i c o n n u m b e r 6 2 7 • 9

Table 3. (Continued)

Element and relationship Relational elements for skull type

of other elements Non-cetacean (Canis) Delphinid (Tursiops)

Sphenoid Bone

Anterior Ethmoid, vomer Ethmoid, frontal, vomer, pterygoid

Posterior Squamosal, basioccipital Basioccipital

Dorsal Ethmoid, cranial cavity Cranial cavity

Ventral Vomer, pterygoid Vomer, pterygoid, basioccipital

Lateral Parietal, frontal, palatine Frontal, parietal, squamosal

Medial Midline element Midline element

Supraoccipital Bone

Anterior Parietal, interparietal cranial cavity Parietal, interparietal cranial cavity

Posterior Posterior element Posterior element

Dorsal Parietal, interparietal Parietal, interparietal

Ventral Exoccipital Exoccipital

Lateral Parietal Parietal

Medial Midline element Midline element

Squamosal Bone

Anterior Sphenoid Sphenoid, parietal

Posterior Exoccipital Exoccipital, tympanic bulla (falciform process)

Dorsal Parietal Parietal, exoccipital

Ventral Ventral element Periotic, tympanic bulla, jugal

Lateral Lateral element Lateral element

Medial Basioccipital Sphenoid, peribullary sinus, parietal, periotic, 

tympanic bulla

Periotic Bone

Anterior Sphenoid Alisphenoid, squamosal

Posterior Exoccipital Exoccipital

Dorsal Dorsal element Squamosal, parietal

Ventral Tympanic bulla Tympanic bulla, ossicles

Lateral Squamosal Squamosal (closely approximated in tursiops?)

Medial Basioccipital Peribullary sinus

Tympanic Bulla

Anterior Anterior element Squamosal (falciform process)

Posterior Exoccipital Peribullary sinus, exoccipital

Dorsal Petrosal Periotic

Ventral Ventral element Ventral element

Lateral Lateral element Squamosal

Medial Medial element Peribullary sinus

Auditory Ossicles: Malleus

Anterior n/a Tympanic bulla

Posterior incus Incus

Dorsal incus Periotic

Ventral Tympanic membrane Incus

Lateral Tympanic membrane Tympanic membrane, tympanic bulla

Medial n/a Incus

Auditory Ossicles: Incus

Anterior n/a Malleus

Posterior n/a n/a

Dorsal n/a Stapes, periotic (fossa incudis)

Ventral Malleus n/a

Lateral n/a Malleus

Medial Stapes n/a

Auditory Ossicles: Stapes

Anterior n/a n/a

Posterior n/a n/a

Dorsal Petrosal Periotic

Ventral n/a Incus

Lateral Incus n/a

Medial Petrosal n/a

(continued)
1 0 • smithsonian contributions to zoolog y the therian skull

Romer (1955) and Gray (1918) for standards. See Appendix A 

for terms that have been used in the past by various authors.

0 Terminal VI Abducens

I Olfactory VII Facial

II Optic VIII Acoustic

III Oculomotor IX Glossopharyngeal

IV Trochlear X Vagus

V Trigeminal (ophthalmic, XI Accessory

 maxillary, mandibular) XII Hypoglossal

GUIDE TO LEXICON ENTRIES

In the sections below, we describe and illustrate the skull as 

disarticulated bones to expose details that are hidden in an articulated skull. The technique is useful when dealing with isolated 

bones, as paleontologists frequently do.

The individual bones are treated alphabetically, and details 

of the bones’ features are then also covered in alphabetical order. 

This method has obvious drawbacks, particularly in dealing with 

structures that are on more than one bone. We have provided 

numerous cross-references and an extensive index to help minimize confusion.

Twenty-two bones or bone groups are presented (the groups 

include the auditory ossicle and the tympanoperiotic). After the 

heading for each bone we list the figure(s) in which the bone is 

illustrated; when multiple figures are listed, the primary figure 

number is in bold type.

Each bone section begins with a general treatment of the 

bone, describing peculiarities of its evolution, relationship(s) to 

other groups of bones, and details of its embryological development. Below this general discussion, the lexicon terms—names 

for features of the bones—are presented alphabetically (letter by 

letter) as individual lexicon entries, which are then described in 

more detail.

Generally these terms are alphabetized by their English 

name which is then followed by the official Latin term (in parentheses) used in the Nomina Anatomica and Nomina Anatomica 

Veterinaria. Exceptions to this include, for example, such Latin 

terms as foramen magnum, which does not have a commonly 

used English equivalent, or foramen ovale, for which the Latin is 

more commonly used than the English “oval foramen.” In these 

cases the Latin term is listed first without parentheses, and the 

English term, if known, is provided in parentheses. Also, if we 

discovered that the original spelling of the term used a diphthong 

such as æ or œ (which are no longer used), the original spelling 

is inserted in square brackets. 

A symbol before each lexicon entry denotes the standing of 

the term, its presence or absence in Tursiops, and/or the presence 

or absence of illustrations in this work:

* indicates the feature is present in Tursiops and illustrated 

herein;

+ indicates the feature is present in Tursiops but not illustrated;

− indicates the feature is absent in Tursiops;

= indicates the feature is is a synonym of another term.

Definitions are typically arranged as follows (although not 

every term has all of these constituents):

symbol anatomical term / alternate term [original spelling / 

additional information] (Latin term) (author citation) 

= synonym(s) (Figures)

General definition of the term in mammals.

Definition of the term in the highest taxonomic unit of cetaceans in which we know it occurs.

Cross references (“See . . . ”).

In addition, a few nonosteological definitions occur in places 

where we felt further amplification of structures was essential. 

Finally, lexicon terms mentioned in other terms’ entries are bold 

to facilitate cross-referencing.

In some cases an author citation is available only for a synonym rather than the entry’s term name, thus the citation appears after the synonym in those lexicon entries.

Table 3. (Continued)

Element and relationship Relational elements for skull type

of other elements Non-cetacean (Canis) Delphinid (Tursiops)

Vomer

Anterior Premaxilla Anterior element

Posterior Presphenoid Ethmoid, sphenoid, frontal

Dorsal Sphenoid, ethmoid, palatine Ethmoid, sphenoid, maxilla?

Ventral Maxilla, palatine Palatine, premaxilla, maxilla

Lateral Maxilla, palatine Palatine, premaxilla, maxilla, pterygoid

Medial Midline element Midline element

a

 For Hyoid Apparatus, first column entries are the relational elements; second and third column entries are the topographical relationships and other 

relational comments.
Basioccipital Bone

Os Basioccipitalis

Figures 3–5, 6b,d,e,g, 7, 28–29, 31a

The basioccipital bone is a midline ossification in the ventral posterior portion of 

cranium. It does not take part in the occipital condyles but may form a small part of the 

ventral margin of the foramen magnum. The basilar part (pars basilaris) of the occipital 

bone is equivalent to the basioccipital ossification (Schulte, 1917:374, 375, 379, 382, 

383, 393, 394; McFarland et al., 1979:8; Schaller, 1992:16; Feneis, 1994:8). The basioccipital bone is also known as the basal process.

The basioccipital is bordered on the posterolateral surface by the exoccipitals; on the 

anterolateral surface by the parietal and sometimes the alisphenoid; and on the anterior 

surface by the basisphenoid.

− basal process = basioccipital crest

Luo and Gingerich (1999:29, 36, fig. 9, in the archaeocete Pakicetus).

See also falcate process.

* basioccipital crest (Figures 2, 7b–e)

The basioccipital crest in cetaceans is the ventrolateral part of the basioccipital in 

adults (Fraser and Purves, 1960:29, 38, 39, 41, 42, 44, 45, 47, 66–68, 70–72, 79, 80, 

136). This part of the basioccipital is produced into crests. The basioccipital crest also 

has contributions from the exoccipital medial to the hypoglossal notch. The basioccipital 

crest tends to isolate the tympano–periotic region from the dorsal pharyngeal region and 

continue onto the pterygoids as the pharyngeal crest (Owen, 1866a:35, pl. 13: figs. 2–5'. 

Schulte (1917) also referred to the basioccipital crest as the otocranial flange (1917:383, 

394, 400), the otocranial plate (1917:373), otocranial process of Owen (1917:374), the 

flange of the basioccipital (1917:379, 381), the flange of the occipital (1917:384), the occipital flange (1917:374) and the great flanges of the occipital (1917:374). Owen referred 

to the basioccipital crest as the otocranial plate (1866a:26, 39), otocranial plate of the 

basisphenoid (1866a:28, 30, 40), and the otocranial plate of the basioccipito-sphenoid 

(1866a:35). He did not refer to the basioccipital crest in his monograph on comparative 

anatomy (Owen, 1866b–1868). Barnes and McLeod (1984:13) used the term “lateral tuberosities of basioccipital.” Other terms include lateral process of basioccipital (Kellogg, 

1936), processus alaris or alar process (de Muizon, 1987:5), and falcate process (q.v.).

= basioccipital process (Fraser and Purves, 1960:13, 77) = basioccipital crest

Fraser and Purves (1960:13, 77) used basioccipital process as a lapsus calami for 

basioccipital crest.

Lexicon
= basioccipital ridge (Fraser and Purves, 1960:48) = basioccipital 

crest

Fraser and Purves (1960:48) used basioccipital ridge as a 

lapsus calami for basioccipital crest.

− basion

See “Exoccipital Bone.”

= basisphenoidal otocranial plate (Owen, 1866a:28, 30, 35, 40, 

pl. 13: fig. 2 [5’]) = basioccipital crest

Owen (1866a:35, pl. 13: fig. 2 [5’]), in describing the holotype of Kogia sima, which has the basioccipital fused to the 

basisphenoid, uses basisphenoidal otocranial plate to refer to the 

basioccipital crest.

* clivus (Figure 7c)

The clivus is the sloping surface between the foramen 

magnum and the dorsum sellae (Gray, 1918:148; Dox et al., 

1979:101; Schaller 1992:12.14; Feneis, 1994:8.6a, 30.5; not in 

Evans and Cristensen, 1979). The clivus consists of the dorsal 

median portion of the basioccipital and the basisphenoid, and 

supports the pons and the medulla oblongata.

Tursiops has a normal clivus.

* endocranial sulcus / foramen for the vestibulocochlear nerve 

[new term] (Figures 30, 31b)

All odontocetes have the periotic bone isolated from the 

skull and suspended in the jugular foramen. The vestibulocochlear nerve runs through a sulcus in the dorsolateral margin of the basioccipital bone. In individuals where the jugular 

foramen is closed with bony growth, that sulcus becomes a 

foramen.

See also cranial hiatus under “Exoccipital Bone.”

= falcate process = basioccipital crest

Falcate process = alar process = basioccipital crest (de 

Muizon, 1987:5); = lateral descending process sensu Kellogg, 

1936 (Luo, 1998:276); falcate crest (Luo and Gingerich, 1999:29, 

36, 41); falcate process (e.g., Schulte, 1916:178; Howell, 1930; 

Thewissen and Hussain, 2000:142; Uhen, 2004:48, fig. 36; Ichishima and Kimura, 2005:658; Geisler, 2001:42 identified as a 

synonym for basioccipital crest). 

Not to be confused with the falcate process (falciform process) of the squamosal bone.

See also basal process.

− groove for ventral petrosal sinus (sulcus sinus petrosi ventralis)

The groove for the ventral petrosal sinus lies on the dorsolateral surface of the basioccipital (Schaller, 1992:16). The groove 

houses the ventral petrosal sinus and forms the medial portion 

of the petrobasilar canal (q.v. under periotic bone) (Evans and 

Christensen, 1979:134, 794).

The ventral cranial venous sinuses (also called inferior sinuses) have been extremely modified in cetaceans. The ventral 

petrosal sinus does exist in phocoenids (Boenninghaus, 1904) 

and probably delphinids as well; but a groove for the ventral 

petrosal sinus has not been demonstrated in delphinids. 

See also cranial hiatus, including comment on foramen for 

the inferior (or ventral) petrosal sinus.

* impression for the medulla oblongata (impressio medullaris) 

(Figure 7a,c)

The impression for the medulla oblongata lies on the dorsal 

surface of the basioccipital just anterior to the foramen magnum

(Schaller, 1992:16).

The impression for the medulla oblongata in delphinids is 

a very shallow depression that lies on the dorsal surface of the 

basioccipital just anterior to the foramen magnum. It is more 

pronounced in older animals (USNM 501197).

= intercondyloid notch

See “Exoccipital Bone.”

− laryngeal arcade (Fraser and Purves, 1960:47, 50)

The laryngeal arcade separates the pharyngeal region from 

the orbital and basicranial regions in cetaceans. The laryngeal 

arcade consists of the basioccipital crests, pharyngeal crests, and 

the free narial margin of the pterygoid bones. It has also been 

called the basioccipital arcade (Fraser and Purves, 1960:44).

* muscular tubercle (tuberculum musculre) (Figures 2, 7b)

The muscular tubercles are rough sagittally elongate areas 

on the basioccipital located medially to the tympanic bullae 

(Evans and Christensen, 1979:123; Schaller, 1992:16). These tubercles form the area of insertion of the rectus capitis ventralis

muscle (Evans and Christensen, 1979:315).

The muscular tubercle in Tursiops varies between small and 

lacking.

= odontoid notch (Wible and Gaudin, 2004:143)

In the yellow armadillo (Wible and Gaudin, 2004:143), 

the odontoid notch is a U-shaped median ventral embayment 

in the basioccipital between the occipital condyles. Intercondyloid notch (see “Exoccipital Bone”) is an alternative use (Wible, 

2003:166; Wible and Gaudin, 2004:143).

See intercondyloid notch under “Exoccipital Bone.”

− otocrane (Owen, 1866a:26, 29, 30, 35)

Owen used the term “otocrane” to refer to the space surrounding the tympanoperiotic. The otocrane is defined by Whitney (1889–1910:[vol. 5]4175) as “the bony structure of the 

middle and inner ear of a vertebrate, containing the essential 

parts of the organ of hearing.”

= otocranial process = basioccipital crest

− peribullary sinus

The peribullary sinus is one of the basicranial air sinuses 

associated with the middle ear and is peculiar to cetaceans. The 

sinus arises at the posteroventral end of the pterygoid sinus and 

lies between the tympanoperiotic and the basioccipital crest (Fraser and Purves, 1960:1, 5, 8–10, 14, 53, 55, 62, 63, 65–74, 76, 

77, 79, 80, 84, 100, 102, 136). Unlike some other parts of the 

pterygoid sinus system in the broad sense, the peribullary sinus 

generally lacks a distinct fossa. The sinus is limited dorsally by 

the dura mater. The sinus does not extend to the ventral surface 

of the tympanoperiotic, but a posterolateral extension of the peribullary sinus (posterolateral sinus) may extend to the paroccipital process to form the posterolateral sinus fossa.

1 2 • smithsonian contributions to zoolog y B asioccipital
Fraser and Purves (1960:5) stated:

Camper (1777) gives reference to Joh. Dan Major as 

the discoverer of the peribullary sinus in the year 1672, 

quoting the latter’s paper he states “one should know 

that the petrous bones are not tightly attached to the 

cranium, but are lying loosely between the flesh and 

the fat close to the base of the brain and the occiput, at 

the side of the head, in a sinus, which is formed by two 

processes which do not touch each other.”

Dan Major thus antedated Tyson (1680) who, in his “Anatomy of a Porpess,” made much the same observation.

* peribullary sinus fossa (Figures 7a,c,d, 30)

The peribullary sinus is one of the basicranial pterygoid air 

sinuses associated with the middle ear. In Tursiops the peribullary sinus fossa is entirely limited to the lateral surface of the 

basioccipital crest. The fossa begins anteriorly at the area immediately adjacent to the ventral carotid foramen. This portion 

of the fossa is delimited by the moderate crest around the ventral carotid foramen. The fossa then continues posteriorly and 

is bounded by the dorsal and ventral surface of the basioccipital 

crest and the jugular notch. Fraser and Purves referred to the peribullary sinus fossa as the peribullary space (1960:40, 43, 46–49, 

52, 53, 55, 56, 58, 67).

* pharyngeal crest [new term] (Figures 2, 30)

The pharyngeal crests in delphinids are the paired crests on 

the ventral surface of the skull that separate the pharyngeal region from the auditory and optic regions. In Tursiops each crest 

is a continuous structure formed by the basioccipital crest posteriorly and the medial lamina of the pterygoid anteriorly. The 

crest ends anteriorly at the Eustachian notch, and posteriorly at 

the jugular notch. In some Cetacea, there is an obvious medial 

exoccipital crest posteriorly, medial to the jugular notch.

− pharyngeal tubercle (tuberculum pharyngeum)

The pharyngeal tubercle is a median triangular area on the 

ventral surface of the basioccipital just anterior to the intercondyloid notch (Evans and Christensen, 1979:123; Schaller, 1992:16). It 

forms the attachment for the pharyngeal raphe (Feneis, 1994:8).

In delphinids, with the hypertrophy of the palatopharyngeal 

sphincter (constrictor) (e.g., Fraser and Purves, 1960:20), the relationships in the pharyngeal region have changed. There does 

not appear to be a pharyngeal raphe or pharyngeal tubercle.

− pituitary fossa = hypophyseal fossa

See basisphenoid.

* pontine impression (impressio pontina) (Figure 7a,c)

The pontine impression lies on the anterodorsal (cranial) 

surface of the basioccipital (Evans and Christensen, 1979:122, 

123; Schaller, 1992:16). The pontine impression holds the pons.

In Tursiops the pontine impression is a very shallow depression just posterior to the sella turcica. It is more pronounced in 

older animals (USNM 501197).

− third condyle (condylus tertius)

Robineau (1968) described a third occipital condyle in a 

specimen of Mesoplodon bidens. Robson and Van Bree (1972) 

described the third condyle in specimens of M. layardii and 

M. grayi, Casinos and Fillela (1981) described a third condyle in 

M. densirostris, and Ross (1984:222) showed a third condyle to 

occur consistently in M. densirostris. Thus, the third condyle is 

at least a relatively common occurrence in ziphiids of the genus 

Mesoplodon. It has not been seen in any other cetacean species.

= trans-basicranial ridge

Anderson (1879:428) used trans-basicranial ridge in his 

table of detailed measurements of the skull of Platanista. This 

ridge is pronounced in a ventral view of an adult Platanista, lying 

just posterior to the spheno-occipital suture. The trans-basicranial ridge extends laterally and then posteriorly to terminate on 

the basioccipital crest. The ridge appears to be homologous with 

the muscular tubercle of the basioccipital, on which the longus 

capitis muscle inserts.

See muscular tubercle.

* tympanic plate of the basioccipital bone (Figure 7b,d,e)

The tympanic plate is used by Anderson to refer to a process of the basioccipital in Platanista (Anderson, 1879:428, 503, 

505). The paired tympanic plates are terminated ventrolaterally 

by the basioccipital crests. The tympanic plates are medial to the 

tympanic bulla. This is not to be confused with the tympanic 

plate of the bulla.

The situation is similar in Tursiops and other delphinids.

ETHMOID BONE

Os Ethmoidale

Figures 1, 3, 4, 8

The ethmoid bone consists of four parts: an anterodorsal 

median perpendicular plate or perpendicular lamina (mesethmoid); two lateral masses (ectethmoids) covered by the external 

lamina (lamina externa); and a posteroventral midline cribriform plate (lamina cribrosa) to which the ethmoturbinates of 

the lateral masses attach. The mesethmoid forms the osseous 

nasal septum (Evans and Christensen, 1979:135). Vesalius 

(1543:23, 25) referred to it as the octavum capitis os. Eustachius and Lancisius (1714:112) referred to the os cristatus and 

processus cristatus in tabula XLVI, figs. XII–XVI, a reference 

that is confusing to us; we believe this reference may instead be 

to the crista galli. 

In odontocetes, with the lack of development of the features 

associated with the sense of smell, all parts of the ethmoid are 

reduced. In Tursiops all four elements are present, but the lamina 

externa does not expand to support any development of turbinals. The ethmoid is bounded in the normal mammalian pattern 

by the vomer anteriorly and ventrally, the frontal dorsally and 

laterally, and the presphenoid and orbitosphenoid posteriorly. 

In odontocetes the olfactory nerve (Schulte, 1917:378) is absent 

and the cribriform plate is imperforate. Mysticetes, on the other 

hand, have a variably developed olfactory apparatus. A rudimentary crista galli is present in both fetuses and adults.

The cribriform plate is posteroventral to the mesethmoid 

and forms the most posterior element of the ethmoid bone. The 

e t h m o i d n u m b e r 6 2 7 • 1 3
cribriform plate forms a part of the anterior wall of the cranium 

in cetaceans. The cribriform plate is perforated by the olfactory 

nerve in other mammals and forms the basis for the olfactory 

epithelium.

De Beer (1937:442), in reference to the mesethmoid, stated, 

“Contrary to previous notions, it is now clear from Broom’s 

(1926) investigations that the mesethmoid was evolved with the 

Mammalia, and only some and not all of the orders of the class 

possess this bone.” De Beer then questions its presence in cetaceans. Schulte (1917:372, 384, 385, 387, 388, 390, 400) found 

it present in Kogia. See Kellogg (1926:7) for a discussion of situation of the ethmoid in extant taxa. 

The ethmoid lies ventral and medial to the frontals; ventral 

to the nasals in adults; posterodorsal to the vomer; medial to the 

orbitosphenoid; anteromedial to the presphenoids; and anterior 

to the basisphenoid.

− ala cristae galli

The alae cristae galli in humans are anterolateral projections 

of the cristae galli that are received into corresponding depressions in the frontal bone (Gray, 1918:153).

In Tursiops and other odontocetes the ala cristae galli is not 

developed.

− cribriform foramina (foramina laminae cribrosae) 

Cribriform foramina are formed in the cribriform plate for 

passage of the branches of the olfactory nerve (Evans and Christensen, 1979:137). Vesalius (1543:25) referred to the cribriform 

foramina as the cribri instar foraminibus. Eustachius and Lancisius (1714:112, tabula XLVI, figs. XII, XIV) mentioned the 

processus papillares in connection with the foramina for the olfactory nerve in the cribriform plate.

In Tursiops and other odontocetes the cribriform plate appears imperforate. Kellogg (1928:200, 201) said the cribriform 

plate is imperforate but illustrated a young Tursiops in which 

several foramina can be seen in the ethmoid in the region of the 

cribriform plate. Schulte (1917:385) interpreted such foramina 

as being for the nasal not olfactory nerve.

Cribriform foramina have been reported in Physeter (Flower, 

1868:316), and Berardius (Flower, 1872:220). In some mysticetes, particularly balaenopterids where turbinals are still present, 

the cribriform foramina may occur.

* cribriform plate (lamina cribrosa) (Figure 8a–e)

The cribriform plate is the posterior of the two midline ethmoid ossifications. It is perforated by branches of the olfactory 

nerve (Gray, 1918:153; Evans and Christensen, 1979:137; McFarland et al., 1979:8; Schaller, 1992:28.29; Feneis, 1994:20.2). 

The cribriform plate is not to be confused with the lamina 

cribrosa of the sclera (Gray, 1918:1005; Feneis, 1994:354.34). 

Eustachius and Lancisius (1714:112) referred to it as the cribriformia ossa. Vesalius (1543:50) and Vesalius et al. (1998:131) 

referred to the cribriform plate of the ethmoid bone as the hac 

sede in octavo capitis osse multa, sed exigua spectantur foramina, odorum and aeris inn inspirationibus ad cerebrum ingressus 

nomine, incisa.

In Tursiops and other odontocetes the cribriform plate is 

well developed though imperforate. A vestigial crista galli is 

present on the cribriform plate in both the fetus and the adult.

* crista galli (Figures 8a,c–d, 28)

The crista galli is a small crest on the cribriform plate that 

divides the cribriform plate into right and left fossae for the olfactory lobes of the brain (Gray, 1918:153; Evans and Christensen, 1979:137; Schaller, 1992:28.30; Feneis, 1994:20.3). 

Vesalius (1543:25) referred to it as the septum . . . quae cerebri 

processibus parantur. It may be the element that Eustachius and 

Lancisius (1714:112) referred to as the processus cristatus (cristati processus). In humans it serves for the attachment of the falx 

cerebri (Gray, 1918:153).

In Tursiops and other odontocetes the crista galli is vestigial.

= dorsal lamina of the ethmoid = roof plate

− dorsal nasal concha (concha nasalis dorsalis) = nasoturbinate

The dorsal nasal concha arises dorsally from the posterior 

part of the cribriform plate as well as from the medial part of the 

roof plate (Evans and Christensen, 1979:138). 

The dorsal nasal concha is an alternative name for the nasoturbinate bone.

In Tursiops and other extant odontocetes the turbinals are 

not developed.

* ectethmoid = lateral wings of mesethmoid (Figures 8a,c–d, 28)

The question of the presence of separate ectethmoid and 

mesethmoid ossifications in cetaceans is still open to debate. 

Rommel (1990:33) provided a concise summary of the problem, 

concluding that supposed ectethmoids could equally arise from 

frontals and/or from vomer. Schulte (1917:378) mentions the 

term “ectethmoid” in referring to Kogia. His usage of the term is 

consistent with ectethmoid being synonymous with lateral wings 

of mesethmoid. Schulte (1917:372, 378, 385) also uses the term 

“lateral ethmoid.”

In referring to the lateral ethmoid, De Beer (1937:443) said, 

“Since it would seem that this bone has been independently 

evolved within the class Aves and has not been inherited directly 

from the fish it should not be called the lateral ethmoid. Perhaps 

the term ‘ectethmoid’ may be restricted to mean the ossification 

in birds, without increasing the nomenclature.”

We shall use the term “ectethmoid” sensu Schulte (1917:378, 

380, 385, 388), realizing the problems brought up by Rommel. 

Kellogg (1928:200, fig. 22) illustrated the ectethmoid in a young 

Tursiops.

− ectoturbinates (ectoturbinalia) 

The ectoturbinates are a division of the ethmoturbinates.

The ectoturbinates are absent in Tursiops and other 

odontocetes. 

See ethmoidal labyrinth.

− endoturbinates (endoturbinalia) 

The endoturbinates are a division of the ethmoturbinates.

The endoturbinates are absent in Tursiops and other 

odontocetes. 

See ethmoidal labyrinth.

− ethmoid air cells (cellulae ethmoidales) 

The ethmoid air cells consist of many thin-walled cavities 

(paranasal sinuses) situated in the ethmoidal labyrinth and com1 4 • smithsonian contributions to zoolog y e t h m o i d
pleted by the frontal, maxilla, lacrimal, sphenoidal, and palatine 

bones (Gray, 1918:998).

In Tursiops and other odontocetes the paranasal sinuses are 

not developed (Fraser and Purves, 1960:5, 75). Paranasal sinuses 

occur in some extinct cetaceans, as discussed under frontal sinus

(“Frontal Bone”).

− ethmoidal bulla (bulla ethmoidalis)

The ethmoidal bulla in humans is caused by the bulging of 

the ethmoid air cells into the nasal cavity (Gray, 1918:995).

This feature is not present in Tursiops or other odontocetes 

because the ethmoid air cells are absent.

− ethmoidal infundibulum (infundibulum ethmoidale) 

The ethmoidal infundibulum is a sinuous passage leading 

from the middle meatus of the nose to the anterior ethmoidal 

cells (Gray, 1918:156).

The ethmoidal cells are not developed in Tursiops and other 

odontocetes, so the ethmoidal infundibulum does not exist.

− ethmoidal labyrinth (labyrinthus ethmoidalis) 

The ethmoidal labyrinth forms the principal portion of the 

lateral mass of the cribriform plate. It is composed of delicate 

bony scrolls or ethmoturbinates, which attach to the external 

lamina of the ethmoid bone by basal laminae and attach caudally 

to the cribriform plate (Evans and Christensen, 1979:137).

In Tursiops and other delphinids the ethmoidal labyrinths 

are not developed. There are structures in the ethmoid of Platanista and all the ziphiid genera that could be interpreted as 

ethmoturbinates. The presence of the olfactory nerves and ethmoturbinals in the mysticetes has been amply demonstrated 

(Flower, 1866:147; Edinger, 1955; Breathnach, 1960:192). An 

olfactory apparatus including turbinals and associated paranasal sinuses was present in archaeocetes (Edinger, 1955), and has 

been inferred for some archaic odontocetes (Fordyce, 2002). 

Buhl and Oelschläger (1988) have demonstrated the presence of 

an olfactory bulb in fetal Phocoena.

− ethmoidal meatus (meatus ethmoidales) 

The ethmoidal meatus is that portion of the nasal passages 

that pass through the ethmoidal conchae or turbinals (Evans and 

Christensen, 1979:513).

In Tursiops and other odontocetes the turbinals are not developed and therefore the ethmoidal meatus is not considered as 

a separate element of the nasal passages.

− ethmoidal process (processus ethmoidalis) 

The ethmoidal process is located on the middle portion of 

the inferior nasal concha. It ascends to join the uncinate process

of the ethmoid bone.

In Tursiops and other odontocetes the turbinals are not 

developed.

− ethmoturbinates (ethmoturbinalia) 

The ethmoturbinates are a series of bony scrolls attached 

to the external lamina of the ethmoid bone. Posteriorly the ethmoturbinates are attached to the cribriform plate. They form 

the contents of the ethmoidal labyrinth (Evans and Christensen, 

1979:137).

In Tursiops and other extant odontocetes the turbinals are 

not developed in the normal mammalian manner, as discrete 

bony structures in adults. 

See ethmoidal labyrinth.

* external lamina of the ethmoid bone (Figure 8b–e)

The external lamina of the ethmoid bone lies lateral to the 

mesethmoid and medial to the orbitosphenoid. In cetaceans the 

lamina externa does not expand to support any development of 

turbinals.

− floor plate = ventral lamina = transverse lamina (lamina basalis) 

The external lamina of the ethmoid bone is divided into dorsal, lateral, and ventral parts. The ventral part is called the floor 

plate or lamina orbitalis (Evans and Christensen, 1979:137).

In Tursiops and other odontocetes the external lamina is 

not subdivided.

* foramen for the nasal nerve (Schulte, 1917:378, 385) (Figure 8b)

In the dog the nasociliary nerve (a branch of the ophthalmic 

nerve) runs anteriorly between the dorsal oblique and medial rectus muscles and enters the cranial cavity by means of the ventral 

ethmoid foramen (Evans and Christensen, 1979:914), becoming 

the ethmoidal nerve. The ethmoidal nerve then leaves the cranial 

cavity through an unnamed foramen in the dorsomedial aspect 

of the cribriform plate (Schaller, 1992:466.4, 7). The ethmoidal 

nerve contributes branches to the nasal conchae (internal nasal 

nerves; ramus nasalis medialis) and terminates in the external 

nasal nerves, which are distributed to the skin of the rostrum 

(Schaller, 1992:466.7). 

We unsuccessfully examined Gray (1918), Sisson and Grossman (1953), Evans and Christensen (1979), Schaller (1992), and 

Feneis (1994) in hopes of finding a named foramen.

Schulte (1917:378, 384, 385) has interpreted the foramina 

in the ethmoid of Kogia breviceps as possibly being for the transmission of the “nasal” nerve. Gray (1918:888) gives the nasal 

nerve as a synonym for the nasociliary nerve, and we presume 

that Schulte used it in this sense. The terminal branches of the 

nasociliary nerve have yet to be studied in sufficient detail in delphinids to permit us to say whether they perforate the ethmoid. 

In an illustration, we labeled a foramen that appeared in the ethmoid of the newborn animal (USNM 504560) as “Foramen for 

the nasal nerve?”. This foramen did not appear in any of the 

adults or calves that we used in this lexicon.

For the fossil odontocete Squalodon, Kellogg (1923:46, 47) 

identified paired foramina at the posterior end of the mesorostral 

groove as likely for nasal branches of the ophthalmic nerve.

− fundus of the nasal fossa

The fundus of the nasal fossa is the area occupied by the 

ethmoturbinates (Evans and Christensen, 1979:159).

The fundus of the nasal fossa is absent in Tursiops and other 

odontocetes. 

See ethmoidal labyrinth.

− lacrimal process (processus lacrimalis) 

The lacrimal process is located on the middle portion of 

the inferior nasal concha. It articulates, by its apex, with the descending process of the lacrimal bone (Gray, 1918:169).

e t h m o i d n u m b e r 6 2 7 • 1 5
In Tursiops and other odontocetes the turbinals are not 

developed.

− maxillary fossa of the ethmoid bone

The maxillary fossa of the ethmoid bone is a depressed area 

of the orbital lamina of the ethmoid bone that forms the medial 

wall of the maxillary sinus (Evans and Christensen, 1979:137). 

The posterolateral portion of the maxillary fossa consists of the 

anterior part of the nasal surface of the palatine bone (Evans and 

Christensen, 1979:144). 

The maxillary fossa of the ethmoid bone is not developed in 

Tursiops or other living cetaceans. It might be present in extinct 

forms in which paranasal sinuses are developed. 

Not to be confused with maxillary fossa (or facial fossa) of 

the maxilla (q.v.).

− maxillary process of the ethmoid bone (processus maxillaris)

The maxillary process of the ethmoid bone is located on the 

middle portion of the inferior nasal concha. It articulates with 

the maxilla and forms a part of the medial wall of the maxillary 

sinus (Gray, 1918:169).

In Tursiops and other odontocetes the turbinals are not 

developed.

* mesethmoid (Figures 8a,c–e, 28, 31a)

The mesethmoid is the most anterior/dorsal midline element 

of the ethmoid ossification. It forms the ventral portion of the 

osseous nasal septum in most mammals, the dorsal portion being 

formed by the frontal and nasal bones (Evans and Christensen, 

1979:135). Posteriorly the mesethmoid fuses with the cribriform 

plate; Schulte (1917:372, 378, 380, 381, 384–387) used it in this 

context in Kogia.

In a newborn Tursiops it has begun developing anteriorly into 

the mesorostral groove of the vomer, forming a posterior termination 

of that groove. In adult Tursiops it is prolonged dorsally to contact 

the nasals. The mesethmoid is attached to the mesorostral cartilage, 

which is homologous with the cartilaginous nasal septum. 

Owen (1866a:27, 30, 37, 38) referred to the mesethmoid as 

the prefrontal. We use a different concept of the prefrontal (q.v. 

under frontal bone). Anderson (1879:507) referred to the central 

portion of the mesethmoid, from which the mesorostral cartilage 

arises as the central plate of the mesethmoid.

= mesethmoid cartilage

See mesorostral cartilage.

* mesethmoid ridge (Figure 8a,e)

The mesethmoid ridge in Platanista is the ridge of the mesethmoid that protrudes anteriorly into the mesorostral canal of 

the vomer. The mesethmoid cartilage attaches to the mesethmoid 

ridge (Anderson, 1879:522).

In Tursiops and other delphinids the mesethmoid ridge is 

low and indistinct.

* mesorostral cartilage = mesethmoid cartilage = septal cartilage 

(Figure 8a,e)

The mesorostral cartilage, mesethmoid cartilage, or septal 

cartilage is an anterior extension of the nasal septum (Evans and 

Christensen, 1979:135).

In Tursiops and most cetaceans the mesorostral cartilage is a 

very prominent cartilage that fills the mesorostral groove, which 

is formed by the vomer and premaxillae. Anderson referred to 

the mesorostral cartilage as the cartilaginous vomer (1879:527) 

and the septal cartilage (1879:450, 451, 507); Schulte (1917:380, 

384, 385) referred to this structure as the septal cartilage.

− middle nasal concha (concha nasalis media) 

The middle nasal concha in humans is the ventral part of the 

labyrinth or lateral mass of the ethmoid (Gray, 1918:156).

In Tursiops and other odontocetes the turbinals are not 

developed.

* nasal fossa (Schulte, 1917:378, 385–389, 394) (Figure 1)

The nasal cavity in mammals is composed of two nasal fossae (Evans and Christensen, 1979:158; not in Nomina Anatomica, 

Nomina Anatomica Veterinaria; Feneis, 1994; Schaller, 1992) 

containing the nasoturbinates and separated by the nasal septum.

The odontocetes have reduced many of the elements of the 

nasal cavity in their transition to an aquatic life, including the 

entire loss of the olfactory system. The nasal fossae, sensu Evans 

and Christensen, in odontocetes are reduced to the portion of the 

nasal passage that lies adjacent to the nasal septum.

The nasal fossae were also known as the olfactory chambers 

(Flower, 1885:124).

− nasoturbinal [nasoturbinate] (concha nasalis dorsalis)

The nasoturbinal (nasoturbinate; dorsal nasal concha of 

veterinary anatomy) is one of several scroll-like bones that arise 

dorsally from the posterior part of the cribriform plate as well as 

from the medial part of the roof plate (Evans and Christensen, 

1979:138). Wible and Gaudin (2004:120) described the nasoturbinal in relation to the ventral surface of the nasal in the armadillo. Uhen (2004:46) described turbinals in the archaeocete 

Dorudon atrox.

In Tursiops and other extant odontocetes the turbinals are 

not developed in the normal mammalian manner, as discrete 

bony structures in adults.

− olfactory foramina (Owen, 1866a:30)

The olfactory foramina transmit the olfactory nerves 

through the cribriform plate.

Odontocetes lack olfactory nerves, and olfactory foramina 

are not positively identifiable in Tursiops.

= orbitosphenoid (Figure 8a–e)

See “Sphenoid Bone.” 

= optic canal (Figure 8a–e)

See “Frontal Bone,” “Sphenoid Bone.”

= perpendicular plate (lamina perpendicularis)

The perpendicular plate is an anteroventral extension of the 

mesethmoid that divides the anterior portion of the nasal passages into right and left halves (Gray, 1918:154). It forms the 

base for the septal cartilage.

In Tursiops and other odontocetes the perpendicular plate is 

weakly developed as the mesethmoid ridge.

See mesethmoid ridge.

1 6 • smithsonian contributions to zoolog y e t h m o i d
= presphenoid (Figure 8a,b,e)

See “Sphenoid Bone.”

− roof plate (lamina tectoria) 

The external lamina of the ethmoid bone is divided into dorsal, lateral, and ventral parts. The dorsal part is called the roof 

plate or lamina orbitalis (Evans and Christensen, 1979:137).

In Tursiops and other odontocetes the external lamina is not 

obviously subdivided.

− semilunar hiatus (hiatus semilunaris)

The semilunar hiatus is a curved cleft caused by the bulging 

of the ethmoidal bulla into the nasal cavity (Gray, 1918:995).

The ethmoidal bulla is not present in Tursiops or other 

odontocetes.

= septal cartilage

See mesorostral cartilage.

− side plate (lamina orbitalis) 

The external lamina of the ethmoid bone is divided into dorsal, lateral, and ventral parts. The lateral part is called the side 

plate or lamina orbitalis (Evans and Christensen, 1979:137).

In Tursiops and other odontocetes the external lamina is 

not subdivided, so side plates are not considered as separate 

elements.

− supreme nasal concha (concha nasalis suprema) 

The supreme nasal concha is the most dorsal of the rudimentary nasal conchae in humans (Feneis, 1994:20). It is also 

known as the superior nasal concha (Gray, 1918:156).

No nasal conchae are present in delphinids.

− terminal nerve foramina

The terminal nerve (cranial nerve 0) is difficult to identify in 

most mammals, although it appears to be a primitive vertebrate 

character. In humans it unites the anterior perforated substance 

(substantia perforata anterior) in the brain with the olfactory region of the nasal cavity (Feneis, 1994:312.2, 352.27). The function of the terminal nerve in humans is unknown but is presumed 

to be autonomic (Feneis, 1994:352.27).

The terminal nerve in the dog is grouped, along with the vomeronasal nerve, with the olfactory nerve and is not given separate 

cranial nerve status (Evans and Christensen, 1979:910; Schaller, 

1992:464.5). The terminal nerve is formed by bundles that arise 

from the vomeronasal nerves as they terminate on the accessory olfactory bulb. They unite to form a trunk that runs caudoventrally 

on the medial surface of the olfactory tract and “appears to enter the 

brain substance 1 or 2 cm caudal to the olfactory bulb” (Evans and 

Christensen, 1979:910). Sisson (1910:440, 772) and Gray (1918:71, 

996) have paragraphs on the vomeronasal organ but did not mention the terminal nerve. Flower (1885) and de Beer (1937) did not 

mention either the vomeronasal organ or the terminal nerve. 

Ridgway et al. (1987) dissected the terminal nerve in 14 

odontocete cetaceans (13 delphinids, including Tursiops and a 

Kogia). They found that fibers of the terminal nerve issue from 

the brain just anterior to the optic chiasma and leave the cranial 

cavity through several minute foramina in the cribriform plate. 

They were unable to trace them outside the cranial cavity.

= turbinals

See ethmoidal labyrinth.

− uncinate notch (incisura uncinata) 

The uncinate notch is located posterodorsal to the uncinate 

process of the ethmoid bone in the meatus between the first two 

endoturbinates (Evans and Christensen, 1979:137).

In Tursiops and other odontocetes the turbinals are not developed, so the uncinate notch does not exist.

− uncinate process (processus uncinatus)

The uncinate process is a part of the first endoturbinate and 

of the orbital lamina (lateral lamina) (Evans and Christensen, 

1979:137; Feneis, 1994:20.16). This feature of the ethmoid 

should not be confused with the uncinate process (accessory ossicle) of the tympanic bulla (q.v.).

In Tursiops and other odontocetes the turbinals are not developed, so the uncinate process does not exist.

− ventral nasal concha (os conchae nasalis ventralis)

In most mammals the ventral nasal conchae (maxilloturbinate) are a series of scrolls that occupy the anterior part of 

the nasal cavity and are attached to the crista conchalis on the 

medial surface of the maxilla (Evans and Christensen, 1979: 

512).

In Tursiops and other odontocetes the turbinals are not developed, so the ventral nasal concha does not exist.

EXOCCIPITAL BONE

Os Exoccipitalis

Figures 1, 3–5, 6b,c,e, 9, 28,29, 31a

The exoccipitals form part of the posterolateral wall of the 

cranium. They are paired ossifications that form the occipital 

condyles on their medial aspects. The exoccipitals are also known 

as the lateral processes (partes laterales) of the occipitals.

The exoccipitals are bounded by the supraoccipitals dorsally, the parietals anterolaterally, the squamosals anteriorly, 

and the basioccipital anteroventrally.

− anterior basi-occipital angle (Anderson, 1879:502)

Anderson (1879:502), in his description of the skull of Platanista made this statement:

The notch in the skull is converted into a foramen. 

The transverse ridge terminates above the inner border 

of the paroccipital process on a line with the anterior 

basi-occipital angle of the bone [exoccipital]; the 

whole of the paroccipital process below that level is 

outside and deeply concave, especially at its lower 

margin, where a distinct pit is formed.

This is the only section in which Anderson used the term, 

and from this we are unable to make any reliable reference to the 

anterior basi-occipital angle.

= anterior condyloid foramen (Anderson, 1879:503) = hypoglossal foramen (Gray, 1918:131)

e x o c c i p i t a l n u m b e r 6 2 7 • 1 7
* basion (Figure 5)

The basion is the craniometric point that is located in the 

middle of the ventral margin of the foramen magnum. The ventral border of the foramen magnum in delphinids consists entirely of exoccipitals.

− bullar process of the exoccipital bone (Luo and Gingerich, 

1999:29, 41)

Luo and Gingerich (1999:29, 41) described the bullar process of the exoccipital bone in some archaeocetes. The process 

articulates with the medial prominence of the tympanic bulla. 

Luo and Gingerich (1999) also used the apparently synonymous 

terms “exoccipital protuberance” and “exoccipital contact.” 

Luo and Gingerich (1999:41) stated that the bullar process of the 

exoccipital bone is separated by the jugular notch from the posterior part of the basioccipital crest (basioccipital falcate process, 

in their terminology). However, judging from Luo and Gingerich 

(1999: fig. 18b), the jugular notch lies immediately posterolateral 

to the bullar process of the exoccipital bone. The bullar process 

of the exoccipital bone should not be confused with features of 

the mammalian tympanic bulla or periotic bone / petrosal (e.g., 

Novaceck, 1986:52; Wahlert, 2000: fig. 1).

In Tursiops the bulla does not contact the exoccipital and 

there is no bullar process of the exoccipital bone.

* cerebellar juga (Figures 9d, 31a)

The cerebellar juga consists of all the bony internal elevations formed by the sulci of the cerebellum (Evans and Christensen, 1979:157). “Cerebral juga” is sometimes used as a 

general term for all the bony internal elevations formed by the 

sulci of the brain.

The cerebellar juga are the same in cetaceans as they are in 

any other mammals.

* concavity for lobes of the cerebellum (Figure 9a)

In all mammals there is a concavity on the internal surface 

of the exoccipital that houses the lobes of the cerebellum.

In Tursiops and other odontocetes it lies just lateral and 

slightly ventral to the foramen magnum.

− condylar canal (canalis condylaris)

The condylar canal lies in the dorsal condyloid fossa. The 

condylar canal contains the sinus condylaris that communicates 

with the transverse sinus (Evans and Christensen, 1979:122; 

Schaller, 1992:16.19; Feneis, 1994:8.15). Gray (1918:131) referred to it as the condyloid canal. Vesalius (1543:53; Vesalius et 

al., 1998:131) referred to the condylar canal as the non insigniter 

amplum foramen, quod ab externa calvariae sede, x posteriori 

nimirum sede capitis occipitii ossis.

The development of the condylar canal is questionable in 

Tursiops. There are a number of “nutrient foramina” that open 

into the condylar foramen externally and into the sulcus for the 

transverse sinus internally. These may be dorsal condyloid foramina (q.v.) in the sense of Wible and Gaudin (2004). It is extremely difficult to probe these and establish whether or not they 

communicate with one another.

= condylar foramen

See condyloid foramen.

= condyloid foramen = condylar foramen = hypoglossal foramen 

(Flower, 1885:210; Flower and Lydekker, 1891:38, fig. 

8; McFarland et al., 1979:8)

Anderson (1879:451, fig. 15) appeared to use this term to 

refer to the foramen magnum. 

See also hypoglossal foramen.

= condyloid fossa

See dorsal condyloid fossa, ventral condyloid fossa.

* cranial hiatus = jugular foramen in part, or posterior lacerate 

foramen (Figure 31b)

In odontocetes the tympanoperiotic does not protrude into 

the cranial cavity but is displaced ventrolaterally so that the periotic no longer contributes to a continuous wall of the cranial 

cavity and is physically separated from dorsally and/or medially 

adjacent bones. Fraser and Purves (1960) introduced the term 

“cranial hiatus” for the resulting space between the dorsal or 

cerebral part of the periotic and the adjacent exoccipital, basioccipital, alisphenoid, parietal, and squamosal. Many later authors 

have referred to the structure but, probably because Fraser and 

Purves (1960) did not explicitly define the cranial hiatus, concepts of the cranial hiatus vary. To help define the cranial hiatus, 

consider the statements of Fraser and Purves (1960).

Fraser and Purves (1960:30) commented: “the paths of the 

[cranial] nerves [on the basicranium] are restricted to three exits, 

that associated with the optic infundibulum, that of the infundibulum of the foramen ovale and that of the ‘cranial hiatus’ 

in the vicinity of the periotic”. And about Grampus, they commented that “the cranial hiatus is obliterated by secondary bone, 

except for the foramina of the auditory nerve and the foramen 

lacerum posterius” (Fraser and Purves, 1960:56). We interpret 

these statements to mean that the cranial hiatus is the confluent 

path for cranial nerves VII to IX and associated vessels not otherwise in named foramina or canals.

Fraser and Purves (1960:34) commented: “The Mysticeti 

differ from the Odontoceti in that the tympano-periotic is not 

completely extruded from the cranial wall—thus there is no cranial hiatus.” We interpret this to mean that the cranial hiatus is 

not developed in Cetacea in which the periotic contributes to the 

cranial wall in the broad sense.

Fraser and Purves (1960:40) commented, for ziphiids: “In 

very young specimens there is a cranial hiatus dorsal to the periotic but this is soon occluded by extensions of the bones adjacent 

to the hiatus.” For the sperm whale Physeter, they commented 

(1960:43): “The tympano-periotic bones are excluded from the 

wall of the cranium and in the specimen examined, no trace of the 

cranial hiatus remains,” and for the porpoise Phocoena they said 

(1960:49): “The cranial hiatus, dorsal to the ear bones is partly 

filled by osteosclerotic extensions of the basioccipital . . . and parietal.” We interpret this to mean that the cranial hiatus may become closed during ontogeny to the extent that it is eliminated.

Finally, Fraser and Purves (1960:63, 64) commented for 

Inia that “the peribullary sinus completely surrounds this bone 

[tympanoperiotic]. As in the previously described species [Pontoporia], the centre of the mass represents the air space between 

the periotic and the skull and coincides with the position of the 

cranial hiatus.” We interpret this to mean that the cranial hiatus 

is functionally associated with the peribullary sinus.

1 8 • smithsonian contributions to zoolog y e x o c c i p i t a l
The term “tympano-periotic hiatus” (Fraser and Purves, 

1960:133) may be a lapsus calami.

“Cranial hiatus” has been used since with various meanings. Here, the cranial hiatus is defined as the confluent opening for the posterior lacerate foramen, jugular foramen, and 

the internal acoustic meatus. The cranial hiatus comprises the 

enlarged basicapsular fissure plus adjacent foramina associated 

with nerves, with the petrosal sinuses, with the posterior lacerate 

foramen, and with the jugular foramen. In the young animal and 

in some fossil species, the foramen ovale may be confluent with 

the cranial hiatus.

Tursiops has a cranial hiatus that may become constricted 

in older specimens by bone outgrowths, producing sulci or endocranial foramina for nerves and vessels, and resulting in distinct 

endocranial foramina for the vestibulocochlear nerve and facial 

nerve, and posterior lacerate and jugular foramina. The cranial 

hiatus occurs in most living Cetacea.

Earlier Owen referred to the cranial hiatus as the otocranial 

vacuity (1866a:30) or the otocranial cavity (1866a:40). Flower 

(1867:94) gave a lucid description but did not use a formal name. 

Schulte (1917:374) used the terms secondary internal auditory 

canal and secondary internal auditory meatus without definition 

in a context that suggests cranial hiatus. The cranial hiatus includes the petrosoparoccipital fissure of Luo and Gingerich (1999: 

tbl. 6, #34b), the basicapsular fissure (sensu Luo and Gingerich, 

1999), and the basicapsular fenestra (or basicochlear fissure) 

(sensu MacPhee, 1981:4948) of other mammals. Luo and Gingerich (1999:41) used the terms tympanic cavity and peribullar 

cavity apparently to refer to the cranial hiatus. Barnes (1985:3) 

indicated that the foramen ovale might be separate from the cranial hiatus, and (Barnes, 1990:21, #19; 22, #23) indicated that the 

cranial hiatus is formed by merging of the middle and posterior 

lacerate foramina. Heyning (1989a:51, character 24) stated that 

the margins of the cranial hiatus are formed from the squamosal, 

parietal, and occipital bones. Yamagiwa et al. (1999) identified the 

cranial hiatus in Grampus as the “foramen lacerum” (for nerves 

IX, X, XI, and internal jugular vein), not including the exit for the 

vestibulocochlear and facial nerves. Geisler and Sanders (2003:87) 

stated that the cranial hiatus is the basicapsular fenestra. Current 

use suggests that the piriform fenestra (q.v.) is also part of the cranial hiatus. Judging from the situation in other mammals (Wible 

and Gaudin, 2004:131), the cranial hiatus may include the equivalent of the mammalian foramen for the inferior petrosal sinus.

See also jugular foramen and endocranial sulcus.

− dorsal condyloid foramen (Wible and Gaudin, 2004:151)

Wible and Gaudin (2004:151) named the dorsal condyloid 

foramina in the yellow armadillo as the small nutrient foramina 

that open into the dorsal condyloid fossa.

Adult specimens of Tursiops have variably developed dorsal 

condyloid foramina in the dorsal condyloid fossa. 

See also condyloid canal.

* dorsal condyloid fossa (fossa condylaris dorsalis) (Figures 5, 

9c,e)

The dorsal condyloid fossa lies immediately dorsal to the occipital condyles on the exoccipital bone. The fossa provides room 

for movement of the atlas. The condylar foramen is perforated 

by the condyloid canal, through which an emissary vein passes 

from the transverse sinus (Evans and Christensen, 1979:122). 

The dorsal condyloid fossa is present and is better developed 

than the ventral condyloid fossa in all cetaceans.

= exoccipital contact of the exoccipital (Luo and Gingerich, 1999)

See bullar process of the exoccipital bone.

– exoccipital plate (Owen, 1866a:35)

Owen uses exoccipital plate (1866a:35) to refer to the 

contribution of the exoccipital to the circumnarial basin

(Owen, 1866a:44) or supracranial basin (Flower, 1868:314) in 

Physeter.

The exoccipital plate is not developed in delphinids.

= exoccipital protuberance (Luo and Gingerich, 1999)

See bullar process of the exoccipital bone.

= falcate crest of the exoccipital (Luo and Gingerich, 1999:41) = 

medial occipital crest

Luo and Gingerich (1999:41) mentioned the falcate crest 

for archaeocetes and archaic odontocetes, but did not define it. 

Uhen (2004:48) noted an exoccipital contribution to the falcate 

process in archaeocetes.

See medial exoccipital crest, pharyngeal crest.

* foramen magnum (Figures 5, 9d,e, 31a)

The foramen magnum is bounded by the posteromedial margins of the basioccipital, exoccipital, and supraoccipital bones 

(Gray, 1918:129, 132, 192; Evans and Christensen, 1979:121, 

123; Schaller, 1992:16.3; Feneis, 1994:8.3). It transmits the spinal cord. Vesalius (1543:22) referred to the foramen magnum as 

merely the “foramen,” but in another section he referred to the 

foramen magnum as the foramen unicum, caeterisque omnibus 

facile maximum, quod occiptis ossi insinuatur, gratia dorsalis 

medullae ex cerebro originem ducentis (Vesalius, 1543:53; Vesalius et al., 1998:131).

The foramen magnum is well developed in cetaceans where, 

in addition to the spinal cord, it transmits branches of the vertebral 

vascular plexus. That plexus forms the main blood supply to the 

brain. The foramen magnum has also been called the occipital foramen (Anderson, 1879:428; Owen, 1866a:34; Schulte, 1917:365).

* hypoglossal canal (canalis hypoglossi) (canalis n. hypoglossi) 

(Figures 9a,d, 28, 31b)

The hypoglossal canal runs in an anteroventral direction 

from the floor of the cerebellar fossa in the cranial cavity to 

the hypoglossal foramen (Evans and Christensen, 1979:122). 

The internal opening is not named (Gray, 1918:131; Schaller, 

1992:16.18; Feneis, 1994:8.16). Vesalius (1543:53; Vesalius et 

al., 1998:131) referred to the hypoglossal canal as the foramen in 

occipitii osse gratia ervi septimi paris nervorum ceebri incisum.

In odontocetes the hypoglossal canal is well developed ventrally and somewhat anterolaterally (Schulte, 1917:375).

− hypoglossal depression

The hypoglossal depression is a small oval depression into 

which opens one or more hypoglossal foramina in the rodent 

Exmus (see Wible et al., 2005:118).

Tursiops lacks a hypoglossal depression.

e x o c c i p i t a l n u m b e r 6 2 7 • 1 9
* hypoglossal foramen (Figure 9b)

The hypoglossal foramen opens on a ridge of bone anterior 

to the ventral condyloid fossa. This foramen forms the opening 

of the hypoglossal canal, which transmits the hypoglossal nerve 

(Schulte, 1917:379, 401; Evans and Christensen, 1979:122). 

McDowell (1958:123, 125) cautioned that the hypoglossal foramen should not be confused with the condyloid foramen (see 

also Wible and Gaudin, 2004:175).

In Tursiops the hypoglossal foramen is situated on a ridge of 

bone between the posterior end of the basioccipital crest and the 

paroccipital process and opens into the jugular notch.

− hypoglossal fossa

Novacek (1986:65) said: “Usually the [paroccipital] process is weak where the hypoglossal fossa of the basioccipital is 

crowded by the large mastoid process and the ventral occipital 

condyle.” We have not found a clear definition for the hypoglossal fossa, and thus cannot identify it in Tursiops.

= hypoglossal notch = jugular notch

The hypoglossal notch is equivalent to the jugular notch. 

This term comes from Kernan (1918:384), where he used it for 

the notch that lies between the paroccipital process and the otocranial process.

* intercondyloid notch (incisura intercondyloidae) (Figures 2, 

5, 28)

The intercondyloid notch lies between the ventral portions 

of the occipital condyles. It forms the ventral border of the foramen magnum and consists, in most mammals, of the posteromedial portion of the basioccipital bones (Evans and Christensen, 

1979:123). Odontoid notch (see under “Basioccipital Bone”) is 

an alternative use (Wible, 2003:166).

The intercondyloid notch is well developed in Tursiops and 

all other cetaceans. The intercondyloid notch is formed by the 

exoccipital ossifications in Tursiops. The exoccipitals fuse posteromedially, preventing the basioccipital from forming part of 

the margin of the foramen magnum.

− intrajugular process of the exoccipital bone (processus intrajugularis)

The intrajugular process of the exoccipital bone is a spicule 

of bone that may project into the posterior part of the jugular 

foramen (jugular notch) (Gray, 1918:131; Schaller, 1992:16.21; 

Feneis, 1994:8.21; not in Evans and Christensen, 1979).

The intrajugular process of the exoccipital bone does not 

appear to exist in Tursiops.

− intraosseous passage

There is an intraosseous passage between the condyloid 

canal and the hypoglossal canal in dogs (Evans and Christensen, 

1979:122). This canal does not appear to be named.

The existence of the intraosseous passage in cetaceans is not 

demonstrated.

= jugal notch [paroccipital notch]

This appears to be a printing error in Rommel (1990). Other 

authors have referred to it as the jugular notch.

* jugular foramen (foramen jugulare) [part of the posterior lacerate foramen] (Figures 6b, 30, 31b)

The jugular foramen in the dog is a large aperture in the 

petro-occipital fissure (Evans and Christensen, 1979:156; 

Schaller, 1992:12.1). In humans it is subdivided into three compartments (Gray, 1918:181; Feneis, 1994:30.18). The anterior 

compartment transmits the ventral petrosal sinus; the intermediate compartment transmits the glossopharyngeal nerve, vagus 

nerve, and accessory nerve; the posterior compartment transmits 

the transverse sinus and some meningeal branches from the occipital artery and ascending pharyngeal artery (Gray, 1918:181). 

McDowell (1958:124) noted that, in some mammals, the posterior lacerate foramen (for nerves IX, X, and XI) might also 

transmit the jugular vein, so that jugular foramen and foramen 

lacerum posterius could be used interchangeably; see also discussion by Wible (2003:176). McDowell (1958) cited Story (1951) 

as differentiating the nervous foramen lacerum posterius from 

the venous jugular foramen. Vesalius (1543:53; Vesalius et al., 

1998:131) referred to the jugular foramen as the foramen occipitis ossi and temporis ossi commune, ac sexto pari nervorum 

cerebri, and maiori internae jugularis venae ramo, minoribus soporalis arteriae soboli exculptu.

In odontocetes the jugular foramen is inferred to be the 

generally undifferentiated most-posterior part of the cranial 

hiatus. The jugular foramen is normally marked by a sulcus, 

presumably for the jugular vein, that runs vertically up the face 

of the exoccipital from the jugular or hypoglossal notch. In 

Cetacea, as in land mammals, the terms jugular foramen and 

posterior lacerate foramen (foramen lacerum posterius, q.v.) 

are commonly interchanged (e.g., McFarland et al., 1979:10). 

Odontocetes in which the cranium is extremely heavily ossified, 

with bony occlusion of the cranial hiatus, may have a more-anteriorly placed posterior lacerate foramen for nerves IX, X, and 

XI that is separate from a distinct more-posterior jugular foramen; we recommend that “jugular foramen” be used only when 

the bony path for the jugular vein is separate from the posterior 

lacerate foramen.

= jugular incisure = jugular notch

See Schulte, 1917:375 for Kogia; Melnikov, 1997:37, for 

fetal Physeter.

* jugular notch (incisura jugularis) (Figures 2, 9a,b,d,e, 28)

The jugular notch forms the posterior or exoccipital portion 

of the jugular foramen (Gray, 1918:131; Schaller, 1992:12.1, 

16.20, 22.26). It lies just medial to the petrous margin of the 

exoccipital. In delphinids the jugular notch is well developed between the paroccipital process and the basioccipital crest. The 

jugular notch is the feature referred to as the paroccipital notch

(Fraser and Purves, 1960:15, 29, 39) and may be the feature referred to as the paroccipital fissure (Fraser and Purves, 1960:13). 

The jugular notch has also been referred to as the jugular incisure (Schulte, 1917:375; Melnikov, 1997:37).

= jugular process (processus jugularis) = paroccipital process

For a discussion of the equivalence of the mammalian paroccipital process and human jugular process, see Gray, 1918:131, 

fig. 129; McDowell, 1958:125, 126; and discussion below under 

2 0 • smithsonian contributions to zoolog y e x o c c i p i t a l
paroccipital process. Wible et al. (2005:110, 111) noted confusion in the use of the term “paroccipital process.” 

See also paracondylar process.

− jugular tubercle (tuberculum jugulare)

The jugular tubercle is an oval eminence that overlies the 

hypoglossal canal in the cranial cavity in humans. It is sometimes 

crossed by an oblique groove for the glossopharyngeal nerve, 

vagus nerve, and accessory nerve (Gray, 1918:131).

The jugular tubercle does not appear to exist in Tursiops.

= jugulo-acoustic canal (Schulte, 1917:379, 384, 399) = jugular 

foramen

= lateral occipital fontanelle = mastoid fontanelle (Kernan, 

1918:384)

− mastoid fontanelle

The mastoid fontanelles occur at the juncture of the parietal, squamosal, and exoccipital centers of ossification (Gray, 

1918:197).

The mastoid fontanelles are closed by the time of birth in 

Tursiops. That area of the skull is one of the most heavily ossified areas in delphinids.

− mastoid margin of the exoccipital (margo mastoideus)

The mastoid margin of the exoccipital is that portion of the 

exoccipital that abuts the mastoid process of the temporal (Sisson 

and Grossman 1953:48; Schaller, 1992:16.23; Feneis, 1994:8.9).

The posterior process of the tympanic bulla does not contact the rest of the skull in Tursiops but is closely approached by 

the mastoid margin of the exoccipitals.

* medial exoccipital crest [new term] (Figure 9b,e)

The medial exoccipital crest is the posterior part of the pharyngeal crest formed by the exoccipital medial to the jugular 

notch in archaic fossil Cetacea and some living species. Because 

an exoccipital component is not apparent, the medial exoccipital 

crest is not distinct in adult Tursiops. 

See basioccipital crest for “falcate crest” and other synonyms; see also pharyngeal crest.

− occipital bone (os occipitale) (McFarland et al., 1979:10)

The bone forming the base and posterior parts of the skull 

is sometimes referred to as the occipital bone (McFarland et al., 

1979:10). It is composed of separate ossification centers known as 

the basioccipital, exoccipital, and supraoccipital, under which heading we discuss it. Schulte (1917:370), in describing Kogia, referred 

to the supraoccipital and parietal as the “occipital complex.”

* occipital condyle (condylus occipitalis) (Figures 5, 9b,c, 28, 

31a)

The occipital condyles are a pair of rounded structures located on the posteromedial ends of the exoccipital bones. They 

form an articular surface for the first vertebra (atlas) (Gray, 

1918:131; Evans and Christensen, 1979:122, 151; Schaller, 

1992:16.13; Feneis, 1994:8.14). Vesalius (1543:22, 23) referred 

to the occipital condyles as capita occipitii ossis.

The occipital condyles are well developed in all cetaceans 

(Schulte, 1917:365, 370).

− occipital fontanelle

See “Interparietal Bone.”

= occipital foramen = foramen magnum (Anderson, 1879:428; 

Owen, 1866a:34; Schulte, 1917:365)

− occipitomastoid suture (sutura occipitomastoidea) 

The occipitomastoid suture lies between the occipital and 

the mastoid process of the temporal (Schaller, 1992:76.7; Evans 

and Christensen, 1979:123; Feneis, 1994:54.5; Gray, 1918:183). 

In some mammals (horse, dog) it is a continuation of the occipitosquamous suture; in others (humans), of the lambdoid suture. 

This suture is visible in the posterior and lateral views of the 

skulls. Vesalius (1543:23) referred to the occipitomastoid suture 

as charactibus.

In delphinids, including Tursiops, isolation of the parts of 

the temporal (tympanic bulla and periotic bone (petrosal)) has 

removed them from contact with the exterior surface of the skull, 

and the occipitomastoid suture, as such, does not occur. In cetaceans whose posterior process of the tympanic bulla is visible 

on the external surface of the skull (e.g., ziphiids), there may also 

exist an occipitomastoid suture. 

See discussion under mastoid portion of the squamosal, 

mastoid process of the petrosal, and posterior process of the 

tympanic bulla.

= oval condyle = occipital condyle (Flower, 1885:211)

= paracondylar process (processus paracondylaris) = paroccipital 

process

Paracondylar process or paracondyloid process is frequently 

used for noncetacean mammals (see e.g., Evans and Christensen, 

1979: fig. 4.9; Wible, 2003:166; Wible et al., 2005:110, 111), 

but the terminology is rare in cetacean literature (e.g., Ridewood, 1922:216, noted as a synonym for paroccipital process; 

Eales, 1950:5), where paroccipital process is used widely. See 

also McDowell’s (1958:126) comment on synonymy of paroccipital and jugular process.

Kernan (1918) used paracondyloid process (p. 358) in 

Ziphius as equivalent to the paroccipital process (p. 357).

− paramastoid process (processus paramastoideus)

The paramastoid process is an obtuse projection of the ventral surface of the jugular process, at the insertion of the rectus 

capitis lateralis muscle (Whitney, 1889–1910:[vol. 6]4746). It is 

variable in humans (Gray, 1918:131). This definition indicates 

that the paramastoid process is the same as the paroccipital process (q.v.) of cetacean use.

There seems to be no distinct insertion of the rectus capitis lateralis muscle in odontocetes, but Geisler et al. (2005:18) described 

a depressed possible insertion in the archaeocete Carolinacetus.

* paroccipital concavity (Figures 2, 9a,b)

The paroccipital concavity (“concavity of the paroccipital 

process,” Fraser and Purves, 1960:9) is the anteroventral surface 

e x o c c i p i t a l n u m b e r 6 2 7 • 2 1
of the paroccipital process that is filled with a branch of the posterior sinus. The paroccipital concavity is unique to cetaceans.

= paroccipital notch = jugular notch (Rommel, 1990:37)

= paroccipital pneumatic sinus (sinus pneumaticus paroccipitalis) (van der Klaauw, 1931:37, 263) = posterior sinus

* paroccipital process (Figures 2, 5, 9b,c)

The paroccipital process in cetaceans is known by various names in some other mammals. According to Mangal et al. 

(2004:335), in humans, “owing to the proximity of diverse osseous landmarks, the PCP [paracondylar process] has also been 

variously termed as the paraoccipital [sic], parajugular, jugular, 

juxtamastoid, or paramastoid process.” For example, in some 

terrestrial mammals, the jugular process is identified as a rounded 

process lateral to the occipital condyles on the exoccipital bones. 

It lies just lateral to the ventral condyloid fossa (Evans and Christensen, 1979:122). In humans this forms the attachment for the 

rectus capitis lateralis muscle and the lateral atlantoccipital ligament (Gray, 1918:131, 181).

In his description of the intact skull of the dog, ventral view, 

Miller labeled the process at the posterolateral angle of the skull 

as the jugular process (Evans and Christensen, 1979:152, figs. 

4–39) and discussed it on page 153. In his description of the occipital bones, Miller labeled the same process the paracondylar 

process (Evans and Christensen, 1979:121, figs. 4–9) and discussed this process on page 122 as the jugular process. Further, 

Wible and Gaudin (2004:138) discussed the term “paroccipital 

process” as applied to features of the petrosal (periotic bone) 

and the adjacent exoccipital; they noted that the so-called paroccipital process of the exoccipital is more appropriately referred 

to as the jugular process (base) and paracondylar process (tip); 

see also Wible et al. (2005:110, 111).

In odontocetes the paroccipital process lies lateral to the 

posterior end of the basioccipital crest and the hypoglossal canal. 

It lies posterior or posteromedial to the postglenoid process of 

the squamosal bone. The paroccipital process articulates via a 

synchondrosis with the lateral end of the stylohyal bone. Paroccipital process in this sense has had a long and unambiguous history of use in cetacean anatomy (see Fraser and Purves, 1960:9, 

15, 35, 37–47, 49–63, 65–68, 72, 73, 77, 108).

Kernan (1918) used paracondyloid process (p. 358) as equivalent to the paroccipital process (p. 357) and Owen (1866a:26, 

30, 34, 35, 36, 40) referred to the paroccipital process as just the 

paroccipital (no process).

− posterior condyloid foramina

The posterior condyloid foramina applies to the two areas 

in Platanista of the occipital shield where bone may be developmentally absent (Anderson, 1879:502). This condition occurs in 

the exoccipital in Platanista. It is reminiscent of the situation in 

monodontids where the foramina occur at the juncture of the 

exoccipitals and supraoccipitals.

= posterior lacerate foramen

MacPhee (1981:60) noted that the posterior lacerate foramen is distinct from the jugular foramen in some mammals, in 

which case it transmits nerves IX, X and XI.

In Tursiops and other odontocetes, the condylar foramen

may become constricted in older specimens by bony outgrowths, 

producing sulci or endocranial foramina for nerves and vessels. 

Heavy ossification may produce a more-anteriorly placed posterior lacerate foramen for nerves IX, X, and XI that is separate 

from a distinct more-posterior jugular foramen for the jugular 

vein. We recommend that “posterior lacerate foramen” be used 

only when the bony path for nerves IX, X, and XI is separate 

from the jugular foramen.

See cranial hiatus and Table 4.

= posterior pterygoid sinus (Luo, 1998:285) = posterior sinus

− posterior sinus

The posterior sinus is one of the accessory air sinuses connected with the tympanic cavity in cetaceans. The sinus arises 

through the elliptical foramen and spreads out over the anteroventral part of the paroccipital concavity occupying the paroccipital fossa (Fraser and Purves, 1960:8–10, 62, 63, 65–68, 

70–72, 74).

In Tursiops the posterior sinus, sensu stricto, has also been 

termed the paroccipital pneumatic sinus (sinus pneumaticus paroccipitalis of van der Klaauw, 1931:37, 263), and the posterior 

pterygoid sinus (Luo, 1998:285). The posterior sinus, sensu 

stricto, is not to be confused with the posterolateral sinus, which 

is a posterolateral extension of the peribullary sinus. This lies 

dorsal to the paroccipital process and posterior to the tympanic 

bulla, and often occupies a marked posterolateral sinus fossa in 

the anterior face of the paroccipital process.

* posterior sinus crest [new term] (Figure 9b,d)

The posterior sinus crest in Tursiops and other odontocetes 

lies at the anterodorsal margin of the posterior sinus fossa in the 

anterior portion of the paroccipital process.

* posterolateral sinus crest [new term] (Figure 9a,d)

The posterolateral sinus crest is unique to cetaceans. The 

crest lies on the anterior surface of the paroccipital process just 

ventral to the level of the jugular notch and immediately dorsal 

to the paroccipital concavity. The crest is formed by the posterolateral sinus, which is a posterolateral extension of the peribullary sinus.

* posterolateral sinus fossa [new term] (Figure 9a,d)

The posterolateral sinus fossa is formed by the posterolateral extension of the peribullary sinus. The posterolateral sinus 

fossa lies on the paroccipital concavity and extends along the 

ventral surface of the paroccipital process (shown by Fraser and 

Purves, 1960:8, 25:fig. 8, 70, who did not differentiate it from 

the posterior sinus fossa), where lies in the posterolateral sinus 

fossa. The posterolateral extension of the peribullary sinus is distinct from the posterior sinus (q.v.), which is identified by its 

origin via the elliptical foramen. The posterolateral sinus fossa is 

terminated anterodorsally by the posterolateral sinus crest.

= precondyloid foramen (Anderson, 1879:502, 504, 510) = cranial hiatus

= precondyloid notch = hypoglossal notch (Anderson, 1879:502)

2 2 • smithsonian contributions to zoolog y e x o c c i p i t a l
= secondary internal auditory canal = cranial hiatus (Schulte, 

1917:374)

= secondary internal auditory meatus = cranial hiatus (Schulte, 

1917:374)

* sulcus for intracranial extensions of the spinal meningeal 

arteries (Figure 9a)

The intracranial extensions of the spinal meningeal arteries 

are a development of cetaceans in response to their increased 

dependence on the vasculature of the spinal column to supply the 

brain (McFarland et al., 1979). The sulcus for the intracranial 

extensions of the spinal meningeal arteries enters the cranial cavity along the dorsolateral aspect of the foramen magnum. The 

sulcus for the intracranial extensions of the spinal meningeal arteries then courses anteriorly across the concavity for lobes of the 

Table 4. Terms applied to the region of the mammalian skull that includes the cranial hiatus sensu lato, namely, foramina or openings 

associated with the periotic and/or tympanic bulla and medially adjacent bones. The authors cited are not necessarily the first users of 

the terms. References to synonyms for foramen ovale and jugular foramen are not included. See discussion under cranial hiatus and 

posterior lacerate foramen.

Term Reference(s) Comments

Basicochlear fissure MacPhee, 1981:48, Wible and Gaudin, Wide gap between basioccipital and petrosal in some

2004 mammals.

Basicapsular fenestra MacPhee, 1981:48, Geisler and Sanders, Basicochlear fissure (see above), according to MacPhee. 

2003:87, Wahlert, 2000 Cranial hiatus, according to Geisler and Sanders, 2003. 

Open basioccipital-petrosal suture according to Wahlert, 

2000.

Piriform fenestra MacPhee, 1981:59; Wible and Gaudin, Large gap occasionally in adult mammals, anterior to 

2004:162; Wible et al., 2005:109; petrosal and/or bulla, usually between petrosal and/or 

Wahlert, 2000:8 bulla and sphenoid (basisphenoid, alisphenoid), and 

squamosal. Middle lacerate foramen of some authors.

Lacerate foramen Gabbert, 2004:185, 186, 189 Confluent piriform fenestra, basicochlear fissure, and 

jugular foramen. See sphenotympanic fissure.

Sphenotympanic fissure Gabbert, 2004:185 Composite foramen ventral to piriform fenestra in 

Toxodontia, probably for the mandibular branch of the 

trigeminal nerve, nerves of the pterygoid canal, and any 

derivative of the internal carotid artery.

Anterior lacerate foramen Sisson, 1910:57 Median lacerate foramen, = incisura carotica, incisura 

ovalis, and incisura spinosum of Sisson; = Sisson’s 

anterior part of the foramen lacerum basis cranii.

Foramen lacerum basis cranii Sisson, 1910:57 = Foramen lacerum et jugulare in sense of Sisson, 

= foramen lacerum anterius + foramen lacerum posterius

in sense of Sisson.

Posterior lacerate foramen MacPhee, 1981:60 As distinguished from jugular foramen when the latter is 

distinct. See text on lacerate foramina in general, and on 

posterior lacerate foramen.

Jugular foramen MacPhee, 1981:60 As distinguished from posterior lacerate foramen when the 

latter is separate. See text on jugular foramen.

Cranial hiatus Fraser and Purves, 1960 See text on cranial hiatus.

Tympano-periotic hiatus Fraser and Purves, 1960:133 Synonym for cranial hiatus.

Petro-occipital fissure [petrooccipital] Gray, 1918:193 Groove between petrosal and basioccipital, anterior to 

jugular foramen, associated with groove for inferior 

petrosal sinus.

Incisura basiparoccipitalis McFarland et al., 1979:21, 38 “A notch in the ventral surface of the skull . . . angled 

somewhat dorsad and outwards to the perioticum . . .”

associated with passage of the internal carotid artery.

Tympano-occipital fissure Evans and Christensen, 1979:135; Contact of the tympanic part of the temporal bone with the 

Fordyce, 2002 basioccipital.

Otocranial vacuity, otocranial cavity Owen, 1866a:30, 40 Synonym for cranial hiatus.

e x o c c i p i t a l n u m b e r 6 2 7 • 2 3
cerebellum, crossing the tentorium at its midpoint. The sulcus 

for the intracranial extensions of the spinal meningeal arteries 

then turns ventrally across the parietal and the alisphenoid and 

breaks up into an internal ophthalmic rete mirabile in the region 

of the hypophysis (pituitary body).

McFarland et al. (1979) presented admirable illustrations 

of the course of the intracranial extensions of the spinal meningeal arteries (IESMA). We have used primarily their figure 42 

(p. 63) in discussing the course of the arteries. They represented 

the arteries in their schematic illustration (p. 17: fig. 2) and give 

angiograms showing the course of those arteries in figures 27 

and 28 (1979:48, 49).

* sulcus for the sigmoid sinus (sulcus sinus sigmoidei) (Figure 9a)

The sulcus for the sigmoid sinus is a continuation of the 

sulcus for the transverse sinus. The sulcus for the sigmoid sinus 

runs from the posterior end of the periotic, medial to the petrooccipital synchondrosis, and terminates at the jugular foramen

(Evans and Christensen, 1979:793, 794).

In Tursiops the sulcus for the sigmoid sinus lies just dorsal to the jugular foramen. The sulcus extends dorsally where 

it joins the sulcus for the transverse sinus. The sulcus is better 

developed in young animals.

* tentorial crest (crista tentoric) (Figures 9a,d, 31a)

The tentorial crest is on the medial (cranial) surface of the 

squamous part of the temporal. It serves as an attachment for the 

tentorium cerebelli (Schaller, 1992:24.35; not in Feneis, 1994).

The squamosal (squamous part of the temporal) does not 

participate in the formation of the cranial cavity in delphinids. 

The attachment of the tentorium cerebelli has moved onto the 

exoccipital bones.

− tentorial process (processus tentoricus)

The tentorial process is the shelf-like body of the tentorium

(q.v.) (Evans and Christensen, 1979:124, figs. 4–12; Schaller, 

1992:16.34, 18.2, 26.4; not in Feneis, 1994).

Owen (1866a:40) used and illustrated the term “tentorial 

process” in Kogia sima. All cetaceans have a tentorial process, 

although they differ in the degree to which it is developed.

* tentorium (tentorial ossification) (tentorium cerebelli osseum) 

(Figure 9a,d)

The tentorium is formed by a leaf of bone that projects 

anteromedially from the dorsal part of the posterior border of 

the parietal and the internal occipital protuberance (Evans and 

Christensen, 1979:124, figs. 4–12; Schaller, 1992:10.10). The 

tentorium separates the cerebellum from the cerebrum. The tentorium is formed by the tentorial process (processus tentoricus) 

(Schaller, 1992:10.10, 16.34, 18.2, 26.4).

The anterolateral margin of the tentorial ossification in 

odontocetes ends on the most medial aspect of the internal surface of the parietal. The primary portion of the tentorium is on 

the exoccipital bone (Schulte, 1917:376, 379).

− ventral condyloid foramen

Wible and Gaudin (2004:166) stated that some armadillos 

may have small ventral condyloid foramina posterolateral to 

each hypoglossal foramen.

Tursiops lacks ventral condyloid foramina.

* ventral condyloid fossa (fossa condylaris ventralis) (Figures 5, 

9c,e)

The ventral condyloid fossa lies between the jugular process

and the occipital condyles on the exoccipital bone. The fossa 

provides room for movement of the atlas (Evans and Christensen, 1979:122).

The ventral condyloid fossa is present but indistinct in cetaceans. It is well developed in some fossil species.

FRONTAL BONE

Os Frontale

Figures 1, 2–5, 6a,c,d, 10, 31a, 32

The frontal bones are paired midline ossifications that form 

the anterior wall of the cranium. They contribute to the orbital 

elements of the face (Schulte, 1917:369–371, 373, 376, 379–381, 

384, 386, 389–394, 398, 400–402). Vesalius (1543:21, 23, 25) 

referred to the frontal bones as the frontis os.

The frontal bones are anterior to the interparietals; posteroventral to the nasals; ventral to the maxillae; posterior to the 

lacrimals; and lateral to the alisphenoids and orbitosphenoids.

= anterior process (Ting et al., 2002:7) = narial process of the 

frontals

− anterolateral part of the frontal sinus (sinus frontals rostralis 

lateralis)

The anterolateral part of the frontal sinus is developed in 

suids and bovids (Sisson, 1910:125, 145; Schaller, 1992:180.15). 

It is not developed in humans (Feneis, 1994:138).

The anterolateral part of the frontal sinus is not developed 

in cetaceans due to the complete lack of the paranasal sinus system (Fraser and Purves, 1960:5, 75).

− aperture to the frontal sinus = nasofrontal opening

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75) but occur in some fossils (Edinger, 1955).

= ascending process of the frontal bone = maxillary surface of 

the frontal

− caudal frontal sinus (sinus frontalis caudalis) = posterior portion of the frontal sinus

Paranasal sinuses are not developed in extant cetaceans 

(Fraser and Purves, 1960:5, 75).

* cerebral juga (Figures 10b,e, 31a)

The cerebral juga consist of all the bony internal elevations 

formed by the sulci of the brain. The elevation formed by the 

sulci of the cerebellum is sometimes distinguished as cerebellar 

juga (Evans and Christensen, 1979:157).

The cerebral juga are the same in cetaceans as they are in 

other mammals.

* cerebronasal plate of the frontal bone (Anderson, 1879:510, 

511) (Figure 10a)

2 4 • smithsonian contributions to zoolog y frontal
The cerebronasal plate of the frontal bone or the vertical 

plate consists of the medial and dorsal parts of the frontal, comprising the maxillary surface of the frontal, frontal eminence, 

and those parts of the external surface of the frontal that project back to the nasal and interparietal margin. The cere­bronasal 

plate is the frontal bone minus the temporoorbital plate.

This concept was described in Platanista but is equally applicable to delphinids.

− cornual process (processus cornulis)

The cornual process is the process that is developed on the 

frontal bones for the horn in horned ungulates. As such, it does 

not occur in cetaceans.

? coronal suture (sutura coronalis)

The coronal suture is the suture formed by the frontal and 

parietal bones in humans (Vesalius, 1543:21, 23, 25; Gray, 

1918:178; Feneis, 1994:54.2) and most mammals (Evans and 

Christensen, 1979:125; Schaller, 1992:76.2).

In odontocetes the parietal is excluded from the dorsal midline by the interparietal ossification, which is not normally recognized in other mammals. We have interpreted the suture formed 

by the parietals / interparietal and the frontals in odontocetes as 

the coronal suture.

− crown of the cornual process (corona processus cornualis)

The crown of the cornual process (literally the “horny” process) is developed only in horned ungulates. It consists of an enlargement on the base of the horn on the frontal bone, distal to 

the neck of the cornual process (Schaller, 1992:28.20).

= digital impressions = cerebral juga, cerebellar juga

The digital impressions are formed on the internal surface 

of the cranial bones by the sulci and gyri of the brain (Evans and 

Christensen, 1979:157). 

The digital impressions are the same in Tursiops and other 

cetaceans as they are in other mammals.

See cerebral juga and cerebellar juga.

* ethmoidal foramen (foramen ethmoidale) (Figure 10b,c,e)

The ethmoidal foramina are two small openings about 1 

cm anterior to the optic canal. In dogs the smaller opening is 

in the frontosphenoidal suture. The larger opening, located posterodorsal to the smaller, passes obliquely through the orbital 

part of the frontal bone (Evans and Christensen, 1979:125; 

Schaller, 1992:14.26). In horses the ethmoid takes part in forming the ethmoidal foramina (Schaller, 1992:30.2). These two foramina carry the ethmoidal vessels and ethmoidal nerve (Evans 

and Christensen, 1979:137).

The ethmoidal foramina exist in Tursiops (the right one is 

patent in USNM 571695). They are most apparent on the internal surface of the cranium where they lie on the frontal about 

2 cm anterolateral to the optic canal. The ethmoidal foramina 

exit the cranial cavity on the ventral orbital crest near the lateral 

extent of the optic canal.

− ethmoidal incisure (incisura ethmoidalis) = ethmoidal notch 

(Gray, 1918:137)

The ethmoid incisure is a smooth concave part of the edge 

of the internal table of the frontal bone, that lies dorsal and lateral to the cribriform plate of the ethmoid (Gray, 1918: fig. 135; 

Evans and Christensen, 1979:126).

The ethmoid incisure is not developed in cetaceans due to 

the modifications to the frontal and ethmoid bones connected 

with the lack of development of the olfactory sense.

* ethmoidal margin of the frontal bone (margo ethmoidalis) 

(Figure 10a,b,d,e)

The ethmoidal margin (articular surface for the ethmoid) 

consists of the margin of the frontal bone that is bounded or 

articulates with the ethmoid. The ethmoidal margin is entirely 

internal to the skull (Evans and Christensen, 1979:125).

The articular surface for the ethmoid bone in odontocetes 

lies on the posterior or cranial wall of the narial passage. In neonatal Tursiops the ethmoid ossification has not expanded dorsally to contact the frontals and thus a wide area of cartilage is 

still present.

= ethmoidal notch = frontal fontanelle = ethmoidal incisure 

(Gray, 1918:137)

= external angular process = zygomatic process of the frontal

See postorbital process of the frontal bone.

− external frontal crest (crista frontalis externa) (Evans and 

Christensen, 1979:125)

The external frontal crest is a continuation of the external 

sagittal crest onto the frontal bone (Schaller, 1992:16.30, 18.3, 

26.6; not in Feneis, 1994).

The external frontal crest is not developed in Tursiops and 

other delphinids due to the lack of an external sagittal crest. The 

development of the nasal ridge on the frontals in Platanista is 

unrelated.

* external surface of the frontal bone (facies externa) (Figure 

10a,c)

The external surface of the frontal bone is the smooth convex surface in which the frontal eminences and superciliary arch 

lie (Gray, 1918:135).

The external surface of the frontal bones in Tursiops and 

other odontocetes is that portion of the frontal squama that is 

not overlain by the maxilla. It is bounded by the maxilla anteromedially, the nuchal crest of the interparietal posteriorly, the 

nasals medially, and the orbit laterally.

− foramen cecum [foramen cæcum]

The foramen cecum is formed by the divergence of the crests 

that unite to form the frontal crest. It lies at the anteroventral end 

of the internal surface of the frontal bone where it articulates 

with the ethmoid. This foramen is variable in size and frequently 

impervious. When it is patent it transmits a vein from the nose to 

the sagittal sinus (Gray, 1918:137).

The frontal crest is not developed in Tursiops or any other 

odontocetes.

− foramen for the frontal diploic vein

In the dog (Evans and Christensen, 1979:796) the frontal 

diploic vein drains from the diploe between the roof of the cranium and the caudal part of the frontal sinus, leaving the skull 

by the small frontal foramen (q.v.). A foramen for the frontal 

frontal n u m b e r 6 2 7 • 2 5
diploic vein occurs in other mammals (Schaller 1992:362.19). 

Wible (2003:171, on Monodelphis) listed frontal foramen and 

supraorbital foramen as synonyms.

Comparable features may be present in some Cetacea; see 

discussion under frontal foramen and supraorbital foramen of 

the frontal bone.

− foramina in frontal, dorsal surface

In some armadillos (Wible and Gaudin, 2004:155), conspicuous scattered foramina may open on the dorsal surface of the 

frontal bone. Wible and Gaudin identified these foramina of the 

dorsal surface of the frontal bone as transmitting branches of the 

external ethmoidal artery and vein.

The dorsal surface of the frontal bone in Tursiops is restricted in area compared to other mammals. The bone surface 

may be quite finely porous, with occasional small foramina, but 

Tursiops lacks conspicuous foramina on the dorsal surface of the 

frontal bone as seen in armadillos.

The multiple foramina that open on the dorsal surface of 

some archaic mysticetes and archaeocetes may represent foramina of the dorsal surface of the frontal bone sensu Wible and 

Gaudin (2004:155).

− foramina in frontal, ventral surface

In the yellow armadillo (Wible and Gaudin, 2004:155) multiple foramina may open on the ventral surface of the frontal 

bone to transmit temporal rami from the orbitotemporal canal

to the temporalis muscle.

Tursiops lacks a consistent pattern of foramina on the ventral (temporal) surface of the frontal bone, between the infratemporal crest and the orbitotemporal or temporal crest.

− fossa for the lacrimal gland (fossa glandulae lacrimals)

The fossa for the lacrimal gland is located at the juncture of 

the palatine / lacrimal / frontal sutures (Evans and Christensen, 

1979:126).

The fossa for the lacrimal gland is not present in cetaceans 

due to the absence of the gland.

− fossa for the postorbital lobe of the pterygoid sinus

See “Sphenoid Bone.”

* fossa for the preorbital lobe of the pterygoid sinus (Figure 10b)

The pterygoid sinus system is peculiar to cetaceans. The 

preorbital lobe of the pterygoid sinus is a lateral diverticulum of the pterygoid sinus that arises just anterior to the optic 

canal and orbital fissure (Beauregard, 1894; Fraser and Purves, 

1960:8, 25:fig. 8, 70, pl. 44). The preorbital lobe of the pterygoid sinus sometimes makes a shallow triangular depression 

in the frontal bone that lies between the ventral orbital crest

and the supraorbital margin of the frontal. This has been referred to as the preorbital smoothed area or recess (Fraser 

and Purves, 1960:51, 53, 54, 59, 61), preorbital extension 

of the smoothed area (1960:57), or the preorbital depression 

(1960:56).

− frons

Frons is Latin for the forehead (Dox et al., 1979:174) and 

in humans it is the anterior surface of the frontal bones lying 

between the orbits, the temporal lines, and the vertex.

Due to the changes in morphology of the facial region as a 

result of telescoping, cetaceans do not express a frons.

= frontal crest (crista frontalis)

See external frontal crest, internal frontal crest.

* frontal eminence (tuber frontale) (Figure 10a,c,d)

The frontal eminence in humans is a low rounded structure 

that occurs just dorsal to the supraorbital margin of the frontal. 

It is the first portion of the frontal bones to ossify and represents 

a manifestation of the bulge that is produced by the anterior 

part of the frontal lobes of the cerebrum (Gray, 1918:135; Feneis, 1994:18.4). In domestic animals the term is used for a flat 

eminence on the external surface of the frontal bone (Schaller, 

1992:26.27). Sisson and Grossman (1953:135, 136) used the 

vernacular term “frontal eminence” in a slightly different context to mean the highest point of the frontals in oxen, and used 

the Latin phrase torus frontalis in connection with frontal eminence. In the sense of Sisson and Grossman, the frontal eminence 

is comparable to the vertex.

The frontal eminence in odontocetes is covered by the ascending process of the maxilla but is noticeable as a slight external bulging of the maxilla and premaxilla just lateral to the 

external bony nares.

− frontal fontanelle

The frontal fontanelle is an unossified membranous interval 

that occurs in early ontogeny at the junction of the frontal and 

parietal sutures on the midline of the young animal.

Because of modification in the arrangement of the cranial 

bones (telescoping) in Cetacea, the parietals no longer occur in 

the midline and the frontal fontanelle is not developed.

− frontal foramen (foramen frontale)

In humans the frontal foramen (or frontal notch) lies on the 

supraorbital margin (external surface of the frontal bone) medial 

to the supraorbital foramen (or notch) (Evans and Christensen, 

1979:152, 913–915; Schaller, 1992:26.30; Feneis, 1994:18.9; not in 

Gray, 1918). It is formed by the arching over of the frontal incisure 

and transmits the supratrochlear artery and the medial branch of the 

supraorbital nerve. The frontal foramen is of sporadic occurrence 

in mammals and is treated incompletely in the references given. We 

suspect there is some confusion with the supraorbital foramen.

Frontal foramen is used in different senses for other mammals. See foramen for the frontal diploic vein; foramina in frontal, dorsal surface; and foramina in frontal, ventral surface.

There is no indication of development of a frontal foramen 

in delphinids in the sense of a foramen or notch on the supraorbital margin of the frontal.

Fordyce (1994:155) identified “frontal foramen” in a different sense, namely a foramen on the ventral surface of the frontal 

bone, some distance lateral to the ethmoid foramina in the fossil 

platanistoid Waipatia. Since Fordyce’s frontal foramen is well 

within the orbital surface of the skull, it is doubtful that it is 

homologous with the frontal foramen that we have defined, but 

is more likely a foramen for the frontal diploic vein (q.v.) or foramen in frontal, ventral surface (q.v.).

− frontal notch (incisura frontalis)

See frontal foramen. 

2 6 • smithsonian contributions to zoolog y frontal
− frontal sinus (sinus frontalis)

The frontal sinus is a paranasal sinus (air cavity) located between the inner and outer tables of the anterior end of the frontal bone (Schaller, 1992:28.24, 180.11). It varies more in size 

than any other cavity of the skull. It may extend into the dorsal 

parts of the maxilla and parietal bones (Evans and Christensen, 

1979:159) and be known as the sinus frontalis rostralis (Schaller, 

1992:180.12), sinus frontalis medialis (ibid., 180.16), sinus 

frontalis lateralis (ibid., 180.17), sinus frontalis caudalis (ibid., 

180.18), sinus frontalis intermedius (ibid., 180.14) sinus frontalis 

rostralis lateralis (ibid., 180.15), or the sinus frontalis rostralis 

medialis (ibid., 180.13). In most mammals the frontal sinus opens 

into the nasal cavity via the nasofrontal opening (apertura sinus 

frontalis). Vesalius (1543:51; Vesalius et al., 1998:131) referred 

to the frontal sinus as the cavitas inter duas frontis os.

The frontal sinus is lacking in delphinids owing to the lack 

of development of the entire paranasal sinus system (Fraser and 

Purves, 1960:5, 75). The situation of the paranasal sinus system in nondelphinid cetaceans is not well known. The paranasal 

sinus system, including frontal and maxillary sinus is developed 

in at least some archaeocetes (Kellogg, 1928:199; Uhen, 2004).

= frontal squama (squama frontalis) = maxillary surface of the 

frontal

In humans (Gray, 1918:135) the frontal squama is the vertical portion corresponding to the region of the forehead. This 

part of the frontal bone is so modified in Tursiops and other 

odontocetes that the term “maxillary surface of the frontal” 

(q.v.) seems more appropriate.

* frontal suture (sutura interfrontalis) (Figure 4)

The frontal suture joins the contralateral frontal bones 

(Evans and Christensen, 1979:126). Metopic suture (q.v.), interfrontal suture, and anterior portion of the sagittal suture are 

alternatives.

All cetaceans have a frontal suture (e.g., Owen, 1866a:27, 

36, 37) at the sagittal margin of each frontal. The suture may 

fuse to become indistinct.

* frontomaxillary suture (sutura frontomaxillaris) (Figure 1)

The frontomaxillary suture is formed between the frontal bone and maxilla (Gray, 1918:189; Evans and Chistensen, 

1979:125, 126, 141; Schaller, 1992:76.22; Feneis, 1994:54.16;). 

Vesalius (1543:23) referred to the frontomaxillary suture as 

merely the sutura.

All Neoceti, as a result of their cranial telescoping, change 

the sutural relationship of the frontal bone and maxilla from a 

dentate to a squamous suture, which does not fuse.

− frontozygomatic suture (sutura frontozygomatica)

The frontozygomatic suture is formed between the frontal and the zygomatic (jugal) in some mammals, such as horses 

(Schaller, 1992:76.24) and humans (Feneis, 1994:54.18). In humans this suture has also been known as the zygomaticofrontal 

suture (Gray, 1918:182). Vesalius (1543:22) mentioned it merely 

as the sutura.

The boundary of the lacrimal and jugal and their relationship with the frontal is not resolved in odontocetes (see discussion of lacrimojugal under “Lacrimal Bone”). It is unlikely that 

the frontal contacts the jugal in Tursiops.

− glabella

The glabella is a low smooth midline elevation that joins the 

superciliary arches (Gray, 1918:135).

The glabella does not occur in cetaceans due to the modifications of telescoping and the overriding of the frontal bone by 

the maxilla.

− groove for angularis oculi vein

The angular vein (vena angularis) is formed by the junction of the frontal vein and supraorbital vein. It courses ventrally 

through the medial angle of the orbit. It may produce a groove 

in the medial part of the supraorbital margin of the frontal bone 

near where the attachment of the m. orbicularis oculi occurs 

(Gray, 1918:136, 644; Evans and Christensen, 1979:125, 126).

The groove for the angularis oculi vein is not known to 

occur in cetaceans.

− infratemporal crest

See “Sphenoid Bone.” 

* infratemporal fossa

See discussion under infratemporal fossa in “Maxilla.”

− interfrontal crest (Owen, 1866a:34)

Owen used the interfrontal crest, without defining it, in a 

table of the cranial measurements of Kogia. As far as we can tell 

he used the interfrontal crest to refer to the unusual modification 

of the vertex of Kogia.

− internal frontal crest (crista frontalis intera) (Evans and Christensen, 1979:126)

The internal frontal crest is formed by the uniting of the crest 

that defines the sagittal sulcus into the internal sagittal crest. The internal frontal crest occurs in the anterior part of the internal surface 

of the frontal bone (Gray, 1918:136; White and Folkens, 1991:58). 

The internal frontal crest consists of the ventral portion of the septum of the frontal sinus (Evans and Christensen, 1979:126).

The internal frontal crest is not developed in Tursiops. The 

sagittal sulcus extends only as far anteriorly as the interparietal. 

The internal frontal crest is well developed in Platanista where the 

frontal suture is relatively well developed (Anderson, 1879:507).

* internal surface of the frontal (facies interna) (Figure 10b,e)

The internal surface of the frontal bone forms a part of the 

braincase and the nasal cavity (Evans and Christensen, 1979:126).

The internal surface of the frontal bone in odontocetes 

forms a part of the braincase and the nasal cavity, as it does in 

most mammals.

* interparietal margin of the frontal bone (Figure 10a–c,e)

The interparietal margin of the frontal bone is that portion 

of the frontal bone that abuts the interparietal bone.

In delphinids the interparietal margin consists of the posteromedial edge of the frontal bone. It is bordered laterally by 

the parietal margin of the frontal bone and anteromedially by the 

frontal margin of the frontal bone. 

See parietal margin of the frontal bone.

= intraorbital fossa (Owen, 1866a:36)

This is a lapsus calami for antorbital fossa.

frontal n u m b e r 6 2 7 • 2 7
− lacrimal fossa

See “Lacrimal Bone.” 

− lateral part of the frontal sinus (sinus frontalis lateralis)

The lateral part of the frontal sinus (q.v.) in many mammals 

occupies the whole of the supraorbital process of the frontal bone.

The frontal sinus is absent in cetaceans due to the absence of 

the paranasal sinuses (Fraser and Purves, 1960:5, 75).

* maxillary surface of the frontal (Figure 1a,c,d)

The maxillary surface of the frontal bone or frontal squama

is the surface that articulates with the maxilla. This term does 

not appear to have been used in noncetacean mammals, instead 

“frontal squama” is the name given to the portion of the frontal 

bone that is bounded posteriorly by the orbitotemporal crest, laterally by the supraorbital margin of the frontal bone, and dorsally 

by the frontonasal suture. It is largely subcutaneous in life and 

forms the forehead in humans (Gray, 1918:131; Evans and Christensen, 1979:126; Schaller, 1992:26.25; Feneis, 1994:18.2). 

Anderson (1879:525) used the maxillary surface of the frontal bone to refer to the surface of the frontal bone that is overlain 

by the ascending process of the maxilla. Kernan (1918:359) used 

the term “ascending process of the frontal” to mean that part 

of the frontal bone that underlies the ascending process of the 

maxilla. The ascending process of the frontal bone is therefore 

equivalent to the maxillary surface. 

The maxillary surface in Tursiops and other odontocetes is 

largely overlain by the ascending process of the maxilla, although 

the frontal is often exposed to dorsal view lateral, posterolateral, 

and posterior to the ascending process of the maxilla.

− metopic suture

The metopic suture is the suture between the two frontals (Gray, 1918:135). Not to be confused with metoptic (e.g., 

metoptic process, q.v.).

Frontal suture (q.v.) is a more widely used alternative.

− narial process of the frontals (Kellogg, 1936:21, 106, 179)

Kellogg (1936:21, 106, 179) referred to a narrow wedgelike narial process of the frontals that separates the posterior 

of the nasals in Archaeoceti, and Fordyce (2002:199) noted an 

equivalent in the archaic odontocete Simocetus. In other mammals the narial process has been termed the anterior process of 

the frontal (e.g., Ting et al., 2002:7).

Tursiops has a variably developed narial process, contributed mainly or wholly by the left frontal.

* nasal margin of the frontal bone (margo nasalis) (Figure 10a,d)

The nasal margin of the frontal bones is that part of the 

bones that is bounded by and articulates with the nasals. It lies 

at the anteroventral border of the frontal bone.

The relationship of the nasals to the frontals has changed in 

odontocetes and the nasal margin now occupies the posterodorsal border of the frontal bone. Topographically it is posterodorsal but phylogenetically it is anterodorsal (anteromedial).

− nasal part of the frontal bone (pars nasals)

The nasal part of the frontal bone is the rostral extension 

of the frontal bone that faces the nasal cavity (Evans and Christensen, 1979:126; Schaller, 1992:28.8; Feneis, 1994: 18.12).

The frontal bone does not extend onto the rostrum in any 

cetaceans nor does it face the nasal cavity.

* nasal ridge of the frontals (Anderson, 1879:525, 527) (Figure 4)

In Platanista the posteromedial part of the frontals forms 

the nasal ridge of the frontals (Anderson, 1879:525, 527). The 

nasal ridge is a transverse elevation that lies immediately posterior to the nasal bones and forms the posterior border of the 

nasal passage and the anterior portion of the vertex. Anderson 

also referred to this as the nasal crest (Anderson, 1879:525).

The nasal ridge of the frontal in Tursiops and other delphinids is a low eminence on the frontal bone just posterior to the 

nasals.

The nasal ridge of the frontal (Carte and Macalister, 

1868:212) in the Mysticeti Balaenoptera acutorostrata is probably not homologous.

− nasal spine of the frontal

In humans the frontal bone develops a process that projects ventrally beneath the nasal bones and frontal process of 

the maxilla that terminates in a spine (Gray, 1918:136; Feneis, 

1994:18.13).

The relationship of the frontal bones to the nasal bones in 

Tursiops and other odontocetes is much simpler and a frontal 

or nasal spine is not developed. Bilateral nasal spines occur in 

minke whale, Balaenoptera acutorostrata.

− nasofrontal opening = aperture to the frontal sinus

The nasofrontal opening is an opening in the partition between the two tables of the frontal bones that allow communication between the frontal sinuses and the nasal cavity (Evans and 

Christensen, 1979:159).

The paranasal sinuses are not developed in Tursiops and 

other odontocetes, and there is no nasofrontal opening.

− neck of the cornual process (collum processus cornualis)

The neck of the cornual process (literally the “horny” process) is developed only in horned ungulates. It consists of the 

base of the horn on the frontal bone (Schaller, 1992:28.20).

* orbit (orbit) (Figures 3, 32)

The orbit is a conical cavity that contains the eyeball and 

associated structures (Evans and Christensen, 1979:1093). The 

orbit in most mammals is readily apparent in the skull owing to 

its bony limitations, particularly in mammals with a closed orbit 

(i.e., with a postorbital bar; Heesy, 2005). Owen (1866a:28) and 

Schulte (1917:373) referred to the orbit as the orbital fossa. Vesalius (1543:23) referred to the orbit as sedis oculorum.

The bony orbit in cetaceans is very open (Schulte, 1917:381, 

384, 390, 391). The external margins are formed by the frontal, 

lacrimal, and jugal. 

See also orbital part of the frontal.

= orbital palate of the frontal (Schulte, 1917:381) = orbital plate 

of the frontal

Orbital palate appears to be a misspelling.

* orbital part of the frontal (pars orbitalis) (Figure 10b)

The orbital part of the frontal bone is a segment of a cone 

with the apex located at the optic canal and the base forming the 

2 8 • smithsonian contributions to zoolog y frontal
medial border of the supraorbital margin (Schaller, 1992:28.10). 

Evans and Christensen (1979:125) actually referred to this as the 

infraorbital margin, which is an obvious lapsus calami.

The orbital part of the frontal bone in delphinids consists 

of the region bounded anteriorly by the antorbital fossa (infratemporal fossa of Davis, 1964:48), posteriorly by the temporal 

fossa, medially by the optic canal and orbital fissure, and laterally by the supraorbital margin. The orbital part has also been 

referred to as the infundibulum for the optic and oculomotor 

nerves (Fraser and Purves, 1960:66) or the optic infundibulum

(Fraser and Purves, 1960:30, 61, 68–70, 72, 73, 100, 102). 

See also orbital surface of the frontal.

= orbital plate of the frontal (Owen, 1866a:28; Schulte, 

1917:378, 380–382, 384, 391, 401) = orbital part 

(Gray, 1918:137)

= orbital process of the frontal (Owen, 1866a:42; Anderson, 

1879:497, 525; Schulte, 1917:391; Fraser and Purves, 

1960:37, 38, 42, 47, 58, 66) = supraorbital process of 

the frontal

= orbital roof (Schulte, 1917:381, 390) = supraorbital process 

of the frontal

− orbital surface of the frontal (facies orbitalis)

The orbital surface of the frontal bone is the portion 

of the frontal facing the orbit (Feneis, 1994:18.22; Schaller, 

1992:28.11); Gray (1918) and Evans and Christensen (1979) 

did not use this term).

In delphinids the orbital surface of the frontal is the same as 

the orbital part. We have chosen to illustrate and use the orbital 

part of the frontal instead of the orbital surface.

= orbital wing of the frontal bone = supraorbital process of the 

frontal (Anderson, 1879:525; Miller, 1923:8)

= orbitofrontal plate (Anderson, 1879:512) = orbital part

− orbitotemporal canal

The orbitotemporal canal opens in the frontal, or sometimes the orbitosphenoid, in various mammals, to transmit a 

branch of the stapedial artery into the orbit (Wible and Gaudin, 

2004:162).

In Tursiops the internal carotid artery is reduced (see section on arterial circulation and basicranial foramina in “Multielement Complexes”), the stapedial foramen is nonpatent, and 

there appears to be no significant stapedial circulation. There is 

no evidence of an orbitotemporal canal in Tursiops.

* orbitotemporal crest (crista orbitotemporalis) (Figure 10a–c,e)

The orbitotemporal crest is the anterior portion of the temporal crest directly posterior to the zygomatic process (postorbital process) of the frontal bone (Evans and Christensen, 

1979:125, 126; Schaller 1992:28.1). It should not be confused 

with the temporal crest (q.v.) or suprameatal crest on the zygomatic process of the squamosal. Davis (1964:48, fig. 17) referred 

to it as the crista orbitalis superior (superior orbital crest).

The orbitotemporal crest in odontocetes lies on the posterior margin of the postorbital process of the frontal bone. This 

has also been referred to as the temporal crest (Fordyce, 1994: 

fig. 5a.) and the supratemporal crest (Schulte, 1917:392).

− orbitotemporal fossa

The orbitotemporal fossa is the confluent orbit and temporal fossa in those mammals that lack a complete postorbital bar 

(Wible and Gaudin, 2004:175; Heesy, 2005:367).

In Tursiops and many other Cetacea, the postorbital process closely approaches the zygomatic process of the squamosal

so that the orbitotemporal fossa, although present in the strict 

sense, is effectively eliminated.

− paranasal sinuses (sinus paranasales)

The paranasal sinuses consist of the frontal sinuses, maxillary sinuses, ethmoidal sinuses, and sphenoidal sinuses (Feneis, 

1994:136.14).

The paranasal sinus system is not developed in Tursiops or 

other extant cetaceans (Fraser and Purves, 1960:5, 75). The situation of the paranasal sinus system in nondelphinid cetaceans is 

not well known. The paranasal sinus system developed in at least 

some archaeocetes (Kellogg, 1928:199; Uhen, 2004:54).

* parietal margin of the frontal bone (margo parietalis) (Figure 

10b,c,e)

The parietal margin of the frontal bone is that margin of the 

bone that is bounded by and articulates with the parietal. The 

parietal margins of the frontal bone lie at the posterior margin 

of the frontals. In many cases this is actually the interparietal 

margin.

The parietal margin of the frontal bone is extensive in odontocetes, forming at least half of the posterior border of the frontal bone.

− pit for reception of the zygoma

The pit for reception of the zygoma lies on the lateral surface of the postorbital process of the frontal bone in Platanista

(Anderson, 1879:510). Here, the apex of the zygomatic process of the squamosal approaches the frontal to within a few 

millimeters, although there does not appear to be an actual 

suture.

The pit for reception of the zygoma does not occur in 

delphinids.

= posterior ethmoidal foramen

See ethmoidal foramen. 

= posteroventral face = temporal surface (Fraser and Purves, 

1960:57)

− postfrontal

The postfrontal is a membrane bone found with extreme 

rarity in human skulls between the frontal and the jugal. This 

element may represent a remnant of the reptilian postfrontal (de 

Beer, 1937:368).

The postfrontal has not been reported in cetaceans.

* postorbital angle (Figure 10c)

The postorbital angle is the point of maximum inflection of 

the postorbital process (Kellogg, 1936:21). The term has been 

used in archaeocetes and other fossil cetaceans.

frontal n u m b e r 6 2 7 • 2 9
− postorbital diverticulum [new term]

Fraser and Purves (1960:108) described a feature of the 

postorbital lobe that they observed in Cephalorhynchus sp. 

(They referred to C. heavisidei and C. commersoni (1960:53) 

and said they were similar enough to be considered together.) 

They observed (1960:108):

In the genus Cephalorhynchus the chief advance in development is in the pre- and post-orbital lobes which 

are moderately approximated to each other. In addition, the post-orbital lobe has a narrow diverticulum 

which passes dorso-posteriorly under the post-orbital 

process of the frontal.

We have chosen to use the name “postorbital diverticulum” 

for this feature.

− postorbital lobe of the pterygoid sinus (Fraser and Purves, 

1960:56, 57, 59, 61, 68, 69, 76, 100, 102, 107, 108)

The postorbital lobe of the pterygoid sinus lies in the orbit, 

posterior to the postorbital ridge. The postorbital lobe originates 

from the pterygoid sinus, posteroventral to the optic foramen

but anterior to the foramen ovale. There is a postorbital diverticulum in Cephalorhynchus (Fraser and Purves, 1960:108).

* postorbital process of the frontal bone (Whitney, 1889–1910: 

[vol. 6]4644) = zygomatic process (Schaller, 1992:28.2) 

(Figure 10a–e)

The zygomatic process of the frontal bone extends posteriorly to meet with the jugal (or zygomatic bone) and form the 

zygomatic arch (Schaller, 1992:28.2, 34.3; Feneis, 1994:18.13). 

It is not to be confused with the zygomatic process of the squamosal (Schaller, 1992.26), which forms the connection of the 

squamosal to the zygomatic arch.

Due to the possibility of confusion with the zygomatic process of the squamosal, and because of a long history of use of 

“postorbital” for Cetacea, we prefer to use the term “postorbital process” for this feature of the frontal bone, as have Schulte 

(1917:365, 370, 373, 381, 382, 392, 393, 401), and Fraser and 

Purves (1960:13, 47, 54, 60, 61, 64, 67–70, 72, 108), and many 

others. Owen (1866a:36) referred to this process as the “postfrontal” or “postorbital process.”

The postorbital process of the frontal bone in odontocetes 

is an angular process that extends posteriorly from the supraorbital process. It defines the posterior limit of the orbit and the 

anterior limit of the temporal fossa, and thus divides the orbitotemporal fossa.

= postorbital ridge = infratemporal crest (Fordyce, 1994:155)

See “Sphenoid Bone.”

− prefrontal bone

The prefrontal bone is a membrane bone that occurs extremely rarely in humans. It lies between the lacrimal and the 

frontal. Such a bone is more common in other mammals and 

may represent a remnant of the reptilian prefrontal bone, which 

in Mammalia would normally be crowded out by the frontal (de 

Beer, 1937:368).

Owen (1866a:27, 30, 37, 38) used the term “prefrontal” 

but in reference to the external exposure of the mesethmoid in 

both Orcaella brevirostris and Kogia sima.

− preorbital lobe of the pterygoid sinus (Fraser and Purves, 

1960:1,67–69, 73, 76, 100, 107)

The preorbital lobe of the pterygoid sinus lies in the orbit

around the ventral infraorbital foramen, anterior to the preorbital ridge. The preorbital lobe originates from the pterygoid 

sinus anteroventral to the optic foramen. The preorbital lobe has 

also been called the pre-orbital extensions of the pterygoid sinus 

(Fraser and Purves, 1960:67).

* preorbital process of the frontal (Kellogg, 1936:21) (Figures 

3, 10a–d)

The preorbital process of the frontal bones is not known in 

humans and other noncetacean mammals. The preorbital process is present in archaeocetes (Kellogg, 1936:21), in other fossil cetaceans (Australodelphis, Fordyce et al., 2002; Simocetus, 

Fordyce, 2002), and in all recent cetaceans (e.g., Kogia, Schulte, 

1917:391, 392, 401).

The preorbital process of the frontal bone in cetaceans is 

a thickening of the orbital process of the frontal that forms the 

anterior border of the orbit. It articulates with the lacrimal and 

sometimes the maxilla.

Diagram 2 shows the complex terminology for structures 

near the preorbital process and antorbital notch. 

See antorbital notch under “Maxilla.”

* sagittal margin of the frontal bone (margo sagittalis) (Figure 

10a,b,d,e)

The sagittal margin of the frontal bone is that margin of the 

frontal bone that participates in the sagittal suture, that is, the 

medial margin of the frontal bone.

The sagittal margin of the frontal bone is reduced in odontocetes. It consists of the medial margin of the frontal bone that 

underlies the nasal bones and a small portion of the frontal that 

extends anterior and posterior to the nasal bones.

− sagittal sinus (sinus sagittalis)

The sagittal sinus drains the dorsal surface of the cranial 

cavity. It begins at the confluence of the rhinal veins and continues posteriorly in the attached edge of the falx cerebri. It terminates posteriorly in the transverse sinus (Evans and Christensen, 

1979:791).

In cetaceans this sinus lies along the interparietal and occipital bones and may extend onto the frontal bones. Anderson (1879:501) referred to the sagittal sinus as the longitudinal 

sinus.

− septal processes of the frontal bone (processus septalis)

The septal processes of the frontal bone form the dorsal part 

of the nasal septum in some mammals (Schaller, 1992:28.27, 

30:17; not in Evans and Christensen, 1979).

The frontal bone does not contribute to the nasal septum in 

delphinids.

− septum of the frontal sinus (septum sinuum frontalium) 

The septum of the frontal sinus is a vertical median partition that separates the right and left frontal sinuses (Evans and 

Christensen, 1979:126).

This feature is not developed in cetaceans because of the 

lack of paranasal sinuses (Fraser and Purves, 1960:5, 75).

3 0 • smithsonian contributions to zoolog y frontal
− sinciput

The sinciput is the upper anterior part of the head from the 

forehead to the crown (Dox et al., 1979:434; Whitney, 1889–

1910:[vol. 7]5643). It has also been spelled synciput and has also 

been used as equivalent to the craniometric point bregma. Eustachius and Lancisius (1714:111) referred to it as syncipite.

Due to changes caused by telescoping of the cetacean skull, 

the sinciput is not expressed.

− superciliary arches (arcus superciliaris)

The superciliary arches are a pair of rounded elevations that 

lie between the frontal eminences and the supraorbital margin 

of the frontal bones (Gray, 1918:135). They contribute to the 

“brow ridges.”

The superciliary arches do not occur in cetaceans due to 

the modifications of telescoping and the overriding of the frontal 

bone by the maxilla.

= superorbital ridge (Owen, 1866a:27) = supraorbital margin of 

the frontal

− supraorbital canal (canalis supraorbitlis)

The supraorbital canal lies in the supraorbital process of the 

frontal bone and carries the supraorbital nerve and the supraorbital vessels (supraorbital artery and supraorbital vein) (Schaller, 

1992:26.32); it is particularly developed in artiodactyls. Thewissen et al. (2001: fig. 3) identified a supraorbital canal in the 

archaeocete Pakicetus.

− supraorbital foramen of the frontal bone (foramen supraorbital)

The supraorbital foramen of the frontal bone is a small foramen in the middle of the supraorbital margin of the frontal that 

houses the supraorbital artery, supraorbital vein, and the lateral 

branch of the supraorbital nerve (Sisson, 1910:53, 55, 66, 119, 

125; Gray, 1918:136; Evans and Christensen, 1979:12, 913–915; 

Schaller, 1992:26.30; Feneis, 1994:18.9). The margin of the supraorbital foramen is sometimes incomplete, in which case it is 

known as the supraorbital notch. There has been a tendency to 

confuse this foramen with the more medial frontal foramen. Vesalius (1543:48; Vesalius et al., 1998:131) referred to the supraorbital foramen as the foramen ad medium supercillii incisum.

The supraorbital foramen does not occur in odontocetes. 

The supraorbital nerve is small and is reflected around the supraorbital process of the frontal bone producing a supraorbital 

notch in some odontocetes. We have noted it in specimens of 

Orcinus orca, Kogia breviceps (Schulte, 1917:369, 392, 401), K. 

sima, and Physeter catodon. A supraorbital notch is not present 

in Tursiops. 

Multiple foramina may open on the dorsal surface of 

some archaic mysticetes and archaeocetes; these may not be 

supraorbital foramina, but rather may represent foramina of 

the dorsal surface of the frontal (q.v.) sensu Wible and Gaudin 

(2004:155).

− supraorbital groove = supraorbital notch

* supraorbital margin of the frontal (margo supraorbitalis) = orbital margin (Figure 10a–c)

The supraorbital margin of the frontal bone lies at the anteroventral end of the frontal and forms the dorsal border of the

orbit (Gray, 1918:136). It is also known as the orbital margin.

The supraorbital margin of the frontal bone occurs on the 

lateral aspect of the frontal in Cetacea. Owen (1866a:27, 36) 

called the supraorbital margin the superorbital ridge.

= supraorbital notch (incisura supraorbitalis)

We have found the supraorbital notch in Orcinus, Kogia

and Physeter but not in Tursiops.

See supraorbital foramen of the frontal bone, groove for angularis oculi vein.

= supraorbital plates (Flower, 1885:212) = supraorbital process 

of the frontal

* supraorbital process of the frontal (Figure 10a–d)

The zygomatic process, supraorbital process, or postorbital 

process of the frontal bone is formed where the supraorbital 

margin of the frontal meets the temporal line (Whitney, 1889–

1910:[vol. 6]4644; Evans and Christensen, 1979:114).

We prefer to restrict the term “supraorbital process” to that 

portion of the orbital part of the frontal bone that is directly dorsal to the orbits. It is bounded anteriorly by the preorbital process of the frontal and posteriorly by the postorbital process of 

the frontal bone. Due to the possibility of confusion with the zygomatic process of the squamosal, we prefer not to use the term 

“zygomatic process.” Owen referred to the supraorbital process 

as the orbital roof (1866a:36) or orbital process of the frontal

(1866a:42). He also referred to the supraorbital process as the 

superorbital process (1866a:37)—a lapsus calami. See Schulte 

(1917:369) and Fraser and Purves (1960:5, 48, 102).

− supraorbital sulcus (sulcus supraorbitalis)

The supraorbital sulcus is a groove leading out of the supraorbital foramen in some ungulates in which the supraorbital 

foramen is placed well dorsal and medial to the orbit (Schaller, 

1992:26.33, 30.15).

A supraorbital sulcus is not developed in delphinids.

= supraorbital wing (Miller, 1923:4) = supraorbital process of 

the frontal

= supratemporal crest (Schulte, 1917:392) = orbitotemporal crest

See supratemporal crest under “Maxilla.”

= temporal line (linea temporalis)

See “Parietal Bone.” 

* temporal plate of the frontal (Anderson, 1879:509) (Figure 10b)

The temporal plate of the frontal is the ventral part of the 

frontal that forms the anterior part of the temporal fossa.

* temporal surface of the frontal (facies temporalis) (Figure 

10b,c)

The temporal surface of the frontal bone is that part that 

is posterior to the orbital part (pars orbitalis), lying in the anterior portion of the temporal fossa (Evans and Christensen, 

1979:126).

frontal n u m b e r 6 2 7 • 3 1
The temporal surface is small in odontocetes. The surface is 

bounded anteriorly by the orbitotemporal crest and posteriorly 

by the frontoparietal suture.

* temporoorbital plate of the frontal (Anderson, 1879:510) (Figure 10c)

The temporoorbital plate of the frontal bone comprises the 

orbital process of the frontal (preorbital process, supraorbital 

process, and postorbital process) and the temporal surface and 

temporal plate. The temporoorbital plate consists of the frontal 

bone minus the cerebronasal plate.

− trochlear pit (fovea trochlearis)

The trochlear pit is situated on the medial portion of the 

orbital plate of the frontal and forms a site of attachment for the 

cartilaginous pulley of the m. superior oblique (Gray, 1918:137). 

It is sometimes replaced by the trochlear spine.

The trochlear pit is not developed in Cetacea.

− trochlear spine (spina trochlearis)

The trochlear spine is situated on the medial portion of 

the orbital plate of the frontal and forms an attachment for the 

cartilaginous pulley (trochlea) of the m. superior oblique (Gray, 

1918:137). It is sometimes replaced by the trochlear pit.

The trochlear spine is not developed in Cetacea.

* ventral orbital crest (crista orbitalis ventalis) (Figure 10b,d)

The ventral orbital crest forms the anteroventral boundary 

of the orbit (Schaller, 1992:2.15) and separates the orbit from 

the antorbital fossa. The ventral orbital crest runs from the optic 

canal to the dorsal border of the maxillary foramen (ventral infraorbital foramen). Davis (1964:48) referred to this crest as the 

inferior orbital ridge (crista orbitalis inferior).

In delphinids the ventral orbital crest is an anteriorly placed 

feature that runs from the anterior margin of the optic canal 

anterolaterally to end in the preorbital process of the frontal and 

the orbital crest of the lacrimal bone.

* vertex (Figure 3)

The vertex of the skull is the highest portion or the crown 

(Schaller, 1992:10.20; Feneis, 1994:28.26; not in Gray, 1918; 

not in Evans and Christensen, 1979). Dox et al. (1979:517) illustrated the vertex as the entire sagittal suture of the parietal. 

Vesalius (1543:21, 22) referred to the vertex as the verticis ossi

or merely the verticis.

In odontocetes the term “vertex” has generally been used to 

apply to the dorsal protuberance on the skull that consists variously of the frontals, interparietal, nasals, premaxillae, and maxillae (Schulte, 1917:362, 370–373, 375, 376, 380, 382, 385, 387, 

388, 391, 392; Moore, 1963; Fordyce et al., 2002:45). Fordyce et 

al. (2002) noted that the vertex is not homologous among odontocetes, and their use would make synvertex of Moore (1968:255) 

a synonym. Flower’s (1867:89) earlier term “postnarial prominence of the frontal bones” appears to be a forgotten synonym.

= vertical plate (Anderson, 1879:510) = cerebronasal plate of 

the frontal

= zygomatic fossa of the frontal bone = infratemporal fossa

= zygomatic process of the frontal (processus zygomaticus) = 

postorbital process of the frontal bone

The zygomatic process, supraorbital process, or postorbital 

process of the frontal bone is formed where the supraorbital 

margin of the frontal meets the temporal line of the frontal bone 

(Whitney, 1889–1910:[vol. 6]4644; Evans and Christensen, 

1979:114; Schaller, 1992:28.2; Feneis, 1994:18.16). 

The zygomatic process of the frontal bone is a thickening 

and lateral extension of the posterior part of the orbital process 

of the frontal. It defines the posterior limits of the orbit and the 

anterior limits of the temporal fossa. It is also known as the external angular process (Whitney, 1889–1910:[vol. 6]4644).

In odontocetes the zygomatic process of the frontal bone is 

an angular process that extends posteriorly from the supraorbital process. It defines the posterior limit of the orbit and the 

anterior limit of the temporal fossa.

Due to the possibility of confusion with the zygomatic process of the squamosal, we prefer to use the term “postorbital 

process of the frontal” for this feature.

HYOID APPARATUS

Apparatus Hyoideus, Os Hyoideum

The hyoid apparatus in mammals consists of a series of ossifications that are remnants of the gill arches of primitive vertebrates. The hyoid arch is the next gill arch posterior to the 

mandible. The hyoid arch is principally involved with supporting the muscles that aid in swallowing. In addition it serves as 

support for the larynx and, in cetaceans, is a link in the chain of 

ventral muscles that function in locomotion.

The hyoid apparatus consists of a single ventral midline 

element, the basihyoid, which has two paired posteriorly projecting elements, the thyrohyoids (Gray, 1918:177; Evans and 

Christensen, 1979:148–150; Schaller, 1992:38.38; Feneis, 

1994:28.16;). Eustachius and Lancisius (1714:96, 97, 114) 

referred to the hyoid apparatus as the hyoides os. These three 

ossifications fuse in older animals. Dorsal to the basihyoid lies 

a pair of stylohyoids. These have an anterior cartilaginous articulation with the basihyoid and a posterior cartilaginous articulation with the paroccipital process. Three more elements are 

present in primitive vertebrates: the ceratohyoid, epihyoid, and 

tympanohyoid. 

In Tursiops and other cetaceans the ceratohyoid and the epihyoid are not ossified and are represented in the cartilaginous 

articulation between the basihyoid and the stylohyoid. The tympanohyoid is a vestigial element that is fused to the posteroventral surface of the periotic. 

The suffixes -hyoid and -hyal are used interchangeably in 

the literature. 

See tympanohyoid under “Hyoid Apparatus” and tympanohyal under “Periotic Bone.”

* basihyoid (basihyoidum, corpus) (Figure 11a–c,e,f)

The basihyoid is the midline element that connects the right 

and left portion of the hyoid apparatus (Evans and Christensen, 

1979:148; Schaller, 1992:39; Feneis, 1994:28). It articulates 

with the paired thyrohyoid elements posteriorly and the cera3 2 • smithsonian contributions to zoolog y h y oid
tohyoid anteriorly. The basihyoid and the thyrohyoid form the 

most ventral part of the hyoid apparatus.

In Tursiops and other odontocetes the basihyoid and thyrohyoid ossify as separate elements connected by a cartilaginous 

joint (Flower, 1885:216; Rommel, 1990:38). This joint fuses 

about the time that the individual becomes sexually mature.

* ceratohyoid (ceratohyoidum, cornu minus) (Figure 11c)

In most mammals the ceratohyoid is a separate bony element that articulates with the anterior portion of the basihyoid

distally and the paired epihyoids proximally (Evans and Christensen, 1979:148; Schaller, 1992:39). In humans the ceratohyoid forms the lesser cornua, which connects via the stylohyoid

ligament with the styloid process of the petrous part of the temporal (periotic). The stylohyoid ligament sometimes contains a 

cartilage in its midportion that is homologous with the epihyoid 

element of other mammals. 

In Tursiops and other odontocetes the ceratohyoid and epihyoid are reduced to a cartilage that lies between the basihyoid 

and the stylohyoid elements. Synovial-like joints exist between 

the cartilage and the basihyoid and stylohyoid elements in at 

least some individuals (Flower, 1885:217; Rommel, 1990:38).

* epihyoid (epihyoideum) (Figure 11c)

The epihyoid element forms an ossification between the ceratohyoid distally and the stylohyoid proximally. In humans the 

epihyoid is sometimes represented by a cartilage that may ossify 

in the midportion of the stylohyoid ligament (Gray, 1918:393).

The epihyoid element may be represented by the variable 

cartilages and ossifications that occur between the stylohyoid 

and the basihyoid in odontocetes (Flower, 1885:217).

− lingual process (processus lingualis) of the basihyoid

The lingual process projects anteriorly from the midportion of 

the basihyoid in some mammals (horse, ox, pig: Sisson, 1910:65, 

122, 144; Schaller, 1992:39) and is absent in others (dog: Sisson, 

1910:159; Evans and Christensen, 1979:148). The root of the 

tongue is attached to the lingual process (Sisson, 1910:65).

The lingual process of the basihyoid is absent in Tursiops

and other cetaceans.

* stylohyoid (stylohyoideum) (Figure 11a–f)

The stylohyoid or stylohyal lies between the epihyoid distally 

and the tympanohyoid cartilage proximally (Sisson, 1910:65; 

Evans and Christensen, 1979:148; Schaller, 1992:39). In humans 

the stylohyoid (stylohyal) element occurs as the distal ossification 

of the styloid process of the temporal bone (Gray, 1918:145).

In Tursiops and other cetaceans the stylohyoid is a long rodshaped bone that forms the attachment of the hyoid apparatus to 

the paroccipital process on the skull (Fraser and Purves, 1960:7). 

Unlike in many other mammals, in cetaceans it is not involved 

in a styloid process associated directly with the tympanic bulla

or periotic. 

See tympanohyoid under “Hyoid Apparatus” and tympanohyal under “Periotic Bone.”

− stylohyoid angle (angulus stylohyoideus)

The stylohyoid angle is situated on the posteroventral portion of the stylohyoid in some mammals (horse, ox: Sisson, 

1910:65, 122). The stylohyoideus muscle attaches to the angle 

(Sisson, 1910:223). It is absent in humans (Gray, 1918:178).

The stylohyoid angle is absent in cetaceans.

* thyrohyoid (thyrohyoideum; cornu majus) (Figure 11a–c,e,f)

The thyrohyoid or thyrohyal is a paired ossification that is 

attached to the posterolateral aspect of the basihyoid. In some 

mammals (horse: Sisson, 1910:445), the thyrohyoid muscle, 

which runs to the thyroid cartilage of the larynx, is attached; in 

others (dog: Evans and Christensen, 1979:148) the thyrohyoid 

element articulates directly with the thyroid cartilage. In humans 

the connection between the thyrohyoid bone and the thyroid cartilage is by means of both the lateral hyothyroid ligament and the 

thyrohyoideus muscle (Gray, 1918:178). Thyreohyoid is a rare 

lapsus calami.

Odontocetes are born with a paired thyrohyoid ossification 

that becomes fused to the basihyoid later in life (Flower, 1885:216; 

Fraser and Purves, 1960:7). The thyrohyoid muscle is present in 

delphinids (Lawrence and Schevill, 1965:18, 53, figs. 5, 14).

* tympanohyoid (tympanohyoideum) (Figure 25k,m,o,t,u)

The tympanohyoid cartilage is the most proximal of the 

hyoid elements. It runs between the stylohyoid and the petrosal

(Sisson, 1910:64, figs. 27, 33; Evans and Christensen, 1979:148; 

Schaller, 1992:39). In humans the tympanohyoid (or tympanohyal) forms the proximal portion of the styloid process of the 

temporal bone (Gray, 1918:145).

In Tursiops and other delphinids the base of the tympanohyoid (tympanohyal) is fused to the posteroventral side of the 

periotic (Figure 25k,m,o,t,u) as discussed further under tympanohyal of “Periotic Bone.” This leaves the hyoid chain broken 

between the tympanohyoid and the proximal end of the stylohyoid element, which attaches to the paroccipital process. In the 

dog (Evans and Christensen, 1979:284, 286) the jugulohyoideus 

muscle runs from the tympanohyoid cartilage to the jugular process (paroccipital process). There may have been a muscular or 

ligamentous connection between the tympanohyoid and the paroccipital process in the ancestral cetacean that has disappeared. 

That may explain the migration of the stylohyoid to the paroccipital process in delphinids. Lawrence and Schevill (1965:19, 20) 

also commented on the changes in the delphinid hyoid anatomy in 

terms of the change in relative position of the larynx and skull. 

See discussion of tympanohyal under “Periotic Bone” of the 

“Tympanoperiotic Complex.”

INTERPARIETAL BONE

Os Interparietale

Figures 3, 5, 6a,c,e, 12a,c,e, 24a–d, 31a

The interparietal ossification is commonly fused to the 

supraoccipital bone in mammals. For example, in the dog the 

interparietal ossification fuses to the supraoccipital on day 45 

of gestation and is rarely present as an independent bone (Evans 

and Christensen, 1979:45).

Flower, in speaking of odontocetes (1885:211), mentioned 

“the immense supraoccipital (SO), with which an interparietal 

interparietal n u m b e r 6 2 7 • 3 3
(IP) is ankylosed.” Schulte (1917:376, 382, 390, 392) described 

the interparietal in Kogia. In odontocetes the interparietal can be 

seen in newborn or fetal specimens as a relatively large ossification lying anterior to the supraoccipital, medial to the parietals, 

and posterior to the frontals. Soon after birth it fuses with the supraoccipital and loses its identity as a discrete element. The interparietal has been noted in adult mysticetes, such as Balaenoptera 

omurai (Wada et al., 2003: fig. 1). It is likely that the interparietal is more common in Cetacea than previously noted, and has 

been overlooked because of fusion with adjacent elements.

The interparietal fuses to the supraoccipital in delphinids 

just before birth. The interparietal in Tursiops forms the dorsal 

midline element of the cranium. It is bordered anteriorly by the 

frontal. In mature animals the ascending process of the maxilla 

overlaps the interparietal. Laterally it abuts the parietal and posteriorly the supraoccipital.

Because some landmarks on the occipital region of the skull 

in Tursiops have not been defined, and dissection is needed to 

help such definitions, we are not entirely certain about the homologies of some features with those of other mammals.

* dorsal sagittal sinus sulcus (sulcus sinus sagittalis dorsalis) 

(Figure 12b)

The dorsal sagittal sinus sulcus is formed in the bones along 

which the sagittal sinus flows.

In most mammals this sulcus lies along the sagittal suture of 

the parietals, but in cetaceans it lies along the median portion of 

the supraoccipital bone, the interparietal bone, and may extend 

a bit onto the frontal bone.

* external occipital protuberance (protuberantia occipitalis externa) (Figures 5, 12a,c,d)

The external occipital protuberance is the median, triangular projection forming the most posterodorsal part of the skull 

(Sisson, 1910:50; Evans and Christensen, 1979:122; Schaller, 

1992:16.26). The ligamentum nuchae is attached to it in horses.

In Tursiops and other odontocetes, the external occipital 

protuberance is limited to the median portion of the nuchal crest. 

This shift in position is the result of the anterior shift of the insertion of the dorsal axial muscles with telescoping.

− external sagittal crest (crista sagittalis externa)

See this term under “Supraoccipital Bone.”

= falciform crest = internal sagittal crest (Evans and Christensen, 

1979:157)

− highest nuchal line

See highest nuchal line under “Supraoccipital Bone.”

− inferior nuchal line

See inferior nuchal line under “Supraoccipital Bone.” 

* internal sagittal crest (crista sagittalis interna) (Figure 12b)

The internal sagittal crest, because it is a feature of the dorsal midline of the skull, occurs on the supraoccipital bone and 

interparietal bone in odontocetes, not the parietal as in other 

mammals. In both odontocetes and other mammals the internal 

sagittal crest extends anteriorly from the internal occipital protuberance and forms the site of attachment of the falx cerebri

(Evans and Christensen, 1979:157).

In odontocetes the internal sagittal crest is a short crest on 

the cranial surface of the interparietal and supraoccipital bones. 

The internal sagittal crest is bifurcated in delphinids by the sagittal sinus.

− interparietal process (processus interparietalis)

In noncetacean mammals a process that projects between the 

parietals represents the interparietal ossification and is called the 

interparietal process. The interparietal process commonly fuses 

with the supraoccipital (Evans and Christensen, 1979:121).

In Tursiops and other odontocetes the interparietal ossification has extended anteriorly to exclude the parietals from the 

dorsal surface of the cranial cavity.

= lambdoid crest = nuchal crest

− lambdoid suture (Schulte, 1917:370, 375)

The lambdoid suture in humans is the suture between the 

parietals and occipital bone, so named because it has the shape, 

when viewed occipitally, of a capital Greek lambda (λ, or inverted Y) (Whitney, 1889–1910:[vol. 4]3334). Vesalius (1543) 

referred to the lambdoid suture as sutura λ exprimens (ibid., 23),

sutura λ imitantis (ibid., 23, 25), sutura λ literam (ibid., 25), 

sutura λ referentis (ibid., 21), sutura λ simili (ibid., 21, 23), or λ

graecorum mainsculae literae assimilatur (ibid., 21). It is abundantly evident that Vesalius likened the shape of the lambdoid 

suture to the Greek letter lambda (λ).

Because of the development of the interparietal and exclusion of the parietals from the midline in Cetacea, the lambdoid 

suture does not exist. Anderson (1879:428, 501) mistakenly 

called the temporal crest the lambdoidal ridge.

* nuchal crest (crista nuchae) (Figures 1, 5, 12a,c,d)

The nuchal crest forms the dividing line between the posterior portion of the skull (occipital region) and the dorsal (anterior) portion. It is normally part of the supraoccipital bone (Evans 

and Christensen, 1979:121; Schaller, 1992:16.28). The nuchal 

crest has also been known as the occipital crest or the lambdoid 

crest (Flower, 1885:135; Wible and Gaudin, 2004:127). In the 

archaeocete Dorudon, Uhen (2004:61) identified the contact between squamosal and exoccipital as forming the lateral part of 

the nuchal crest.

In Tursiops and other odontocetes the nuchal crest extends 

from the midline, where it forms on the interparietal bone laterally where it terminates on the parietal bone adjacent to and 

nearly perpendicular to the prominent temporal crest. The frontal bone abuts the nuchal crest laterally, but as far as we can tell 

forms only a supporting structure for the crest. The nuchal crest 

shifts anteriorly as the cranial vault develops in ontogeny.

Fraser and Purves (1960:8, 89) referred to the nuchal crest 

as the occipital crest, but Uhen (2004:159) commented that 

modern cetaceans lack a nuchal crest in the sense of the structure 

present in archaeocetes.

= nuchal line (linea nuchae)

See highest nuchal line, inferior nuchal line, superior nuchal 

line.

3 4 • smithsonian contributions to zoolog y interparietal
= nuchal tubercle

See this term under “Supraoccipital Bone.”

= occipital crest = nuchal crest

* occipital fontanelle (Figure 12a,e)

The occipital fontanelle is a developmental feature that normally occurs in the fetus at the junction of the parietal and occipital centers of ossification (Gray, 1918:196).

In Tursiops and other odontocetes the dorsal midline of 

the skull is occupied by the interparietal. There is evidence of a 

developmental structure (foramen) in the center of the parietointerparietal suture (USNM 571643) that may represent the occipital fontanelle.

− parietal foramen (foramen parietale)

The parietal foramen is a variable feature in humans, located at the posterior sagittal surface of the parietal bone (Gray, 

1918:178). It transmits a vein that communicates with the sagittal sinus and sometimes a small branch of the occipital artery 

(Feneis, 1994:16.39).

We can find no trace of the parietal foramen in the interparietal, supraoccipital, or temporal exposure of parietal in Tursiops

or other delphinids. There are variable paired or unpaired foramina on the parietal in some archaeocetes that may have been 

identified as postparietal foramina (q.v. under Parietal). Gingerich et al. (2005: fig. 4) showed the parietal foramen opening 

at the junction of the parietal, squamosal, and occipital in the 

archaeocete Makaracetus.

* parietal margin of the interparietal bone (margo parietalis) 

(Figure 12a,c,e)

The parietal margin of the interparietal bone in noncetacean 

mammals represents those parts of the interparietal and supraoccipital ossifications that border the parietal. It consists of the 

posterior and lateral margins of the interparietal and the anterior 

margin of the supraoccipital (Evans and Christensen, 1979:121).

Delphinids and most odontocetes have modified the relationships of the parietal through telescoping. The interparietal 

is relatively large and has extended anteriorly and developed a 

new anterior margin with the frontal. The parietal margin of the 

interparietal bone has become the posterolateral border of the 

interparietal.

− preinterparietals

The preinterparietals are ossifications that occur rarely in 

humans and other mammals. They are regarded as either Wormian ossicles or separate centers of ossification that are variously related to the more complex condition in reptiles (de Beer, 

1937:444).

Preinterparietal ossifications have not been reported in 

cetaceans.

− sagittal crest

See this term under “Supraoccipital Bone.”

* sagittal sinus (sinus sagittalis) (Figure 12b)

The sagittal sinus drains the dorsal surface of the cranial 

cavity. It begins at the confluence of the rhinal veins and continues posteriorly in the attached edge of the falx cerebri. It terminates posteriorly in the transverse sinus (Evans and Christensen, 

1979:791).

In cetaceans the sagittal sinus lies along the interparietal and 

occipital bones and may extend onto the frontal bones. 

See dorsal sagittal sinus sulcus.

− septum sinuum frontalium (septum of the frontal sinus)

See septum of the frontal sinus under “Frontal Bone.” 

− sinus frontalis caudalis (caudal frontal sinus)

See caudal frontal sinus under “Frontal Bone.”

− sulcus for the transverse sinus

See sulcus for the transverse sinus under “Parietal Bone.”

− superior nuchal line (linea nuchae superior)

The superior nuchal line is formed by the insertion of the 

m. trapezius and m. sternocleidomastoideus in humans (Gray, 

1918:129).

These muscles are normally absent in cetaceans. However, 

Schulte (1916) reported trapezius in a fetus of Balaenoptera borealis. Yamada et al. (1998) have tracked down the innervation 

of what was called the anterior portion of the rhomboideus and 

have demonstrated accessory nerve input, hence it is trapezius. 

It is possible that the superior nuchal line may be identifiable in 

cetaceans as the line on the interparietal bone dorsal to the insertion of the m. semispinalis capitis.

− temporal line (linea temporalis)

See term under “Parietal Bone.”

− tentorial process (processus tentoricus)

See term under “Exoccipital Bone.”

− transverse sinus

See groove for transverse sinus under “Supraoccipital Bone.”

JUGAL BONE

Malar, Os Zygomaticum

Figures 3–5, 13, 14, 32

The jugal in most mammals forms part of the zygomatic arch 

that bridges the ventral portion of the temporal fossa. Vesalius 

(1543:22, 23) referred to it as the os iugale or first bone of the 

upper jaw (os maxillae superioris ossium primum). Eustachius 

and Lancisius (1714:111) referred to the jugal as the os jugale 

in one section but os zygoma or zygoma os in another (ibid., 95, 

105). Schulte (1917:398, 399, 401) referred to the zygomatic arch 

as the suborbital arch or suborbital bar of the malar. The jugal 

contacts the maxilla and/or the lacrimal anterodorsally and is sutured to the squamosal posteriorly. The jugal has also been called 

the malar (cheek bone) (Owen, 1866a:27, 28, 36, 38, 39, 41; 

Schulte, 1917:369–371, 373, 380, 383, 389–391, 393, 398, 401) 

and the zygomatic bone (Gray, 1918:164; Evans and Christensen, 

j u g a l n u m b e r 6 2 7 • 3 5
1979:142; Schaller, 1992:36; Feneis, 1994:26.1). We prefer to 

limit use of the term “zygomatic” because of possible confusion 

with other structures (zygomatic process, zygomatic recess, zygomatic nerve, etc.).

Danois (1910:161, figs. iii, iv) described a fibrous infraorbital arcade that runs between the area of the antorbital notch 

and the exoccipital as the jugal. This structure turned out to be 

the facial nerve (Schulte, 1917:390). The infraorbital arcade is 

synonymous with the zygomatic arch (Schulte, 1917:401).

In Tursiops and most odontocetes other than Ziphiidae, the jugal is fused with the lacrimal to form a conspicuous lacrimojugal element anterior to the orbit, as detailed under 

lacrimal. That part of the element anterior to the lacrimojugal 

cleft presumably is jugal, but the only certainly identified jugal 

is the slender rod (styliform part) that forms the ventral border 

of the orbit (Fraser and Purves, 1960:26,51). With such provisos, the jugal in Tursiops articulates with the maxilla dorsally 

and medially, with the lacrimal posterodorsally, and with the 

squamosal posteroventrally.

= anterior process of the jugal = maxillary process of the jugal = 

antorbital process (Lavrov and Emry, 1998:753; Muirhead and Wroe, 1998; Ting et al., 2002:29)

Tursiops and other delphinids do not have a distinct anterior process of the jugal in the sense of the maxillary process of 

the jugal (q.v.) seen in humans.

The term “anterior process of the jugal” was recently used, 

without definition, for fossil dolphins. Kazar (2005:59) mentioned 

that “the anterior process of the jugal is ankylosed to the lacrimal,” and Lambert (2005:658, text-fig. 3) used anterior process of 

the jugal for what is here termed the “antorbital process” (q.v.). 

See also infraorbital border of the jugal.

= antorbital portion (Owen, 1866a:28) = lacrimal

The antorbital portion, as defined by Owen (1866a:28, pl. 

9, figs. 1, 3(26′)) for the delphinid Orcaella brevirostris, consists 

of the fused lacrimal and jugal, or lacrimojugal of our use (see 

introduction to “Lacrimal Bone”), except for the styliform part

of the jugal. Owen (1866a:34) also referred to it as the antorbital 

process of the malar.

Antorbital portion in the sense of Owen is not used for Tursiops, but see antorbital process of the lacrimal.

= ascending process of the jugal (Naples, 1982: fig. 3, ascending 

process of jugal, in the sloth Bradypus) = frontal process of the jugal

= dorsal process of the jugal = frontal process of the jugal

− frontal process of the jugal (processus frontalis)

The frontal process of the jugal bone unites with the zygomatic process (postorbital process of our use) of the frontal 

bone in humans and other mammals (Feneis, 1994:26.6; Schaller, 

1992:36.31). In mammals without a postorbital bar, the frontal process is an origin for the postorbital ligament (Wible, 

2003:146). Synonyms include ascending process (e.g., Naples, 

1982: fig. 3), dorsal process, postorbital process (e.g., Geisler, 

2001:43), and zygomatic process (Huxley, 1865:54; Frick and 

Taylor, 1971:10).

The jugal has lost direct connection with the frontal in delphinids, and the frontal process is not identifiable. However, an indistinct frontal process may be present in archaeocetes, separating 

the jugal into orbital (anterior) and temporal (posterior) portions.

* infraorbital border of the jugal (margo infraorbitalis) (Figure 

13c)

The infraorbital border of the jugal bone forms the ventral 

margin of the orbit in most mammals. It is relatively thick and 

beveled medially. 

The jugal in Tursiops and other delphinids has been reduced. 

The bone still forms the ventral margin of the orbit posteriorly, 

but the anterior portion of the jugal has shifted medially to where 

it still lies along the ventral surface of the orbital contents, but it 

no longer forms the ventral or anterior margin of the orbit.

See also anterior process of the jugal.

* lacrimal border of the jugal [new term] (Figure 13a)

The lacrimal border of the jugal bone in delphinids consists 

of the contact between the jugal and the lacrimal. In Tursiops

and most odontocetes other than ziphiids, this contact is fused 

before birth. Owen (1866a:39) referred to the lacrimal border as 

the “outer facet.”

− lateral surface of the jugal (facies lateralis)

The lateral surface of the jugal bone in most mammals is convex longitudinally and transversely. This surface usually lies immediately beneath the skin (Evans and Christensen, 1979:142).

In Tursiops and other odontocetes the concept of defining 

surfaces is not applicable. In odontocetes the anterior end of the 

jugal lies close to (medial in the case of Tursiops) the antorbital 

notch and thus the anterior part of the bone lies under the superficial muscles and connective tissue associated with the antorbital notch. In mysticetes there is a definable lateral surface and 

the bone lies in the normal mammalian situation.

= malar = jugal bone

= malar foramen = zygomaticofacial foramen (Hrdlicˇka, 1902; 

Simons, 2001)

− marginal tubercle (tuberculum marginale)

The marginal tubercle is a prominence usually present on the 

posterior margin of the frontal process of the jugal in humans (Feneis, 1994:26.7; not mentioned in Gray, 1918). The marginal tubercle serves as one of the points of origin of the temporalis muscle.

The jugal has lost direct connection with the postorbital 

part of the frontal in delphinids and the frontal process is not 

developed. The temporal muscle originates entirely from the 

temporal fossa.

− masseteric border of the jugal = masseteric margin

The masseteric border of the jugal bone forms the ventral 

portion of the bone and serves as origin for the strongly developed m. masseter.

The masseter is reduced in delphinids to a thin sheet of muscle, highly invested with fat, that originates on the zygomatic 

process of the squamosal, not the jugal bone (Fraser and Purves, 

1960:19, 23, 76, 84).

3 6 • smithsonian contributions to zoolog y j u g a l
* maxillary border of the jugal (Figure 13b)

The maxillary border or surface of the jugal is that portion 

of the jugal that articulates with the maxilla. In the dog it normally forms an unusually stable articulation with the zygomatic 

process of the maxilla (Evans and Christensen, 1979:143).

The homology of structures in Tursiops with those of other 

mammals is not clear. We cannot judge how the maxillary border of the jugal relates to the maxillary process of the jugal (q.v.) 

in Tursiops or to Owen’s (1866a:39) antero-internal facet in 

Kogia sima.

* maxillary process of the jugal [new term] (Figure 13a,d,e)

The maxillary process of the jugal in humans articulates 

with the maxilla below the orbit (Gray, 1918: fig. 165); it carries 

the infraorbital border. In an alternative use, the term “maxillary process” (of the zygomatic arch) has also been applied to 

the posterolateral extension of the maxilla that bounds the temporal fossa in monotremes and the extinct Multituberculata (see 

comment by Wible and Rougier, 2000:83). The names anterior 

process of the jugal (Lavrov and Emry, 1998:753, for the Eocene 

mammal Hyaenodon) or anterior process of the zygomatic (e.g., 

marsupials: Muirhead and Wroe, 1998; basal gliroids: Ting et 

al., 2002:29) appear to be synonyms for maxillary process of the 

jugal in the sense of Gray (1918).

Tursiops and other delphinids do not have a distinct maxillary process of the jugal in the sense of other mammals (although see comment under antorbital process of the lacrimal). 

Accordingly, “maxillary process of the jugal” is used here in a 

new sense for Tursiops: the rounded anteromedial portion of the 

fused lacrimojugal, anterior to the lacrimojugal cleft (and thus 

presumably formed by jugal) that is lodged in the zygomatic recess of the maxilla. The homology with parts of the jugal as seen 

in other mammals is not clear.

− orbital eminence (eminentia orbitalis)

The orbital eminence is a small tubercle just within the lateral margin of the orbit in humans (Feneis, 1994:26.6a). It serves 

for attachment of the lateral palpebral ligament.

The bony orbit has been modified in cetaceans and the 

jugal is markedly reduced. The palpebral ligaments have been 

absorbed into the dense connective tissue around the lateral and 

dorsal surface of the orbit.

− orbital process of the jugal

The orbital process of the jugal in humans is a thick strong 

plate projecting posteriorly from the orbit. Its anteromedial or 

orbital surface (q.v.) forms part of the floor and lateral wall of 

the orbit (Gray, 1918:165).

Anderson (1879: pl. 40, fig. 15) labeled the styloform (sic) 

process the orbital process in Platanista. He did not discuss the 

term in the text, where he refers to the styloform process as styloform posterior half. 

See styliform portion.

− orbital surface of the jugal (facies orbitalis)

The orbital surface or border of the jugal bone in most mammals is concave longitudinally and transversely. This surface lies 

adjacent to the orbit (Evans and Christensen, 1979:143) and forms 

the ventral (inferior) border of the orbit in humans (Gray, 1918).

In Tursiops and other odontocetes, where the only readily identifiable part of the jugal is reduced to a narrow rod, the 

concept of defining surfaces is not applicable. However, Owen 

(1866a:39) used “orbital surface” in describing Kogia sima. In 

mysticetes there is a definable lateral surface and the bones lie 

in the normal mammalian situation. In archaeocete whales the 

orbital surface of the jugal is that part of the jugal anterior to the 

frontal process of the jugal.

= postorbital process of the jugal = frontal process of the jugal 

(Geisler, 2001:43)

* rostral border of the jugal (Figure 13a,b)

In Tursiops the rostral border is the anterior border of the 

jugal (or lacrimojugal) between the antorbital process of the 

jugal and the maxillary process of the jugal. The rostral border 

may be exposed to dorsal view within the antorbital notch.

− squamosal articulation (Owen, 1866a:28)

The squamosal articulation in odontocetes is an extremely 

small, simple planar suture between the jugal and the squamosal bone. This suture is almost never fused with age. Owen 

(1866a:28) described the squamosal articulation in Orcaella.

See temporal border of the jugal.

* styliform part (Figure 13b)

The bulk of the jugal, posterior to the maxillary process of 

the jugal, is known as the styloform part (sic; styliform part) 

(Flower, 1868:319; Anderson, 1879:524). Owen (1866a:39) referred to this as the “slender zygomatic style.” Schulte (1917:398, 

399, 401) referred to the styliform part as the suborbital bar 

of the malar or the zygomatic process of the malar (Schulte, 

1917:390, 391).

= styliform portion (Owen, 1866a:28) = styliform part

* temporal border of the jugal (Figure 13a,c)

The temporal border of the jugal bone (Hrdlicˇka, 1902:274) 

is that part posterior to the frontal process of the jugal that forms 

the lateral boundary to the temporal fossa and posteriorly forms 

a simple suture with the squamous part of the temporal bone

(squamosal).

Tursiops and other delphinids lack a frontal process, and 

the temporal border of the jugal is lost in association with the 

proximity of the postorbital process of the frontal bone with the 

tip of the zygomatic process of the squamosal.

− temporal process of the jugal (processus temporalis)

The temporal process of the jugal is an elongation of the 

jugal bone that lies on the posteroventral margin of the jugal 

(Evans and Christensen, 1979:143). It increases the area of the 

jugalotemporal suture.

The temporal process is not developed in delphinids.

− temporal surface of the jugal (facies temporalis)

The temporal surface of the jugal bone is that portion of 

the bone that lies adjacent to the temporal fossa in most mammals. In delphinids the jugal bone is not adjacent to the temporal fossa.

j u g a l n u m b e r 6 2 7 • 3 7
= zygomatic bone = jugal bone

− zygomatic fossa of the jugal

Meng and Wyss (2001:41) noted the presence of a zygomatic 

fossa for the m. masseter lateralis on the lateral surface of the 

thin, deep zygomatic arch of lagomorphs. The zygomatic fossa of 

the jugal should not be confused with the zygomatic fossa of the 

frontal bone in the sense of the infratemporal fossa (q.v.).

The jugal in Tursiops and other odontocetes lacks a zygomatic fossa on the lateral face of the jugal.

− zygomaticofacial foramen (foramen zygomaticofaciale)

The zygomaticofacial foramen or malar foramen opens 

on the lateral surface of the jugal bone in humans (Feneis, 

1994:26.9). It transmits the zygomaticofacial nerve.

The zygomaticofacial nerve is a branch of the maxillary division of the trigeminal nerve. It supplies sensory innervation to 

the lateral portion of the lower eyelid and surrounding skin in 

dogs (Evans and Christensen, 1979:916). The ventral area of the

orbit is relatively open in Cetacea, there is no obvious foramen in 

the jugal of Tursiops, and the zygomaticofacial nerve can reach 

its destination without penetrating bone.

− zygomaticoorbital foramen (foramen zygomaticoorbitale)

The zygomaticoorbital foramen lies on the orbital surface 

of the temporal bone in humans (Feneis, 1994:26.8). It transmits 

the zygomatic nerve.

The zygomatic nerve is a branch of the maxillary division 

of the trigeminal nerve (Evans and Christensen, 1979:914). The 

zygomatic nerve branches from the maxillary nerve shortly after 

the maxillary nerve exits the foramen rotundum. The zygomatic 

nerve divides into two rami, the zygomaticofacial nerve and the 

zygomaticotemporal nerve. 

The ventral area of the orbit is relatively open in Cetacea 

and the zygomatic nerve does not penetrate bone.

− zygomaticotemporal foramen (foramen zygomaticotemporale)

The zygomaticotemporal foramen lies on the temporal surface of the jugal in humans (Feneis, 1994:26.10). It transmits the 

zygomaticotemporal nerve.

The zygomaticotemporal nerve supplies sensory innervation 

to the upper eyelid and surrounding skin (Evans and Christensen, 

1979:914–916). The orbit is relatively open in cetaceans and the 

zygomaticotemporal nerve reaches its destination without penetrating bone.

= zygomatic process of the jugal

See zygomatic process of the malar.

= zygomatic process of the malar = zygomatic process of the 

jugal = frontal process of the jugal

Frick and Taylor (1971:10) referred to the zygomatic process of the malar in the camel Michenia; Owen, cited in Huxley 

(1865:54), referred to the zygomatic process of the malar in the 

sloth Glyptodon.

Owen (1866a:39) referred to the zygomatic process of the 

malar in Kogia sima, presumably in reference to the robust, 

short, descending jugal.

LACRIMAL BONE

Os Lacrimale

Figures 3, 4, 6b, 13a,c–e, 14, 32

The lacrimal (also spelled lachrymal) is normally a small 

bone in mammals, wedged between the ascending process of the 

palatine, the maxilla, and the frontal. The lacrimal lies in the 

medial or anterior portion of the orbit and conveys the lacrimal 

duct from the orbit to the nasal cavity (Owen, 1866a:39; Flower, 

1885:128). In Tursiops and odontocetes other than Ziphiidae, 

the lacrimal is fused with the jugal to form a conspicuous lacrimojugal (q.v.) anterior to the orbit. Early fusion (in fetus or 

neonate) in Tursiops eliminates the lacrimojugal suture. Further, 

with change in orientation of the orbit, loss of the lacrimal sac 

and associated bony features, and development of the antorbital 

notch, the bones differ markedly in shape and position from 

other mammals. Thus, homologies of parts of the lacrimal and 

jugal are not clear.

In Tursiops the distal slender rod of the jugal (styliform part) 

is readily identifiable; comparison with Ziphiidae suggests that 

the anterior and anteromedial parts of the lacrimojugal probably 

also represent the jugal. The medially placed lacrimojugal cleft 

may be homologous with part of the lacrimojugal suture; the relationship of the cleft to the lacrimal foramen, fossa, and sulcus 

of other mammals is uncertain. The posterior part of the lacrimojugal is presumed to consist of lacrimal. The lacrimal is notably 

enlarged in Kogia (Schulte, 1917:369, 380, 389–391, 398, 401).

In Tursiops the lacrimal is a thin, broad, wedge-shaped bone 

lying ventral to the antorbital process of the maxilla, anterior to 

the preorbital process of the frontal bone, and posterior to the 

anterior end of the jugal. Cetaceans are considered to lack the 

lacrimal gland and lacrimal duct (Slijper, 1962:229), and it appears that the lacrimal is imperforate.

= anterior lacrimal crest = anterior lacrimal crest of the maxilla

− anterior lacrimal process (processus lacrimalis rostralis)

The anterior lacrimal process is a small process on the facial surface of the lacrimal bone in horses and pigs (Schaller, 

1992:30.27).

The anterior lacrimal process is not developed in cetaceans.

= antorbital notch

See “Maxilla.”

= antorbital pit of the lacrimal = external lacrimal fossa (Geisler, 

2001:43)

Not to be confused with antorbital fossa.

= antorbital process

See “Maxilla.” 

= antorbital process of the lacrimal

See anterior process of the jugal. 

* antorbital process of the lacrimal [new context] (Figure 14a,b)

3 8 • smithsonian contributions to zoolog y lacrimal
In Tursiops and other delphinids the anterolateral part of the 

lacrimal or lacrimojugal may project anteriorly, beyond the level 

of the antorbital notch. The projection, which is conspicuous 

ventrally and may be visible dorsally, is the antorbital process; 

the term is modified from that of Owen (1866a:28). “Antorbital” 

is preferred because of the close association with the antorbital 

region in general (see Diagram 2, associated with “antorbital 

notch” entry under “Maxilla”). “Antorbital process” should not 

be confused with the more-posteriorly placed preorbital process 

of the lacrimal, which is the ventral process of presumed lacrimal 

adjacent to the preorbital process of the frontal.

The term “anterior process of the jugal” was recently used, 

without definition, for fossil dolphins (see Kazar, 2005:59; Lambert, 2005:658, text-fig. 3), apparently in the sense of antorbital 

process as used here. The feature illustrated by Lambert (2005: 

text-fig. 3) could be jugal or lacrimal. To reduce uncertainty, we 

use the term “antorbital process of the lacrimal” (q.v.). 

See also infraorbital border of the jugal.

− antorbital vacuity (Brooke, 1879:884)

The antorbital vacuity (Brooke, 1879:884) forms at the 

junction of the lacrimal, frontal, nasal, and maxilla so that the 

lacrimal is excluded from contact with the nasals. This forms 

an open space at the junction of (between) the lacrimal, frontal, 

nasal, and maxilla and occurs independently in a number of artiodactyls (Janis and Scott, 1987:22). Geisler and Uhen (2003:

S23) referred to the antorbital vacuity as the antorbital pit.

Cetaceans do not develop an antorbital vacuity.

− aperture for the lacrimal sinus (apertura sinus lacrimalis)

The aperture for the lacrimal sinus is the opening from 

the nasal cavity into the lacrimal sinus in artiodactyls (Sisson, 

1910:126; Schaller, 1992:32.2).

The lacrimal sinus is a paranasal sinus and is not developed 

in cetaceans (Fraser and Purves, 1960:5, 75).

* dacryon (Dox et al., 1979:119) (Figures 3, 4, 14a,c)

The dacryon in humans is the craniometric point where the 

lacrimal, frontal, and maxillary meet, at the angle of the ocular 

orbit (Dox et al., 1979:119).

The cetacean orbit has been modified extensively from terrestrial mammals and humans. In Tursiops and other delphinids, 

the dacryon is on the facial surface of the lacrimal where it meets 

the frontal and maxilla.

− external lacrimal fossa (fossa lacrimalis externa)

The external lacrimal fossa lies on the anterior portion of 

the facial surface of the lacrimal bone in artiodactyls, including 

deer (Janis and Scott, 1987:23), and pigs and sheep (Schaller, 

1992:30.28). Antorbital pit of the lacrimal (Geisler, 2001:43) is a 

synonym. The external lacrimal fossa should not be confused with 

the lacrimal fossa (q.v.), that is, the fossa for the lacrimal sac.

The external lacrimal fossa is not developed in Tursiops or 

other cetaceans.

− facial surface of the lacrimal

The facial surface of the lacrimal is that portion of the lacrimal bone exposed outside of the orbit on the face, separated 

from the orbital part by the orbital crest of the lacrimal bone. 

The facial surface is variable in size in mammals, being negligible 

in the dog but large in Odocoileus and other artiodactyls. The 

facial surface is also apparent in Archaeoceti (see Uhen, 2004) 

and the archaic odontocete Simocetus (Fordyce, 2002).

Major changes in shape and position of the lacrimal and 

jugal in Tursiops and most other odontocetes means that the facial surface and associated features cannot be identified clearly. 

See lateral surface of the lacrimojugal bone.

− fossa for the lacrimal sac (fossa sacci lacrimalis)

The fossa for the lacrimal sac lies at the middle of the dorsal 

surface of the orbital surface of the lacrimal bone, at the orbital 

opening of the lacrimal canal.

The fossa for the lacrimal sac in cetaceans is missing due to 

the absence of the lacrimal gland.

− fossa for the ventral oblique muscle (fossa m. obliqui ventralis)

A groove for the origin of the ventral oblique muscle (m. obliqui 

ventralis) frequently exists on the palate adjacent to the suture between the palatine, lacrimal, and maxillary bones in dogs, pigs, and 

cattle (Evans and Christensen, 1979:287; Schaller, 1992:30.33).

Tursiops appears not to have a fossa for the origin of the 

ventral oblique muscle. The bony origins of extrinsic eyeball 

muscles in odontocetes are poorly known.

− frontal process of the lacrimal (processus frontalis)

The frontal process of the lacrimal bone is a narrow strip of 

the orbital margin of the lacrimal bone that projects dorsally on the 

orbital surface in carnivores (Evans and Christensen, 1979:145; 

Schaller, 1992:30.25). In such cases, the frontal process is more or 

less equivalent to the orbital crest of the lacrimal bone. The lacrimal is enlarged in Odocoileus and other artiodactyls, so that there 

is a large facial surface rather than a frontal process.

A frontal process of the lacrimal bone does not appear to be 

distinct in Tursiops.

− infratrochlear notch (incisura infratrochlearis)

The infratrochlear notch lies in the anterior margin of the 

lacrimal bone where it passes the infratrochlear nerve in cattle 

(Schaller, 1992:30.24). The infratrochlear nerve is a branch of 

the ophthalmic division of the trigeminal nerve serving the anterior surface of the upper eyelid.

In cetaceans the orbit is open and the infratrochlear nerve 

reaches the eyelid without notching bones.

− lacrimal bulla (bulla lacrimalis)

The lacrimal bulla is a large thin-walled protuberance into 

the orbit in ruminants (Sisson, 1910:121; Schaller, 1992:30.34). 

It contains an extension of the maxillary sinus.

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the maxillary sinus is absent in Tursiops.

− lacrimal canal (canalis lacrimalis)

The lacrimal canal begins in the fossa for the lacrimal sac, 

runs ventrolaterally through the lacrimal bone and exits in the 

nasal cavity at the anteroventral apex of the lacrimal bone. It 

carries the lacrimal duct.

lacrimal n u m b e r 6 2 7 • 3 9
The lacrimal canal is absent in Tursiops and other Cetacea, 

and the lacrimal glands and ducts have not been described. However, a lacrimal canal, with associated channels in the lacrimal, 

has been reported in Archaeoceti (Kellogg, 1936: fig. 31c; Uhen, 

2004:56, fig. 26).

− lacrimal fenestra (Wible and Gaudin, 2004:125)

Wible and Gaudin (2004:158) noted this variably developed 

depression (sometimes a foramen) for the origin of an extraocular muscle, the musculus obliquus. The feature occurs in some 

armadillos, and in the dog (Evans and Christensen, 1979:1111, 

figs. 20–26); it may be at the junction of the lacrimal, frontal, 

and maxilla (Wible and Gaudin, 2004) or in the lacrimal immediately dorsal to the infraorbital foramen (Novacek, 1986).

Tursiops appears not to have a lacrimal fenestra for the origin of the oblique muscle. The bony origins of extrinsic eyeball 

muscles in odontocetes are poorly known.

− lacrimal foramen (foramen lacrimale)

The lacrimal foramen is the opening for the lacrimal duct in 

the lacrimal bone (Schaller, 1992:30.30). The foramen may be 

paired, as in Odocoileus and other cervids (e.g., Janis and Scott, 

1987, as the lacrimal orifice).

The lacrimal gland and its accessories are not developed in 

Cetacea (Owen, 1866a:30), and Tursiops appears to lack a lacrimal foramen.

− lacrimal fossa

In humans (Gray, 1918:137, 164) the lacrimal fossa is developed in the lacrimal, maxilla, and sometimes the frontal. The 

lacrimal sulcus contributes posteriorly. It contains part of the 

lacrimal sac (Gray, 1918: fig. 159, fossa for the lacrimal sac) and 

nasolacrimal duct.

The lacrimal fossa is absent in Tursiops and other delphinids.

See also lacrimal sulcus.

− lacrimal hamulus (hamulus lacrimalis)

The lacrimal hamulus in humans is a small, hook-like projection at the ventral end of the posterior lacrimal crest at the 

entrance to the nasolacrimal canal (Gray, 1918:164; Feneis, 

1994:20.24).

The lacrimal hamulus and posterior lacrimal crest are not 

developed in odontocetes.

= lacrimal orifice = lacrimal foramen (Janis and Scott, 1987:24)

− lacrimal pit (Brooke, 1879:884)

Brooke (1879:884) defined a lacrimal pit or lacrimal fossa

as a depression in the facial plate of the lacrimal that served as a 

diagnostic character of some cervids. The relationship of this lacrimal pit to the preorbital fossa (q.v.) of some other artiodactyls 

(e.g., pig: Sisson, 1910:140) needs to be clarified.

Cetaceans do not develop a lacrimal pit.

− lacrimal sinus (sinus lacrimalis)

The lacrimal sinus is a paranasal sinus developed in artiodactyls (Schaller, 1992:32.1; Sisson, 1910:126). It lies in the lacrimal bone and opens through the aperture for the lacrimal sinus

into the nasal cavity.

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the lacrimal sinus is absent in Tursiops.

− lacrimal sulcus (sulcus lacrimalis)

The lacrimal sulcus is a longitudinal groove on the lacrimal, which, together with a groove on the medial or nasal surface of the maxilla, forms the lacrimal fossa in humans (Gray, 

1918:159f; Feneis, 1994:22.19). It lodges the lacrimal sac and 

the nasolacrimal duct (Gray, 1918:189; Feneis, 1994:334.21).

The lacrimal sulcus is lacking in Tursiops and other delphinids; the lacrimojugal cleft is not clearly homologous with the 

lacrimal sulcus.

See this term also under “Maxilla.”

− lacrimojugal bone

In Tursiops as in many other Odontoceti (e.g., Kogia; 

Schulte, 1917:400), the jugal becomes fused to the lacrimal sufficiently early in development that it is not possible to differentiate the two ossifications. The bone in this situation has been 

referred to as the “lachrymo-malar” (Schulte, 1917:400). We 

prefer “lacrimojugal.”

See also lateral surface of the lacrimojugal bone and introduction to “Lacrimal Bone.”

* lacrimojugal cleft [new term] (Figure 14b,d,e)

In Tursiops the medial face of the fused lacrimal and jugal 

has a reentrant, conspicuous in ventral view, which is here termed 

the lacrimojugal cleft. It is possible that the cleft is homologous 

with part of the lacrimojugal suture. Whether it is a vestige of 

structures associated with the lacrimal sulcus is uncertain. In 

Tursiops the cleft is occupied by the lacrimojugal crest of the 

maxilla. In one skull, USNM 550403, three grooves (associated 

with two ridges) are directed medially into the right lacrimojugal 

cleft. It is not known what soft tissues are associated with the 

grooves and ridges.

* lacrimomaxillary fossa [new term] (Figures 2, 14b)

In Tursiops the ventral surface of the lacrimal and associated maxilla may develop a prominent lacrimomaxillary fossa 

between the medial and posteromedial processes of the lacrimal 

and the region of the ventral infraorbital foramen. The soft tissue relationships are uncertain for the lacrimomaxillary fossa. 

This fossa may be the structure that Owen (1866a:28) termed 

the malomaxillary fossa in Orcaella, but his description was not 

clear enough to be sure, and he did not identify the feature on 

an illustration.

= lateral part of the frontal sinus

See “Frontal Bone.” 

* lateral surface of the lacrimojugal bone (Figure 14a–e)

In Tursiops and other cetaceans major changes in shape and 

position of the lacrimal and jugal mean that the facial surface 

and orbital crest as seen in other mammals are not readily identifiable. Alternative names are thus needed for lateral parts of the 

lacrimojugal.

The lateral surface of lacrimal (or lacrimojugal bone) is defined as the elongate to sometimes triangular face exposed to 

lateral view, lying ventral and/or anteroventral to the preorbital 

4 0 • smithsonian contributions to zoolog y lacrimal
process of the frontal and the anterolateral portion of the maxilla. In Tursiops the lateral face carries the preorbital process 

(posteroventrally), the ventrolateral crest of the lacrimojugal

(ventrally), and the maxillofrontal crest (dorsally).

= malomaxillary fossa (Owen, 1866a:28) = lacrimomaxillary 

fossa

Owen, in his description of the skull of Orcaella, described 

the “rough malomaxillary fossa” as lying external to the antorbital fossa (pterygopalatine fossa). He labeled the malomaxillary 

fossa as (e) and the antorbital fossa as (d) in the text (1866a:28) 

but did not include (d) and (e) in the illustrations (Owen, 1866a: 

pl. 9). We have interpreted this as the lacrimomaxillary fossa

(q.v.). Because the malomaxillary fossa is not clearly identified, 

and the name appears not to have been used in later literature, it 

is not applied to Tursiops here. The new term “lacrimomaxillary 

fossa” may be equivalent.

= maxillary process

See maxillary process of the jugal. 

* maxillofrontal crest [new term] (Figure 14a,e)

The maxillofrontal crest on the lacrimal in odontocetes consists of the portion of the lacrimal bone that projects dorsally 

into the cleft formed between the ascending process of the maxilla and the preorbital process of the frontal.

* medial process of the lacrimal [new term] (Figure 14a,b,d,e)

The medial process of the lacrimal bone is here defined as 

the medially projecting process that lies posterior to the lacrimojugal cleft. Its shape in Tursiops is extremely variable, particularly in ontogeny. In delphinids, it is affected by resorption 

associated with development of the fossa for the anterior sinus; 

in Tursiops specimen USNM 550403, the ventral surfaces of 

both left and right medial processes are smoothed and more or 

less continuous anteromedially with the smooth surface of the 

antorbital sinus fossa.

− nasal surface of the lacrimal bone (facies nasalis)

The nasal surface of the lacrimal bone forms a small portion 

of the nasal cavity.

The lacrimal bone is excluded from the nasal cavity in 

cetaceans.

− nasolacrimal canal (canalis nasolacrimalis)

The nasolacrimal canal lies in the lateral wall of the nasal cavity and contains the nasolacrimal duct (Schaller, 1992:14.9; Feneis, 

1994:32.7). The nasolacrimal canal begins in the lacrimal, runs 

ventrally into the maxilla, issuing forth ventral to the nasoturbinate 

crest in the dog. The nasolacrimal canal is also known as the lacrimal canal (Gray, 1918:164; Evans and Christensen, 1979:141,144). 

Vesalius (1543:48; Vesalius et al., 1998:131) referred to the nasolacrimal canal as the foramen . . . quod ex magno internove oculi 

angulo in narium cavitatem recta deorsum pertinet.

The nasolacrimal canal is not developed in modern cetaceans.

* orbital crest (Figure 14a–e)

The orbital crest forms the lacrimal bone’s contribution to 

the orbital margin (Evans and Christensen, 1979:144). In the dog 

the orbital crest and frontal process of the lacrimal are the same. 

The structure is also termed orbital rim and orbital margin of the 

lacrimal (e.g., in artiodactyls; Janis and Scott, 1987:23, 24).

In Tursiops and other delphinids the lacrimal and jugal are 

so modified that the orbital crest in the sense of artiodactyls is 

not identifiable. 

See lateral surface of the lacrimojugal bone, preorbital process of the lacrimal, and ventrolateral crest of the lacrimojugal.

= orbital margin = orbital crest (Janis and Scott, 1987:23, 24)

= orbital rim = orbital crest (Janis and Scott, 1987:23, 24)

* orbital surface of the lacrimal (facies orbitalis) (Figure 14a–e)

The orbital surface of the lacrimal bone is the surface that is 

exposed in the orbit. It is concave and bears the opening of the 

lacrimal canal and the fossa for the lacrimal sac.

In Tursiops and other odontocetes the only portion of the 

lacrimal bone that is on the orbital surface is the small orbital 

crest.

– outer facet of the malar

Owen (1866a:39) referred to a structure he called the outer 

facet of the malar. This may be related to the lateral surface of 

the lacrimojugal bone, preorbital process of the lacrimal, ventrolateral crest of the lacrimojugal, or the orbital crest of the 

lacrimal bone.

− posterior lacrimal crest (crista lacrimalis posterior)

The posterior lacrimal crest in humans is a vertical ridge 

that divides the orbital surface of the lacrimal into two parts (Feneis, 1994:20.22). It forms the posterior border of the entrance 

to the nasolacrimal canal.

The nasolacrimal canal and posterior lacrimal crest are not 

developed in Tursiops and other cetaceans.

See also anterior lacrimal crest.

− posterior lacrimal process (processus lacrimalis caudalis)

The posterior lacrimal process lies on the supraorbital 

margin of the lacrimal bone in ruminants and horses (Schaller, 

1992:30.26). It forms the dorsal border to the infratrochlear 

notch.

The orbit has become simplified in cetaceans and the infratrochlear notch and posterior lacrimal process are absent.

* posteromedial process of the lacrimal [new term] (Figure 14a–e)

The posteromedial process of the lacrimal in Tursiops is the 

lobe-like posterior projection of the medial surface of the lacrimal, as seen in ventral view, that lies just anterior to the frontal. 

It is conspicuous in juveniles but may be partly obscured by maxilla in adults.

* preorbital process of the lacrimal [new term] (Figures 3, 14c)

The preorbital process of the lacrimal in adult Tursiops is 

the ventral projection of the facial surface (or lateral border) 

of the lacrimal, pronounced in lateral view that arises at the 

posterior end of the lacrimal just anterior to the orbit. It is associated closely with the preorbital process of the frontal. A preorbital ridge may develop medial to the preorbital process.

lacrimal n u m b e r 6 2 7 • 4 1
* preorbital ridge of the lacrimal [new term] (Figure 2)

The preorbital ridge of the lacrimal in adult Tursiops is 

a variably distinct ventral elevation on the lacrimal that arises 

at the apex of the preorbital process and extends medially or 

posteromedially.

* rostral border of the lacrimal (Schulte, 1917:390) (Figure 

14a,b,d)

The rostral border of the lacrimal is the anterior border. The 

rostral border is just medial to the facial surface.

* ventrolateral crest of the lacrimojugal [new term] (Figures 2, 

14b–d)

In Tursiops major changes in shape and position of the lacrimal and jugal mean that the facial surface and orbital crest as 

seen in other mammals are not readily identifiable. Alternative 

names are thus needed for lateral parts of the lacrimojugal.

In Tursiops the ventrolateral crest is the prominent inflection between the lateral surface and the ventral surface of the lacrimal or lacrimojugal. Posteriorly, the ventrolateral crest passes 

into the preorbital process of the lacrimal.

MANDIBLE

Mandibula

Figure 15

The mandible, or lower jaw (Schaller, 1992:38.1; Evans and 

Christensen, 1979:146; Feneis, 1994:26.11; Gray, 1918:172), is 

usually joined to the skull by a synovial joint, the temporomandibular joint. This joint is one of the characteristics of mammals in that 

it lies between the mandible and the squamosal and not between the 

articular and the quadrate as it does in reptiles. Embryologically the 

mandible in Cetacea arises from the dentary; the articular and the 

quadrate have been incorporated into the middle ear as the malleus 

and the incus, respectively (Romer, 1955:520). Vesalius (1543:43) 

referred to the mandible as maxilla inferiori (lower jaw).

In odontocetes the temporomandibular joint has lost its synovial cavity (Perrin, 1871:807; Pivorunas, 1977:299) and become an extended fibrous joint or syndesmosis (sensu Evans and 

Christensen, 1979:225). In delphinids the mandible has become 

long and narrow and the coronoid process has been reduced. 

The mandibular foramen has become extremely large and filled 

with relatively clear adipose tissue (intra-mandibular fat body). 

Schulte (1917:376) described the mandible in Kogia. 

The term “mandible” is used as both singular and plural in the 

literature. “Mandibles” is often used for the plural (e.g., Wible and 

Gaudin, 2004:146), whereas “hemi-mandible” is rarely used for the 

single right or left element in the mammalian literature. Symphysis 

is the feature that necessarily involves both mandibles, whereas the 

symphyseal surface may be viewed on a single mandible.

* acoustic window (Norris, 1968:298, 308–312) (Figure 15c)

Norris (1968:298, 308–312) defined the acoustic window 

as an area in the external lamina of the mandible, directly lateral to the mandibular foramen, that was markedly thin. Norris 

hypothesized that this area had thinned to form an “acoustic 

window” for the reception of sound. This area of the mandible 

is central to the “pan bone” of sperm whalers (Whitney, 1889–

1910:[vol. 5]4253).

* alveolar border of the mandible (arcus alveolaris) (Figure 15c)

The alveolar border of the mandible in the dog is the dorsal border that bears the dental alveoli (Evans and Christensen, 1979:146). 

The term is applicable to Tursiops and other delphinids.

= alveolar foramina of the mandible (Kellogg, 1968: figs. 40, 48) 

= gingival foramina

* alveolar groove of the mandible (sulcus alveolaris) = alveolar 

gutter (Figure 15a)

The alveolar groove of the mandible is the groove on the dorsal surface of the mandible that contains the dental alveoli. This 

feature appears early in embryonic life, before the embryonic teeth 

have formed, and controls the sites at which teeth are formed. It 

also is known as the dental groove (Whitney, 1889–1910:[vol. 

11]548). Alveolar grooves are found in adults of some species 

of odontocetes and baleen whales (Owen, 1866a:38; Schulte, 

1917:375–377, 389), and in the fossil delphinid Australodelphis

(see Fordyce et al., 2002). The term “dental sulcus” was used by 

Schulte (1917:376) to refer to confluent or indistinctly separate 

dental alveoli in Kogia, in other words, the alveolar groove.

= alveolar gutter

See alveolar groove of the mandible.

− alveolar juga (juga alveolaria)

Alveolar juga are smooth elevations caused by roots of teeth 

that are expressed on the external surfaces of the maxilla and 

mandible.

Alveolar juga are not present in delphinids and are not developed in most odontocetes. In some ziphiids that have relatively well-developed teeth (e.g., Mesoplodon densirostris), there 

is a structure that could be homologous with the alveolar juga. 

The alveolar juga are present in some fossil cetaceans, for example Waipatia.

* alveolar margin of the mandible (margo alveolaris) (Figure 15c)

The alveolar margin of the mandible is the border of the 

process alveolaris (Schaller, 1992:38.7).

Odontocetes have a normal alveolar margin.

= alveolar portion (pars alveolaris) = alveolar process of the 

mandible

* alveolar process of the mandible (processus alveolaris) (Figure 

15c)

The alveolar process of the mandible is the part of the 

mandible that bears the dental alveoli. The alveolar process of 

the mandible is also known as the alveolar portion (Schulte, 

1917:376). We have chosen to use the term “alveolar process 

of the mandible” to parallel the terminology use for the maxilla 

(i.e., alveolar process of the maxilla).

= alveolar sulcus (Schulte, 1917:375–377) = alveolar groove of 

the mandible

4 2 • smithsonian contributions to zoolog y mandible
= alveolar walls = interalveolar septa

= alveolus (Owen, 1866a:29) = dental alveoli

* angle of the mandible (angulus mandibulae) (Figure 15b,c,e)

The angle of the mandible is the posteroventral portion of 

the bone. It bears the angular process (Evans and Christensen, 

1979:148). Gonion (q.v.) is equivalent.

The angle is present in Tursiops and other odontocetes 

(Owen, 1866a:41; Fraser and Purves, 1960:6, 16).

Angle of the mandible and angular process have been used 

interchangeably. The former appears more common in human 

anatomy; the latter is more common in comparative anatomy 

and vertebrate paleontology.

* angular process of the mandible (processus angularis) (Figure 

15c,e)

The angular process of the mandible is the area of insertion of the medial pterygoid muscle (m. pterygoideus medialis) 

medially and the masseter muscle (m. masseter) laterally (Evans 

and Christensen, 1979:148, 294; Schaller, 1992:102.22; Feneis, 

1994:80.17). The medial pterygoid muscle is also known as 

the internal pterygoid muscle (m. pterygoideus internus) (Gray, 

1918:387; Fraser and Purves, 1960:12).

The m. pterygoideus medialis is weakly developed in Tursiops and other delphinids. The angular process is the ventrolateral surface of the posterior portion of the mandible and the 

medial edge of the mandible that lies ventral to the mandibular 

fossa (Fraser and Purves, 1960:1, 6, 12, 13, 14, 18, 22, 23, 26).

See also angle of the mandible.

* base of the mandible (basis mandibulae) (Figure 15c)

The base of the mandible is the lower portion of the body of 

the mandible minus the alveolar portion (Feneis, 1994:26.13).

* body of the mandible (corpus mandibulae) = mandibular body 

(Figure 15c)

In the dog the mandible consists of paired horizontal bodies, 

one right and one left, that bear the teeth. The vertical parts or 

ramuses (rami) form most of the area for muscular attachment 

(Evans and Christensen, 1979:146). Owen (1866a:41) referred 

to the body of the mandible as the horizontal ramus or the mandibular ramus (1866a:42).

In Tursiops we have defined the body of the mandible as 

ending at the level of the last tooth.

* buccal surface of the mandible (facies buccalis) (Figure 15a)

The buccal surface of the mandible is that part of the lateral 

surface that faces the cheeks in the dog (Evans and Christensen, 

1979:147). It is posterior to the labial surface. In some mammals 

with extremely mobile lips and cheeks, the distinction between 

the buccal and labial surface is not well defined and the terms 

buccal, facial, and labial are sometimes confused.

In odontocetes, with relatively rigid lips and cheeks, the distinction between buccal and labial is obvious in live or freshly 

dead animals. The border between the two surfaces lies slightly 

anterior to the posterior teeth, at the level of the angle of the 

mouth. The position of the border between buccal and labial 

surfaces is not distinct on the isolated mandible.

* condylar articular surface (Flower, 1885) (Figure 15c)

The condylar articular surface in Tursiops, as in other mammals, is that surface of the mandibular condyle that is in direct 

articulation with the mandibular fossa of the squamosal bone.

= condylar plate = pan bone (in Platanista, Anderson, 1879:528)

− condylar process of the mandible

In the yellow armadillo (Wible and Gaudin, 2004:146) the 

condylar process carries but is distinct from the mandibular condyle, and forms an attachment for the lateral pterygoid muscle. 

In the laboratory mouse the condylar process is that part of the 

mandible that projects posteriorly, distinct from the adjacent 

coronoid and angular processes (Hall, 2003: fig. 4). The condylar process is also known as the mandibular neck.

Tursiops lacks a distinct condylar process in the sense of other 

mammals. Murie (1873:284; see Fraser and Purves, 1960:8) mentioned the association of pterygoid muscles with the “articulating 

condylar process of the mandible” in Globicephala. In the medial 

face of the mandible of Tursiops (USNM 550403), the region of the 

mandibular notch between the mandibular condyle and the coronoid 

process is thickened and rough, possibly reflecting muscle insertion.

The condylar process of the mandible is not to be confused 

with the condyloid process (mandibular condyle).

= condyloid articular process (Anderson, 1879:365) = mandibular condyle

* condyloid crest (Figure 15a,c)

The condyloid crest is a low crest that extends anteriorly on 

the buccal surface of the mandible from the condyloid process

(Evans and Christensen, 1979:148).

In Tursiops and other odontocetes the low condyloid crest 

disappears just below the coronoid crest.

= condyloid process = mandibular condyle

Not to be confused with condylar process (mandibular neck).

* coronoid crest (Figure 15a,c,e)

The coronoid crest lies on the anterior surface of the coronoid process in the dog (Evans and Christensen, 1979:148).

In Tursiops the coronoid crest lies between the coronoid 

process and the tooth row. It is a low, wide crest in newborns 

that forms a distinct narrow ridge as the animal matures.

* coronoid process (processus coronoideus) (Figure 15a,c,e)

The coronoid process in the dog is the most dorsal part of 

the mandible, located between the teeth and the mandibular condyle (Evans and Christensen, 1979:148). It serves for attachment 

of the tendon of insertion of the m. temporalis (Evans and Christensen, 1979:148).

In Tursiops and other delphinids the coronoid process is 

relatively low and situated immediately anterior and dorsal to 

the mandibular condyloid process (condyle) (Owen, 1866a:29, 

41; Fraser and Purves, 1960:6, 22).

* dental alveoli (alveoli dentales) (Figure 15a)

The dental alveoli are receptacles in the mandible and maxilla for the tooth roots.

mandible n u m b e r 6 2 7 • 4 3
= dental canal (Anderson, 1879:528) = mandibular canal

= dental foramen (Anderson, 1879:528; Flower, 1885:216; 

Schulte, 1917:376) = mandibular foramen

− digastric fossa (fossa digastrica)

The digastric fossa is a small depression at the ventromedial 

portion of the body of the mandible near the symphysis. It is 

the attachment site for the anterior belly of the digastric (Feneis, 

1994:26.20; not in Evans and Christensen, 1979; not in Schaller, 

1992). The anterior attachment of the digastric in delphinids is 

extremely fatty and difficult to define (Lawrence and Schevill, 

1965:12) and there is no digastric fossa.

= external mandibular angle = angle of the mandible (angulus 

mandibulae)

− facial vessel notch (incisura vasorum facialium)

The facial vessel notch is a wide, low depression on the ventral 

surface of the mandible just anterior to the angular process (Schaller, 

1992:38.9). The facial artery and vein pass over the notch.

In Tursiops and other delphinids the facial vessels pass 

around the lower jaw without apparently affecting it. There does 

not seem to be a facial vessel notch.

= gingival foramina (Cope, 1895:141) = alveolar foramina of the 

mandible

Kellogg (1968: figs. 40, 48) identified the gingival or alveolar foramina of the mandible dorsally on the medial face of the 

mandible in fossil mysticetes. The gingival foramina are the medial openings of the terminal branches of the mandibular canal. 

The lateral openings are the mental foramina. We prefer to use 

“gingival foramen” because alveolar foramen is likely to be confused with alveolar foramina of the maxilla, which are internal 

to the alveoli.

Although the nerves and vessels from the mandibular canal 

reach the medial surface of the mandible, they do not coalesce 

into discrete foramina in Tursiops.

* gnathion (Figure 15a)

Gnathion is the lowest point of the midline of the mandibular symphysis (Dox et al., 1979:187).

Tursiops has a normal gnathion.

= gonion = angle of the mandible

The gonion in humans is the most posterior, inferior, and lateral point of the external mandibular angle (Dox et al., 1979:187).

Tursiops has a normal gonion; it is equivalent to the angle 

of the mandible.

= gonys (Dall, 1874:298 in Scammon, 1874) = symphysis

Gonys is the term applied to the keel or lower outline of the 

bill (in birds) as far as the mandibular rami are united (Whitney, 

1889–1910:[vol. 3]2572). We have seen it used in only one instance (Dall, 1874:298 in Scammon, 1874), where it pertained to 

the symphysis of the jaw in Orcinus.

* groove for remains of Meckel’s cartilage (Figure 15)

Meckel’s cartilage is the remains of the primitive cartilaginous jaw that the mandible forms around (Flower, 1885:147, 

221, fig. 67). Depending on the ontogenetic development of the 

species, the remains of this cartilage form a groove at one or both 

ends of the ventral portion of the mandible.

In delphinids this groove is present on the medial side of 

the anteroventral portion of both sides of the mandible. Eales 

(1950:9) documented it quite well in the narwhal (Monodon 

monoceros).

− incisive portion of the mandibular body (pars incisiva)

The pars incisiva of the mandibular body bears the incisor 

teeth (Evans and Christensen, 1979:146).

Tursiops and other odontocetes are homodont, the lower 

incisors are not identifiable, and the incisive portion is not applicable. However, the pars incisiva should be identifiable in heterodont extinct Cetacea.

= inferior dental canal (Flower, 1885:211 fig.) = mandibular canal

= inferior dental foramen (Schulte, 1917:376) = mandibular foramen

− interalveolar margin (margo interalveolaris)

In the dog the dorsal border of the mandible between the 

canine and first premolar is larger than the others and is known 

as the interalveolar margin (Evans and Christensen, 1979:147). 

The term may be applied to any mammal in which there are diastemata between the teeth, such as moose (see Clifford and Witmer, 2004:346, fig. 6). The interalveolar margin is also known 

as the diastematic ridge.

Tursiops and other delphinids have closely spaced teeth, 

and the interalveolar margin is not developed. An interalveolar 

margin may be present in heterodont extinct Cetacea.

* interalveolar septa (septa interalveolaria) (Figure 15a)

Interalveolar septa are the bony partitions between adjacent 

teeth (Evans and Christensen, 1979:140; Schaller, 1992:34.14). 

The term “interalveolar septa” is also used to refer to spaces on 

the alveolar border of the mandible between the adjacent premolar teeth (Evans and Christensen, 1979:147).

Interalveolar septa are variably developed in Tursiops. The 

septa are characteristic of all odontocetes except those with reduced dentition.

= internal alveolar plate (Anderson, 1879:528)

See symphysial plate.

− interradicular septa (septa interradicularia)

Interradicular septa are the bony partitions between the 

roots of an individual tooth (Evans and Christensen, 1979: 

140).

Tursiops and other odontocetes have simple teeth with only 

one root, so this term does not apply. Interradicular septa are 

present in heterodont extinct Cetacea.

* labial surface of the mandible (facies labialis) (Figure 15a,c)

The labial surface of the mandible faces the lips (Evans and 

Christensen, 1979:147). In some mammals with extremely mobile lips and cheeks, the distinction between the buccal and labial 

surface is not well defined and the terms buccal, facial, and labial 

are sometimes confused.

4 4 • smithsonian contributions to zoolog y mandible
In odontocetes, with relatively rigid lips and cheeks, the distinction between buccal and labial is obvious in live or freshly 

dead animals. The border between the two surfaces lies slightly 

anterior to the posterior teeth, at the level of the angle of the 

mouth. In Tursiops the position of the border between buccal 

and labial surfaces is not distinct on the isolated mandible.

* lingual surface of the mandible (facies lingualis) (Figure 15a)

The lingual surface of the mandible faces the tongue (Evans 

and Christensen, 1979:147).

− lingula mandibulae

The lingula mandibulae is a sharp bony spine that projects 

posteriorly from the anterior margin of the mandibular foramen. 

It gives attachment to the sphenomandibular ligament in humans 

(Gray, 1918:173).

Tursiops and other delphinids do not appear to develop a 

lingula mandibulae.

= mandibular body = body of the mandible

* mandibular canal (canalis mandibulae) (Figure 15b,e)

The mandibular canal is a continuation of the mandibular 

foramen anteriorly. The mandibular canal runs the full length 

of the mandibular body and contains the mandibular nerve (or 

inferior maxillary nerve (Schulte, 1917:374) and vessels (Evans 

and Christensen, 1979:148; Schaller, 1992:38.30).

The mandibular canal, which is present in Tursiops and 

other odontocetes, has been called the dental canal (Owen, 

1866a:41; Anderson, 1879:528; Schulte, 1917:376, bottom).

* mandibular condyle = condyloid process = articular process 

(processus condylaris)) (Figure 15a–c,e)

The mandibular condyle in the dog is a transversely elongate process that forms the mandibular portion of the temporomandibular joint (Evans and Christensen, 1979:148) as in 

humans (Gray, 1918:174; Feneis, 1994:28.12) and other mammals (Schaller, 1992:38.34). Vesalius (1543:22) referred to the 

mandibular condyle as the capitulum inferioris maxillae (head 

of the lower jaw).

In Tursiops and other delphinids the mandibular condyle 

is located in the middle of the posterior margin of the mandible 

(Owen, 1866a:41, 42). The mandibular condyle is also known as 

the condylar process of the mandible (Fraser and Purves, 1960:6) 

or the articular condyle (Schulte, 1917:366).

* mandibular foramen (foramen mandibulae) (Figure 15b,d,e)

The mandibular foramen in the dog lies on the medial 

(lingual) surface of the mandible at the junction of the ramus 

and body (Gray, 1918:173; Schaller, 1992:38.29; Feneis, 

1994:28.6). Vesalius (1543:22) referred to the mandibular foramen as merely the sinus. The mandibular foramen houses the 

mandibular nerve and mandibular vessels (Evans and Christensen, 1979:148).

In Tursiops and other odontocetes, the mandibular foramen 

is greatly enlarged, houses the intra-mandibular fat body, and is 

generally termed the mandibular fossa (q.v.). The mandibular 

foramen in odontocetes has also been called the dental foramen

(Anderson, 1879; Flower, 1885:216; Schulte, 1917:376), the inferior dental foramen (Schulte, 1917:376), the mandibular hiatus (Boenninghaus, 1904:46, Fraser and Purves, 1960:13) or the 

proximal infundibular cavity (Murie, 1873; Fraser and Purves, 

1960:6).

* mandibular fossa of the mandible (Figure 15d)

The mandibular fossa of the mandible (not of the squamosal) is the enlarged (high, long, and voluminous) mandibular 

foramen as seen in Tursiops, Phocoena, and other odontocetes. The mandibular fossa houses the intramandibular fat body 

(intra-mandibular fatty body of Fraser and Purves, 1960:10, 13, 

24, 26, 27, 29, 32, 133, 140), which is homologous with the 

marrow of the mandible) (Boenninghaus, 1904:46, fig. K; Fraser 

and Purves, 1960:27). The fossa occupies about one-third of the 

lingual surface of the mandible, extending from the mandibular condyle nearly to the most posterior tooth. The mandibular 

fossa is bounded laterally by the pan bone. This use of mandibular fossa has wide and consistent application in odontocetes and 

sometimes other Cetacea; see, for example, Norris (1968:310), 

Perrin (1975: fig. 2, item 40, for a recommended measurement 

in dolphins), Fordyce (1994:162), Wang et al. (2000:149), and 

Geisler et al. (2005:24). Geisler and Sanders (2003:71 “small 

mandibular fossa”) appeared to use mandibular fossa in some 

mysticetes as equivalent to mandibular foramen. 

The term “mandibular fossa of the squamosal” as used in 

humans and other mammals (e.g., Gray, 1918:139, fig. 137) 

is rarely used in the cetacean literature, and there seems little 

chance of confusing the feature of the squamosal bone with that 

of the mandible.

= mandibular head (caput mandibulae) = mandibular condyle

= mandibular hiatus (hiatus mandibularis) = mandibular fossa

Fraser and Purves (1960:13, in Phocoena phocoena, citing 

Boenninghaus, 1904:46) appeared to use this term to mean the 

mandibular fossa (q.v.). See also Rommel (1990:37).

− mandibular neck (collum mandibulae)

In humans the mandibular neck connects the mandibular 

condyle to the mandibular ramus (Gray, 1918:172).

There is no distinct mandibular neck in Tursiops, the mandibular condyle being closely attached to the ramus.

* mandibular notch (incisura mandibulae) (Figure 15c,e)

The mandibular notch in the dog is located between the 

mandibular condyle and the coronoid process (Evans and Christensen, 1979:148).

The mandibular notch is present in Tursiops.

− mandibular space

The mandibular space is the area between the two articulated bodies of the mandibles (Evans and Christensen, 1979:147). 

Tursiops and other delphinids have a mandibular space.

− mandibular sulcus

In the yellow armadillo, the lingual surface of the mandible

carries faint, narrow, longitudinal sulci, each sometimes carrying one or more tiny foramina that have been called mandibular 

sulci (Wible and Gaudin, 2004:159).

Tursiops lacks a consistent pattern of mandibular sulci, but 

the term could be applied to variably developed fine grooves in 

mandible n u m b e r 6 2 7 • 4 5
the mid-length to posterior of the lingual face of some mandibles. 

The occupants of these sulci are currently unknown.

− mandibular symphysis (symphysis mandibulae)

The bodies of the mandible in the dog and other mammals 

are united at the mandibular symphysis, a strong fibrous articulation that frequently fuses with age (Evans and Christensen, 

1979:146; Feneis, 1994:26.14; not in Schaller, 1992). Strictly, 

the term “symphysis” should apply only to the two associated 

or fused mandibles. The symphysis is fused in adults of many 

but not all odontocetes but never fuses in mysticetes. Schulte 

(1917:365, 366, 376, 401) described the symphysis in Kogia and 

Anderson (1879:496, 528) described it in Platanista.

− mandibular torus (torus mandibularis)

Mandibular tori are variable ossifications that occur as 

thickenings of the ventral surface of the mandible (Whitney, 

1889–1910:[vol. 8]6396).

− masseteric fossa (fossa masseterica)

The masseteric fossa is the area of insertion of the m. masseter. The masseteric fossa in the dog lies on the dorsolateral surface of the ramus and is limited by the coronoid crest anteriorly / 

dorsally and the condyloid crest posteriorly / ventrally (Evans 

and Christensen, 1979:148).

The masseter is a relatively small, diffuse, and fat-laden 

muscle in delphinids. The insertion of the masseter has extended 

ventrally to the angular process in delphinids, and the masseteric fossa generally lacks distinct boundaries (Fraser and Purves, 

1960:19, 23, 76, 84).

* masseteric line (Figure 15b,c,e)

The masseteric line in the dog lies on the lateral surface of 

the mandible and extends forward from the angular process. It 

marks the ventral limit of insertion of the m. masseter (Evans 

and Christensen, 1979:147).

Because of the diffuse nature of the masseter muscle in Tursiops and other delphinids, its insertion generally does not produce a definable masseteric line. In one specimen of Tursiops

(USNM 550403), however, the ventral border of the angular 

process carries a small laterally produced flange that might be 

the masseteric line.

− masseteric tuberosity (tuberositas masseterica)

The masseteric tuberosity is located on the lateral surface 

of the angle of the mandible in humans (Feneis, 1994:26.4). It 

is formed by the tendon of insertion of the m. masseter (Gray, 

1918:172f). It is hence a specialization of the masseteric line.

A masseteric tuberosity is not present in Tursiops.

* mental foramina (foramina mentalia) (Figure 15c)

The mental foramina are located on the anterior portion of 

the labial surface of the mandible in the dog (Evans and Christensen, 1979:147). They are commonly multiple and contain 

branches of the mental nerve (trigeminal; mandibular).

The mental foramina are well developed toward the anterior of the mandible in Tursiops and other delphinids. In Cetacea the mental foramina are extremely variable in number and 

position.

− mental protuberance (protuberantia mentalis)

The mental protuberance or mental point in humans is a 

triangular eminence at the anteroventral portion of the mandibular body (chin) (Gray, 1918:172; Feneis, 1994:26.15). This is 

exceedingly variable in development in humans and appears to 

be sexually dimorphic. No functional element is associated with 

it. The term seems to have little use other than in humans; “pogonion” is used in other species.

− mental spine (spina mentalis) (Figure 15b)

The mental spines are small spinous processes on the internal surface of the ventral portion of the symphysis. They serve 

as origins for the m. genioglossus and m. geniohyoideus (Gray, 

1918:172).

We can find no trace of a mental spine in delphinids.

− mental tubercle (tuberculum mentale)

The mental tubercles are small raised areas on either side of 

the mental protuberance.

Mental tubercles are lacking in cetaceans.

− molar portion (pars molaris)

The pars molaris of the mandibular body bears the molar 

teeth in the dog (Evans and Christensen, 1979:146).

Tursiops and other odontocetes are homodont, the molars 

are not identifiable, and the mandibles do not have a pars molaris. Because of the uncertainty of homologies in the cheekteeth 

of heterodont extinct Cetacea, the pars molaris is likely to be 

identifiable only in archaeocetes.

− mylohyoid crest

Miller (Evans and Christensen, 1979:147) illustrated a low 

crest on the lingual surface of the mandible that he labeled the 

mylohyoid crest. He did not mention it in the text and there was 

no mention of it in the other anatomical works we used. We treat 

this as a lapsus calami, probably for the mylohyoid line.

* mylohyoid groove (sulcus mylohyoideus) (Figure 15d)

The mylohyoid groove runs anteroventrally from the ventral margin of the mandibular foramen. It contains the mylohyoid vessels and mylohyoid nerve (Schaller, 1992:38.31; Feneis, 

1994:28.9). Wible and Gaudin (2004:165) identified a weak sulcus for the mylohyoid nerve on the mandibular ramus below the 

mandibular foramen in some armadillos.

In some dolphins there is a well-marked groove on the ventromedial aspect of the posterior portion of the mandible near 

the mandibular foramen. This groove is evident where the posterior border of the mandibular foramen lies close to the bottom of 

the mandible. This might be the mylohyoid groove in Tursiops; 

dissection is needed for confirmation.

* mylohyoid line (linea mylohyoidea) (Figure 15d)

The mylohyoid line in the dog is a smooth longitudinal 

ridge located in the posterior section of the lingual surface of 

the mandible for the attachment of the m. mylohyoideus (Evans 

and Christensen, 1979:147; Schaller, 1992:38.17; Feneis, 

1994:26.22).

The mylohyoid line starts near the dorsal lingual aspect of 

the mandible just anterior to the mandibular foramen (USNM 

4 6 • smithsonian contributions to zoolog y mandible
571952). Anteriorly it drops ventrally, reaching the middle of 

the body of the mandible and disappearing just posterior to the 

symphyseal region.

= neck = mandibular neck = condylar process

− oblique line (linea obliqua)

The oblique line is a line on the lateral surface of the mandible that runs from the mental tubercles to the anterior border 

of the ramus. It serves as the attachment for the m. quadratus 

labii inferioris and m. triangularis (Gray, 1918:172).

Tursiops and other odontocetes have lost the facial muscles 

associated with the lips on the lower jaw and the oblique line is 

not identifiable.

= pan bone = acoustic window

The term “pan” has been applied to the human skull, the 

patella, and the socket of the hip or shoulder joint and, as pan 

bone, to “the broad posterior end of the lower jawbone of a 

marine mammal” (Benbow et al., 2002).

In Tursiops and other odontocetes, pan bone refers to the 

thin lateral wall of the mandible over the mandibular foramen, 

especially in sperm whales (Brown, 1884:293; Whitney, 1889–

1910:[vol. 5]4253). Schulte (1917:366, 401) coined the term 

“pars papyracea” for this structure. Anderson referred to it as 

the condylar plate (1879:528).

= papyraceous portion (pars papyracea) = pan bone (in Kogia, 

Schulte, 1917:366, 376, 401)

* pogonion (Figure 15a,b)

The pogonion in the dog is the most anterior part of the 

mandible, at the symphysis, located between the roots of the most 

anterior teeth (Evans and Christensen, 1979:118). In humans the 

pogonion is the foremost point of the chin in the midline, for which 

feature, however, the term “mental protuberance” is often used.

The pogonion is identifiable in Tursiops and other 

odontocetes.

= postalveolar tubercle = coronoid crest

Schulte (1917:377) used postalveolar tubercle in Kogia to 

refer to a process on the dorsal profile of the mandible between 

the last alveolus and the coronoid process. As seen in lateral view, 

“the postalveolar tubercle separates two well marked concavities 

in the outline.” Schulte thus appeared to refer to the coronoid 

crest.

− precoronoid crest

The precoronoid crest is a distinct elevation between the 

coronoid process and the posterior of the vestigial alveolar 

groove in the fossil delphinid Australodelphis (see Fordyce et al., 

2002: fig. 3a). The precoronoid crest represents a dorsal bulge in 

the coronoid crest.

A precoronoid crest is present in Tursiops; dissection is 

needed to establish its function.

− preorbital fossa (Sisson, 1910:140)

The preorbital fossa is illustrated by Sisson (1910:140) in the 

domestic pig, but he did not discuss it—we found no reference to 

it in the surrounding pages nor in the index. The preorbital fossa 

lies on the external surface of the maxilla, jugal, and lacrimal. 

The preorbital fossa may house the m. levator labii superioris 

proprius (levator rostri) (Sisson, 1910:311). A topographically 

similar depression exists in the skull of the dromedary where it 

lies near the juncture of the cranium with the rostrum and occupies the dorsal portion of the maxilla, nasal, and frontal (Smuts 

et al., 1987:2, fig. 1.2; 4, fig. 1.4). The depression contains the 

posterior dilation of the lateral nasal diverticulum (Smuts et al., 

1987:106, fig. 4.5).

Although the facial muscles in odontocetes are diverse and 

extensive (Mead, 1975), they do not develop a homologue to the 

preorbital fossa.

* pterygoid fovea (fovea pterygoidea) (Figure 15d)

The pterygoid fovea is a pit associated with the mandibular 

neck for the insertion of the lateral pterygoid muscle; in humans 

it lies on the anterior portion of the neck of the mandible (Feneis, 

1994:28:15), whereas in horse and pig it lies more ventrally, 

close to the condyle (Schaller, 1992:38:37).

There is a small rounded eminence on the lingual side of 

the mandible of Tursiops, just below the coronoid process and 

anterior to the mandibular notch, that we have interpreted as the 

pterygoid fovea. The insertion for the lateral pterygoid muscle 

is not detailed in the literature for Tursiops, and there is not a 

clear pterygoid fovea. Murie (1873:284; see Fraser and Purves, 

1960:8) mentioned the association of pterygoid muscles with the 

“articulating condylar process of the mandible” in Globicephala. 

In the medial face of the mandible of Tursiops (USNM 550403), 

the region of the mandibular notch between the condyle and the 

coronoid process is thickened and rough, possibly marking a 

muscle insertion.

− pterygoid tuberosity (tuberositas pterygoidea)

The pterygoid tuberosity is located on the medial surface of 

the angle of the mandible in humans. It is formed by the tendon 

of insertion of the medial pterygoid muscle (m. pterygoideus medialis) (Feneis, 1994:28.5) (= m. pterygoideus internalis; Gray, 

1918:172f). This is not to be confused with the pterygoid tubercle of the pterygoid bone on the skull base.

The insertion of the medial pterygoid muscle is a diffuse tendon and no pterygoid tuberosity is developed in Tursiops or other 

delphinids. For Phocoena, Boenninghaus (1904: fig. K) showed 

the medial pterygoid muscle inserting into what Fraser and Purves 

(1960:13) identified as the medial periosteal wall of the intramandibular fat body. We cannot identify an obvious pterygoid tuberosity associated with the angular process in Tursiops.

* ramus of the mandible (ramus mandibulae) (Figure 15c)

The ramus of the mandible is the vertical non-tooth-bearing 

portion of the bone (Schaller, 1992:38.23; Feneis, 1994:28.1). 

The ramus is vertical in the dog but not necessarily in other taxa 

(Evans and Christensen, 1979:148). Davis (1964) regarded the 

ramus as the portion of the mandible posterior to the teeth; thus, 

it has both horizontal and vertical components. Such use appears 

to be common. Owen (1866a:41) divided the mandible into the 

tooth-bearing horizontal ramus and the ascending ramus.

The mandible in odontocetes is not divided into vertical 

and horizontal parts, in contrast to many other mammals. Owen 

mandible n u m b e r 6 2 7 • 4 7
(1853:444; 1866a:41) referred to the mandibular parts as the 

ascending ramus, which is comparable to the ramus of Evans 

and Christensen (1979:148), and the horizontal or descending 

ramus, which is comparable to the body of the mandible. This 

was based mainly on his human experience.

Fraser and Purves (1960:24, 26) used “ramus” to mean 

the entire mandible. We take the expanded definition of Davis 

(1964) and treat the ramus in Tursiops as that portion of the 

mandible that is posterior to the dental alveoli. In species where 

the dentition is reduced, such as beaked whales, the mandibular 

ramus extends from the mandibular condyle to the anterior end 

of the coronoid crest.

= sockets = dental alveoli

− sternomandibular tuberosity (tuberositas m. sternomandibularis)

The sternomandibular tuberosity is a feature on the posterior margin of the mandible of the horse (Schaller, 1992:38.26). 

It is dorsal to the angular process. The sternomandibular tuberosity is formed by the insertion of the sternomandibular muscle. 

This muscle is homologous with the sternal portion of the m. 

sternocleidomastoideus in humans (Sisson, 1910:225); it is also 

known as the m. sternocephalicus.

The muscular connection between the sternum and the skull 

in cetaceans has become limited to attachments through the 

hyoid. The sternohyoid muscle forms the distal link and various combination of the occipitohyoid muscle, m. hyomandibularis, and omohyoid muscle form the proximal link (Schulte, 

1916:416, 417, pls. 46–48; Schulte and Smith, 1918:36–41; 

Lawrence and Schevill, 1965:17). There is no sternomandibularis or any other muscle that inserts on the middle portion of 

the mandibular condyle.

− sublingual fovea (fovea sublingualis)

The sublingual fovea is the small pit that the sublingual salivary gland occupies in humans (Feneis, 1994:26.24). It is located 

dorsal to the mylohyoid line and ventral to the root of the canine 

tooth. It is also known as the fossa for the sublingual gland (Gray, 

1918:173) or the sublingual depression (Gray, 1918:1136).

Salivary glands are rudimentary or absent in Cetacea (Slijper, 1962:285), hence the sublingual gland is likely to be absent 

in Tursiops and other delphinids.

− submandibular fovea (fovea submandibularis)

The submandibular fovea is the depression that the submandibular salivary gland occupies in humans (Feneis, 1994:26.25). 

It is located ventral to the mylohyoid line in the posterior half 

of the body of the mandible. It is also known as the fossa for 

the submaxillary gland (Gray, 1918:173) or the submaxillary 

depression (Gray, 1918:1136). Gray called the gland in question the “submaxillary gland” because of its relationship with 

the submaxillary triangle (Gray, 1918:1135).

Salivary glands are rudimentary or absent in Cetacea (Slijper, 1962:285); hence, the submandibular (submaxillary) gland 

is likely to be absent in Tursiops and other delphinids.

* symphyseal surface (Figure 15d)

The symphyseal surface in the dog is the most anterior portion of the lingual surface of the mandible that bears the mandibular symphysis (Evans and Christensen, 1979:147). More 

strictly, the symphyseal surface is the feature that can be seen on 

either the left or right mandible, whereas the symphysis is apparently only in two associated or fused mandibles.

The symphyseal surface is generally quite distinct in Tursiops as an irregularly planar surface, unfused, and less than 

twice as long as deep. There is a long, narrow, shallow groove 

in the symphyseal surface of USNM 504560, similar to that described in mysticetes: “at the symphyseal end there was a distinct 

fissure, the remains of the channel for the distal extremity of the 

Meckelian cartilage” (Carte and Macalister, 1868:212). Owen 

(1866a:41) referred to the symphyseal part of the mandible.

= symphysial plate (Anderson, 1879:528)

Anderson, in his description of Platanista (1879:528), used 

symphysial plate (or internal alveolar plate) in referring to the 

symphyseal surface of the mandible. He did not differentiate the 

symphysial plate from the symphyseal surface.

* ventral margin of the mandible (margo ventralis) (Figure 15d)

The ventral margin of the mandible consists of the entire 

ventral border of the mandible from the symphysis to the angular process.

MAXILLA

Os Maxilla

Figures 1, 3, 4, 6c,d, 16, 32

The maxilla is the principal tooth-bearing element of the 

upper jaw, forming the site for development of the canines, premolars, and molars (Gray, 1918:157; Evans and Christensen, 

1979:140; Schaller, 1992:32.6; Feneis, 1994:22.2). Vesalius 

(1543:23) referred to the maxilla as the superiori maxillae, 

fourth bone of the upper jaw (quartum maxillae superioris os) 

(ibid., 22, 23), largest bone of the upper jaw (maximo superioris maxillae ossi) (ibid., 22, 23), or just the maxilla (ibid., 25). 

Eustachius and Lancisius (1714:113) referred to the maxilla as 

the maxilla. The maxilla is developed from the dorsal portion 

of the primitive cartilaginous jaw apparatus. The maxilla is intimately related the nasal passage; it forms the bulk of the floor 

(the palate) and the lateral walls, including some of the paranasal 

sinuses. In most terrestrial mammals the maxilla articulates with 

the jugal, forming the zygomatic arch. In delphinids and other 

Cetacea, the jugal has moved its anterior articulation to the lacrimal. The principal changes to the maxilla involve the increase 

in relative size, posterior movement of the external bony nares, 

and development of the extensive ascending process.

The maxilla forms a significant portion of the rostrum. The 

maxilla was also known as the maxillary bone or just the maxillary (Owen, 1866a:27). Wible and Gaudin (2004:122) found 

it convenient to recognize five components to the mammalian 

maxilla: the facial, palatine, zygomatic and orbital processes, 

and the contribution of the maxilla to the lateral wall of the 

nasal cavity.

See also Schulte’s references to the maxilla (1917:362, 

369–375, 377, 378, 380, 381, 383, 385–389, 391, 393, 394, 

398–400, 402) in Kogia.

4 8 • smithsonian contributions to zoolog y maxilla
− aditus nasomaxillaris (nasomaxillary opening)

The aditus nasomaxillaris in the dog forms the communication between the nasal passage and the maxillary sinus (Evans 

and Christensen, 1979:159).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75) and the aditus nasomaxillaris is absent in 

Tursiops.

− alveolar canal (canalis alveolaris)

The alveolar canals in the dog lead from the infraorbital 

canal in the maxilla to the individual roots of the incisors, canines, and premolar teeth, in both the mandible and the maxilla 

(Evans and Christensen, 1979:140; Schaller, 1992:32.14, 38.5).

In Tursiops the alveolar canals lead from the infraorbital 

canal or the mandibular canal to the roots of the teeth.

* alveolar foramina (foramina alveolaria) (Figure 16c)

Alveolar foramina in the dog are the openings of the alveolar canals at the apex of each dental alveolus. They contain 

the alveolar nerves and alveolar vessels (Evans and Christensen, 

1979:141). In the neonatal specimen of Tursiops illustrated (Figure 16c), the alveolar canal is open in the region of the anterior 

teeth, forming an alveolar sulcus. It is only in the posterior alveoli that the alveolar canals are closed and the alveolar foramina 

have formed. This situation occurs on both the upper and the 

lower dentitions.

= alveolar groove (sulcus alveolaris)

See alveolar groove of the mandible under “Mandible.”

= alveolar juga (juga alveolaria)

See this term under “Mandible.”

* alveolar margin of the maxilla (margo alveolaris) (Figure 16c)

The alveolar margin of the maxilla is the border of the processus alveolaris (Schaller, 1992:34.11).

Odontocetes have a normal alveolar margin.

= alveolar portion of the maxilla (pars alveolaris) = alveolar 

process

* alveolar process of the maxilla (processus alveolaris) (Evans 

and Christensen, 1979:140; Schaller, 1992:34.10) (Figure 16c)

The alveolar process of the maxilla in the dog is the ventrolateral surface, which forms the thickest and most cancellous portion of the bone. It houses the dental alveoli (Evans and 

Christensen, 1979:140).

The alveolar process is present in Tursiops and other odontocetes that bear teeth in the maxilla. The alveolar process is also 

known as the alveolar portion of the maxilla in humans (Feneis, 

1994:26.26).

− anterior lacrimal crest of the maxilla (crista lacrimalis 

anterior­)

The anterior lacrimal crest of the maxilla forms the anterior 

border of the fossa for the lacrimal sac and associated lacrimal 

foramen in humans (Gray, 1918:164). The anterior lacrimal 

crest is absent in Odocoileus and other artiodactyls in which one 

or two lacrimal foramina open within the lacrimal.

Tursiops has a lacrimojugal crest (q.v.) of the maxilla that 

is associated with the lacrimal and jugal but is not, however, 

clearly homologous with the anterior lacrimal crest in humans.

− anterior maxillary sinus (sinus maxillaris rostralis)

The anterior maxillary sinus is the anterior part of the sinus 

that lies in the maxilla in equids (Sisson and Grossman, 1953:80; 

Schaller, 1992:32.29, 180.2).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the anterior maxillary sinus is absent in 

Tursiops.

− anterior sinus (Fraser and Purves, 1960:62) = anterior lobe

Fraser and Purves (1960) used different definitions for anterior sinus and anterior sac (q.v.), names that, from perusal of 

their text, refer to the same structure. Here, “anterior sinus” is 

preferred.

According to Fraser and Purves (1960:62), Beauregard 

(1894) used the term “pterygoid sac” [or sinus] only for “that 

part of the air sinus system which occupies the pterygoid hamuli, 

the remainder of the system anterior to the tympanic cavity being 

designated the anterior sinus.” Under discussion of Pontoporia, 

Fraser and Purves (1960:63) redefined the anterior sinus (q.v.) as 

comprising those parts of the pterygoid sinus system (sensu lato) 

that extend farther forward than the most anterior limits of the 

pterygoid. Fraser and Purves gave the examples of the anterior 

sinus in Inia (1960:64; a sinus that penetrates the bony rostrum), 

Grampus (ibid., 69; a sinus on the ventral surface of the hard 

palate of the maxilla), Tursiops (ibid., 70; a sinus on the ventral 

surface of the maxilla), and Delphinus (ibid., 72; a long sinus on 

the ventral surface of the maxilla).

* anterior sinus fossa (Figure 2)

The anterior sinus fossa lies on the ventral portion of the 

base of the rostrum anterior to the ventral infraorbital foramen

(Fraser and Purves, 1960:8, 25, fig. 8, 70, 72). The anterior sinus

arises from the preorbital lobe of the pterygoid sinus, and the 

boundary of the posterior extent of the anterior sinus fossa is 

indeterminant. The fossa can be seen in preparations of adult 

Tursiops as a smooth area around the ventral infraorbital foramen, involving maxilla and sometimes the medial process of the 

lacrimal. The fossa may extend anteriorly to about the level of 

the last dental alveolus. Medially the fossa may develop onto 

the palatine, being limited by the origin of the pterygoid muscles 

ventrally. The border of the anterior sinus / pterygoid muscles 

can be followed as a crest across the perpendicular lamina of the 

palatine.

* anterior surface of the maxilla (facies anterior) = facial surface 

(Figure 16a)

The anterior surface of the maxilla is on the external surface of the maxilla and faces anteriorly and laterally (Feneis, 

1994:22.8).

The anterior surface of the maxilla in Tursiops and other 

Cetacea forms the laterodorsal surface of the rostrum.

= antorbital angle = antorbital process

= antorbital foramen = dorsal infraorbital foramen = ventral infraorbital foramen (Diagram 1; Table 6)

maxilla n u m b e r 6 2 7 • 4 9
Antorbital foramen has had a long occasional use for the 

anterior or dorsal opening of the infraorbital foramen or infraorbital canal in mammals; see e.g., Owen (1859:312) for the marsupial Thylacoleo.

Use in Cetacea varies; Kellogg (1928:38) commented about 

the antorbital foramen in “zeuglodonts” (archaeocetes): “The 

premaxillary has an ascending process which does not reach the 

frontal, but terminates behind the antorbital foramen (above 

upper premolar 2 or 3).” (See also Gingerich et al., 2005: fig. 4, 

in the archaeocete Makaracetus). Fraser and Purves (1960:137, 

and pl. 9ff.) identified the antorbital foramen only in illustrations, as the structure identified in Tursiops as the ventral infraorbital foramen.

* antorbital fossa (Figures 2, 6f, 30, 32)

Novacek (1986:30) identified the antorbital fossa in the extinct Leptictis as a depression on the lateral surface of the maxilla 

and associated with the infraorbital foramen (anterior opening 

of the infraorbital canal), serving as an origin for various snout 

muscles. Antorbital pit and antorbital depression (Wible et al., 

2004:41, for Zalambdolestes) appear to be synonyms.

In Cetacea, Tursiops, and other odontocetes, the facial fossa

similarly serves as the origin for facial muscles. It is likely that 

the facial fossa and antorbital fossa are homoplastic, having 

evolved independently in odontocetes and other mammals. We 

recommend that “antorbital fossa” not be used in this sense for 

Odontoceti.

In Cetacea, Owen (1866a:28) described the “rough malomaxillary fossa” as lying external to the “antorbital fossa” in the 

skull of Orcaella. He labeled the malomaxillary fossa as (e) and 

the antorbital fossa as (d) in the text (1866a:28) but did not include (d) and (e) in his figures (Owen, 1866a: pl. 9). Later, antorbital fossa was used for the enlarged vacuity around the ventral 

infraorbital foramen in Mesoplodon densirostris (see Besharse, 

1971:308) and in species of Stenella (see Perrin, 1975:91, fig. 

39). Confusingly, Fraser and Purves (1960:137) used the term 

“antorbital foramen” (q.v.) in this part of the skull.

The antorbital fossa is recognized here in Tursiops and other 

delphinids as the dorsally excavated region anterior to the preorbital ridge, variably involving the ventral infraorbital foramen, 

preorbital recess, and anterior sinus fossa. Fraser and Purves 

(1960:51) mentioned some taxonomic variation in this feature 

(e.g., for Orcinus: “pre-orbital smoothed area”). The feature is 

quite variable in form across the Odontoceti, probably because 

of the variable influence of the infraorbital vessels and nerves, 

and anterior parts of the pterygoid sinus.

= antorbital maxillary tuberosity (Kellogg, 1928:61, in Hyperoodon) = maxillary tubercle 

* antorbital notch (Figures 1, 16a,d, Diagram 2; Table 5)

There is no antorbital notch in noncetacean mammals. The 

infraorbital notch (q.v.) in humans and some rodents may be 

analogous.

In Tursiops the antorbital notch is the notch formed laterally 

in the maxilla and lacrimal (lacrimojugal) at the base of the rostrum (Owen, 1866a:21, 34; Schulte, 1917:365, 373, 387–391, 

400). The antorbital notch is medial to the antorbital process

and transmits the facial nerve. In those odontocetes that develop 

a prominential notch (ziphiids), the prominential notch is anteromedial to the antorbital notch (Moore, 1963:424, fig. 14). 

Mitchell (1968:270, 271) described a situation in Ziphius cavirostris where the dorsal outline of the jugal did not coincide with 

the dorsal outline of the maxilla, and two notches were formed 

that Mitchell termed the internal antorbital notch (medial to the 

antorbital tubercle and jugal) and the external antorbital notch 

Diagram 1. Schematic cross section of the rostrum and antorbital fossa, showing generalized distribution and names of features associated 

with the foramina of the palatine. 

greater palatine sulcus

= palatine sulcus/groove

incisive foramen

= incisive canal

= nasopalatine duct

= palatine fissure

= anterior palatal vacuity

nasal

oral

pterygopalatine canal

= palatine canal

transmits: 

caudal palatine nerve

greater/ major palatine nerve

greater palatine artery = ?descending palatine artery

septal branch of caudal nasal nerve = nasopalatine nerve

posterior palatine foramen

= caudal palatine foramen 

major palatine foramen

(+ minor palatine foramen)

= greater palatine foramen

= anterior palatine foramen

in maxilla

or at maxillopalatine suture

or in palatine

pterygopalatine sulcus

in pterygopalatine fossa

ventral to infraorbital foramen

infraorbital foramen

sphenopalatine foramen

= naso-palatine foramen

minor palatine foramen/ina

= accessory palatine foramen

= postpalatine foramen

= postero-lateral palatine foramen

= posterolateral vacuity or foramen

may have minor palatine sulcus/sulci

orbital/ 

infraorbital anterior posterior

greater/major and

lesser/minor 

are interchangeable in 

the literature

5 0 • smithsonian contributions to zoolog y maxilla
(lateral to the antorbital tubercle and jugal). Owen (1886a:34, 

38, 39, 41; pl. 12: fig. 1k; pl. 13: fig. 1k) referred to the antorbital notch in Kogia sima as the malo-maxillary fissure).

* antorbital process (Diagram 2; Table 5; Figure 16a,c,d)

There is no antorbital process, in the cetacean sense, in noncetacean mammals.

Tursiops has an antorbital process, which is the anterior 

projection of the skull lateral to the antorbital notch, involving 

the anterolateral portion of the maxilla and the underlying lacrimojugal bone. More broadly, the antorbital process in Cetacea 

is the anterior projection of one or more of maxilla, lacrimal, 

frontal, or jugal that lies lateral to the antorbital notch (path of 

facial nerve).

The literature reveals various combinations of antorbital and 

preorbital with the terms process, angle, and tubercle. The term 

“process” is preferred because it implies less about the shape and 

degree of projection than the terms angle, tubercle, or prominence, 

and “antorbital” is preferred over preorbital because of association with the path of the facial nerve at the antorbital notch.

There has been confusion regarding the nomenclature of 

the features around the antorbital process and antorbital notch. 

Table 5 and Diagram 2 summarize the terms that we use in 

this paper and the history of prior usage. The literature was reviewed to get a representative but not exhaustive idea of past 

use; anatomical use in recent cladistic literature was not checked 

in detail. In many cases, especially involving features medial to 

the antorbital notch, the original meaning was not clear, so we 

often give quotes and page numbers. Some new or significantly 

redefined terms are proposed for previously confused landmarks: 

supraorbital crest, supraorbital ridge, maxillary crest, maxillary 

tubercle, and rostral (or rostral maxillary) crest. The homology is not clear for the so-called maxillary crest in Physeter and 

Kogia.

Synonyms for antorbital process include antorbital eminence, 

antorbital tuberosity, antorbital prominence, antorbital tubercle, 

antorbital protuberance, preorbital apophysis, preorbital angle, 

preorbital process (not to be confused with the antorbital process 

in Mysticeti), large smooth tuberosity, round anterior extremity, 

and frontal protuberance (see Diagram 2).

Diagram 2. Schematic dorsal view of named osteological structures in and around the antorbital notch in Odontoceti.

Antorbital notch = path for facial nerve, VII

anteorbital notch

malo-maxillary fissure (Kogia)

preorbital notch

infraorbital notch?

maxillary notch

Antorbital process: 

antorbital eminence

antorbital tuberosity

antorbital prominence

antorbital tubercle

antorbital protuberance

preorbital apophysis

preorbital angle

preorbital process = not same as antorbital 

process of Mysticeti

large smooth tuberosity (Kogia)

round anterior extremity (Platanista)

frontal protuberance Maxillary crest/ridge: feature lateral or posterior to 

antorbital notch developed on maxilla but not frontal:

posterior expanded plate of maxilla (Kogia)

longitudinal crest (Pontoporia)

incurved extremity of transverse crest (Kogia)

maxillary crest, non-pneumatized (Pontoporia, Parapontoporia)

supraorbital crest (Parapontoporia)

Supraorbital crest/ridge: feature lateral to antorbital 

notch developed on edge of maxilla and/or frontal:

lateral crest of maxilla (Platanista)

bony incurved crest (Platanista)

frontal plate (Zarhachis)

vertical crest of frontal plate of maxilla (Inia)

maxillary crest (Platanistidae)

pneumatic maxillary crest (Platanista)

crest of supraorbital process of frontal and maxilla (Zarhachis)

upward prolongation of maxilla (Inia)

vertical crest of maxilla (Inia)

Rostral [maxillary] ridge/crest: a feature medial 

to antorbital notch, associated with maxillary 

tubercle and prominential notch, or with rostrum in absence of tubercle and notch: 

maxillary crest (Hyperoodon, Berardius, 

 Indopacetus)

low roughed rugosity (Ziphius)

maxillary tuberosity (Ziphius, Mesoplodon)

rugose eminence (Berardius)

longitudinal ridge (Mesoplodon, Hyperoodon)

pronounced elevation (Berardius)

immense bony mass (Hyperoodon)

supraorbital ridge (Hyperoodon)

low maxillary ridge (Mesoplodon)

maxillary ridge ‘behind” [medial to] antorbital 

notch (Mesoplodon)

dorsal maxillary tuberosity extending into maxillary 

tubercle (Mesoplodon)

maxillary prominence (Mesoplodon)

end of maxillary tubercle (Mesoplodon)

prominential crest (Mesoplodon)

maxillary eminence (Parapontoporia)

maxillary crest (Physeter) [homology uncertain]

Maxillary tubercle: 

tubercle anterior to antorbital notch (Mesoplodon)

protuberance which projects into antorbital notch 

(Mesoplodon)

maxillary tubercle (Mesoplodon, Indopacetus)

maxillary prominence

antorbital tubercle (Indopacetus)

apex of maxillary prominence (Mesoplodon)

Prominential notch: 

pseudo-notch (Mesoplodon)

inner notch (Mesoplodon)

second sinus (Mesoplodon)

angle formed by anterior margin

angular break

notch formed by 

 maxillary prominence

a large dorsal infraorbital foramen is 

commonly present medial to rostral ridge 

or crest

Maxillary groove, not bounded by crest (Indopacetus)

frontal

maxilla

jugal, or 

lacrimojugal

many 

different 

positions/ 

profiles

maxilla n u m b e r 6 2 7 • 5 1
Table 5. Terms used by selected authors to designate landmarks in the vicinity of the antorbital notch, with page and/or figure numbers 

given in parentheses for the citation in first column. A dash (–) indicates term not used in the indicated report; a question mark indicates 

a relationship that is questionable.

Author(s),

date, taxa

Antorbital

process

Supraorbital

crest

Maxillary

crest

Antorbital

notch

Maxillary

tubercle

Rostral

[maxillary] crest

Prominential

notch

Owen, 1866a, 

Delphinidae, 

Kogia

Antorbital 

process of the 

malar (25), large 

smooth tuberosity (38, Kogia)

— Posterior expanded 

plate of the maxilla 

(38, Kogia)

Antorbital 

notch (21), 

malomaxillary 

fissure (38, 

Kogia)

— — —

Flower, 1867, 

Inia, Pontoporia, 

Odontoceti

Antorbital 

process (89), 

antorbital 

eminence (91), 

antorbital 

tuberosity (108)

Large bony 

incurved crest 

[Platanista] 

(114)

Sharp, straight 

and nearly 

parallel crest . . . 

narrow upward 

prolongation of the 

maxilla [Inia] (91), 

longitudinal crest 

[­Pontoporia] (108)

Antorbital 

notch (89)

— — —

Flower, 1868, 

Physeter

Antorbital 

process (319)

— Elevated edge of 

broadly expanded 

maxilla, posteriorly 

continuous with 

but not the same as 

the occipital crest 

(314) [homology 

uncertain]

Antorbital 

notch (318)

— — —

Flower, 1872, Berardius and other 

Ziphiidae

— — — Antorbital 

notch (207)

— “Low roughed 

rugosities” (207), 

maxillary tuberosity 

[supposedly not in 

Mesoplodon] (209), 

rugose eminences on 

outer edge of upper 

surface of maxillae 

at base of rostrum 

[Berardius] (212), 

maxillary crest 

[of Hyperoodon, 

rostrum + cranium] 

(206)

—

Flower, 1878, 

Mesoplodon and 

other Ziphiidae

— — — Antorbital 

notch (417)

Tubercle 

of maxilla 

in front of 

antorbital 

notch (417)

Longitudinal 

ridge on upper 

surface of maxilla 

[Mesoplodon], . . . 

pronounced 

elevation 

[Berardius], . . . 

immense bony mass 

[Hyperoodon]” 

(423)

—

Anderson, 1879, 

Platanista

“Round anterior 

extremity [of 

malar]” (524)

“Great lateral 

crests of the 

maxillary 

bones” (449)

— Preorbital 

notch (363), 

= ? infraorbital notch 

(524)

— — —

(continued)

5 2 • smithsonian contributions to zoolog y maxilla
Table 5. (Continued)

Author(s),

date, taxa

Antorbital

process

Supraorbital

crest

Maxillary

crest

Antorbital

notch

Maxillary

tubercle

Rostral

[maxillary] crest

Prominential

notch

Flower, 1882, 

Hyperoodon

— — — Antorbital 

notch (395)

— = Supraorbital ridge 

(392), Maxillary 

crest (394)

—

Flower, 1885, 

Globicephala, 

Physeter, 

Hyperoodon

Antorbital 

prominence 

(212)

— Maxillary crest [in 

Physeter] (218) 

[­homology not 

clear]

Antorbital 

notch (213)

— Thick high 

longitudinal ridge 

(218, Hyperoodon)

—

True, 1910, 

Ziphiidae

— — — Antorbital 

notch (5), 

maxillary 

notch (13, 

26, 65)

“Tubercle 

anterior to 

antorbital 

notch . . .” 

(5); 

protuberance 

which 

projects into 

antorbital 

notch (12, 

26)

“Low maxillary 

ridge” (5) 

[Mesoplodon, 

apparently 

associated with 

tubercle], maxillary 

ridge behind 

[in lateral view, 

= medial to ?] 

antorbital notch 

(13)

“‘pseudonotch’ . . .” (26)

True, 1913a, 

Mesoplodon

— — — Antorbital 

notch (2)

Maxillary 

protuberance 

(2) [context 

not clear]

Maxillary 

prominence (1), = 

maxillary ridge (2)

Maxillary notch 

(1) [identity 

not clear, but 

apparently not = 

antorbital notch]

True, 1913b, 

Mesoplodon

— — — Antorbital 

notch (653)

Apex of 

maxillary 

prominence 

(653)

Maxillary 

prominence (653, 

654)

Maxillary notch 

(653) [context 

not clear]

Schulte, 1917, 

Kogia

Antorbital 

process (370)

— “Incurved 

extremities of the 

transverse crest” 

(364)

Antorbital 

notch (373)

— — —

Kernan, 1918, 

Ziphius

Maxillary 

tuberosity (351)

— — Antorbital 

notch (351)

— Maxillary prominence (353)—

Harmer, 1924: 

543, Mesoplodon

Antorbital 

tubercle: 

externally 

bounds the 

antorbital notch

— — Antorbital 

notch: 

bounded 

on medial 

side by 

maxillary 

tubercle

Maxillary 

tubercle: 

medial to 

antorbital 

notch; 

rostrum often 

separated 

from tubercle 

by the inner 

notch; not to 

be confused 

with rostral 

maxillary 

tuberosity 

sensu 

Harmer 

(544)

“Dorsal maxillary 

tuberosity . . . 

extends into 

. . . maxillary 

tubercle,” stated as 

homologous with 

maxillary crests of 

Hyperoodon

“Second 

sinus . . . [or] 

inner notch”

(continued)

maxilla n u m b e r 6 2 7 • 5 3
Table 5. (Continued)

Author(s),

date, taxa

Antorbital

process

Supraorbital

crest

Maxillary

crest

Antorbital

notch

Maxillary

tubercle

Rostral

[maxillary] crest

Prominential

notch

Kellogg, 1924, 

Platanista, 

Zarhachis

— “Vertical 

crest . . . of 

frontal plate 

of maxilla 

[Inia]” (7), 

“frontal plate 

[Zarhachis]” 

(13), maxillary 

crest (13)

— Maxillary 

notch (5)

— — —

Kellogg, 1926, 

Zarhachis

Preorbital 

apophysis (11)

Combined 

crest of supraorbital process 

of frontal and 

maxilla (3–4)

— Antorbital 

notch (17)

— — —

Kellogg, 1936, 

Archaeoceti

Preorbital angle 

(21)

— — — — — —

Fraser, 1945, 

Hyperoodon

Antorbital 

tubercle (24)

— — Antorbital 

notch (23, 

24)

— Maxillary crest 

(23, 25), as feature 

developed medial to 

antorbital notch

—

Fraser, 1955, 

Mesoplodon

Antorbital 

tubercle (626)

— — Antorbital 

notch (628)

— Maxillary 

prominence [as an 

elevated feature] 

(625); = “end of 

maxillary tubercle” 

(625, table)

“Angle . . . formed 

by . . . anterior 

margin . . . 

angular break” 

(625)

Moore and Wood, 

1957, Mesoplodon

Antorbital 

tubercle (12)

— — Antorbital 

notch (20)

“Anterior 

margin 

of each 

maxillary 

prominence 

protrudes” 

(10, 12, 23)

Maxillary 

prominence 

(compare 9, 10, 12, 

23) = used in sense 

of prominential 

crest of later 

authors

“Notches . . . 

formed by 

maxillary 

prominences” 

(20)

Moore, 1960, 

Mesoplodon

Antorbital 

tubercle (16)

— — — Protrusion 

of maxillary 

prominence 

(13)

Maxillary 

prominence (13, 18)

Notch associated 

with maxillary 

prominence (13)

Moore, 1963, 

Ziphiidae

Antorbital 

tubercle (407, 

fig. 14)

— — Antorbital 

notch (407)

“Apex of . . . 

maxillary 

prominence” 

(fig. 14) 

Maxillary 

prominence 

(407, item 7) = 

used in sense of 

prominential crest 

of later authors

Prominential 

notch (406, 

fig. 14)

Mitchell and 

Houck, 1967, 

Ziphius

Preorbital 

process [of 

frontal] (2509)

— — Maxillary 

notch, = 

internal and 

external 

antorbital 

notches 

(2509)

Maxillary 

prominence 

(2510)

— Prominential 

notch (2509)

(continued)

5 4 • smithsonian contributions to zoolog y maxilla
Table 5. (Continued)

Author(s),

date, taxa

Antorbital

process

Supraorbital

crest

Maxillary

crest

Antorbital

notch

Maxillary

tubercle

Rostral

[maxillary] crest

Prominential

notch

Azzaroli, 1968, 

Indopacetus

— — Not present, 

although a 

maxillary groove is 

shown posterior to 

antorbital process 

(fig. 5, 7)

Antorbital 

notch (fig. 

5)

Maxillary 

tubercle 

(fig. 5), a 

projection 

medial to the 

antorbital 

notch, 

= antorbital 

tubercle of 

fig. 9

Maxillary crest (fig. 

5)—a dorsal feature 

posterior to her 

maxillary tubercle; 

= maxillary ridge of 

fig. 7; bounded by 

maxillary groove 

(figs 5, 7)

—

Mitchell, 1968, 

Ziphius

Frontal 

protuberance, 

antorbital 

protuberance 

(271)

— — Antorbital notch: 

external 

antorbital 

notch, 

internal 

antorbital 

notch (271)

Maxillary 

prominence 

(271)

— Prominential 

notch (269)

Moore, 1968, 

Ziphiidae 

— — — — See rostral 

[maxillary] 

crest, right; 

maxillary 

tubercle 

sensu 

McCann = 

maxillary 

prominence 

sensu Moore 

(219 b, c)

Maxillary prominence of Ziphius

and Tasmacetus = 

maxillary tubercle 

of Mesoplodon = 

maxillary crest of 

Hyperoodon (219, 

c; 274, 283, fig. 20)

Prominential 

notch (219)

Barnes, 1985, 

Pontoporiidae

Antorbital 

process (14)

— Nonpneumatized 

maxillary crest 

on supraorbital 

process medial to 

margin of maxilla 

(3, 19, fig. 12)

Antorbital 

notch (4)

— Maxillary eminence 

[anteromedial to 

antorbital notch] 

(14, 19)

—

de Muizon, 1988, 

Kogiidae, Scaphokogia

Preorbital 

process (66)

— Maxillo-occipital 

crest [as in 

Physeter] (66, 69)

Preorbital 

notch (66)

— — —

Balcomb, 1989, 

Berardius

— — — — — Maxillary crest [on 

rostrum] (281)

—

Heyning, 1989a, 

Ziphiidae

Antorbital 

tubercle (5; 

fig. 8)

Maxillary 

crest (5) to be 

used only for 

the elevated 

structures in 

Platanista and 

Hyperoodon

Maxillary ridge 

(5), different from 

maxillary crest 

sensu Platanista 

and Hyperoodon

Antorbital 

notch (5; 

fig. 8)

Maxillary 

prominence 

(5, under 

discussion 

of antorbital 

tubercle)

Maxillary tubercle 

(5, under discussion 

of maxillary 

ridge; also fig. 8); 

maxillary crest in 

Hyperoodon (5)

Prominential 

notch (5; fig. 8)

Mead, 1989a, 

Hyperoodon

— — — — — Maxillary crest 

(327, 339)

—

Mead, 1989b, 

Mesoplodon

— — Maxillary 

prominence, 

associated with 

more lateral 

maxillary groove 

(393)

— — — —

(continued)

maxilla n u m b e r 6 2 7 • 5 5
= antorbital tubercle = antorbital process

= antrum or Highmore’s antrum = maxillary sinus (Gray, 

1918:158, 999; Feneis, 1994:22.24)

No to be confused with tympanic antrum under “Periotic 

Bone” or antrum under “Tympanic Bulla.”

* ascending process of the maxilla (Figures 3, 16a–e)

The ascending process of the maxilla is developed where 

the frontal surface of the maxilla is extended posterodorsally 

over the frontal bone, resulting in a squamous suture (Miller, 

1923:5). This was also termed the ascending plates of the maxillaries (Anderson, 1879:510); fronto-nasal portion, fronto-nasal 

surface (Anderson, 1879:526); frontonasal region (Anderson, 

1879:450); suprafrontal process (Schulte, 1917:380); suprafrontal extension (Schulte, 1917:398); facial plate, frontal plate, facial surface, superorbital plate, or nasal plate by 

Owen (1866a:28, 36, 38, 44); and frontal plate by Anderson 

(1879:522, 523).

In Tursiops and other odontocetes the ascending process is 

extremely well developed, with the maxillae extending over the 

anterior surface of the braincase and, in some species, contacting the interparietals in a developmental process known as “telescoping” (Winge, 1918; Miller, 1923).

− basirostral groove

The basirostral groove (Flower, 1878:417, 421; True, 

1910:10) runs anteriorly along the lateral surface of the maxilla 

from a blind pit medial to the antorbital notch in Mesoplodon 

grayi and M. layardii. The basirostral groove continues anteriorly for a variable distance. It is thought to represent a vestigial 

alveolar groove (Harmer, 1924:542).

The basirostral groove (per se) is not present in Tursiops, 

although it is present in at least one delphinid that lacks upper 

teeth (i.e., Grampus griseus).

* body of the maxilla (corpus maxillae) (Figure 16a)

The body of the maxilla is the central portion of the maxilla 

(Feneis, 1994:22.3), including the alveolar portion of the maxilla

(q.v.).

The body is differentiated from the ascending process of the 

maxilla in Tursiops and other odontocetes. Owen (1866a:28) 

referred to the body as the rostral part of the maxilla. Anderson 

(1879:524, 526, 528) calls the body the dental portion of the 

maxilla or the mandible.

− canine fossa (fossa canina)

The canine fossa of the maxilla lies lateral to the canine eminence formed by the roots of the canine tooth. The canine fossa 

gives origin to the m. caninus (Gray, 1918:158).

Because they lack a differentiated canine tooth, there is no 

distinct canine fossa in Tursiops or other odontocetes.

− caudal maxillary sinus (sinus maxillaris caudalis)

The caudal maxillary sinus is the posterior part of the maxillary sinus in animals where the sinus is separated by a maxillary septum (Schaller, 1992:32.5, 32.30, 36.35, 180.3; Sisson, 

1910:73). It is also called the posterior maxillary sinus or the 

Table 5. (Continued)

Author(s),

date, taxa

Antorbital

process

Supraorbital

crest

Maxillary

crest

Antorbital

notch

Maxillary

tubercle

Rostral

[maxillary] crest

Prominential

notch

Barnes, 1990, 

Tursiops

Preorbital 

process (22); 

is not same 

as antorbital 

process of 

maxilla in 

Mysticeti (21:9)

Maxillary 

crest (23)

Maxillary crest (23) Antorbital 

notch, 

Odontoceti 

(21:10)

— — —

de Muizon, 

1991, Ziphiidae, 

Odontoceti

Preorbital 

process (288)

— Occipital crest in 

sense of maxillary 

crest of Physeter

(294:20) 

Antorbital 

notch (288)

— Thickening on 

border between 

rostrum and 

cerebral skull in 

Mesoplodon (283)

—

Barnes, 1995, 

Pontoporiidae

Antorbital 

process (14)

— Maxillary crest, 

non-pneumatized 

(3, 19)

Antorbital 

notch (4)

— Maxillary eminence 

(14, fig. 6) [on 

maxilla on rostrum]

—

Messenger and 

McGuire, 1998

Antorbital 

tubercle = 

maxillary 

tubercle (117); 

context not clear

Pneumatic 

maxillary crest 

(117: 1421)

?Maxillae, low 

crest (117: 1421)

— Antorbital 

tubercle = 

maxillary 

tubercle 

(117: 1425)

— Antorbital 

notch (117: 

1426); context 

could mean 

prominential 

notch

5 6 • smithsonian contributions to zoolog y maxilla
superior maxillary sinus (Sisson, 1910:73). Paranasal sinuses are 

not developed in cetaceans (Fraser and Purves, 1960:5, 75) and 

the caudal maxillary sinus is absent in Tursiops.

= cavity for the zygomatic articulation = zygomatic recess

− cerebral area (Schulte, 1917:389)

Schulte (1917:389) used the term “cerebral area” in describing the maxilla of Kogia: “The concavity of the frontal process 

of the maxilla is increased by sagittal flange which participates 

in the facial crest, the right being excluded by the premaxillary. 

Finally on the ventral surface the ridge between the cerebral and 

lachrymal areas is less pronounced.”

Several things are unclear in this series of statements, one of 

which is the reference to “less pronounced.” We think that cerebral area and lachrymal area might refer to those portions of the 

maxilla that abut directly on the brain and the lachrymal bone. 

See the following description of his usage of cerebral surface.

− cerebral surface of the maxilla (Schulte, 1917:389)

Schulte (1917:389) used the term “cerebral surface of the 

maxilla” in this description: “In this suture are the beginnings 

of arterial sulci, one passing mesad and one caudad to reach the 

cranial cavity by way of the fronto-maxillary suture and to be 

continued as branched systems of grooves on the cerebral surface 

of the maxilla. The remainder of the ventral surface consists of a 

cerebral surface entad and a broad marginal area for articulation 

with the lachrymal and frontal.”

We interpret “cerebral surface” in that series of statements to 

mean the surface of the maxilla that is in direct contact with the 

brain. Schulte (1917:390) also uses cranial surface in the same way.

− circumnarial basin (Owen, 1866a:44)

Owen uses the term “circumnarial basin” to refer to the facial area of Hyperoodon, Ziphius, Euphysetes (Kogia), Physeter,

and Platanista. These are members of the odontocete families 

Ziphiidae, Kogiidae, Physeteridae, and Platanistidae that have 

the lateral edges of the maxilla, sometimes also involving adjacent frontal, turned up. The elevated supraorbital crest (q.v.) or 

ridge may produce a basin. This structure has also been termed 

the supracranial basin (Flower, 1868:314).

Tursiops and other delphinids do not develop a circumnarial 

basin. Note that the exact contribution of maxilla and/or frontal 

to the supraorbital crest, or supraorbital ridge, varies with species (see Diagram 2).

− conchal crest [crest of the ventral concha] (crista conchalis)

The conchal crest lies on the medial surface of the palatine 

bone in humans, just dorsal to the nasal surface of the palatine. 

It forms a horizontal ridge for articulation with the inferior nasal 

concha (Gray, 1918:167). See dorsal nasal concha under “Ethmoid Bone.”

The crest of the ventral concha in the dog lies on the internal 

surface (nasal surface) of the maxilla. The crest begins near the 

maxilla–premaxilla suture and ends just anterior to the opening 

of the maxillary sinus (Evans and Christensen, 1979:141).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the conchal crest and maxillary sinus 

are absent in Tursiops.

= dental furrow (Anderson, 1879:524) = alveolar groove of the 

mandible

See “Mandible.”

− diastema

The diastema in mammals is the interval or space between two 

consecutive teeth, or two kinds of teeth (Benbow et al., 2002). The 

term has wide use in comparative anatomy and vertebrate paleontology. Interdental space (q.v.) of veterinary anatomy is equivalent.

Tursiops and most other odontocetes lack a diastemata.

− dorsal ethmoidal crest of the maxilla (crista ethmoidalis dorsalis)

The dorsal ethmoid crest of the maxilla limits the maxillary 

sinus dorsally in the dog and marks the line of attachment of the 

lateral lamina of the ethmoid to the maxilla (Evans and Christensen, 1979:141).

There is no recognizable dorsal ethmoid crest or maxillary 

sinus in Tursiops, but the maxillomesethmoid suture within the 

bony nares may be excavated.

* dorsal infraorbital foramen (Diagram 2; Table 6; Figures 1, 

16a,d)

In odontocetes the infraorbital foramina have become highly 

modified through telescoping of the maxillae, lengthening of the 

canals for infraorbital vessels and branches of the trigeminal nerve, 

and movement of some of the “infraorbital” foramina to various 

positions on the face and on the rostrum. As a result of changed 

relationships, the foramina have been referred to widely as maxillary and premaxillary foramina. This brings the difficulty of the 

duplication of the term “maxillary foramen.” We follow Rommel 

(1990:36) in using the term “dorsal infraorbital foramen,” or foramina, to refer to the distal openings on the maxilla: the maxillary 

foramina of some authors. Premaxillary foramen (q.v.) is retained.

We recommend that in Tursiops and other odontocetes, the 

foramina that were previously and widely known as the maxillary 

foramina (namely, foramina at the distal or facial end of the infraorbital canal) should be known as the dorsal infraorbital foramina.

= ectomaxillary groove (Owen, 1870:15) = alveolar groove of 

the mandible

− ethmoidal crest of the maxilla (crista ethmoidalis)

The ethmoidal crest of the maxilla lies on the internal 

(medial) surface of the frontal process of the maxilla (Gray, 

1918:159f; Schaller, 1992:34.2). The ethmoidal crest is the line 

of attachment of the dorsal nasal concha.

The ethmoidal crest of the maxilla is not present in Tursiops

and other delphinids due the loss of the nasal conchae.

− external plate of the maxilla (Anderson, 1879:524)

The external plate of the maxilla is the dorsal of the two 

plates that are produced by the pneumaticization of the maxilla 

in the region of the antorbital notch (Anderson, 1879:524).

Pneumaticization of the maxilla is restricted to Platanista.

* external surface of the maxilla (Figure 16a)

The external surface of the maxilla (dorsal surface of the 

maxilla) in the dog is smooth and forms a large part of the face 

(Evans and Christensen, 1979:140).

maxilla n u m b e r 6 2 7 • 5 7
In Tursiops the external surface comprises both the ascending process and dorsal surface of the maxilla on the rostrum.

− facial crest (crista facialis)

The facial crest is a continuation of the masseteric border of 

the jugal onto the maxilla. The facial crest gives origin to the m. 

masseter (Schaller, 1992:32.10).

The facial crest is not present in odontocetes in the general mammalian sense due to the reduction of the m. masseter

in odontocetes.

Schulte (1917:382, 387, 389) used the term “facial crest” 

for the prominent crest that is composed of right maxilla and the 

left premaxilla and that lies between the nasal septum and the 

vertex. Schulte also used mid-facial crest (1917:361, 362, 380, 

400), sagittal crest (ibid., 371), sagittal facial crest (ibid., 372), 

mid-facial sagittal crest (ibid., 399), midcrest (ibid., 385) and 

mid-frontal crest (ibid., 402) for this structure.

* facial fossa (Figure 16a,d)

In horses (e.g., Woodburne and MacFadden, 1982: fig. 3), the 

facial fossa is a depression on the face anterior to the orbit, variably involving maxilla, lacrimal, and nasal. A comparable feature 

in some ruminants has been termed the maxillary fossa (q.v.).

In Tursiops and other odontocetes, the facial fossa is the 

concave surface of the ascending process of the maxilla that lies 

between the nasal process of the premaxilla and the supraorbital 

margin of the maxilla (Kernan, 1918; Heyning, 1989a:5). The 

facial fossa is present in all odontocetes and gives origin to the 

major nasofacial muscles. The facial fossa has also been called 

the maxillary fossa (Schulte, 1917:372).

= facial process (Wible and Gaudin, 2004:122)

Wible and Gaudin (2004:122) recognized the facial process 

in the yellow armadillo as comprising most of the external lateral 

surface of the maxilla, the bulk of the lateral wall and part of the 

roof of the nasal cavity. This is more or less equivalent to the facial surface or external surface of the maxilla of other authors.

= facial surface of the maxilla (facies facialis) = external surface 

of the maxilla

The facial surface of the maxilla in humans is that portion 

of the external surface of the maxilla that is lateral to the external bony nares, ventral to the orbit, and medial to the zygomatic 

process (Gray, 1918:158).

The facial surface in Tursiops and other delphinids is homologous with the external surface of the maxilla.

− facial tuberosity (tuber faciale)

The facial tuberosity is at the anterior end of the facial crest of the maxilla (Sisson and Grossman, 1953:137; 

Schaller, 1992:32.11). The facial tuberosity is only expressed in 

ruminants.

− frontal plate of the maxillary (Owen, 1866a:36)

Owen used “frontal or nasal plate of the maxillary” to indicate that portion of the maxilla immediately anterior to the 

ventral infraorbital foramen in Kogia sima.

It is debatable whether the maxillary border of the ventral 

infraorbital foramen is developed enough in Tursiops and other 

delphinids to warrant using this term. The feature probably represents part or all of the anterior sinus fossa (q.v.).

= frontal process of the maxilla (processus frontalis) = ascending 

process

The frontal process of the maxilla lies at the posterodorsal 

apex of the maxilla in the dog. It forms a squamous suture with 

the frontal (Evans and Christensen, 1979:141).

The frontal process of many mammals is equivalent to the 

ascending process of the maxilla of Tursiops and other odontocetes (Miller, 1923). Schulte (1917:389) used the term “frontal 

process” to refer to that portion of the left maxilla that contributed medially to the facial crest in Kogia. The facial crest (sensu 

Schulte) is present only in Kogia.

* frontal surface of the maxilla (Figure 16b)

The frontal surface of the maxilla is that portion of the maxilla that articulates with the frontal bone. It is the ventral surface 

of the ascending process.

Schulte (1917:388) uses frontal surface in just this way. He 

also used frontal portion (Schulte, 1917:386–388) and pars frontalis (Schulte, 1917:388) in exactly the same way, indicating that 

in his mind there was no difference between the three terms.

* greater palatine foramen (foramen palatinum majus) (Figures 

2, 6f)

The greater palatine foramina lie at the posterior end of the 

palatine sulcus on the suture between the maxilla and palatine 

bones. In the dog the greater palatine nerve, coming off the maxillary nerve, and the descending palatine artery exit the major 

palatine foramen (Evans and Christensen, 1979:141; Schaller, 

1992:12.24, 36.21; Feneis, 1994:30.22). Vesalius (1543:53; Vesalius et al., 1998:131) referred to the greater and lesser palatine 

foramina as the ad palati sinem iuxta maxillae superioris sexta 

ossa, utrinque duo uisuntur foramina.

In Tursiops the greater palatine foramen may have up to 

four apertures at or just anterior to the maxillopalatine suture

near the midline. In mammals, smaller foramina associated with 

a greater palatine foramen have been named variously the minor 

palatine foramen or lesser palatine foramen or accessory palatine 

foramen or postpalatine foramen or posterolateral palatine foramen or posterolateral vacuity.

See lesser palatine foramen.

* greater palatine sulcus (sulcus palatinus major) (Diagram 1; 

Figure 16b)

The greater palatine sulcus lies on the posterior border of the 

maxilla in humans. The descending palatine artery and greater 

palatine nerve lie in this sulcus (Feneis, 1994:22.23). This sulcus 

was also known as the pterygopalatine sulcus (sulcus pterygopalatinus) (Feneis, 1994:22.23), and in humans it forms part of the 

wall of the pterygopalatine canal (Gray, 1918:168). The pterygopalatine canal originates in the antorbital fossa and terminates 

in the greater palatine foramen (Gray, 1918:185).

In Tursiops the mouth of the greater palatine sulcus lies in 

the maxillopalatine suture ventral to the ventral infraorbital foramen. The mouth of the greater palatine sulcus is frequently 

hidden by a flange of the maxilla that forms the anterior border 

of the ventral infraorbital foramen. The greater palatine sulcus 

5 8 • smithsonian contributions to zoolog y maxilla
then forms the pterygopalatine canal with the palatine and runs 

anteriorly along the palatomaxillary suture to exit on the palatal 

surface of the maxilla by the greater palatine foramen.

− great occipital crest

Flower’s (1868:314) use of a “great occipital crest” did not 

refer to a structure on the maxilla in Physeter but to the bony 

elevation at the posterior of the supracranial basin. The occipital crest is continuous anteriorly with “the elevated edges of the 

broadly expanded maxillae.” This is homologous with the nuchal crest of the rest of the odontocetes. 

See also discussion under supratemporal crest.

* hard palate (palatum osseum) (Figure 16b)

The hard palate in most mammals is principally composed 

of the palatine processes of the maxillae and serves to separate 

the nasal cavity from the oral cavity (Evans and Christensen, 

1979:141).

The palatine process of the maxilla has been interpreted 

as the roof of the oral cavity (Walmsley, 1938:142; Fraser and 

Purves, 1960:38) in mysticetes. We agree with Walmsley’s interpretation. The whole of the oral surface of the maxilla in 

Tursiops is the palatine process (Anderson, 1879:497; Schulte, 

1917:374, 375, 378, 381, 386, 388, 389, 393, 400), although 

the oral cavity no longer lies immediately dorsal.

See palatine process of the maxilla; see also hard palate

under “Palatine bone.”

* incisivomaxillary canal (Figure 16d)

The incisivomaxillary canal in the dog leaves the medial 

wall of the infraorbital canal within the infraorbital foramen, 

passes dorsally to the apex of the canine alveolus, with which 

it communicates, and enters the premaxilla. It continues anteriorly where it gives off branches to the incisor alveoli (Evans and 

Christensen, 1979:141).

The incisivomaxillary canal branches from the infraorbital 

canal at the level of the antorbital notch in Tursiops. It then 

passes to the premaxilla and continues through that bone to exit 

on the lateral surface of the alveolar part of the premaxilla.

= infrafrontal process (Schulte, 1917:380, 400) = infraorbital 

process 

See also orbital plate of the maxilla.

− infraorbital border of the maxilla = infraorbital margin (margo 

infraorbitalis) 

The infraorbital margin of the maxilla is that part of the 

maxilla that forms the ventromedial margin of the orbit in humans (Feneis, 1994:22.7).

“Telescoping” has modified the relationships of the maxilla, 

antorbital notch, orbit, and associated structures, so that the maxilla is removed from the orbit, and there is no infraorbital margin 

in Tursiops or other living odontocetes. An infraorbital border of 

the maxilla is present in a few archaic extinct odontocetes.

− infraorbital canal (canalis infraorbitalis) (Table 6)

The infraorbital canal in the dog and other noncetacean 

mammals begins proximally (posteriorly, within the orbit) at the 

maxillary foramen and terminates distally (anteriorly, facially) 

at the infraorbital foramen (Evans and Christensen, 1979:141). 

The distal (anterior, facial) opening in humans is also known as 

the infraorbital foramen (Gray, 1918: fig. 157).

The infraorbital canal carries the infraorbital nerve (infraorbital branch of the trigeminal) and infraorbital vessels. It lies entirely in the maxilla and usually lies lateral to the maxillary sinus.

The problem with the infraorbital canal in both odontocetes 

and mysticetes is the nomenclature of both the proximal and distal 

openings of the canal. The proximal (orbital/posterior) opening 

has been variously called infraorbital foramen, maxillary foramen 

(trou dentaire superior), suborbital foramen (trou sous-orbitaire), 

and the common inferior outlet. The distal (facial/­anterior) opening has been called the antorbital foramen, infraorbital foramen, 

maxillary foramen, supraorbital foramen (trou sous-orbitaire). 

Table 6 gives some idea of the confused historical usage of the 

nomenclature of the openings of the infraorbital canal.

The only term that is used consistently and unambiguously is 

the infraorbital canal. The other terms are used variously to refer 

to either the distal/anterior or proximal/posterior opening. We 

therefore propose to use the term “ventral infraorbital foramen” 

in odontocetes and mysticetes to refer to the proximal (orbital/

posterior) aperture and dorsal infraorbital foramen to refer to the 

distal (facial/anterior) aperture. Such a terminology has been used 

for Tursiops by Rommel (1990; Table 6 herein) and for the extinct 

dolphin Australodelphis by Fordyce et al. (2002:46, fig. 3).

The infraorbital canal is relatively large in Tursiops and 

other odontocetes. It begins on the ventral surface of the hard 

palate of the maxilla between the supraorbital process and the 

frontal, lacrimal, and posterior margin of the palatine. The canal 

may start within a distinct antorbital fossa. It branches immediately into the infraorbital canal and superior alveolar canal. The 

branches of the infraorbital canal exit onto the facial surface of 

the maxilla (dorsal infraorbital foramina) and premaxilla (premaxillary foramina) (q.v.) medial to the antorbital notch.

= infraorbital foramen (foramen infraorbitale) (Diagram 1; 

Table 6)

Vesalius (1543:48; Vesalius et al., 1998:131) referred to the 

infraorbital foramen as the foramen, quo dictae minoris tertii 

paris nervorum cerebradicis soboles.

See infraorbital canal, dorsal infraorbital foramen, and 

maxillary foramen. 

= infraorbital fossa (Schulte, 1917:388) = ventral infraorbital 

foramen

See also comments under antorbital fossa.

− infraorbital notch = malar notch (incisura malaris) 

In humans, the infraorbital notch (Callender, 1869; Lieberman, 1995: fig. 3; not in Gray, 1918) is a groove in the profile of 

the maxilla below the orbit, as seen in anterior view.

Tursiops and other delphinids lack an infraorbital notch in the 

human sense. The antorbital notch may be broadly equivalent.

Anderson (1879:524) used infraorbital notch for the antorbital notch in Platanista.

− infraorbital plates of the maxilla (Anderson, 1879:509)

Platanista is unique in developing and pneumaticizing the 

maxillary crests so that each crest develops two plates of the maxillamaxilla n u m b e r 6 2 7 • 5 9
that are separated by pneumatic spaces. Anderson (1879:509) 

called these two plates infraorbital plates of the maxilla.

Tursiops and other cetaceans do not have infraorbital plates 

of the maxilla.

Geisler and Sanders (2003:69) discussed the infraorbital 

plate as used in Miller (1923). In that paper, Miller (1923:7, 14, 

55, pl. 1) discussed the same plate but called it the orbital plate 

(q.v.) not the infraorbital plate.

− infraorbital process = infraorbital plate (Kellogg, 1928:44)

The infraorbital, or orbital, process or plate of Mysticeti 

does not occur in Tursiops or other delphinids. Miller (1923:7) 

stated, of mysticetes: “the orbital portion of the body of the 

maxillary is present and well developed as a large ‘horizontal 

ventral’ plate projecting conspicuously behind and beneath the 

infraorbital foramen.” Miller (e.g., 1923:8, 14) repeatedly used 

the term “orbital plate” (q.v.). Kellogg (1928:44) may have been 

the first to use infraorbital plate for the orbital plate of Miller. 

“Infraorbital” has come into wider use, and is preferred here. 

Geisler and Sanders (2003:69) stated that the presence of an 

infraorbital plate is not a mysticete synapomorphy, equating it 

with the maxillary tuberosity of other mammals.

= infraorbital sulcus (sulcus infraorbitalis) = infraorbital canal 

(Table 6)

The infraorbital sulcus lies on the posterior part of the orbital surface in humans and holds the infraorbital vessels and 

infraorbital nerve (Gray, 1918:159).

The infraorbital sulcus is closed in odontocetes and is known 

as the infraorbital canal.

* infratemporal fossa (fossa infratemporalis) = zygomatic fossa 

of the frontal bone (Figure 2)

In humans the infratemporal fossa is an irregularly shaped 

cavity situated on the skull base. The infratemporal fossa is 

bounded anteriorly by the infratemporal surface of the maxilla

and the ridge that descends from the zygomatic process of the 

maxilla; posteriorly by the articular tubercle of the squamosal; 

dorsally by the zygomatic process of the jugal anterior to the articular tubercle, and the alisphenoid; and medially by the lateral 

pterygoid plate (Gray, 1918:184, fig. 189; Feneis, 1994:30.13).

The infratemporal fossa is not in Evans and Christensen 

(1979) but is in Schaller (1992:10.27), where no details are given. 

The best treatment of it we can find in a nonhuman subject is in 

the giant panda (Davis, 1964:48, fig. 17): 

In Ailuropoda the infratemporal fossa is separated 

from the orbit above by the well-marked inferior orbital ridge [crista orbitalis inferior] throughout most 

of its length. Behind the orbital fissure it is separated 

from the temporal fossa by an indistinct elevation 

extending from the superior orbital ridge in front of 

the orbital fissure to the anterior lip of the glenoid 

fossa. The infratemporal fossa is relatively small. The 

anterior half of the infratemporal fossa contains the 

entrance to the infraorbital foramen, the common foramen for the sphenopalatine (sphenopalatine artery 

and nerve; nasal branches of sphenopalatine ganglion) 

and pterygopalatine (descending palatine artery and 

Table 6. Terms used by selected authors for the antorbital canal 

and the distal and proximal openings of the canal. Definitions: 

a.c., antorbital canal; a.f., antorbital foramen; c.i.o., common 

inferior outlet; d.i.f., dorsal infraorbital foramen; i.c., infraorbital canal; i.f., infraorbital foramen; i.s., infraorbital sulcus; m.f., 

maxillary foramen; o.i.c., orifice of the infraorbital canal; p.i.f., 

posterior infraorbital foramen; s.f., supraorbital foramen; s.o.f., 

trou sous-orbitaire (suborbital foramen); t.d.s., trou dentaire 

superior (maxillary foramen); t.s.o., trou sous-orbitaire (supraorbital foramen); t.s.o.l., trou sous-orbitaire in Physeter, not referred to in any other species; v.i.f., ventral infraorbital foramen; 

a dash (–) = feature not treated; ? = questionable treatment.

Proximal Distal

Author, date (orbital) (facial) Canal

Barnes, 1978:15, 19 i.f. m.f. —

Bolk, 1967(II):588 — i.f. —

Cuvier, 1837(vol.5, part 1): 496 s.o.f. t.s.o.l. ?

Davis, 1964:48 i.f. i.f. i.f.?

de Muizon, 1984:37 — i.f. i.c.

Feneis, 1976:22 i.s. i.f. i.c.

Flower, 1869:318 i.f.? i.f. i.f.?

Flower, 1878:417 — m.f. —

Flower, 1882:394 — i.f. —

Flower, 1885:138 — i.f. —

Forbes, 1893:221 — m.f. —

Fordyce, 1994:153, 155 i.f. m.f. —

Fordyce and de Muizon, 2001:196 — p.i.f. —

Fraser and Purves, 1960:51 m.f. — —

Jayne, 1898:187 ? i.f. ?

Kellogg, 1927:14, 18, 53 i.f. m.f. i.c.

Kellogg, 1936:108, 109 i.f. a.f. ?

Kernan, 1918:369, 351 i.f. m.f. i.c.

Miller, 1923:7, 10, 47, 48 i.f. a.f. i.c.

Miller, 1979:151, 141 m.f. i.f. i.c.

Mivart, 1892:80 i.f.? i.f. i.c.

Moore, 1960:9 — m.f. —

Moris, 1969:699 t.d.s. t.s.o. —

Nishiwaki, 1958:68 — m.f. —

Owen, 1866a:38 c.i.o. a.f. ?

Owen, 1869:10 — a.f. a.c.

Raven, 1937:6 — m.f. —

Romer, 1955:255 i.f. — i.c.

Rommel, 1990:36 v.i.f. d.i.f. i.c.

Schaller, 1992:32 m.f. i.f. i.c.

Schulte, 1917:373, 388, 389 o.i.c. i.c. i.c.

Sisson and Grossman, 1953:60 m.f. i.f. i.c.

Starck, 1967:510 ? i.f. i.c.

True, 1910:9 — — m.f.

True, 1913:653 — — m.f.

6 0 • smithsonian contributions to zoolog y maxilla
nerve) canals. . . . The posterior half of the fossa, from 

which the pterygoid muscles arise, exhibits muscle 

rugosities. The areas of origin of the pterygoid muscles 

are sharply marked on the bone. The area of pterygoid 

origin is much reduced, both vertically and horizontally, as compared with Ursus.

Davis conceived of the lateral view of the skull, with the 

exclusion of the facial region, being composed of the temporal 

fossa, the orbit, and infratemporal fossa (1964: fig. 17). Given 

that concept, the infratemporal fossa is the remnant after the 

temporal fossa and orbital contents have been removed. 

Wible (2003:153) indicated that the infratemporal fossa in 

Monodelphis is separated from the temporal fossa by the infratemporal crest. Alternatively, Meng and Wyss (2001) identified 

the zygomatic fossa of the jugal in lagomorphs as the distinctive, 

elongated fossa for attachment of the m. masseter lateralis on the 

lateral face of the jugal.

As “zygomatic fossa,” the feature is only mentioned once 

in Anderson (1879:508): “From the upper border of the pterygomaxillary fissure, the ridge dividing the temporal and zygomatic fossae is prolonged backwards to the foramen ovale.” By 

following a “ridge” forward from the foramen ovale we have 

concluded that what Anderson meant by the “zygomatic fossa” 

in Platanista was the contents of the orbit.

In Tursiops and other delphinids the infratemporal fossa is 

bounded anteriorly by the medial surface of the maxillary process of the jugal, the anterior margin of the anterior sinus fossa, 

and the lateral edge of the palatine surface of the pterygoids. 

Medially the infratemporal fossa is bounded by the ventral edge 

of the pterygoids; and posteriorly by the posterior edge of the 

pterygoids and the crest that forms the posterior margin of the 

fossa for the postorbital lobe of the pterygoid sinus. Laterally 

the infratemporal fossa is bounded by the lateral margin of the 

alisphenoid and orbitosphenoid, and the lateral margin of the 

antorbital fossa. The infratemporal fossa contains the entire lateral surface of the pterygoid bone, the antorbital fossa (pterygopalatine fossa), and the anterior sinus fossa.

− infratemporal surface of the maxilla (facies infratemporalis)

In humans the infratemporal surface is the posterolateral 

portion of the external surface of the maxilla that lies just ventral 

to the temporal fossa (Feneis, 1994:22.14).

The maxilla in Tursiops does not lie ventral to the temporal 

fossa but, as a consequence of “telescoping,” lies dorsal to the 

temporal fossa. Odontocetes do not have an infratemporal surface of the maxilla.

− inner plate of the maxilla (Anderson, 1879:524)

The inner plate of the maxilla is the ventral of the two plates 

that are produced by the pneumaticization of the maxilla in the 

region of the antorbital notch (Anderson, 1879:524).

Pneumaticization of the maxilla is restricted to Platanista.

* interalveolar margin

See “Mandible.”

* interalveolar septa (Figure 16b)

See “Mandible.”

− interdental spaces

The interdental spaces in the dog are spaces between the 

teeth when the teeth are set relatively far apart (Evans and Christensen, 1979:140). The interdental spaces grade into the interalveolar margin (q.v.). Diastema (q.v.) appears to be equivalent.

In Tursiops and other delphinids the teeth are set close together and interdental spaces do not occur.

− interradicular septa

See “Mandible.”

− lachrymal area (Schulte, 1917:389)

See cerebral area.

− lacrimal canal of the maxilla (canalis lacrimalis)

The lacrimal canal of the maxilla in the dog continues from 

the lacrimal bone into the maxilla where it opens ventral to the 

nasoturbinate crest (Evans and Christensen, 1979:141; Schaller, 

1992:30.32). The lacrimal canal carries the nasolacrimal duct 

(ductus nasolacrimalis).

The lacrimal canal is absent in Tursiops and other delphinids.

* lacrimal margin of the maxilla (margo lacrimalis) (Figure 16b)

The lacrimal margin of the maxilla is that portion of the 

bone that articulates with the lacrimal. It is on the medial border 

of the orbit and forms the posterior margin of the frontal process 

of the maxilla in humans (Gray, 1918:158f).

The lacrimal margin of the maxilla in Tursiops and other delphinids is centered on the antorbital notch and antorbital tubercle. 

The lacrimal margin is on the ventral surface of the hard palate of 

the maxilla posterior and lateral to the zygomatic recess.

− lacrimal notch (incisura lacrimalis)

The lacrimal notch is a crescentic notch at the entrance to 

the nasolacrimal duct (Feneis, 1994:22.27).

The lacrimal notch is absent in delphinids.

− lacrimal sulcus (sulcus lacrimalis)

The lacrimal sulcus lies on the medial or nasal surface of the 

maxilla and extends ventrally from the ventral angle of the orbit

(Gray, 1918:159f; Feneis, 1994:22.19). It lodges the lacrimal sac 

(Gray, 1918:189; Feneis, 1994:334.21).

The lacrimal sulcus is lacking in delphinids.

See this term also under “Lacrimal Bone.”

− lacrimal tubercle (Gray, 1918:164, fig. 157)

According to Gray (1918:164, fig. 157) the lacrimal tubercle 

is a structure of the maxilla in humans, contributing with part of 

the lacrimal hamulus to the upper opening of the lacrimal canal.

Tursiops does not have an obvious lacrimal tubercle and 

lacks the lacrimal canal. Novacek (1986:84, character 24) reported the lacrimal tubercle as absent in Cetacea.

* lacrimojugal crest [new term] (Figures 2, 16b)

In Tursiops the lacrimojugal crest is the prominent small 

ridge of maxilla that is exposed to ventral view in the lacrimojugal cleft of the fused lacrimal and jugal. The lacrimojugal crest 

is bounded anteriorly by the maxillary process of the jugal and 

maxilla n u m b e r 6 2 7 • 6 1
posteriorly by the medial process of the lacrimal. The relationship of the lacrimojugal crest to the anterior lacrimal crest of the 

maxilla and to the lacrimal sulcus in humans is uncertain.

= lamelliform extension (Flower, 1885:212) = ascending process

= lateral basirostral groove = basirostral groove

= malar process = zygomatic process of the maxilla

= malomaxillary fissure = antorbital notch (Owen, 1866a:34, 38, 

39, 41; pl. 12: fig. 1k; pl. 13: fig. 1k) as malo-maxillary 

fissure or malomaxillary fissure)

* maxillary crest (Diagram 2; Table 5; Figures 1, 16a,c,d)

In odontocetes “maxillary crest” normally refers to the structure located on the lateral part of the dorsal surface of the supraorbital part of the maxilla, lateral to the antorbital notch (Fraser and 

Purves, 1960:44, 83, 107). However, there has been considerable 

variation in the use of this term. For example, Harmer (1924:543) 

used it to refer to the crests in Hyperoodon that extend from the 

maxillary prominences medial to the antorbital notch. Further, 

the position, shape, and contribution of frontal to the maxillary 

crest varies among living species, and between living species and 

fossils, so that homologies are not always clear (particularly in 

Physeter and Kogia). Here we modify the use of Fraser and Purves: 

the maxillary crest (or maxillary ridge) is that feature developed 

lateral or posterior to the antorbital notch on the frontal but not 

involving the maxillo-frontal suture or the frontal itself. The terminology shown in Diagram 2 appears to deal satisfactorily with 

structures in living odontocetes other than Physeter and Kogia.

The maxillary crest in the broader sense is hypertrophied in 

Physeter. Flower (1868:314) referred to the supracranial basin, 

with the transverse occipital crest at the posterior boundary, and 

referred to the elevated edges of the maxillae without using the 

term “maxillary crest” and to the maxillary component of “the 

crest” (Flower, 1868:314, 317).

The maxillary crest in the broader sense is referred to as 

the great transverse crest (crêtes frontales) by Blainville in Kogia 

breviceps (Blainville, 1838:337; Schulte, 1917:371, 381). The 

great transverse crests form the cirque faciale of van Beneden 

and Gervais (1880:350; Schulte, 1917:371). Schulte (1917:372, 

373) also referred to it as the maxillary crest and the transverse 

crest (1917:375, 376, 382, 391, 392, 400). See further discussion 

under supraorbital crest and supratemporal crest.

The maxillary crest in the broader sense is also hypertrophied in Platanista (Anderson, 1879:450, 496, 512, 525, 526) 

where it consists of two distinct plates, the external plate of the 

maxillary crest and the internal plate of the maxillary crest (Anderson, 1879:525, 526). Anderson (1879:449) also referred to 

this structure as the great lateral crests of the maxillary bones. 

Supraorbital crest (see Diagram 2) is the recommended term.

The maxillary crest is formed by the origin of the externus

group of the facial muscles (pars anteroexternus and pars posteroexternus of the m. maxillonasolabialis) (Mead, 1975).

* maxillary flange (Figures 2, 16a)

The maxillary flange is the lateral portion of the maxilla 

that transitions between the rostrum and the ascending process. 

The maxillary flange is medial to the maxillary prominences, if 

present, and the antorbital notch. The term “maxillary flange” 

was used by Harmer (1924:544) where he said it was strongly 

developed in Mesoplodon bidens and lacking in M. layardii.

Maxillary flanges are variably developed in delphinids. They 

are relatively strong in Tursiops; in USNM 550403, each flange 

originates anteriorly level with the fourth or fifth last tooth, and 

extends posteriorly into the antorbital notch. Each flange has a 

thick rough projection; the homology is uncertain with the maxillary tubercle as seen in ziphiids. The maxillary flange is associated with the origin of the rostral muscle (Mead, 1975).

= maxillary foramen (foramen maxillare) = dorsal, ventral infraorbital foramina (Table 6)

The maxillary foramen, in the dog and other noncetacean 

mammals, lies on the orbital surface of the maxilla just medial to 

the zygomatic bone. It carries the branches of the infraorbital nerves 

and infraorbital vessels that exit via the superior alveolar foramina

and infraorbital foramina (Evans and Christensen, 1979:141).

In cetaceans the term “maxillary foramina” has been used 

to refer to foramina on the facial or orbital surface of the maxilla 

(e.g., Fraser and Purves, 1960:51). We propose to follow Rommel (1990:36) and call the foramen on the orbital surface of the 

maxilla, the “ventral infraorbital foramen” and the foramina on 

the facial surface “dorsal infraorbital foramina.” See the discussion under infraorbital canal for more details.

= maxillary fossa (Schulte, 1917:372) = facial fossa

A maxillary fossa occurs on the face anterior to the orbit in 

various land mammals including Perissodactyls (e.g., Holbrook, 

1999:336). See also antorbital fossa, facial fossa.

For maxillary fossa in Cetacea, see facial fossa.

− maxillary groove (Azzaroli, 1968:75; Mead, 1989b:393) (Diagram 2)

The maxillary groove is a deep longitudinal groove on the 

lateral surface of the ascending process of the maxilla (Azzaroli, 

1968:75). The anterior extent of the maxillary groove is clearly 

limited by a pit dorsal to the lacrimal bone. Posteriorly the maxillary groove disappears gradually. The maxillary groove has been 

reported only from specimens of Indopacetus pacificus. Besharse 

(1971:303) reported a maxillary groove in Mesoplodon densirostris, but the feature could not be discerned in the published figures.

− maxillary hiatus (hiatus maxillaris)

The maxillary hiatus is the large opening in the medial wall 

of the maxillary sinus (Feneis, 1994:22.22). The maxillary sinus 

communicates with the nasal cavity through the maxillary hiatus.

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the maxillary hiatus is absent in Tursiops.

= maxillary notch (Kernan, 1918) = antorbital notch

True (1910:19), Kellogg (1924:10) and Brimley (1943:200) 

used maxillary notch for antorbital notch (not in Schaller, 1992; 

not in Feneis, 1994).

= maxillary plate (Moore, 1960:16) = ascending process

Following True (1910:21; Moore, 1963), maxillary plate 

has had some use for odontocetes (e.g., Moore, 1960:16; Dale6 2 • smithsonian contributions to zoolog y maxilla
bout et al., 2002:595; Kemper, 2004:31). Ascending process is 

preferred here.

The maxillary plate was also used by Fraser and Purves 

(1960:46) to refer to the following structure in Inia: “As in Stenodelphis there is a posteriorly projecting, but in this genus much 

fenestrated, maxillary plate. This plate was considered by Flower 

(1889 [sic, 1867]) to be a portion of the palatine fused anteriorly 

to the maxilla, but the lateral suture between the palatine and the 

maxillary plate is situated in the deep fossa formed between the 

aforementioned plate and the palatine.”

We have examined an ontogenetic series of Pontoporia

(Stenodelphis in the sense of Fraser and Purves) and determined 

that Flower was correct. In USNM 482712 the sutures for the 

maxilla and palatine are clearly visible and it is the palatine that 

forms the lateral wall of the pterygoid sinus fossa.

− maxillary process of the zygomatic arch

The term “maxillary process of the zygomatic arch” has 

been used for the posterolateral extension of maxilla that bounds 

the temporal fossa in monotremes and the extinct Multituberculata (see comment by Wible and Rougier, 2000:83). It is distinct 

from the maxillary process of the jugal, also confusingly known 

as the maxillary process of the zygomatic, as seen in some mammals including primates (“maxillary process of the zygomatic 

bone”: Begun, 1994:43; Nishimura et al., 2005).

Tursiops and other Cetacea lack a maxillary process of the 

zygomatic arch.

− maxillary prominence

In the odontocete family Ziphiidae, there develops a feature 

medial to the antorbital notch and on the posterolateral surface 

of the rostrum that has been termed the “maxillary prominence” 

(True, 1913a:653; Moore, 1960:13). The maxillary prominence projects into the antorbital notch dividing it into an anteromedial prominential notch and a posterolateral antorbital 

notch. Tubercle of the maxilla or maxillary tubercle, of Flower 

(1878:417) appears to be the oldest available name for the maxillary prominence of later authors. See the discussion under maxillary tuberosity.

= maxillary protuberance = antorbital process (True, 1910:20, 

21)

= maxillary recess (recessus maxillaris) = maxillary sinus

The maxillary recess is synonymous with the maxillary sinus

in carnivores (Sisson and Grossman, 1953:61; Evans and Christensen, 1979:141, 159; Schaller, 1992:14.13, 180.5). Rossie 

(2006) discussed issues of homology and nomenclature for the 

maxillary recess in primates.

− maxillary sinus (sinus maxillaris)

The maxillary sinus or maxillary recess is a paranasal sinus, 

a large lateral diverticulum of the nasal cavity, that lies medial 

to the infraorbital canal and lacrimal canal in most mammals, 

both of which protrude slightly into the sinus. The lateral wall 

of the maxillary sinus is formed largely by the maxilla with 

the addition of the palatine posteriorly. The medial wall of the 

maxillary sinus is formed by the lateral lamina of the ethmoid 

bone. The maxillary sinus opens into the nasal cavity through 

the nasomaxillary opening (Evans and Christensen, 1979:159). 

The sinus may expand laterally and be subdivided as in equids 

into a posterior maxillary sinus (sinus maxillaris caudalis) and 

an anterior maxillary sinus (sinus maxillaris rostralis) (q.v.) (Sisson and Grossman, 1953:80; Schaller, 1992:32.5, 29; 180.2, 3). 

The sphenopalatine foramen opens near the posterior limit of the 

sinus in canids. The maxillopalatine suture lies within the sinus.

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the maxillary sinus is absent in Tursiops. The situation of the paranasal sinus system in nondelphinid cetaceans is not well known. The paranasal sinus system is 

present in archaeocetes (Kellogg, 1928:199; Uhen, 2004).

− maxillary tubercle (Diagram 2; Table 5)

Flower (1872:209) used maxillary tuberosity to refer to the 

rugosity at the anterior end of the “maxillary crests” of Hyperoodon but later (Flower, 1878:417) referred to the “tubercle of 

the maxilla” in Mesoplodon grayi and M. densirostris. “Tubercle” in the latter sense, and our preferred use, is the prominence 

medial to the antorbital notch and apparent in dorsal or ventral 

view (see Diagram 2). The maxillary tubercle should be differentiated from any elevation that may develop on the maxilla posterior and dorsal to the maxillary tubercle; such a crest is the 

rostral [maxillary] ridge or crest.

Past use of tubercle and tuberosity is confusing. For example, Schulte (1917:371, 373, 400) used “maxillary tuberosity” to 

refer to the anterior end of the maxillary crests in Kogia, namely, 

for structures lateral to the antorbital notch. Harmer (1924:543) 

used “maxillary tubercle” to indicate a rugosity at the anterior 

end of his maxillary tuberosity. See Table 5 and discussion under 

“antorbital process” for the complex history of names for what 

we here term the rostral (maxillary) ridge or crest of the face.

Tursiops lacks a maxillary tubercle.

− maxillary tuberosity (tuber maxillae / eminentia maxillae)

The maxillary tuberosity or tuber in mammals is a posterior 

projection of the maxillary portion of the maxillary sinus associated with the posterior molars, and often developed in the 

floor of the orbit (Sisson, 1910:58; Gray, 1918:159; Evans and 

Christensen, 1979:141; Feneis, 1994:22.17; Wible and Gaudin 

2004:123, orbital process of the maxilla).

Tursiops lacks a maxillary tuberosity in the sense of terrestrial mammals.

Maxillary tuberosity should not be confused with the dorsal feature on the face of ziphiids, termed “maxillary tubercle” 

(q.v.).

− maxillopalatine suture (Owen, 1866a:29)

The maxillopalatine suture is the serrate joint between the 

maxillae and the palatine bones. In Cetacea this joint has become 

relatively large. Fusion of the elements does not take place with 

age.

− maxilloturbinal = maxilloturbinate

In many terrestrial mammals the maxilloturbinal (maxilloturbinate; ventral nasal concha of veterinary anatomy) is one of 

several scrolls that occupy the anterior part of the nasal cavity and are attached to the crista conchalis on the medial surface of the maxilla (Flower, 1885:130; Evans and Christensen, 

maxilla n u m b e r 6 2 7 • 6 3
1979:512). Wible and Gaudin (2004:121) commented on the 

maxilloturbinal in the armadillo. Uhen (2004:46) described turbinals in the archaeocete Dorudon atrox.

In Tursiops and other odontocetes the turbinals are not 

developed in the normal mammalian manner, as discrete bony 

structures in adults. Cave (1988) indicated that the maxilloturbinal may be present in highly modified and vestigial form as 

the bilateral Meckelian ossicle, which may be a distinct bone in 

adults including Tursiops.

= maxilloturbinate

See maxilloturbinal.

* mesorostral canal

See “Premaxilla.” 

* nasal crest of the maxilla (crista nasalis) (Figure 16b,c,e)

The nasal crest of the maxilla is the anterior edge of the 

medial border of the palatine process of the maxilla, which is 

raised into a ridge (Gray, 1918:163; Schaller, 1992:36.23; Feneis, 1994:24.2) for reception of the vomer.

Modifications of the relationships among the bones of the 

rostrum in cetaceans have produced some drastic changes. The 

nasal crest of the maxilla is that surface of the maxilla that is in 

contact with the vomer. The nasal crest has broadened considerably and is the ventromedial portion of the maxilla that is in direct 

contact with the vomer (i.e., is not overlain by the premaxilla).

* nasal notch of the maxilla (incisura nasalis) (Figure 16a)

The nasal notch of the maxilla is that portion of the maxilla 

that forms the lateral border of the external bony nares (Gray, 

1918:158; Feneis, 1994:22.11).

The nasal notch of the maxilla is represented by the posteromedial surface of the maxilla that borders the external bony 

nares in delphinids.

= nasal process of the maxilla (Gray, 1918:161) = frontal process 

of the maxilla

* nasal surface of the maxilla (facies nasalis) (Figure 16a)

The nasal surface of the maxilla is the medial surface of the 

maxilla in the dog that forms the wall of the nasal cavity (Evans 

and Christensen, 1979:141).

The nasal surface of the maxilla in delphinids is the posteromedial portion of the ventral surface of the hard palate of the 

maxilla that forms the anterodorsal wall of the nasal cavity.

= nasomaxillary opening (aditus nasomaxillaris) = maxillary hiatus

− occipital crest

See great occipital crest.

− orbital plate of the maxilla (Miller, 1923:7, 14)

The orbital plate of the maxilla (Miller, 1923:7, 14, 55, 

pl. 1) is the posterior part of the maxillary border that projects 

obliquely downward and backward under the anterior margin 

of the supraorbital process of the frontal bone in mysticete telescoping (Miller, 1923:4, 55). Miller (1923:8) also called this the 

horizontal ventral plate. Kellogg (1928:44) may have been the 

first to use the term “infraorbital” plate or process, which has 

come into common use and is preferred here for the feature in 

Mysticeti (see infraorbital process). The orbital plate overlies (is 

dorsal and posterior to) the ventral infraorbital foramen. Schulte 

(1917:380, 400) terms this feature the infrafrontal process and 

states that it may be present in a reduced condition in some 

Kogia skulls.

In Tursiops and probably most delphinids the surface of the 

maxilla anterior to the ventral infraorbital foramen is smooth 

and shows no sign of an orbital plate.

= orbital process

See “Palatine Bone,” “Jugal Bone.”

− orbital surface of the maxilla (facies orbitalis)

The orbital surface of the maxilla is the part of the maxilla 

that lies within the orbit in humans (Gray, 1918:159; Feneis, 

1994:22.4).

The maxilla does not take part in the formation of the orbit

in odontocetes. See discussion under maxillary tuberosity and 

infraorbital process.

− palatal groove

Bilateral palatal grooves (Perrin et al., 1981:593) occur in 

the maxillae of the delphinids, Delphinus, Stenella, and Lagenodelphis, on the ventral surface of the rostrum. Each groove holds 

a rostral extension of the anterior sinus (Fraser and Purves, 

1960:72 “deep groove in maxilla”). True (1889:44) termed these 

the lateral grooves in the palate. Gray (1846:41) also referred to 

the “deep grooves.” Palatal grooves are absent in Tursiops.

See also anterior sinus fossa.

* palatal surface of the maxilla (Owen, 1866a:38) (Figure 2)

The palatal surface of the maxilla is the ventral surface of 

the hard palate that forms part of the palate. The palatal surface 

is homologous with the palatine process of the maxilla.

= palatine fissure (fissura palatina)

See “Premaxilla.” 

* palatine grooves of the maxilla (sulci palatinae) (Figure 16b)

The palatine grooves or palatine sulci are depressions leading from the greater palatine foramen on the surface of the palate 

that contain branches of the greater palatine nerve and descending 

palatine artery (Schaller, 1992:34.6; Feneis, 1994:24.7). In some 

mammals the greater palatine groove (sulcus palatinus major) of 

the maxilla forms the greater palatine canal with the greater palatine groove of the palatine bone (Schaller, 1992:32.27, 36.7).

* palatine process of the maxilla (processus palatinus) (Figures 

2, 16b)

The palatine process of the maxilla, in the dog and other 

mammals, is a transverse shelf of bone medial to the teeth that 

forms most of the hard palate (q.v.) (Evans and Christensen, 

1979:141; Schaller, 1992:34.4; Feneis, 1994:24.1; Wible and 

Gaudin, 2004:122). The palatine process is in contact with the 

oral cavity and encompasses all of the maxillary surface medial 

to the tooth row.

6 4 • smithsonian contributions to zoolog y maxilla
The palatine process of the maxilla has been interpreted as 

the roof of the oral cavity (Walmsley, 1938:142) in mysticetes. 

We agree with Walmsley’s interpretation. The whole of the oral 

surface of the maxilla in odontocetes is the palatine process. 

Owen (1866a:27, 29) referred to the palatine process as the palatine plate of the maxillary.

* palatine prominence (Figure 16c)

“[The palatine] receives in a groove on its upper and anterior border the palatine prominence of the upper maxillary bone. 

The maxillary expands from its palatine prominence—the essential point of the suspension—backwards, outwards, but chiefly 

forwards, where it gradually diminishes to an obtuse point.” 

(Owen, 1853:443).

The palatine prominence, as described by Owen and confirmed on a newborn Physeter catodon skull (USNM 49488), 

lies on the ventromedial margin of the maxilla, just anterior to 

the anterior edge of the palatine. The palatine prominence forms 

a low but pronounced buttress on which the palatine bone sits. 

This is a feature of the palatomaxillary articulation and is only 

expressed in those mammals that have a wide palatomaxillary 

suture. This suture occurs on the hard palate of noncetacean animals, which is normally smooth (without prominences).

The palatine prominence can be seen in Tursiops as the 

change in orientation of the ventral margin of the maxilla where 

the palatine articulates with the maxilla. Schulte (1917:388, 

393) called this the pterygoid elevation or pterygoid eminence 

(Schulte, 1917:394) in Kogia. A palatal ridge or palatal crest

(q.v.) may develop on the palatine, posterior to the palatine 

prominence.

− palatine sinus (sinus palatinus)

The palatine sinus excavates the palatal process of the maxilla in ruminants (Schaller, 1992:34:8). See also palatine sinus

under “Palatine Bone.”

Cetacea do not develop a palatine sinus in the maxilla.

− palatine spines (spinae palatinae)

In humans the palatine spines are bony ridges along the 

palatine grooves of the maxilla (Feneis, 1994:24.6).

Palatine spines are not developed in the palatine grooves of 

odontocetes.

* palatine sulcus (sulcus palatinus) (Figures 2, 6f)

The palatine sulcus or palatine groove lies on the ventral 

surface of the hard palate (or oral surface) of the palatine process 

of the maxilla and extends anteriorly from the greater palatine 

foramina to the palatine fissure (incisive foramen) (Evans and 

Christensen, 1979:141, 152, 672; Schaller, 1992:34.6; Feneis, 

1994:24.7). The palatine sulcus contains the greater palatine 

nerve and greater palatine artery. In some mammals the greater 

palatine groove (sulcus palatinus major) of the maxilla forms 

the greater palatine canal with the greater palatine groove of the 

palatine bone (Schaller, 1992:32.27, 36.7).

The palatine sulcus in Tursiops is reduced to a series of short 

grooves that radiate anteriorly from the greater palatine foramina; minor palatine foramina and sulci may be developed in some 

Cetacea. The palatine fissure (incisive canal, sometimes known 

as the incisive foramen) is not present in Tursiops, and dolphins 

reportedly lack the nasopalatine nerve that in other mammals 

runs through the incisive canal / incisive foramen.

= posterior infraorbital foramen (Fordyce, 1981:text-fig. 2; 

Fordyce and de Muizon, 2001:196, fig. 12) = dorsal 

infraorbital foramen (Table 6)

− posterior maxillary sinus (sinus maxillaris caudalis)

The posterior maxillary sinus is the posterior part of the 

maxillary sinus (Schaller, 1992:32.5, 180.3).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the posterior maxillary sinus is absent 

in Tursiops.

* posterior palatine foramen (foramen palatinum caudale) (Diagram 1; Figures 16b, 18e)

The posterior palatine foramen in the dog is situated in the 

antorbital fossa next to the sphenopalatine foramen (Evans and 

Christensen, 1979:144, figs. 4–38) and is the entrance to the palatine canal, which transmits the greater palatine nerve and the 

greater palatine artery (Sisson and Grossman, 1953:61; Schaller, 

1992:12.22). This is also known as the caudal palatine foramen.

The posterior palatine foramen (Fraser and Purves, 1960:26) 

in delphinids is the communication between the infraorbital canal

and the greater palatine sulcus. It lies at the posterior end of the 

greater palatine sulcus and is entirely covered by the palatine 

bone. The posterior palatine foramen in Tursiops opens on the 

posterior wall (nasal surface) of the ethmoidal crest of the palatine just anteroventral to the sphenopalatine foramen. It communicates with a canal for palatine vessels and nerves, which 

opens at major palatine foramina and minor palatine foramina. 

In adult Tursiops the posterior palatine foramen may be confluent with the opening of the sphenopalatine foramen. 

− postnarial cavity (Owen, 1866a:37, 38, 42)

Owen used postnarial cavity (1866a:37, 42), postnarial 

tract, or spermacetic cavity (1866a:38) to refer to the paired 

cavities that are formed by the maxillae posterior to the nasals 

in Kogia. These are formed in the facial fossae of the maxilla by 

dorsal proliferation of the bones surrounding the facial fossa, 

primarily the frontals. This is correlated with the unusual development of the spermaceti organ and associated tissues in Kogia

(Schenkkan and Purves, 1973).

* premaxillary surface of the maxilla (Figure 16d)

The premaxillary surface of the maxilla (Anderson, 

1879:526) is the surface of the maxilla that articulates with the 

premaxilla.

In delphinids the premaxillary surface is the dorsomedial 

surface that extends from the anterior extremity of the maxilla 

to nearly the posteromedial corner of the ascending process. The 

premaxillary surface is defined dorsally by strong lateral angles 

that are formed between the premaxillary and dorsal surfaces of 

the maxilla. The premaxillary surface is defined ventrally by a 

ridge and corresponding sulcus for reception of the ventral portion of the premaxilla. The medial surface of the maxilla consists 

of the premaxillary surface and the vomerine shelf.

= preorbital notch (Anderson, 1879:363) = antorbital notch

maxilla n u m b e r 6 2 7 • 6 5
− prominential crest of the maxilla [new term]

The prominential crest of the maxilla in cetaceans is the crest 

that extends posteriorly along the dorsal surface of the maxilla 

from the maxillary prominence. See the discussion under antorbital prominence. The prominential crest is formed by the origin of 

the -internus group of the facial muscles (pars anterointernus, pars 

posterointernus of the m. maxillonasolabialis) (Mead, 1975).

A prominential crest is not present in delphinids but is a 

marked feature of some ziphiids.

− prominential notch (Diagram 2; Table 5)

The prominential notch is formed between the maxillary 

prominence and the base of the rostrum in ziphiids (Moore, 

1963:406, fig. 14). Harmer (1924:543) referred to the prominential notch as the inner notch.

A prominential notch is not present in delphinids but is a 

marked feature of some ziphiids.

− pterygoid elevation (Schulte, 1917:388) = palatine prominence

− pterygoid process of the maxilla (processus pterygoideus)

The pterygoid process of the maxilla is a small pointed spur 

located on the palatal surface of the maxilla posteromedial to 

the alveolus for the last tooth. In the dog the pterygoid process 

and the palatine bone form a notch, rarely a foramen, through 

which the minor palatine vessels pass (Evans and Christensen, 

1979:141, 151; Schaller, 1992:250.36 unlabeled).

There is no distinct pterygoid process of the maxilla in 

Tursiops.

= pterygopalatine fossa (fossa pterygopalatina) = antorbital fossa

In humans the pterygopalatine fossa is a small triangular 

space associated with the orbit, medial to the infratemporal 

fossa. It is bounded dorsally by the body of the sphenoid and by 

the orbital process of the palatine; anteriorly by the infratemporal surface of the maxilla; posteriorly by the base of the pterygoid 

process of the sphenoid and the alisphenoid; and medially by 

the vertical portion (including orbital and sphenoid processes) of 

the palatine (Gray, 1918:185; Feneis, 1994:30.14; Daniels et al., 

1998: “Determining the exact margins of the PPF [pterygopalatine fossa] is problematic, because they are not strictly defined 

even in the anatomic literature”). In humans, it is distinct from 

the adjacent temporal fossa and infratemporal (or zygomatic) 

fossa. Vesalius et al. (1998:131) referred to the pterygopalatine 

fossa as the structure that is indicated by the symbol φ. In this 

translation of pages 47–55 of Book I of Vesalius (1543)—the 

section on the foramina in the bones of the head and upper 

jaw—Richardson and Carman indicate that φ occurs but do not 

give any other relevant facts.

The pterygopalatine fossa in humans communicates with 

the orbit by the inferior orbital fissure, with the nasal cavity by 

the sphenopalatine foramen, and with the infratemporal fossa 

by the pterygomaxillary fissure. The foramen rotundum, pterygoid canal, and the pharyngeal canal open into the posterior wall 

of the pterygopalatine fossa; the sphenopalatine foramen opens 

into its medial wall; and the pterygopalatine canal opens into its 

ventral wall. The pterygopalatine fossa contains the maxillary 

nerve, the sphenopalatine ganglion (Schulte, 1917:378), and the 

terminal part of the internal maxillary artery (Gray, 1918:185).

Owen (1866a:27) called the pterygopalatine fossa the superorbital fossa.

There is confusion in application to carnivores. For the dog 

Evans and Christensen (1979:150) used the term in a broad sense 

for those structures ventral to the ventral orbital crest between 

the maxillary foramen and the posterior end of the pterygoid. 

Conversely, in the panda Davis (1964: fig. 17) identified the area 

ventral to the ventral orbital crest as the infratemporal fossa. 

Davis’s terminology more closely follows that of Gray (1918).

For the horse, Sisson and Grossman (1953:72) also used 

pterygopalatine fossa in the broader sense, namely, the fossa 

bounded by the pterygoid process of the sphenoid, the perpendicular plate of the palatine, and the maxillary tuberosity of the 

maxilla. The maxillary foramen, sphenopalatine foramen, and 

posterior palatine foramen open into the pterygopalatine fossa.

McFarland et al. (1979:11) define the pterygomaxillary region (regio pterygomaxilaris) as a “region at the base of the skull 

encompassing the pterygoid process of the sphenoid bone (a 

perpendicular process extending down from the junction of the 

greater wing and body of the sphenoid bone) and the maxilla, 

the upper jaw bone.” The pterygomaxillary region is another 

part of the complex anatomy of the pterygopalatine fossa. Fraser 

and Purves (1960:65) probably had the pterygopalatine fossa in 

mind when they referred to the pre-orbital concavity and the preorbital recess (1960:53, 54, 58).

In and around the orbit in Tursiops the maxilla, frontal, palatine, and sphenoid have been so modified by changes in topography, particularly involving fossae for the pterygoid air sinuses, 

that the pterygopalatine fossa is no longer identifiable, and the 

term cannot be applied clearly. The superorbital fossa (q.v.) of 

Owen (1866a:28) is here used for the main depression associated 

with the maxilla anterior to the orbit.

* pterygopalatine surface of the maxilla (facies pterygopalatina) 

(Figure 16b)

The pterygopalatine surface of the maxilla is that part of the 

posterior surface maxilla that borders the pterygopalatine fossa

(antorbital fossa) (q.v.) (Schaller, 1992:32.17).

The pterygopalatine surface of the maxilla cannot be identified clearly in Tursiops or other delphinids.

− rostral maxillary sinus (sinus maxillaris rostralis)

The rostral maxillary sinus is the anterior part of the maxillary sinus in animals in which the sinus is separated by a maxillary septum (Sisson, 1910:72, 73, 126, 146; Schaller, 1992:32.29, 

180.2). The rostral maxillary sinus is also called the anterior maxillary sinus or the inferior maxillary sinus (Sisson, 1910:73).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the rostral maxillary sinus is absent in 

Tursiops.

* rostral portion of the maxilla (Schulte, 1917:386–388) (Figure 

16a)

The rostral portion of the maxilla lies anterior to the antorbital 

notches, and thus it contributes to the formation of the rostrum.

* rostral surface of the maxilla (Schulte, 1917:389) (Figure 16a)

The rostral surface of the maxilla consists of the external 

surface of the rostral portion of the maxilla.

6 6 • smithsonian contributions to zoolog y maxilla
− septum of the maxillary sinus (septum sinuum maxillarium)

The septum of the maxillary sinus separates the caudal maxillary sinus from the rostral maxillary sinus in equids (Schaller, 

1992:32.31, 180.4).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the septum of the maxillary sinus is 

absent in Tursiops .

= socket = dental alveolus

= sphenomaxillary fossa (Schulte, 1917:373, 378, 387) = pterygopalatine fossa (Osborn, 1979) = antorbital fossa

= suborbital canal (Owen, 1870:7) = infraorbital canal

= subvomerine shelf (Schulte, 1917:388) = vomerine shelf

= supracranial basin (Flower, 1868:314) = circumnarial basin 

(Owen, 1866a:44)

= suprafrontal process (Schulte, 1917:380) = ascending process

= supraorbital crest (Barnes, 1984:9) = maxillary crest (Diagram 

2; Table 5)

A supraorbital crest is reported in various mammals, forming, for example, the thickened rim of the frontal in the fossil 

mammal Kryptobaatar (see Wible and Rougier, 2000:22) and 

Matutinia (see Ting et al., 2002:12).

In Cetacea, crests on the maxilla have received several different names (Diagram 2). Crests are not normally considered present in mysticetes, although Ridewood (1922:224) commented, 

about a fetus of Megaptera novaeangliae, “The supraorbital crest 

is already strongly developed.” For the extinct dolphin Parapontoporia, Barnes (1984:9) stated that the “supraorbital crest on the 

maxilla is in the same location as in Pontoporia blainvillei,” and 

later (Barnes, 1985:3, fig. 12) emphasized that the crest in Pontoporia and Parapontoporia is a non-pneumaticized structure located 

medial to the margin of the maxilla, termed the maxillary crest.

We recognize the supraorbital crest as the structure developed on the lateral margin of the maxilla at the suture with the 

frontal, and involving a contribution of frontal. The supraorbital 

crest or ridge in this sense does not occur in Tursiops or other 

delphinids but is seen in Platanista (as an elevated pneumaticized 

crest) and in Inia.

* supraorbital margin of the maxilla (Figure 16b)

The supraorbital margin of the maxilla is the lateral margin 

of the maxilla that overlies the supraorbital process of the frontal 

bone in Tursiops and other odontocetes.

= supraorbital plate (Anderson, 1879:364) = supraorbital process of the maxilla

* supraorbital process of the maxilla (Figure 16b)

The maxilla does not extend over the orbit in most mammals.

The supraorbital process of the maxilla is that part of the 

ascending process of the maxilla in odontocetes that lies over 

the supraorbital process of the frontal and the orbit (Schulte, 

1917:369; Fordyce, 1994:153).

− supratemporal crest = supratemporal ridge

The supratemporal crest is the crest that lies on the dorsolateral surface of the maxilla in Kogia (Schulte, 1917:376, 392). 

It is continuous with the nuchal crest. Delphinids have not developed a supratemporal crest per se, limiting the crest development 

on the maxilla to the maxillary crest. The anterior portion of the 

supratemporal crest is homologous with the maxillary crest. This 

feature has also been called the supratemporal ridge.

The supratemporal crest should not be confused with 

Flower’s (1868:314) “great occipital crest” in Physeter, which is 

a feature posterior to the supracranial basin. The posterior part 

of this crest seems to be homologous with the crest in Kogia, but 

the anterior part is not. In Physeter the occipital crest terminates 

anteriorly at a position medial to the antorbital notches (Flower, 

1868: pl. 57). In Kogia the anterior portion of the crest terminates lateral to the antorbital notch (Schulte, 1917:371, 373, pls. 

35, 36). Clearly additional work needs to be done on the physeterids before the homologies are straightened out.

= tubercle of the maxilla (Flower, 1878:417) = maxillary 

tuberosity

− ventral ethmoidal crest of the maxilla (crista ethmoidalis 

ventralis)

The ventral ethmoidal crest of the maxilla in the dog is a 

small sagittofrontal crest that serves as an attachment for the 

floor plate or transverse lamina of the ethmoid bone (Evans and 

Christensen, 1979:140, 141). The ventral ethmoidal crest lies on 

the ventromedial surface of the maxilla just anterior to the maxillary tuberosity (not in Schaller, 1992).

Due to the elongation of the rostral elements and the posterodorsal movement of the bony nares in odontocetes, the ethmoid no longer contacts the maxilla and the ventral ethmoidal 

crest has disappeared.

* ventral infraorbital foramen (Figures 16b,c,e, 30; Table 6)

In odontocetes the foramen that was previously known as 

the maxillary foramen, at the proximal end of the infraorbital 

canal, is now known as the ventral infraorbital foramen (Rommel, 1990:36). This foramen was also known as the infraorbital 

fossa (Kernan, 1918:388) and the preorbital foramen (Fraser 

and Purves, 1960:67–69, 71, 73), and the antorbital foramen

(Fraser and Purves, 1960:137, pl. 9ff.). 

See discussion under infraorbital canal.

− ventral surface of the hard palate (facies palatina)

The ventral surface of the hard palate in the dog forms part 

of the roof of the mouth (Evans and Christensen, 1979:141).

The ventral surface of the hard palate in odontocetes is composed of the palatine process of the maxilla (q.v.).

* vomerine shelf (Figure 16e)

The vomerine shelf is a sharp ridge that delimits the ventral 

border of the premaxillary surface on the ventromedial aspect of 

the maxilla (Kernan, 1918:368).

− zygomaticomaxillary suture (sutura zygomaticomaxillaris)

The zygomaticomaxillary suture is the sutural connection 

between the maxilla and zygomatic bone, here known as jugal 

maxilla n u m b e r 6 2 7 • 6 7
bones (Gray, 1918:189; Evans and Christensen, 1979:142, 

143; Schaller, 1992:76.26; Feneis, 1994:22.13, 54.19). Vesalius 

(1543:23) referred to the zygomaticomaxillary suture as merely 

the sutura.

As noted under discussion of jugal, the homologies of parts 

of the jugal and lacrimal in Tursiops are difficult to establish. The 

presumed jugal in Tursiops (namely, that part of the lacrimojugal immediately dorsal to the fused anterior of the styliform part) 

sutures with the maxilla dorsally just below the antorbital notch, 

while the medially developed maxillary process of the jugal projects into the zygomatic recess of the maxilla. The anterior end of 

the jugal bone in odontocetes lies in the zygomatic recess and is 

not suturally connected with the maxilla.

− zygomatic process of the maxilla (processus zygomaticus)

The zygomatic process of the maxilla in mammals is on 

the posterolateral aspect of the external surface of the maxilla

(Wible and Gaudin, 2004:122). It is bounded both dorsally and 

ventrally by the jugal. It contributes to the strength of the zygomaticomaxillary suture (Evans and Christensen, 1979:140, 141, 

151). The zygomatic process of the maxilla extends along the 

margin of the orbital plate of the maxilla from the posterolateral angle of the plate to a point distinctly above the antorbital 

foramen (Miller, 1923:9, 10, pl. 3; as malar process). Hopson 

et al. (1989) described the zygomatic process of the maxilla in 

the extinct Multituberculata. This is a posterolateral process 

from the maxilla, that bounds the temporal fossa and contacts 

the squamosal posteriorly. Simpson (1937) earlier referred to the 

zygomatic process as the zygomatic root of the maxilla.

Due to the change in relationship between the zygomatic 

and maxilla, the zygomatic process of the maxilla has disappeared in Tursiops and other odontocetes.

* zygomatic recess [new term] (Figure 16b,c)

The cavity for the zygomatic articulation lies posteroventral 

to the frontal process of the maxilla on the external surface of 

the maxilla. It receives the articulation of the zygomatic (jugal) 

(Evans and Christensen, 1979:140).

The zygomatic recess in Tursiops is a small groove or recess 

on the ventral surface of the hard palate just medial to the antorbital notch, and anterior to the lacrimojugal crest (q.v.). The 

maxillary process of the jugal fits into the zygomatic recess. In 

very old specimens of Tursiops the anterior portion of the jugal 

becomes fused to the maxilla.

NASAL BONE

Os Nasale

Figures 1, 3, 4, 6a,c,d, 17

The nasal bone is a paired midline bone that forms the dorsal margin of the external bony nares, hence its name. The nasal 

bone in generalized mammals articulates with the premaxilla, 

maxilla, and frontal.

The evolutionary movement of the nasal passage posterodorsally with the elaboration of the facial region has led to a change 

in the relationships and shape of the nasal bone in cetaceans, 

particularly odontocetes. In Tursiops and other delphinids the 

nasals are nodular, elevated, and anteroposteriorly compressed, 

rather than plate-like and dorsoventrally thin. They have come 

to form part of the posterior wall of the nasal passage and the 

nucleus of the bony mass that forms the vertex. The nasals keep 

their articulation with the frontals, now sutured at extensive surfaces rather than thin borders, but their articulation with the 

premaxillae and maxillae becomes variable. It is difficult to identify homologues for some of the features seen in other mammals. 

Mysticetes and the extinct archaeocetes have nasals more like 

those of other mammals.

− anterior border of the nasal [new term]

The anterior border of the nasal bone is equivalent to the 

inferior border of the nasal in humans (Gray, 1918:156), the 

most anterior transverse border of the nasal, which does not articulate with other elements. The anterior border of the nasal 

bone is present in other mammals but does not seem to have been 

named (Evans and Christensen, 1979:139; ICVGAN, 1983:A23; 

Schaller, 1992:30).

Tursiops and other delphinids lack an anterior border in the 

sense of other mammals, but the border is present in some fossil 

Cetacea (Archaeoceti, and certain Neoceti) in which the nasals 

retain a dorsoventrally thin plate-like form. The anterior border 

is probably equivalent to the rounded anterodorsal border (q.v.) 

of the nasal, at the junction of the external (dorsal) and internal 

(anterior) faces as seen in Tursiops and more obviously in extinct 

dolphins such as Kentriodon and Delphinodon.

− anterior process of the nasal

The anterior process (e.g., Novacek, 1986:27) of the nasal 

bone appears to be that part that protrudes beyond the point of 

contact with the anterior edge of the premaxilla. Alternatively, 

Evans and Christensen (1979:139) used the term “nasal process” 

for the lateral part of the anterior end of the nasal. “Anterior 

process of the nasal” seems preferable.

Tursiops and other delphinids lack an obvious anterior process of the nasal.

* anterodorsal border of the nasal or anterodorsal crest of the 

nasal [new term] (Figure 17a,c,d)

The anterodorsal border (or anterodorsal crest, if markedly 

elevated) of the nasal bone in Tursiops runs from a point on the 

ventrolateral margin of the nasal bone to a point on the dorsomedial margin. The anterodorsal border divides the internal 

(anterior) surface of the nasal from the external (dorsal) surface 

of the nasal.

* anterodorsal groove [new term] (Figure 17a,d)

The anterodorsal crest of the nasal delimits an oblique 

groove immediately dorsal to it, the anterodorsal groove. This 

groove appears to be more evident in younger specimens. In 

the newborn specimen that we illustrated (USNM 504560), the 

anterodorsal groove is distinct when the specimen is properly 

lighted.

* central caudorostral ridge (Figure 4)

Kernan, in his description of the skull of a fetal Ziphius

(1918:389, paragraph 3), delineated a central caudorostral ridge. 

6 8 • smithsonian contributions to zoolog y N asal
In examining USNM 504732, which is a partly disarticulated 

calf, the complex terminology of Kernan can be worked out. 

Ziphius differs from delphinids in that the internal surface of the 

nasal is rather well developed and the central caudorostral ridge 

is formed on the medial border of the internal surface where it 

abuts the contralateral nasal bone.

The central caudorostral ridge appears in some adult Tursiops and other delphinids.

− dorsal nasal meatus (Wible and Gaudin 2004:120)

Wible and Gaudin (2004:120) identified the dorsal nasal 

meatus in armadillos and the dog as a deep longitudinal trough 

on the ventral surface of the lateral part of the nasals, in which 

the ossified nasoturbinal is present.

Tursiops and other delphinids lacks the dorsal nasal meatus.

− ethmoidal crest of the nasal bone (crista ethmoidalis)

The ethmoidal crest of the nasal bone in the dog lies on 

the internal surface of the nasal bone and articulates with the 

dorsal nasal concha (Gray, 1918:161; Evans and Christensen, 

1979:156).

Tursiops and other odontocetes have reduced their olfactory 

functions and nasal elements. The ethmoidal crest is nonexistent 

in Tursiops and other odontocetes.

− ethmoidal fossa (sulcus ethmoidalis)

The ethmoidal fossa in the dog is located on the posterior 

part of the ventral surface of the nasal bone and bounds the 

dorsal part of the ethmoid (Evans and Christensen, 1979:139). 

Rowe et al. (2005:320) identified the ethmoid fossa in Monodelphis as an endocranial feature.

Tursiops and other odontocetes have reduced their olfactory 

functions and nasal elements. The ethmoidal fossa is nonexistent 

in Tursiops and other odontocetes.

* external surface of the nasal (Figure 17a,c,d)

In most mammals (Evans and Christensen, 1979:139; 

Schaller, 1992:30.14), including the extinct archaeocete cetaceans, the external surface of the nasal bone is readily identifiable as the convex surface that faces dorsally, or anteriorly in 

humans (outer surface of the nasal bone, Gray, 1918:156). 

In Tursiops and other delphinids the external surface is 

presumed to be the most dorsal part of the nasal bone, which 

contributes to the vertex. The anterodorsal border of the nasal

(q.v.) separates the external surface of the nasal from the now 

anteriorly facing internal surface of the nasal. The relationship 

of the external surface to the internal surface is clearer in extinct 

kentriodontids (Kentriodon, Delphinodon) in which the former 

faces dorsally and the latter faces anteriorly.

* frontal margin of the nasal (Figure 17b,c,e)

The frontal margin of the nasal is that part of the nasal bone 

that articulates with the frontal. In most mammals, this is the 

posterior margin of the nasal. It includes the frontal process of 

the nasal (q.v.). 

Homologies are not clear with Tursiops and other delphinids, in which both the posterior and ventral surfaces of the 

nasal bone broadly contact the frontal bone. 

See also frontonasal suture.

− frontal process of the nasal

In the dog the frontal process of the nasal is the normally 

pointed posterior part of the nasal near the mid-sagittal plane 

(Evans and Christensen, 1979:139; not in Schaller, 1992). The 

frontal processes of the nasals are bounded posteriorly and laterally by frontals. Although the nasal bears the same relationship 

to the frontal in humans, the frontal process is not named (Gray, 

1918:157; Feneis, 1994:20).

Tursiops and other delphinids lack a frontal process in the 

sense of other mammals.

− frontonasal suture

The frontonasal suture lies on the posterior part of the nasal 

bone and articulates with the frontal bone.

The frontonasal suture is well developed in odontocetes 

(e.g., Owen, 1872:175). The frontonasal suture is visible along 

the posterior of each nasal as viewed dorsally in Tursiops and 

other delphinids. In young animals, in which the maxilla and 

mesethmoid do not contact the nasal bone, the posterior, lateral, 

and anteroventral surfaces of the nasal contact the frontal bone, 

forming an extensive frontonasal suture in the broader sense. It 

lies on the internal surface of the nasal bones. The frontonasal 

suture at the anteroventral part of the nasal is obliterated during 

ontogeny, as the mesethmoid grows to contact the nasal bone.

− groove for nasociliary nerve

In humans (Gray, 1918:157, 881: fig. 771, 888) the inner 

surface of the nasal carries a fine groove for the passage of a 

branch of the nasociliary nerve.

The anterior face of the nasal (equivalent to internal surface of the nasal) in Tursiops carries a relatively open groove 

that may be subvertical to oblique. Whether the feature is related to the groove for the nasociliary nerve in humans, to the 

epicranial sinuses (nasal diverticula), or to some other structure 

is uncertain.

= inferior border of the nasal = anterior border of the nasal

In humans the inferior border of the nasal bone (Gray, 

1918:156) is the most anteroventral part of the nasal that does 

not articulate with other elements. The term “anterior border of 

the nasal” (q.v.) is more applicable to most mammals.

* internal surface of the nasal (Figure 17a,c,d)

In the dog and other mammals, the internal surface is the 

ventral part of the nasal, which is covered with mucus membrane 

(Evans and Christensen, 1979:139).

Because of dramatic changes in the shape of the delphinid 

nasal, the homologous surface in Tursiops, namely, the surface 

that is in direct contact with the epithelium of the nasal cavity, now faces anteriorly. It forms the anteroventral portion of 

the nasal bone. The internal surface is, however, identifiable in 

mysticetes and extinct archaeocete cetaceans, forming the ventral 

border of the bone.

= internarial groove (Fraser, 1945:24) = internasal gap

− internasal gap (Fraser, 1945:24)

Fraser (1945:24) commented, of Hyperoodon, that the premaxillae at the vertex form massive “narial prominences” which 

N asal n u m b e r 6 2 7 • 6 9
are “separated from each other [medially] by a parallel-sided 

gap bounded by the nasals.” The internasal gap diverges to the 

left, and has parallel sides. The name apparently refers to the 

gap between the adjacent medial faces of the massive premaxillary crests above the nares on the vertex. Fraser (1945:24) used 

internarial groove as an apparent synonym for internasal gap. 

“Internasal” is preferred, because “internarial” could be taken 

to mean a feature at the nares.

Because the premaxillae do not approach each other medially above the nares, Tursiops lacks an internasal gap.

* internasal suture (Figure 4)

The internasal suture lies on the medial surface of the nasal 

bones and articulates with the contralateral nasal bone (e.g., 

Owen, 1872:178).

Tursiops and other delphinids (e.g., Australodelphis; 

Fordyce et al., 2002:47, nasal) may have a well-developed internasal suture on the medial edge of each nasal bone. In young 

delphinids, the nasals may be separated to the extent that the 

internasal suture is not developed.

* maxillary margin of the nasal (Figure 4)

The maxillary margin of the nasal bone is that portion of 

the nasal bone that articulates with the maxilla. In Tursiops the 

extent of the maxillary margin is extremely variable (depending 

on the contact of maxilla and nasal) and it occupies the lateral 

surface of the nasal bone. The maxillary margin is conspicuous 

in some archaeocetes.

* medial margin of the nasal (Figure 17a,d,e)

The medial margin of the nasal bone is that part of the nasal 

bone that articulates with the contralateral nasal bone at the internasal suture (q.v.). The medial margin occupies the medial 

surface of the nasal bone.

* mesethmoid margin of the nasal (Figure 17a–e)

The mesethmoid margin of the nasal bone is on the anteroventral surface of the nasal bone where it contacts the mesethmoid. The margin develops ontogenetically, as the frontonasal 

suture becomes obscured. The mesethmoid may come to overlie 

the anteroventral border of the nasal bone.

− nasal foramen

In some mammals, including the dog and armadillo, the 

nasal is pierced by one or more nasal foramina of uncertain vascular or nervous function (Gray, 1918: fig. 155, “foramen for 

vein”; Wible and Rougier, 2000; Wible and Gaudin, 2004:161, 

and citations therein).

Tursiops does not appear to have nasal foramina. Clarke 

(2003:249) used the term “nasal foramina” as a synonym for the 

external bony nares in Kogia. 

See external bony nares.

= nasal process (Evans and Christensen, 1979:139, 140) = anterior process of the nasal 

This use of nasal process here should not be confused with 

the nasal process of the maxilla or the nasal process of the 

premaxilla.

See anterior process of the nasal.

− nasomaxillary suture

The nasomaxillary suture lies on the ventrolateral surface of 

the nasal bones and articulates with the maxilla.

The posteromedial edge of the maxilla in Tursiops and other 

delphinids sometimes does not contact the nasal bone or it comes 

to rest over the nasal bones without a sutural attachment. In some 

odontocetes, including many fossil species, the maxilla is separated 

from the nasal by the premaxilla, so the suture cannot form.

− nasoturbinate crest

The nasoturbinate crest is a thin shelf of bone that gives 

rise to the nasal turbinate (dorsal nasal concha). It is located on 

the internal surface of the nasal bone. Evans and Christensen 

(1979:136, figs. 4–25) illustrated this shelf in the dog but did 

not name it.

Tursiops and other delphinids lack development of the turbinate complex.

− septal process of the nasal (processus septalis)

The septal process on the nasal bone lies at the anterior end 

of the internal surface of the nasal and contributes to the bony 

nasal septum (Schaller, 1992: 28:27, 30:17).

The odontocetes have reduced their olfactory functions and 

nasal elements. The nasal septum is composed solely of the mesethmoid and vomer and the septal process of the nasal is nonexistent in odontocetes.

PALATINE BONE

Os Palatinum

Figures 3, 6b,c, 18, 31a, 32

The palatine takes part in the formation of the back of the 

mouth, the hard palate, and the nasal passage in mammals. It is 

one of the rostral bones that does not appear on the surface of the 

skull (Gray, 1918:166–169; Evans and Christensen, 1979:143, 

144; Schaller, 1992:3.1–26; Feneis, 1994:24.15–33). The horizontal lamina, with distinct oral and nasal surfaces, usually forms 

the bulk of the bone. Vesalius (1543:23) referred to the palatine as 

sextis superioris maxill ossibus (sixth bone of the upper jaw).

In delphinids, with the movement of the nasal passage from 

subhorizontal (as in most mammals) to subvertical, the relationships of the palatine to the nasal passage and palate cavity between the oral and nasal cavities but is dorsoventrally deep and 

somewhat short anteroposteriorly. 

In delphinids, the posterior portion of the hard palate, at 

the opening of the internal bony nares, is now formed mainly 

by the pterygoid instead of the palatine, but the palatine forms 

much of the middle part of the anterior wall of the nasal passage. 

The palatine is exposed on the palate between the pterygoid and 

the maxilla, and in Tursiops and other delphinids forms the 

anterodorsal and dorsolateral walls of the fossa for the hamular lobe of the pterygoid sinus. Because of radical changes in 

topography, it is hard to apply some terms used for the palatine in other mammals. The palatine is bounded by the maxilla, frontal, vomer, and pterygoid. See Gray (1918:166–169), 

Schulte (1917:375, 378, 383, 386, 393, 399, 400); Fraser and 

7 0 • smithsonian contributions to zoolog y p a l a t i n e
Purves (1960:8, 13, 18, 33, 35, 38–41, 46–57, 60, 61, 69, 84, 

87, 89, 100), Evans and Christensen (1979:143, 144), Schaller, 

1992:36:1–26), Feneis (1994:15–33).

= accessory palatine foramen (Wible and Gaudin, 2004)

See minor palatine foramen.

= ala palatina = perpendicular process

Boenninghaus used “ala palatina” in a caption for his illustration of Phocoena (1904: pl. 12, figs. 3–4, 5(19); Fraser and 

Purves, 1960:13, pl. 1b). Those figures illustrated the palatal 

aspect of the body of the palatine bone, specifically the lateral 

lamina of the palatine.

* base of the palatine (Fraser and Purves, 1960:26) (Figure 18c)

Fraser and Purves (1960:26) refer to the base of the palatine 

as that portion of the palatine that is exposed on the palatal 

view of the skull, which we recognize as the horizontal portion 

of the palatine, contributing to the hard palate. In the human, 

from which the terms “horizontal lamina” and “perpendicular 

lamina” were derived, it would seem to us useful to have a term 

for the part of the palatine bone that represents the junction of 

the horizontal and perpendicular laminae. We according define 

the base of the palatine to consist of that junction. In the loose 

palatine of delphinids, the bone is seen to be thick ventrally and 

ventrolaterally so that the horizontal portion and lateral lamina 

of the palatine merge without distinct boundary. If developed, 

a palatal crest or palatal ridge approximates the base of the 

palatine.

= choanal border = nasal surface of the palatine

− conchal crest [crest of the ventral concha] (crista conchalis)

The nasal conchae are not developed in Tursiops or other 

odontocetes. See conchal crest under “Maxilla.”

* ethmoidal crest of the palatine (crista ethmoidalis) (Figure 

18a,b,d,e)

The ethmoidal crest of the palatine in most mammals occurs 

at the juncture of the ethmoid bone to maxilla, palatine, or nasal 

(Evans and Christensen, 1979:141, 144; Schaller, 1992:30.18, 

34.2; Daniels et al., 1998: fig. 3B). It forms the point of attachment of the dorsal nasal concha. The ethmoidal crest of the palatine is a thin, irregularly convex border near the anterior edge 

of the perpendicular plate of the palatine bone. It borders the 

maxillary sinus dorsally and bears the sphenopalatine foramen

(Evans and Christensen, 1979:144).

The ethmoidal crest in Tursiops has been displaced anteriorly with the posterodorsal movement of the narial passage. It 

no longer contacts the ethmoid but, with the vomer, forms the 

anteromedial wall of the nasal passage.

* free border of the palatine (margo liber) (Figures 2, 18e)

The free border of the palatine bone is the posterior edge 

that bears the soft palate and that borders the nasopharynx 

(Schaller, 1992:36.18). It is also known as the caudal border of 

the palatine.

The free border of the palatine in Odontoceti is restricted to 

the median portion of the posterior edge of palatine bone that is 

not bounded posteriorly by the pterygoid. In Tursiops and other 

delphinids, the free border is small to nonexistent because the 

pterygoid hamulus expands medially to form the posterior margin of the hard palate and the border of the internal bony nares 

(e.g., Flower, 1883: figs. 1–9).

= free lamina of the palatine (Owen, 1866a:28) = free border

= greater palatine foramen = major palatine foramen

See greater palatine foramen of “Maxilla.”

− groove for sphenopalatine artery

The groove for the sphenopalatine artery lies on the anteromedial surface of the palatine bone, just ventral to the ethmoidal crest of the palatine (Evans and Christensen, 1979:143). 

The sphenopalatine artery is a branch of the maxillary artery 

that leaves the pterygopalatine fossa (antorbital fossa) by passing through the sphenopalatine foramen. The terminal branches 

of the sphenopalatine artery are the caudal lateral nasal arteries 

(Evans and Christensen, 1979:674).

In delphinids the groove for the sphenopalatine artery is confluent with the greater palatine sulcus on the maxilla. It did not 

groove the palatine bone in the Tursiops specimens examined.

= groove for the sphenopalatine canal = greater palatine sulcus

− hard palate (palatum osseum)

The hard palate forms the division between the oral cavity 

and the nasal cavity in mammals. The anterior portion is formed 

by the premaxilla, the middle portion, the maxilla and the posterior portion, the palatine (Evans and Christensen, 1979:143). 

The surface of palatine in the hard palate is the oral surface of 

the palatine.

The oral or ventral or palatine surface of the palatine forms 

a small part of the hard palate in Tursiops and other delphinids. However, in the sense of “roof of mouth,” the delphinid 

hard palate is formed mainly by the maxilla. The nasal surface 

of the palatine no longer lies immediately dorsal to most of the 

hard palate but is prolonged into a subvertical surface in the 

nasal passage. In most dolphins, the medially apposed pterygoid 

hamuli form the posterior of the hard palate. 

See horizontal lamina of the palatine and horizontal portion 

of the palatine. See also hard palate under “Maxilla.”

− horizontal lamina of the palatine (lamina horizontalis)

The horizontal lamina of the mammalian palatine is a thin 

and usually long sheet of bone that forms the posterior portion 

of the hard palate, bordering the oral cavity and nasal cavity 

(Evans and Christensen, 1979:143; Schaller, 1992:36:15; Feneis, 

1994:24:27). The horizontal lamina usually has two closely parallel surfaces: oral (ventral, palatine) and nasal (dorsal).

In Tursiops and other delphinids, the equivalent of the 

horizontal lamina is so thickened that it no longer forms a true 

lamina [viz., a thin layer], and the term “horizontal portion of 

the palatine” (q.v.) is preferred.

* horizontal portion of the palatine [new term] (Figure 18a,c,e)

Due to the radical transformation of the nasal passage, the 

palatine no longer forms a thin horizontal lamina between the 

p a l a t i n e n u m b e r 6 2 7 • 7 1
nasal cavity and oral cavity in Tursiops and other delphinids. 

Whereas in most mammals, the oral and nasal surfaces are opposite surfaces of a sheet-like horizontal lamina, the equivalents 

in Tursiops are perpendicular to each other. The term “horizontal portion” is used here for the dorsoventrally thick part of the 

palatine that is exposed ventrally on the hard palate, between the 

maxilla and pterygoid hamulus. 

The horizontal portion bears the oral surface of the palatine. 

Posteriorly, the horizontal portion ends at the free border where 

the palatine is bounded by the pterygoid. Laterally, in Tursiops, 

the horizontal portion passes into the lateral lamina via the base 

of the palatine; this junction may be marked by the development 

of a palatal crest or ridge.

= internal-orbital foramen = sphenopalatine foramen

Kellogg (1936:110) indicated that the terms internal-orbital 

foramen and sphenopalatine foramen are synonyms. Internal-orbital foramen in this sense should not be confused with the “internal orbital foramen” as mentioned by Wible et al. (2005:103), 

namely, a feature internal to the optic foramen in some rodents 

and not known to occur in Cetacea.

* lateral lamina of the palatine (Fraser and Purves, 1960:18, 48, 

59, 65) (Figure 18b–e)

The lateral lamina of the palatine is unique to odontocetes. 

In Tursiops the palatine posterodorsal to the horizontal portion

is split, by development of the hamular fossa, into the lateral and 

medial laminae of the palatine. Fraser and Purves (1960:18, 48, 

59, 65) used “lateral lamina,” while de Muizon (1988:3) used 

both “lateral” and “medial laminae” (q.v.) for the duplications 

of the palatine characteristic of the Delphinida (Delphinoidea + 

Pontoporia + Inia + Lipotes). The perpendicular lamina is thus 

present dorsally but not ventrally.

In Tursiops and other delphinids, the lateral lamina is a posterolateral extension of the palatine over the hamular sinus. Ventrally, the lateral lamina of the palatine joins the lateral lamina 

of the pterygoid (the latter forming the ventral half of the wall 

of the hamular fossa). Posteriorly, the lateral lamina has a free 

margin at the entrance to the fossa for the hamular sinus. The 

lateral lamina thus separates the hamular fossa from the region 

of the antorbital fossa. Anteroventrally, the lamina merges with 

the diffuse region comprising the base of the palatine and the 

maxillary process of the palatine. Dorsally, above the level of 

the hamular fossa, the lateral and medial laminae of the palatine 

meet to form the thin perpendicular lamina that separates the 

nasal passage from the region of the antorbital fossa.

In Tursiops, Delphinus, and other delphinids, the lateral 

lamina is the origin for part of the internal and external pterygoid muscles (Fraser and Purves, 1960:17, 18; Seagars, 1982:50–

56, fig. 10c). In land mammals (dog, Evans and Christensen, 

1979:143; giant panda, Davis, 1964: fig. 17) the perpendicular 

lamina forms the origin for the external and much of the internal 

pterygoid muscles; lateral lamina and perpendicular lamina are 

thus homologous.

The boundaries of the lateral lamina may be difficult to 

trace (particularly for Inia and Pontoporia), which may explain 

why the lateral lamina of the palatine has sometimes been mistaken for maxilla (e.g., Miller, 1923:34, “freely-projecting platelike process” of maxilla; 51, “backwardly projecting maxillary 

plate”). Owen (1866a:27) referred to the perpendicular plate as 

the orbital plate of the palatine; Flower (1867:93) named it the 

projecting plate of the palatine. Lateral lamina should not be 

confused with lateral palatal lobe of the palatine (q.v.).

− lateral palatal lobe of the palatine

In some odontocetes the ventral exposure of the palatine 

on the hard palate is split into two, the medial lobe and the lateral lobe (Arnold and Heinsohn, 1996: fig. 10, Orcaella) by the 

contact of the pterygoid and maxilla. See also, e.g., Fraser and 

Purves, 1960: pls. 9 (Berardius), 16 (Kogia), and 32 (Orcaella). 

Tursiops lacks such a double ventral exposure. To avoid 

confusion with the lateral lamina of the palatine (q.v.), we propose a slight modification of the Arnold and Heinsohn term thus: 

lateral palatal lobe of the palatine.

= lesser palatine foramen = minor palatine foramen

* major palatine foramen = greater palatine foramen (Diagram 1)

See greater palatine foramen in “Maxilla.”

− maxillary fossa

The maxillary fossa is part of the anterior portion of the 

nasal part of the perpendicular lamina of the palatine bone. This 

fossa forms a posterior portion of the maxillary sinus (Evans and 

Christensen, 1979:144).

The maxillary fossa is not developed in odontocetes since 

the paranasal sinuses are not developed (Fraser and Purves, 

1960:5, 75).

See also maxillary fossa of the ethmoid bone. 

* maxillary process of the palatine (processes maxillaris) (Figure 

18a–e)

The maxillary process of the palatine bone is the anteroventral portion of the perpendicular lamina that articulates with the 

maxilla (Evans and Christensen, 1979:144). In humans (Gray, 

1918:168), the maxillary process is a lamina associated with part 

of the opening of the maxillary sinus. It is also known as the 

maxillary surface of the palatine.

The maxillary process of Tursiops and other delphinids is 

greatly expanded because the suture with the maxilla has become 

larger. The maxillary process consists of the bone between the 

nasal passage and the anterodorsal border of the palatine bone 

that is exposed between the antorbital fossa and the hard palate. 

The suture is fully apparent only in the disarticulated palatine; 

otherwise, in contrast to many other mammals, the maxillary 

process is not a distinct part of the palatine bone.

= maxillary recess = maxillary fossa

See maxillary recess under “Maxilla.”

= maxillary surface of the palatine (facies maxillaris) = maxillary 

process of the palatine (processes maxillaris)

− medial lamina of the palatine

De Muizon (1988:3) noted that a unique characteristic of 

the Delphinida is the duplication of the palatine into lateral and 

medial laminae. Fraser and Purves (1960), who used lateral lamina extensively, apparently did not name the medial lamina. In 

7 2 • smithsonian contributions to zoolog y p a l a t i n e
Tursiops most or all of the medial border of the hamular fossa

(and the adjacent lateral wall of the nasal passage) is formed by 

pterygoid, not palatine. In Lagenorhynchus obscurus, in which 

the hamular sinus is anteromedially deeper than in Tursiops, a 

medial lamina more clearly separates the hamular fossa from the 

nasal passage. The nasal surface (q.v.) of the medial lamina thus 

forms some of the nasal passage. Dorsally, above the level of the 

hamular fossa, the lateral and medial laminae of the palatine in 

delphinids meet to form the perpendicular lamina that separates 

the nasal passage from the region of the antorbital fossa.

The medial lamina is conspicuous in Inia (USNM 239667) 

and Pontoporia (USNM 482708).

See also lateral lamina of the palatine.

− median palatal lobe of the palatine

In some odontocetes the ventral exposure of the palatine 

on the hard palate is split into two, the medial lobe and lateral 

lobe (sensu Arnold and Heinsohn, 1996: fig. 10, Orcaella) by the 

contact of the pterygoid and maxilla. 

Tursiops lacks such a double ventral exposure. To avoid 

confusion with the medial lamina (q.v.), we propose a slight 

modification of the Arnold and Heinsohn term thus: medial palatal lobe of the palatine.

See also lateral palatal lobe of the palatine. 

= mesial portion = median palatal lobe of the palatine

= middle palatine foramen (Novacek, 1986)

See minor palatine foramen. 

− minor palatine canals (canales palatini minores)

The minor palatine canals lead from the palatine canal to 

the minor palatine foramina and transmit branches of the palatine artery, palatine vein, and palatine nerve (Evans and Christensen, 1979:143; Feneis, 1994:24.22).

Minor palatine canals have not been distinguished in 

odontocetes.

* minor palatine foramen (foramina palatina minora) (Figure 

18a)

The minor palatine foramen lies just posterior to the major 

palatine foramen. There are frequently several lesser palatine foramina that transmits branches of the minor palatine nerve and 

minor palatine vessels (Evans and Christensen, 1979:143). These 

minor palatine foramina lie within the palatine not at the palatomaxillary suture. The minor palatine foramen is also known as 

the lesser palatine foramen or accessory palatine foramina.

The minor palatine foramina appear to be irregularly developed in delphinids. There are none in the Tursiops we have 

used, but there is a large foramen in the body of the palatine in 

a specimen of Orcaella (USNM 284430) in its anterodorsal aspect that would be considered (topographically) a minor palatine 

foramen. See also Arnold and Heinsohn (1996: figs. 10, 12) on 

Orcaella.

= narial process of the palatine = nasal surface of the palatine

Miller (1923:47) said, of Inia, “narial process of palatine 

[is] well developed and forming an important part of the anterior 

wall of the nasal passage.”

* nasal crest of the palatine (crista nasalis) (Figure 18a,b,e)

The nasal crest of the palatine is that surface of the palatine bone adjacent to the medial palatine suture and raised into 

a crest that articulates with the vomer (Evans and Christensen, 

1979:143; Schaller, 1992:34.5). It forms the basis for attachment of the nasal septum.

In Tursiops and other delphinids the nasal crest is markedly 

reduced to the anterior one-quarter to one-third of the medial 

portion of the palatine that lies in the midline between the pterygoid bones and the vomer, immediately adjacent to the suture 

with the vomer.

* nasal spine of the palatine (spina nasalis) (Figures 2, 18b,e)

The nasal spine of the palatine bone is the posterior midline 

portion of the hard palate. It forms the posterior margin of the 

nasal crest (Gray, 1918:167; Evans and Christensen, 1979:143; 

White and Folkens, 1991:77). The nasal spine has also been 

termed the postpalatine spine (e.g., Novacek, 1986:34, fig. 14, in 

Leptictis; Asher, 1999:244, in tenrecs).

The nasal spine of the palatine bone in Tursiops and other 

delphinids is situated between the pterygoid bones and usually 

does not have a free projection into the palatal surface.

* nasal surface of the palatine (facies nasalis) (Figure 18e)

The nasal surface of the palatine bone consists of the dorsal surface of the horizontal lamina of the palatine bone. This 

surface forms the posterior floor of the nasal cavity (Evans and 

Christensen, 1979:143). The nasal surface is also called the choanal border.

Due to the radical transformation of the nasal passage, the 

palatine no longer forms a thin horizontal lamina between the 

nasal cavity and oral cavity in Tursiops and other delphinids, 

and the nasal surface is not applied closely to what we recognize 

as the horizontal portion of the palatine. The nasal surface in 

Tursiops comprises all the surface of the palatine that lines the 

nasal passage. Given that perpendicular lamina (as recognized 

here for Tursiops) may bound the nasal passage, this concept of 

nasal surface is broader than that used for the dog (above), in 

which the nasal surface is horizontal but not lateral. Ventrally, 

the nasal surface lies partly on the medial lamina of the palatine

(that is, on the medial wall of the hamular fossa). Ventromedially, the nasal surface in Tursiops ends at the vestigial free border of the palatine, or at the medial margin of the pterygoid. 

Dorsally, beyond the limit of the medial and lateral laminae, the 

nasal surface lies on the perpendicular lamina.

Miller (1923:47) said, of Inia, “narial process of palatine

[is] well developed and forming an important part of the anterior 

wall of the nasal passage.” Narial process in this sense embodies 

the nasal surface and the perpendicular lamina.

* nasopharyngeal duct (meatus nasopharyngeus) (Figure 31a)

The nasopharyngeal duct or nasopharyngeal meatus in 

mammals (Wible and Gaudin, 2004) is the air passage rostral 

to the choanae. Together with the sphenoethmoid recess (or olfactory recess), the nasopharyngeal duct forms the nasal cavity 

(Rowe et al., 2005).

Tursiops has a nasopharyngeal duct between the external 

bony nares and choanae, although as in other odontocetes, the 

geometric relationship with the palate is dramatically different 

p a l a t i n e n u m b e r 6 2 7 • 7 3
from other mammals. Cetacean literature makes little mention 

of the nasopharyngeal duct. Less specialized terms, such as nasal 

passage, are commonly used (e.g., Raven and Gregory, 1933; 

Messenger and McGuire, 1998; Houser et al., 2004). We consider the latter acceptable for Odontoceti. Ridewood (1922:221) 

termed the nasopharyngeal duct the postnasal passage (in part) 

and the oro-nasal passage.

= oral surface of the palatine = palatine surface of the palatine

* orbital process of the palatine (processus orbitalis) (Figure 

18a–e)

The orbital process of the palatine is barely distinct in the 

dog but is well developed in humans; it is the dorsal part of the 

bone lying dorsal to the ethmoidal crest of the palatine and sphenopalatine foramen, rising anterodorsally from the latter. It is 

separated from the body of the palatine by a thin neck. It consists 

of five surfaces, some of which are articulating, which enclose an 

air cell in humans. The articulating surfaces are: anterior or maxillary, posterior or sphenoidal, medial or ethmoidal. The nonarticulating surfaces are: superior or orbital, and lateral (Gray, 

1918:167, 168; Schaller, 1992:36.12; Feneis, 1994:24.25).

In adult Tursiops the orbital process, which has the sphenopalatine foramen at the base, is a small part of the palatine that 

projects laterally and slightly anterodorsally toward the antorbital fossa. Limits may be obscure in adult Tursiops but are more 

clear in e.g., Cephalorhynchus.

= oro-nasal passage (Ridewood, 1922:221) = nasopharyngeal duct

= palatal crest = palatal ridge

* palatal ridge (Fordyce, 1994:149) (Figure 17b–d)

The palatal crest is defined (Schaller, 1992:36:24) as a ridge 

on the palatal face of the palatine, occasionally present in suids.

Palatal ridge and palatal crest (a synonym) were mentioned 

in passing by Fordyce for the rostrum in the extinct dolphin 

Waipatia (1994:149 “Palatal ridges are indistinct”). Fordyce 

used crest to indicate a more pronounced elevation, as seen in 

the long sharp palatal crests in the extinct delphinid Australodelphis (see Fordyce et al., 2002:45). In Tursiops the palatal ridge 

separates the ventral and lateral faces of each palatine; the feature is better developed in some other delphinids (e.g., Fraser and 

Purves, 1960: pls. 43, 47).

Judging from the account of Seagars (1982:50–56, fig. 10) 

on pterygoid muscles in delphinids, the palatal ridge or crest 

probably marks the anteroventral limit of insertion of the internal pterygoid muscle.

See also palatine crests.

* palatine canal (canalis palatinus major) (Figure 18d)

In the dog the palatine canal runs through the palatine bone 

from the antorbital fossa posteriorly to the major palatine foramina 

and minor palatine foramina anteriorly. It carries the major palatine branches and minor palatine branches of the maxillary nerve 

and the palatine vessels (Evans and Christensen, 1979:143).

The palatine canal in Tursiops lies along the palatomaxillary 

suture. It runs anteriorly from near the sphenopalatine foramen

in the antorbital fossa to exit via the major palatine foramina 

and minor palatine foramina.

− palatine crests (crista palatina)

The palatine crests are variably expressed features on the 

ventral surface of the horizontal plate just posterior to the anterior margin (Schaller, 1992:36.24; Feneis, 1994:24.33). (The 

palatine crests are not discussed in Sisson, 1910; Gray, 1918; 

Evans and Christensen, 1979; or White and Folkens, 1991.)

There do not appear to be structures that are homologous 

with the palatine crests in Cetacea. The palatal ridge or palatal 

crest (q.v.) of some odontocetes appears not to be homologous 

with the feature in land mammals.

= palatine foramen

See major palatine foramen and minor palatine foramen. 

− palatine sinus (sinus palatinus)

The palatine sinus excavates the pars perpendicularis in 

horses and the pars horizontalis (soft palate) of the palatine in 

ruminants (Schaller, 1992:36.25, 180)

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the palatal sinus is absent in Tursiops.

− palatine sinus septum (septum sinuum palatinorum)

The palatine sinus septum is a median septum that separates the right and left palatine sinuses in ruminants (Schaller, 

1992:34.9, 36.26).

Paranasal sinuses are not developed in cetaceans (Fraser and 

Purves, 1960:5, 75), and the palatal sinus is absent in Tursiops.

= palatine sulci

See greater palatine sulcus in “Maxilla.” 

* palatine surface of the palatine (facies palatina) (Figure 18b,c)

The palatine surface of the palatine bone forms the posterior 

roof of the oral cavity, namely, part of the hard palate. In the dog, 

it lies posterior to the ventral exposure of the maxilla (Evans and 

Christensen, 1979:143). The palatine surface is also known as the 

ventral surface of the palatine or oral surface of the palatine.

The palatine surface of the palatine bone in Tursiops and 

other delphinids is the surface of the horizontal portion that is 

exposed between the maxilla anteriorly and the pterygoid posteriorly. The palatine surface is the same as the oral surface of the 

palatine and ventral surface of the palatine, and is the palatine 

contribution to the hard palate. It extends posteriorly as far as 

the free border of the palatine and/or the suture with the pterygoid hamulus.

* perpendicular lamina of the palatine (lamina perpendicularis) 

(Figure 18b–e)

In the dog the perpendicular lamina of the palatine bone 

forms the lateral wall of the nasopharyngeal duct and the medial 

wall of the antorbital fossa (q.v. under maxilla). It joins the horizontal lamina of the palatine nearly at right angles (Evans and 

Christensen, 1979:143). Externally, the perpendicular lamina 

forms the wall of the infratemporal fossa (e.g., in the panda, 

Davis, 1964: fig. 17), which provides origins for the internal and 

external pterygoid muscles.

In Tursiops and other Delphinidae, the palatine is extensively 

modified by development of the hamular lobe of the pterygoid 

sinus. The resulting lateral and medial laminae are neomorphic 

structures partly equivalent to the perpendicular lamina. See dis7 4 • smithsonian contributions to zoolog y p a l a t i n e
cussion of pterygoid muscle origins under lateral lamina of the 

palatine. 

In Tursiops we recognize the perpendicular lamina as that 

part of palatine present dorsal to the lateral and medial laminae (that is, dorsal to the hamular fossa), forming a thin surface 

between the lateral wall of the nasal passage and the antorbital 

fossa. 

See also nasal surface of the palatine and medial lamina of 

palatine.

= posterior nasal spine = nasal spine of the palatine

The posterior nasal spine is at the posterior end of the nasal 

crest of the palatine. The posterior nasal spine projects dorsally 

into the back of the nasal cavity (Gray, 1918:167; Evans and 

Christensen, 1979:143; White and Folkens, 1991:77).

= posterior palatine canal

See palatine canal. 

* posterior palatine foramen

See “Maxilla.”

− posterior wing of the lateral lamina

In the delphinid Orcaella, the posterior part of the lateral 

lamina of the palatine carries a wing-like horizontal flange that is 

directed outward and back toward foramina associated with the

orbit. Arnold and Heinsohn (1996:149, 156, fig. 11) termed this 

the wing-like process, wing-like posterior extension, and posterior wing of the lateral palatine.

Tursiops lacks a posterior wing of the lateral lamina.

= postnasal passage (Ridewood, 1922:221) = nasopharyngeal duct

= postpalatine spine (Novacek, 1986:34, fig. 14; Asher, 1999:244) 

= nasal spine of the palatine

− postpalatine torus

McDowell (1958:127) described the postpalatine torus as 

the transverse bony thickening at the rear of the bony palate. See 

also Novacek (1986: fig. 14).

Tursiops and other delphinids lack a postpalatine torus.

= projecting plate of the palatine (Flower, 1867:93) = lateral 

lamina of the palatine

− pterygoid fossa of the palatine

In humans (Gray, 1918:166) the pterygoid fossa for origin of the internal pterygoid muscle is developed in part on the 

posterior face of the palatine. For leptictid insectivores Novacek 

(1986:45) used the name ectopterygoid fossa for the origin of 

the internal pterygoid muscle, noting that the entopterygoid crest

forms the internal wall of the pterygoid fossa. 

In Tursiops and many other odontocetes the internal pterygoid muscle arises on the lateral lamina of the palatine (q.v.) and 

lateral lamina of the pterygoid (the latter forming the ventral 

half of the wall of the hamular fossa). The pterygoid sinus fossa

of Odontoceti and Mysticeti, and the extinct Archaeoceti, is not 

homologous with the pterygoid fossa of many land mammals.

See also pyramidal process of the palatine and pterygoid 

fossa of the sphenoid.

= pterygopalatine canal = palatine canal (Gray, 1918:168) (Diagram 1)

= pterygopalatine fossa

See antorbital fossa under “Maxilla.”

* pyramidal process of the palatine (processus pyramidalis) (Figures 3, 18b,c,e)

The pyramidal process of the palatine bone in humans projects posterolaterally from the junction of the horizontal lamina 

of the palatine and vertical laminae. It articulates with the pterygoid bones and forms part of the origin of the internal pterygoid 

muscle (Gray, 1918:168; Feneis, 1994:24.21). In domestic animals it is a posteroventral process inserted between the pterygoid 

process of the basisphenoid (alisphenoid) and the pterygoid bone 

(Schaller, 1992:36.9). It is absent in dogs.

The pyramidal process in delphinids extends posteriorly 

forming the most posterolateral extension of the palatine bone. 

Its boundaries may be marked by variably developed ridges that 

produce a semicircular to triangular region, concave posteriorly, 

on the lateral lamina of the palatine. The pyramidal process does 

not form the wall of the pterygoid sinus. The pyramidal process 

gives origin to part of the internal pterygoid muscle (Seagars, 

1982:51–56, fig. 10c). The pyramidal process may be the feature 

that is called the palatal process of the pterygoid by Fraser and 

Purves (1960:13).

− ridge impressions (impressiones rugae)

The ridge impressions are found on the ventral surface of 

the hard palate and are caused by the palatal ridges. The palatal 

ridges are hard ridges of non-bony tissue that lie transversely on 

the roof of the hard palate (Evans and Christensen, 1979:413, 

414; Schaller, 1992:140.31).

Palatal ridges and ridge impressions are not developed in 

cetaceans.

− soft palate (palatum molle) (Gray, 1918:167, 1112)

The soft palate is the posterior continuation, in soft tissue, 

of the hard palate (palatum durum / palatum osseum) (Evans and 

Christensen, 1979:141, 143, 413; Schaller, 1992:140.14, 12.23; 

Feneis, 1994:108.17). In humans the lower border of the soft 

palate is free and hangs like a curtain between the mouth and the 

pharynx. It is called the palatine vellum (velum palatinum).

The soft palate is absent in odontocetes, the space that it would 

occupy having been taken over by the pterygoid bones (Fraser and 

Purves, 1960:19, 20, 22, 82). The soft palate persists in mysticetes.

* sphenoethmoid lamina of the palatine (lamina sphenoethmoidalis) (Figure 18d)

The sphenoethmoid lamina of the palatine bone comes 

off the perpendicular lamina of the palatine and articulates 

with the vomer (Evans and Christensen, 1979:144; Schaller, 

1992:36.11).

In Tursiops the sphenoethmoid lamina is reduced to a vertically oriented ridge on the medial surface of the palatine bone. It 

forms the posterior margin of the vomeropalatine suture.

* sphenoidal process (processus sphenoidalis) (Figure 18b,c,e)

The sphenoidal process is the posterior portion of the perpendicular lamina between the pterygoid bone medially and 

p a l a t i n e n u m b e r 6 2 7 • 7 5
the sphenoid bone laterally (Evans and Christensen, 1979:144; 

Schaller, 1992:36.13). In humans, the sphenoidal process lies 

posterior and slightly dorsal to the sphenopalatine foramen

(Gray, 1918: figs. 168, 169).

In Tursiops the sphenoidal process is the indistinctly 

bounded part of the palatine posterodorsal to the sphenopalatine 

foramen. The sphenoidal process, which has the sphenopalatine 

foramen at the base, is a small part of the palatine that projects 

laterally and slightly anterodorsally toward the antorbital fossa. 

Limits may be obscure in adult Tursiops but are more clear in 

e.g., Cephalorhynchus.

= sphenoidal sinus (sinus sphenoidalis)

See “Sphenoid Bone.” 

= sphenopalatine canal or sphenopalatine opening

See sphenopalatine foramen. 

* sphenopalatine foramen (foramen sphenopalatinum) (Diagram 

1; Figures 18e, 30)

In the dog (Evans and Christensen, 1979:674) the sphenopalatine foramen lies at the anterior margin of the sphenopalatine 

lamina of the palatine, in the pterygopalatine fossa (antorbital 

fossa) (Evans and Christensen, 1979:144; Schaller, 1992:14.12, 

36.6). It is also known as the sphenopalatine foramen in humans 

(Feneis, 1994:32.11, 322.20). It transmits the sphenopalatine artery and caudal nasal nerve from the pterygopalatine fossa [antorbital fossa] to the nasopharyngeal duct. In some armadillos 

(Wible and Gaudin, 2004:164), the sphenopalatine foramen and 

caudal palatine foramen (opening of the palatine canal) may be 

confluent.

In Tursiops the sphenopalatine foramen lies in the antorbital fossa anterior to the orbit, close to the ventral infraorbital 

foramen, and opens medially into the bony narial passage. The 

sphenopalatine foramen lies just anterior to the middle of the 

ethmoidal crest of the palatine on the medial (vomerine) surface 

of the palatine bone.

Schulte (1917:373) referred to the sphenopalatine foramen 

in Kogia as the naso-palatine foramen.

For the archaeocete Zygorhiza, Kellogg (1936:110) indicated that the internal-orbital foramen or sphenopalatine foramen is the foramen at junction of palatine, maxilla, and frontal. 

The name internal-orbital foramen (q.v.) should not be used because of confusion with a foramen in some rodents (see Wible 

et al. 2005:103).

− sphenopalatine notch of the palatine (incisura sphenopalatina)

The sphenopalatine notch of the palatine bone lies between 

the orbital process of the palatine and sphenoidal processes (Gray, 

1918:169; Feneis, 1994:24.19). Gray noted that in humans the 

notch may be bridged by the orbital and sphenoidal processes to 

form a complete sphenopalatine foramen. The sphenopalatine 

notch lies on the posterodorsal aspect of the palatine bone and is 

part of the sphenopalatine foramen (Schaller, 1992:36.5).

The topography of the palatine bone has changed dramatically in cetaceans. The sphenopalatine foramen is now entirely 

within the palatine bone and the notch is closed over.

= ventral surface of the palatine = palatine surface of the palatine

PARIETAL BONE

Os Parietale

Figures 1, 3–5, 6a,c, 19, 32

The parietal bone forms the lateral walls of the cranium 

and, in most mammals, meets with the contralateral bone in the 

midline (Gray, 1918:133; Evans and Christensen, 1979:124; 

Schaller, 1992:26.1; Feneis, 1994:16.24). Vesalius (1543:21,23) 

referred to the parietal as dextrum uerticis os, sinstrum uerticis os, or verticis sinistrum os. The parietal in most mammals is 

bounded by the frontal, basisphenoid, squamosal, interparietal, 

and supraoccipital. The exoccipital normally is excluded from 

contacting the parietal by the squamosal. Cetaceans are unusual 

in that the interparietal ossification is discrete and forms the 

midline ossification of the cranial walls, excluding the parietals 

from the midline. The parietal is bounded by the frontal, alisphenoid, squamosal, interparietal, supraoccipital, and exoccipital 

(Schulte, 1917:370, 375, 376, 382, 383, 391–393).

* alisphenoid border of the parietal (Figure 19b,c)

The alisphenoid border of the parietal is the border that articulates with the alisphenoid part of the sphenoid bones. It lies 

on the anteroventral surface of the parietal bone, posterior and 

ventral to the frontal border of the parietal.

− caudal frontal sinus (sinus frontalis caudalis)

See “Frontal Bone.”

− dorsal sagittal sinus sulcus (sulcus sinus sagittalis dorsalis)

See “Interparietal Bone.” 

* exoccipital border of the parietal (Figure 19a–c,e)

The exoccipital border of the parietal is that portion of the 

parietal margin that articulates with the exoccipital. It is located 

ventromedially on the posterior border of the parietal (lateral 

and ventral to the occipital border).

− external sagittal crest (crista sagittalis externa)

The external sagittal crest is formed by the medial borders 

of the temporal fossae on the dorsal surface of the skull (Schaller, 

1992:16:30, 18:3, 26:6).

Because the parietals do not meet in the midline in cetaceans and the dorsal temporal line is situated laterally on the 

skull, the external sagittal crest is not a feature of extant cetacean skulls.

* external surface of the parietal (facies externa) (Figure 19a–e)

The external surface of the parietal bone is that surface the 

bone that is external to the cranial cavity; the outside of the parietal bone.

* free border of the parietal [new term] (Figure 19b)

The free border of the parietal bone lies between the alisphenoid border of the parietal and the exoccipital border. It is the 

border that projects into the posterior lacerate foramen in odontocetes. The parietal bone does not participate in the posterior 

lacerate foramen of most mammals.

7 6 • smithsonian contributions to zoolog y parietal
− frontal angle of the parietal (angulus frontalis)

The frontal angle is the craniometric angle formed by the 

intersection of a line from the center of the orifice of the external 

auditory meatus to the ophryon and a line from the ophryon (the 

middle of the supraorbital line, which, drawn across the narrowest part of the forehead, separates the face from the cranium) 

to the bregma (Whitney, 1889–1910:[vol. 2]1331). The frontal 

angle is the angle formed at the bregma by the sagittal and frontal borders of the parietal (White and Folkens, 1991:61, 62).

Because the parietals do not meet in the midline, this feature 

is not found on the cetacean skull.

* frontal border of the parietal (margo frontalis) (Figure 19a–d)

The frontal border of the parietal is the border that articulates with the frontal bones. It lies on the anterior surface of the 

parietal bone (Schaller, 1992:26.13).

The frontal border of the parietal is present in cetaceans.

* inferior anterior external angle of the parietal (Anderson, 

1879:504) (Figure 19c)

Anderson (1879:504) describes the inferior posterior external angle of the parietal as “being external to that process with 

the frontal process of the pterygoid external to it and excluding it from appearing in the outer wall of the skull, although in 

the temporal fossa it is close behind the superior border of the 

isolated portion of the pterygoid, that is wedged in between the 

frontal, parietal and squamosal.” In determining the location of 

this structure it became apparent that is was on the anterior not 

the posterior angle of the parietal.

The inferior anterior external angle of the parietal is present 

in delphinids.

− internal sagittal crest (crista sagittalis interna)

See occipital bone and “Interparietal Bone.” 

* internal surface of the parietal (facies interna) (Figure 19d,e)

The internal surface of the parietal bone is the medial or 

cranial surface of that bone.

* interparietal border of the parietal (margo interparietalis) (Figure 19a,c,d)

The interparietal border of the parietal is the border that 

articulates with the interparietal bone. It lies anteromedially on 

the dorsal surface of the parietal bone.

− mastoid angle (angulus mastoideus)

The mastoid angle is the angle formed at the asterion by the 

occipital border and temporal borders of the parietal (White and 

Folkens, 1991:61, 62).

It appears that this measurement is possible but difficult in 

Cetacea.

* nuchal plane (planum nuchale) (Figure 5)

The nuchal plane is the caudal surface of the skull formed by 

the exoccipitals, supraoccipital, and mid-ventrally by the basioccipital with its intracondyloid closure. It is limited by the nuchal 

crest (Evans and Christensen, 1979:154; Schaller, 1992:26.20).

In cetaceans the nuchal plane has been modified to include 

the interparietal, which bears the median portion of the nuchal 

crest. It is limited laterally by the temporal crests and ventrally 

by the ventral border of the exoccipital bones. The nuchal plane 

is more planar in adults than juveniles.

− occipital angle (angulus occipitalis)

The occipital angle of Broca is the craniometric angle 

formed by the intersection of the lines drawn from the opisthion

(the middle point of the posterior border of the foramen magnum) to the basion (the middle point of the anterior margin of 

the foramen magnum) and nasion or nasal points (the middle of 

the frontonasal suture at the root of the nose) (Whitney, 1889–

1910:[vol. 2]1331).

The occipital angle of Daubenton is the angle that the line of 

Daubenton (a line drawn through the opisthion and the projection, on the medial plane of the skull, of the lower border of the

orbit) makes with a line joining the basion (the middle point of 

the anterior margin of the foramen magnum) and the opisthion

(the middle point of the posterior border of the foramen magnum) (Whitney, 1889–1910:[vol. 2]1331).

The occipital angle is the angle formed at lambda by the 

sagittal and occipital borders (White and Folkens, 1991:61, 62).

Because the parietals do not meet in the midline, this feature 

is not found on the cetacean skull.

= occipital border of the parietal (margo occipitalis)

The occipital border is that portion of the parietal margin 

that articulates with the occipital. It is located posteromedially 

on the dorsal border of the parietal. In delphinids it is composed 

of the supraoccipital border and the exoccipital border.

− parietal eminence (tuber parietale)

The parietal eminence is the feature on the external surface of the parietal that indicates where the parietal ossification 

began.

The parietal eminence is not evident in Tursiops or other 

odontocetes.

− parietal foramen (foramen parietale)

Gingerich et al. (2005: fig. 4) show a parietal foramen opening at the junction of parietal, squamosal, and occipital in the 

archaeocete Makaracetus.

See this term under “Interparietal Bone.” 

= parietal plane (planum parietale) = temporal fossa (adult)

The parietal plane is bounded by the temporal line and the 

external sagittal crest medially and the nuchal line posteriorly 

(Evans and Christensen, 1979:150). It is equivalent to the temporal fossa.

* parietointerparietal suture (Figure 5)

The parietointerparietal suture is the suture between the parietal and interparietal centers of ossification. In delphinids the 

parietointerparietal suture occurs on the interparietal border on 

the anterodorsal aspect of the parietal and on the parietal margin 

on the posterolateral aspect of the interparietals.

* parietosupraoccipital suture (Figure 5)

The parietosupraoccipital suture is the suture between the 

parietal and supraoccipital centers of ossification. In delphinids 

parietal n u m b e r 6 2 7 • 7 7
the parietosupraoccipital suture occurs on the supraoccipital 

border on the posterodorsal aspect of the parietal and on the parietal margin on the anterolateral aspect of the supraoccipital.

− postparietal foramen (Uhen, 2004:132)

Some archaeocete whales may have a prominent postparietal foramen opening dorsally in the parietal, in the wall of the 

temporal fossa (Kellogg, 1936: fig. 31c; Uhen, 2004:132). Uhen 

identified the postparietal foramen as for passage of a vessel 

from the otic region.

Tursiops lacks a postparietal foramen.

− sagittal border of the parietal (margo sagittalis)

The sagittal border of the parietal is the border that articulates with the contralateral bone.

Because the parietals do not meet in the midline, the sagittal 

border of the parietal is not a feature of the cetacean skull.

− sagittal sinus

See this term under “Frontal Bone” and “Interparietal Bone.”

− sagittal suture (sutura sagittalis)

The sagittal suture is formed by the right and left parietal 

bones in the midline of the skull (Gray, 1918:178; Evans and 

Christensen, 1979:125; Schaller, 1992:76.3; Feneis, 1994:54.3). 

Vesalius (1543:23, 25) and Eustachius and Lancisius (1714:111) 

referred to the sagittal suture as the sagittalis sutura.

Because the parietals are excluded from the midline in modern Cetacea, the sagittal suture does not occur.

− septum of the frontal sinus (septum sinuum frontalium)

See “Frontal Bone.” 

− sphenoidal angle (angulus sphenoidalis)

The sphenoidal angle is the angle between the lines drawn 

from the basion (the middle point of the anterior margin of the 

foramen magnum; Whitney, 1889–1910:[vol. 2]1331) and nasion (the middle of the frontonasal suture at the root of the nose; 

ibid.) to a point in the median line where the sloping anterior 

surface of the sella turcica passes over into the horizontal surface 

of the olivary eminence (a small rounded transverse process of 

the body of the sphenoid bone, just in front of the pituitary fossa, 

in relation with the optic chiasma; also called the olivary process 

or tuberculum sellae; ibid., [vol. 5]4103).

The sphenoidal angle is the angle formed at pterion by the 

frontal and sphenoid borders (White and Folkens, 1991:61, 62). It 

appears that this measurement is possible but difficult in Cetacea.

* squamous border of the parietal (margo squamosus) (Figure 19c)

The squamous border of the parietal is the portion of the 

parietal margin that articulates with the squamosal. It is located 

ventromedially in cetaceans.

− sulci for intracranial extensions of spinal meningeal arteries

See “Exoccipital Bone.” 

* sulcus for the middle meningeal artery (Figure 31a)

The sulcus for the middle meningeal artery starts at the posterior-ventral angle of the parietal and branches over its internal 

surface of the parietal (Evans and Christensen, 1979:124). The 

sulcus for the middle meningeal artery is also called the groove 

for the middle meningeal artery

In Tursiops the sulcus for the middle meningeal artery appears to start on the alisphenoid and extend laterally onto the 

parietal. Two major branches of the sulcus are preserved on the 

parietal, the sulcus having divided on the alisphenoid.

* sulcus for the transverse sinus (transverse sulcus) (sulcus sinus 

transversi) (Figure 31b)

The sulcus for the transverse sinus (Evans and Christensen, 

1979:122; Schaller, 1992:16.37, 18.6; Feneis, 1994:8.32) is located 

on the supraoccipital bone and the parietal bone. The sulcus is formed 

by one of the endocranial venous sinuses, the transverse sinus.

The sulcus for the transverse sinus in Tursiops occupies the 

area of the internal surface of parietal bone just lateral to the 

tentorial process. The transverse sinus broadens remarkably here 

compared to the situation in the dog (Evans and Christensen, 

1979:124). The sulcus for the transverse sinus appears to be approximately 2 cm wide laterally (USNM 571695).

* supraoccipital border (Figure 19a,c,e)

The supraoccipital border of the parietal bone is that border 

of the parietal that abuts the supraoccipital. The supraoccipital 

border of the parietal lies between the exoccipital border of the 

parietal and the interparietal border of the parietal.

* temporal line (linea temporalis) (Figures 6c, 19c)

The temporal lines bound the temporal fossa. They are a 

continuation of the sagittal crest in dogs (Evans and Christensen, 

1979:124; Schaller, 1992:16.31, 26.7). The temporal fascia is 

attached to the temporal line. In humans the temporal line is 

differentiated into a superior temporal line (linea temporalis superior), to which the temporal fascia is attached, and the inferior 

temporal line (linea temporalis inferior), to which the temporal 

muscle is attached (Feneis, 1994:16.28, 16.29). In other animals 

in which this differentiation occurs, the superior temporal line 

is known as the dorsal temporal line and the inferior temporal 

line is known as the ventral temporal line. Temporal crest and 

supratemporal crest have been used for comparable features in 

other mammals (e.g., Novacek, 1986). In humans the temporal 

line continues onto the frontal bone (Feneis, 1994:18.12).

In Tursiops the dorsal temporal line (q.v.) forms the posterior limit of the temporal fossa, which constitutes the posteromedial margin of the external surface of the parietal bone. Dorsally 

the temporal line comes to lie on the parietal only. Anterodorsally it continues onto the postorbital process of the frontal 

bone, where ventrally it runs onto the zygomatic process of the 

squamosal bone. The ventral temporal line is not developed. The 

dorsal temporal line becomes the temporal crest of adults.

The situation is different in some other Cetacea, especially 

archaic forms with an intertemporal constriction in which parietals and interparietal broadly separate face from supraoccipital. 

In Simocetus, each parietal is smooth with two indistinct subparallel parasagittal temporal crests (Fordyce, 2002).

− temporal plane (planum temporale)

The temporal plane is the temporal surface of the cranium 

(Whitney, 1889–1910:[vol. 6]4528), essentially the temporal fossa.

7 8 • smithsonian contributions to zoolog y parietal
= tentorial process (processus tentoricus)

See “Exoccipital Bone.” 

= tentorium (tentorial ossification) (tentorium cerebelli osseum)

See “Exoccipital Bone.”

= transverse sulcus = sulcus for the transverse sinus

PREMAXILLA

Os Incisivum

Figures 1, 3, 4, 6c,d, 20

The premaxilla forms the most anterior part of the skull, 

contacting the contralateral bone in the midline. It is one of three 

dentulous (tooth bearing) bones, the other two being the maxilla 

and mandible. The premaxilla bears the incisor teeth and forms 

the anterior part of the canine alveolus (alveolus for the canine 

tooth). The premaxilla also forms the floor of the anterior nasal 

passage. The premaxilla is bounded by the maxilla, vomer, and 

the nasal.

The premaxilla in odontocetes has been modified from the 

basic mammalian plan by the movement of the bony nares posteriorly and the accompanying development of the ascending process of the maxilla. The premaxilla forms most of the anterior 

border of the external bony nares. The premaxilla is bounded by 

the maxilla and vomer. The premaxilla rarely, if ever, contacts 

the nasal and frontal (Schulte, 1917:362, 365, 371, 372, 374, 

377, 378, 380–383, 385–389, 400).

= alveolar border (arcus alveolaris)

See “Mandible.”

= alveolar juga (juga alveolaria)

See this term under “Mandible.”

= alveolar margin (margo alveolaris)

See alveolar margin of the maxilla under “Maxilla.” 

= alveolar process (processus alveolaris)

See alveolar process of the maxilla under “Maxilla.”

= alveolar walls

See “Mandible.”

− alveolus for the canine tooth

The alveolus for the canine tooth in most terrestrial mammals lies between the premaxilla and maxilla and forms an oval 

depression in both bones.

The teeth in odontocetes are homodont, i.e., there is no differentiated canine tooth. There is usually a small tooth whose 

alveolus lies between the premaxilla and maxilla.

− anterior nasal spine (spina nasalis anterior)

The anterior nasal spine of the premaxilla is the prolongation of the incisor crest anteriorly to form a spine that projects 

dorsally into the external narial aperture (Gray, 1918:158, 163; 

Feneis, 1994:22.12). This is commonly located on the maxilla 

in humans since the premaxillary ossification fuses in utero at 

an extremely early stage and is not recognized as a separate 

ossification.

The anterior nasal spine appears to be a neomorph in humans and is not present in Cetacea or domestic animals.

* anteromedial sulcus (Figure 20a)

The anteromedial sulcus lies on dorsal surface of the nasal 

process of the premaxilla. It contains the premaxillary foramen

and forms the boundary between the anterior portion of the premaxillary sac fossa medially and the dorsal portion of the rostral 

process laterally (Fordyce, 1981: fig. 2; 1994:153).

− body (corpus ossis incisivi)

The premaxillary bone.

= dental groove = alveolar gutter = alveolar groove of the mandible

See alveolar groove of the mandible under “Mandible.”

− dorsal sulcus (sulcus septi nasi)

The dorsal sulcus of the premaxilla is formed by the palatine 

process of the premaxilla, which, together with the contralateral 

palatine process, forms a groove for the cartilaginous nasal septum (Evans and Christensen, 1979:139).

The palatine process of the premaxilla is not developed in 

Tursiops.

* external bony nares (apertura nasi ossea) (Figures 1, 4)

The external bony nares form the anterior opening of the 

nasal cavities in the skull (Schaller, 1992:14.3). In most terrestrial mammals the external bony nares is formed by the premaxillae ventrally and the nasals dorsally (Evans and Christensen, 

1979:508). It is known as the piriform aperture (apertura piriformis / apertura nasalis anterior) in humans (Feneis, 1994:32.3).

In delphinids the external bony nares are bounded by the 

premaxillae anteriorly and the nasals posteriorly. Depending on 

individual variation and type of preparation of bony specimens, 

the mesethmoid may be considered as forming part of the posterior border, the frontals, and the maxillae part of the lateral 

border, and a small slip of the maxilla may form part of the 

anterior border of the external bony nares. Clarke (2003:249) 

used the term “nasal foramina” as a synonym for the external 

bony nares in Kogia.

− frontal process of the premaxilla (Schulte, 1917:387)

Schulte used the term “frontal process of the premaxilla” 

to denote the contribution of the right premaxilla into the facial 

crest in Kogia. The facial crest (sensu Schulte) is present only in 

Kogia.

− incisive canal (canalis incisivus)

The incisive canals (foramina of Stenson) open into the 

incisive foramen in humans and carry the terminal branch of 

the descending palatine artery and the nasopalatine nerve 

(Gray, 1918:162; Evans and Christensen, 1979:139; Schaller, 

1992:466.27; Feneis, 1994:24.4; Wible and Gaudin, 2004). The 

incisive canal lies in the interincisive suture.

p r e m a x i l l a n u m b e r 6 2 7 • 7 9
The incisive canal is lacking in Neoceti because of the apparent lack of a nasopalatine nerve.

− incisive foramen (foramen incisivum) (Diagram 1)

The incisive foramen in humans is a shallow opening in the 

ventral midline of the palatal surface of the premaxilla and maxilla just posterior to the incisor teeth. It contains the apertures 

of the incisive canals, or foramina of Stenson (Gray, 1918:162, 

180; Feneis, 1994:24.14). The incisive foramen is also known as 

the palatal fissure (Evans and Christensen, 1979:139; Schaller, 

1992:12.25). Vesalius (1543:53; Vesalius et al., 1998:131) referred to the incisive foramen as the foramen hoc iuxta posteriorem dentium incisoriorum.

The incisive foramen is not developed in Neoceti.

− incisive suture (sutura incisiva)

The incisive suture is the suture between the right and left 

premaxillae.

The right and left premaxillae often bear a sutural relationship in delphinids.

− incisor crest

The incisor crest is a continuation of the nasal crest of the 

maxilla on the dorsomedial aspect of the premaxilla (Gray, 

1918:163). The incisor crest continues anterodorsally where it 

forms the anterior nasal spine.

The incisor crest is not developed in delphinids due to the 

lack of fusion of the premaxilla medially.

* infraorbital canal (Table 6; Figure 20b,c,e)

See discussion under premaxillary foramen under 

“Premaxilla.”

= infraorbital foramen

See “Maxilla.”

= interalveolar margin (margo interalveolaris)

See “Mandible.”

= interalveolar septa (septa interalveolaria)

See “Mandible.” 

= interradicular septa (septa interradicularia)

See “Mandible.”

* labial surface of the premaxilla (facies labialis) (Figure 20a)

The labial surface of the premaxilla is that part of the anterior surface that faces the lips.

In odontocetes, this term is applicable to the anteroventral 

margin of the premaxilla.

* lateral nasal crest [new term] (Figure 20a,c)

The lateral nasal crest forms the functional border of the 

narial region laterally and differentiates it from the rest of the 

facial region. It is asymmetrically developed, being most prominent on the left side. The lateral nasal crest lies on the lateral 

edge of the nasal process of the premaxilla immediately lateral 

to the external bony nares. The lateral nasal crest lies lateral to 

the premaxillary cleft and medial to the posterolateral plate of 

the premaxilla (when developed). The lateral nasal crest also lies 

posteromedial to the posterolateral sulcus, and passes back into 

the “crest on maxilla” (sensu Fordyce, 1994:153).

= major palatine foramen (foramen palatinum majus)

See “Palatine Bone.” 

* mesorostral canal (Figure 1)

The mesorostral canal or groove is a characteristic feature 

of cetaceans. It lies dorsal to the vomer, medial to the maxilla 

and premaxilla, and anterior to the mesethmoid (Kernan, 1918, 

Rommel, 1990; Fordyce 1994). The mesorostral groove becomes 

occupied by the mesorostral ossification with age in ziphiids 

(Flower, 1878; Fraser, 1942; Heyning, 1984).

* nasal portion (Owen, 1866a:28) (Figure 20b)

The nasal portion of the premaxilla is that part of the bone 

lined by extensions of the nasal epithelium that cover the premaxillary sac and the inferior vestibule (Mead, 1975:6–8, fig. 2). 

The nasal portion is posterior to the rostral portion.

* nasal process of the premaxilla (processus nasalis) (Figure 

20a,b,d,e)

The nasal process of the premaxilla is the posterodorsal 

portion of the premaxilla. The free rostral border of the nasal 

process forms part of the external bony nares (Evans and Christensen, 1979:139; Schaller, 1992:34.28).

The nasal process of the premaxilla in delphinids is that portion of the premaxilla that lies posterior to the anterior margin 

of the external bony nares. It is equivalent to the spiracular surface of the vertex in ziphiids (Heyning, 1989a) and has also been 

called the naso-frontal plate (Owen, 1866a:42) and nasal plate

(Owen, 1866a:30). Schulte (1917:372, 373) referred to the nasal 

process as the postnarial process in Kogia.

= os rostrale = premaxilla

− palatine fissure (fissura palatina)

The palatine fissure is an oval opening formed at the junction of the palatal surfaces of the maxilla and premaxilla. The 

palatine vessels anastomose with the infraorbital vessels and 

nasal vessels through the palatine fissure (Evans and Christensen, 

1979:141, 154). It also contains the bulk of the vomeronasal 

organ in most mammals (Evans and Christensen, 1979:510).

Schulte (1917:373) stated: “somewhat more caudally at the 

junction of the maxilla, pterygoid and frontal is the naso-palatine foramen.” We are unable to find any other reference to the 

naso-palatine foramen, but the nasopalatine nerve goes through 

the palatine fissure (Schaller, 1992:466.27), and that structure 

could have been what Schulte had in mind. The foramen that 

Schulte describes is the sphenopalatine foramen.

The palatine fissure is absent in delphinids, as is the vomeronasal organ.

= palatine foramen

See “Palatine Bone.” 

* palatine process of the premaxilla (processus palatinus) (Figure 2)

The palatine process of the premaxilla is a pointed and 

laterally compressed process extending posteroventrally. This 

8 0 • smithsonian contributions to zoolog y p r e m a x i l l a
process, together with the opposite one, forms the dorsal sulcus

into which the dorsal part of the cartilaginous nasal septum fits 

(Evans and Christensen, 1979:139). The palatine process is the 

contribution of the premaxilla to the palate (Evans and Christensen, 1979:152).

In Tursiops the palatine process is the anteroventral portion 

of the premaxilla that projects onto the palate. The palatine process is equivalent to the palatine surface of the premaxilla.

= palatine sulcus (sulcus palatinus)

See “Maxilla.” 

* palatine surface of the premaxilla (facies palatina) (Figure 

20b,d)

The palatine or ventral surface of the premaxilla is that portion of the premaxilla that is exposed on the palate. It is the 

most anteromedial surface of the premaxilla. The palatine surface of the premaxilla is equivalent to the palatine process of the 

premaxilla.

* porcelanous part (Figure 1)

The porcelanous part is the dorsal surface of the rostral process of the cetacean premaxilla. Because the porcelanous part has 

no muscular insertions on it, the external surface is extremely 

smooth (Lawrence and Schevill, 1956: fig. 23).

= posteroexternal plate (Fordyce and de Muizon, 2001:196, fig. 

12) = posterolateral plate

= posterointernal plate (Fordyce and de Muizon, 2001:196, fig. 

12) = posteromedial splint

− posterolateral plate

The posterolateral plate of the premaxilla is the most posterolateral portion of the nasal process of the premaxilla. It is bounded 

medially by the premaxillary cleft (Fordyce, 1994:153). The posterolateral plate was described in a fossil platanistoid, Waipatia.

* posterolateral sulcus (Figure 20a,d)

The posterolateral sulcus lies on the dorsal surface of the 

nasal process of the premaxilla, posterior to the premaxillary 

foramen. It is a continuation of the anteromedial sulcus and 

forms the boundary between the premaxillary sac fossa medially 

and the lateral portion of the premaxilla that is a continuation 

posteriorly of the dorsal surface of the rostral process (Fordyce, 

1994:153). The posterolateral sulcus was described in a fossil 

platanistoid, Waipatia.

− posteromedial splint

The posteromedial splint of the premaxilla, when developed, 

is the most posteromedial portion of the nasal process of the premaxilla. It is limited by the external bony nares medially, the frontal or maxillary posteriorly, and the premaxillary cleft laterally 

(Fordyce, 1994:153). The posteromedial splint was described in a 

fossil platanistoid, Waipatia, and is not developed in Tursiops.

* posteromedial sulcus (Figure 20a,d)

The posteromedial sulcus lies medial to the premaxillary 

foramen and forms the boundary between the premaxillary sac 

fossa and the rugose area immediately anterior to it, which is 

the area of origin of the nasal plug muscle (prenarial triangle) 

(Fordyce, 1994:153).

The posteromedial sulcus was described in a fossil platanistoid, Waipatia, and is developed variably in delphinids. It is developed in Tursiops.

− premaxillary cleft

The premaxillary cleft lies on the posterodorsal surface of 

the nasal process of the premaxilla. It lies between the premaxillary sac fossa and the posterolateral plate (if present) of the 

premaxilla. The premaxillary cleft lies posteromedial to the posterolateral sulcus (Fordyce, 1994:153).

The premaxillary cleft was described in a fossil platanistoid, 

Waipatia. The premaxillary cleft is not developed in delphinids.

− premaxillary crest

The premaxillary crest is formed by the elevation of the premaxillaries to form a distinct crest on the nasal vertex in ziphiids (Moore, 1968:255). The nasals and maxillae commonly take 

part in the formation of the premaxillary crest.

The premaxillary crest is absent in modern delphinids. 

Cowan’s (1944:300) use of the term “premaxillary crest” was in 

reference to the premaxillary eminence on Phocoenoides dalli.

− premaxillary eminence (Barnes, 1984:19, 1985:151)

The premaxillary eminence or premaxillary boss is an 

abruptly raised elongate structure that makes up most of the 

premaxillary sac fossa in Phocoenidae and the extinct family 

Albireonidae. The medial premaxillary foramen and associated sulci may be involved. Hamilton (1941:232) used the term 

“prenasal protuberance” for premaxillary eminence; de Muizon 

(1983:1205) called it the posterior swelling of the premaxilla 

(renflement postérieur du prémaxillaire).

In Tursiops and most other Odontoceti, the premaxillary 

sac fossa is concave to flat, without a premaxillary eminence. 

However specimens of Grampus show a swelling that could be 

considered a premaxillary eminence.

* premaxillary foramen (Figures 1, 20a)

The premaxillary foramina in odontocetes are part of the 

infraorbital nerve complex. The infraorbital canal begins at the 

ventral infraorbital foramen and ends at the dorsal infraorbital foramen and premaxillary foramen. The premaxillary foramina are 

located on the dorsal surface of the nasal process of the premaxilla

at or near the anterior apex of the premaxillary sac fossa.

* premaxillary sac fossa (Figure 20a,d)

The premaxillary sac fossa is located on the posterodorsal 

surface of the premaxilla (Fordyce, 1981, 1994:149) and is well 

developed in Tursiops. This shallow fossa outlines the anterior 

extent of the premaxillary sac but extends posterodorsally beyond the limits of the premaxillary sac. Owen (1866a:30) referred to this portion of the premaxilla as the “prenarial plate of 

the right maxillary,” when he really meant the right premaxilla. 

Heyning (1989a:5) used spiracular sac for this structure. As we 

note in the discussion concerning structures associated with the 

nares, we prefer not to use the term “spiracular” because it has 

many anatomical meanings.

p r e m a x i l l a n u m b e r 6 2 7 • 8 1
The premaxillary sac fossa is the only bony fossa for any 

part of the epicranial sinuses or nasal diverticula, which otherwise are contained within soft tissues of the odontocete face 

(Mead, 1975; Heyning, 1989a; Cranford et al., 1996). We follow Heyning (1989a:2) in use of the term “epicranial sinuses.”

= premaxillary sulci

See anteromedial sulcus, posterolateral sulcus, and posteromedial sulcus.

= premaxillary tubercle

See tubercle of the premaxilla.

− prenarial basin

The prenarial basin is a feature limited to adult males of 

Ziphius cavirostris (Heyning, 1989b:297). The prenarial basin 

is an excavation on the premaxillae, maxillae, and vomer immediately anterior to the external bony nares. Heyning has found 

that the prenarial basin is filled with the enlarged right nasal 

plug. The prenarial basin has also been called the pre-nasal fossa 

(Turner, 1872) and the prenarial fossa (Owen, 1870).

* prenarial triangle (Figure 20a)

The prenarial triangle in delphinids is situated on the dorsal 

surface of the premaxilla between the posteromedial and anteromedial premaxillary sulci and the medial border of the premaxilla (Perrin et al., 1987). The prenarial triangle has a relatively 

rugose surface, particularly in comparison to the dorsal surface 

of the rostral portion of the premaxilla, which it borders. The 

prenarial triangle serves as the direct bony origin for the nasal 

plug muscle and overlaps both the rostral portion anteriorly and 

the nasal portion posteriorly.

= prenasal protuberance (Hamilton, 1941:232) = premaxillary 

eminence

− prespiracular plate

The prespiracular plate is that part of the external surface 

of the premaxilla immediately anterior to the spiracular plate

(premaxillary sac fossa) in ziphiids (Mitchell, 1968:271).

The prespiracular plate appears to be homologous with the 

most anterior end of the premaxillary sac fossa in delphinids. 

Mitchell (1968:270) defined the prespiracular plate groove, which 

we have homologized with the posteromedial sulcus, as lying on 

the prespiracular plate. There does not seem to be differentiation 

of those two areas on the premaxillary sac fossa in delphinids.

− prespiracular plate flange

The prespiracular plate flange is a “slight, broadly arcuate 

flange (called the prespiracular plate flange herein) proximally, 

with a slight emargination distally (called the prespiracular plate 

notch herein) on the medial margin of the right premaxillary in 

the area of the prespiracular plate.” (Mitchell, 1968:270, fig. 2; 

271).

The prespiracular plate flange appears to be restricted to 

ziphiids and may be restricted to Ziphius.

− prespiracular plate groove = posteromedial sulcus (Mitchell, 

1968:270, 271)

− prespiracular plate notch

See prespiracular plate flange.

− prosthion

The prosthion is the craniometric point at the anterior end 

of the interincisive suture.

The premaxillae do not fuse in an interincisive suture in delphinids. The position of the prosthion can only be estimated in 

delphinids.

* rostral portion of the premaxilla (Schulte, 1917:386) (Figure 

20a,b,d,e)

The rostral portion is the portion of the premaxilla that lies 

anterior to the antorbital notches, that is, that contributes to the 

formation of the rostrum (Schulte, 1917:386).

* rostral surface of the premaxilla (Schulte, 1917:389) (Figure 20a)

The rostral surface of the premaxilla is the external surface 

of the premaxilla on the rostrum. The middle portion of the rostral surface is known as the porcelanous part (q.v.) in cetaceans 

where the surface of that portion is extremely smooth and hard.

= sockets = alveoli (alveoli dentales)

See “Mandible.”

= spiracular plate (Moore, 1963) = premaxillary sac fossa

= spiracular surface of the vertex = nasal process of the premaxilla

− tubercle of the premaxilla (Schulte, 1917:372, 380) = premaxillary tubercle

In Kogia the nasal process of the right premaxilla is expanded posteriorly into a ridge that ends at the vertex and is 

known as the tubercle of the premaxilla (Schulte, 1917:372, 

380). Schulte also referred to this structure as the tuberosity of 

the premaxilla.

Tursiops and other delphinids have not developed a premaxillary tubercle.

= ventral surface of the premaxilla

See palatine surface of the premaxilla.

PTERYGOID BONE

Os Pterygoideum

Figures 3–5, 6b–d, 21, 31a, 32

The pterygoid is a paired bone that forms the back of the 

hard palate (Evans and Christensen, 1979:145). In most mammals that have an extensive soft palate, there is no contact with 

the pterygoid of the opposite side. The pterygoid forms the lateral 

and part of the dorsal walls of the nasal passage. The pterygoid is 

bounded by the basisphenoid, presphenoid, and the palatine.

In humans the pterygoid is recognized, not as a separate 

bone, but as the pterygoid process of the sphenoid (Gray, 

1918:151; Feneis, 1994:121.1–5). The pterygoid may fuse with 

adjacent bones in other mammals (e.g., Novacek, 1986:45), 

8 2 • smithsonian contributions to zoolog y pter y goid
which has resulted in misleading early accounts of homologies 

for the cetacean pterygoid. Ridewood (1922:260) gave a useful 

review of issues.

In odontocetes the pterygoid bridges the floor (namely, anteroventral part) of the choanae and sometimes there contacts its 

contralateral element. The pterygoid also forms the lateral wall of 

the choanae, contacting the vomer dorsally. The other bones that 

the pterygoid contacts are the basioccipital, basisphenoid, palatine, and the presphenoid. See Schulte (1917:373–375, 378–384, 

387–389, 393, 394, 398–401) and Fraser and Purves (1960:8, 10, 

12–14, 16, 18, 22, 33–41, 42, 44–51, 53–55, 57, 58, 60, 61, 63, 

64, 68, 71, 73, 74, 76, 82–89, 100, 101, 132, 136).

To ensure that osteological features are clearly defined, we 

consider details of some soft tissues involving the pterygoid sinus 

system in the broad sense. This approach should resolve some 

inconsistencies in the work of Fraser and Purves (1960), such as 

the interchangeable use of cavity, lobe, sac, and sinus for parts of 

the pterygoid sinus complex. Table 7 illustrates the components 

of the air sinus complex in odontocetes.

− accessory air sinuses (Fraser and Purves, 1960:4, 16)

The accessory air sinus system is unique to cetaceans and 

is an extension of the middle ear cavity. This system has sometimes been referred to as the Eustachian apparatus (Anderson, 

1879:455) or the guttural pouch (Anderson, 1879:452, 453, pl. 

37, fig. 7), Eustachian system (Anderson, 1879:454), Eustachian 

sacs (Fraser and Purves, 1960:7), or pterygoid sinus system (Fraser and Purves, 1960:19, 20, 26, 30, 34, 35, 39, 41, 42, 53, 119). 

Flower (1867:93, 113; see also Gill, 1871:728) referred to the 

pterygoid sinus complex as the postpalatine sinus, a term that 

seems to have been forgotten. The accessory air sinuses cover 

most of the basicranium and, in some species, are adjacent to the 

maxilla, palatine, frontal, lacrimal, pterygoid, alisphenoid, basisphenoid, squamosal, basioccipital, exoccipital, tympanic bulla, 

and periotic. The anterior portion of the system arises from the 

auditory tube near the opening of the tympanic bulla. It consists 

of the pterygoid sinus proper, with the hamular lobe, postorbital lobe, preorbital lobe, and anterior lobe in some species. The 

pterygoid sinus also gives rise to the basisphenoidal sinus in phocoenids. Posteriorly the tympanic cavity gives rise to the middle 

sinus, peribullary sinus, and the posterior sinus. 

− alisphenoidal portions of the external plate (Anderson, 

1879:509)

Alisphenoidal portions of the external plate of the pterygoid are those portions of the lateral plate of the pterygoid 

that, in Platanista, lie external to the alisphenoid (Anderson, 

1879:509).

Tursiops and other delphinids do not develop their lateral 

plate such that it extends over the alisphenoids.

= anterior air sinus system (Fraser and Purves, 1960:62)

In the course of discussion, Fraser and Purves only once 

used the term “anterior air sinus system” (1960:62) for what 

they otherwise identified as the pterygoid sinus. Given this single 

mention, we recommend that the term “anterior air sinus system” not be used. Similarly, Fraser and Purves (1960:12) only 

once used the term “anterior pneumatic cavities,” which we likewise recommend discarding.

= anterior pneumatic cavities (Boenninghaus, 1904; Fraser and 

Purves, 1960:12) = anterior air sinus system

= anterior pterygoid sinus = pterygoid sinus

Luo and Gingerich (1999:28, 38) proposed the term “anterior pterygoid sinus” for part of the pterygoid sinus fossa in 

archaeocete whales. In Tursiops the equivalent structure is probably homologous with part of the pterygoid sinus (sensu stricto).

We recommend that the term “anterior pterygoid sinus” not 

be used because of confusion with the anterior sinus, which is a 

rostral extension of part of the pterygoid sinus complex (Fraser 

and Purves, 1960).

− anterior sac (Beauregard, 1894; Fraser and Purves, 1960:8, 9, 

100)

The term “anterior sac” was used by Beauregard (1894) to 

mean that portion of the pterygoid sinus complex that lay anterior to the falciform process, that is, the anterior lobe, hamular 

lobe, postorbital lobe, preorbital lobe, and the pterygoid sinus

(sensu stricto) (Fraser and Purves, 1960:8). Fraser and Purves 

(1960:8) modified Beauregard’s concept, restricting the term anterior sac “to that part of the system projecting beyond the posterior limit of the rostrum.” This definition of anterior sac conflicts 

with Fraser and Purves’ (1960:62) definition of the same feature 

under the name of anterior sinus (q.v.).

Tursiops and some other delphinids have an anterior sac, 

for which we prefer the term “anterior sinus.”

= anterior sinus

See treatment under “Maxilla.” 

− bony nasopharynx

Fraser and Purves (1960:12) quoted Boenninghaus’ (1904) 

study of Phocoena and stated that the bony nasopharynx is filled 

by the naso-pharyngeal muscle mass that rises into the nose 

through the “false choanae.”

See also nasopharyngeal duct under “Palatine Bone.”

* choanae (Figure 2)

The choanae are posterior openings between the nasal cavity and the nasopharynx (Whitney, 1889–1910:[vol. 2]972; 

Schaller, 1992:14.11, 176.5; Feneis, 1994:136.3), also known as 

the internal bony nares.

The choanae in odontocetes consist of the posterior borders 

of the pterygoids and the vomer.

= choanal fossa = interpterygoid fossa (McDowell, 1958:203)

* dorsal lamina of the pterygoid (Fraser and Purves, 1960:100, 

102) (Figures 21a,c,d, 30)

The dorsal lamina of the pterygoid is that part of the pterygoid bone that forms a dorsal bridge between the lateral and 

medial laminae of the pterygoid.

Fraser and Purves also referred to the dorsal lamina as the 

superior lamina of the pterygoid (1960:35, 38–40, 49–61, 83–

85, 87, 89, 100, 102, 107, 108, 138, pl. 43), superior lamina 

of the pterygoid hamulus (1960:64, 87), and superior lamina of 

the pterygoid plate (1960:85). Schulte (1917:373) called it the 

lateral process of the pterygoid in Kogia.

pter y goid n u m b e r 6 2 7 • 8 3
The dorsal lamina is best understood with reference to cetaceans in which the pterygoid sinuses do not invade the orbit, 

such as the Monodontidae and the Balaenopteridae. There, the 

pterygoid sinus fossa has a distinct bony roof or dorsal lamina. 

The situation is complicated—and homologs often uncertain—in 

delphinids because the pterygoid sinus is expanded dorsally and/

or anteriorly. Fraser and Purves noted (1960:100) that the dorsal 

or superior lamina is vestigial in Tursiops. They labeled the dorsal lamina in various delphinids as the narrow strip of pterygoid 

anteromedial to the path of orbital nerves, sometimes ventral to 

the orbitosphenoid.

− ectopterygoid crest

In some mammal groups the pterygoid includes two components, the ectopterygoid crest and the entopterygoid crest, 

that delimit the ectopterygoid fossa (Novacek, 1986:45). The 

ectopterygoid fossa forms the origin for the internal pterygoid 

muscle (Novacek, 1986).

To consider the situation in Tursiops, it is helpful to review 

other Cetacea. In Neoceti (Mysticeti and some Odontoceti) and 

the basilosaurid Archaeoceti, the pterygoid includes lateral laminae and medial laminae that bound the pterygoid sinus (Fraser 

and Purves, 1960). The presence of a pterygoid sinus bounded 

Table 7. Components of the accessory air sinus complex in odontocetes.

Name of sinus (plus selected 

synonyms) Position and comments Main bony elements

Basisphenoidal sinus In ventral part of skull medial to the alisphenoid, and within 

the basioccipital. Arises as a medial to posteromedial lobe 

of the pterygoid sinus. Occurs in phocoenids only.

Basioccipital, basisphenoid.

Anterior lobe Rostral or antorbital extension of the frontal may form 

pterygoid sinus, anterior to the preorbital lobe. Originates 

from preorbital lobe. An anterior lobe has probably 

evolved convergently in several different groups of 

odontocetes.

Maxilla, palatine; lacrimal and frontal may 

form some of the fossa.

Hamular lobe In hamular fossa, ventral and immediately anterior to the 

bony nares. Originates from pterygoid sinus at about the 

level of the Eustachian notch.

Pterygoid, palatine.

Middle sinus In tympanosquamosal recess of the squamosal. Originates 

as lateral projection from the tympanic cavity via the 

epitympanic hiatus.

Squamosal only.

Peribullary sinus Between basioccipital crest, paroccipital process, tympanic 

bulla, and periotic, extending dorsally around the periotic.

Originates from basioccipital crest, 

paroccipital process, tympanic bulla, and 

periotic.

Posterior sinus 

[= sinus pneumaticus paroccipitalis

= posterior pterygoid sinus]

Posterior to the tympanic bulla, in the space between bulla 

and paroccipital process. Originates from the tympanic 

cavity via the elliptical foramen.

Tympanic bulla and paroccipital process.

Posterolateral lobe of peribullary 

sinus 

[= posterior sinus of some authors]

Between tympanic bulla, periotic, and paroccipital process, 

and possibly squamosal. Originates as a posterolateral 

extension of the peribullary sinus.

Tympanic bulla, periotic and paroccipital 

process; possibly squamosal.

Postorbital lobe In the orbit posterior to postorbital ridge. Originates from 

pterygoid sinus posteroventral to the optic foramen 

but anterior to foramen ovale. There is a postorbital 

diverticulum in Cephalorhynchus.

Frontal, alisphenoid.

Preorbital lobe In orbit around ventral infraorbital foramen, anterior 

to preorbital ridge. Originates from pterygoid sinus 

anteroventral to optic foramen.

Frontal, maxilla; may have some 

contribution from lacrimal and palatine

Pterygoid sinus (in the strict sense) 

[= anterior pterygoid sinus; = 

middle pterygoid sinus]

In ventral part of skull lateral to basioccipital crest and to 

pharyngeal crest (in part, medial lamina of pterygoid). 

Passes back into tympanic cavity. Ultimately originates as 

a diverticulum of Eustachian tube immediately anterior to 

the tympanic bulla.

Pterygoid, alisphenoid, basioccipital

Tympanic cavity In tympanic cavity of tympanic bulla and epitympanic recess 

of periotic.

Tympanic bulla, periotic

8 4 • smithsonian contributions to zoolog y pter y goid
by lateral laminae and medial laminae is a synapomorphy for 

Neoceti and Basilosauridae; more-basal Cetacea lack the sinus 

and bounding laminae. Accordingly, the pterygoid laminae in 

Neoceti and Basilosauridae are probably not homologous with 

the ectopterygoid and entopterygoid crests of some other mammals. Developmental studies would help to resolve matters. 

Thus, in Tursiops and many other Delphinidae, the terms 

“ectopterygoid” and “entopterygoid” are not clearly applicable.

− ectopterygoid fossa

As noted under ectopterygoid crest (q.v.), the ectopterygoid 

crest and entopterygoid crest in mammals delimit the ectopterygoid fossa (Novacek, 1986:45) for the internal pterygoid muscles. In humans (e.g., Gray, 1918:151) the fossa is commonly 

referred to as the pterygoid fossa of the palatine and it may include a significant component from the palatine.

See discussion under pterygoid fossa of the palatine, where 

we outline why the pterygoid sinus fossa of Odontoceti and Mysticeti, and the extinct Archaeoceti, is not homologous with the 

pterygoid fossa of many land mammals. Ridewood (1922:260ff) 

also offered pertinent comment.

Tursiops and other delphinids do not have an ectopterygoid 

fossa in the sense of other mammals. The internal pterygoid muscle originates from the lateral lamina associated with the pterygoid hamulus, the palatine, and adjacent structures (Seagars, 

1982:51).

− entopterygoid crest

In some mammal groups the pterygoid includes two components, the ectopterygoid crest and the entopterygoid crest, that 

delimit the ectopterygoid fossa (Novacek, 1986:45). Details are 

given under ectopterygoid crest.

Wible and Gaudin (2004:127) noted that in armadillos and 

other mammals, the paired entopterygoid crests form the lateral 

walls of the basipharyngeal canal.

There is no evidence at present to suggest that, in Tursiops, 

the medial lamina of the pterygoid (sensu Fraser and Purves, 

1960) is homologous with the entopterygoid in the sense of Novacek (1986).

* Eustachian notch (Figures 21a,c, 30, 32)

The Eustachian notch in Tursiops and other delphinids 

is on the dorsal corner of the free edge of the medial lamina 

of the pterygoid, dorsal to the pterygoid hamulus. The Eustachian notch passes the Eustachian tube (auditory tube). Schulte 

(1917:374, 394) referred to it as the tubal notch in addition to 

the Eustachian notch (Schulte, 1917:394).

= external lamina [of the pterygoid] (Owen, 1866a:28) = lateral 

lamina of the pterygoid

= external plate of the pterygoid (Owen, 1866a:38; Anderson, 

1879:507–509; Schulte, 1917:399) = lateral lamina of 

the pterygoid

= external reduplication of the pterygoid = lateral lamina of the 

pterygoid (Miller, 1923:33)

= false choanae = bony nasopharynx (Fraser and Purves, 1960:12)

− frontal process of the pterygoid (Anderson, 1879:504)

Anderson (1879:504) stated: 

The anterior division of the alisphenoid is applied by 

its front margin to the orbitosphenoid, while by its 

thickened superior rough surface it articulates with the 

inferior thickened rough angle of the parietal; it also 

rests on the external surface of the inferior posterior 

external angle of the parietal, i.e., being external to 

that process with the frontal process of the pterygoid 

external to it and excluding it from appearing in the 

outer wall of the skull, although in the temporal fossa

it is close behind the superior border of the isolated 

portion of the pterygoid, that is wedged in between 

the frontal, parietal and squamosal.

We attempted to discern this structure but were unsuccessful. This feature appears to be unique to Platanista and may not 

have homologues in other cetaceans.

− groove of the pterygoid hamulus (sulcus hamuli pterygoidei)

The groove of the pterygoid hamulus is located at the base 

of the pterygoid hamulus (Schaller, 1992:20.29, 152:16; Feneis, 1994:12.11). It contains the tendon of the m. tensor veli 

palatini.

The nasopharynx of cetaceans is considerably modified from 

terrestrial mammals. A large palatal sphincter holds the larynx 

up into the nasopharynx and effectively isolates the respiratory 

and gustatory functions. Because of this modification the small 

muscles of the pharyngeal area, including the tensor veli palatini

muscle, have probably been lost. However, Boeninghaus (1904) 

(fide Fraser and Purves, 1960:10, 11) mentioned the tensor veli 

palatini muscle in Phocoena and Fraser and Purves mentioned 

it in a number of families (1960:10–12, 19, 22, 26, 29, 31, 76, 

82–84, 132.

* hamular crest [new term] (Figure 2)

The hamular crest lies on the ventral surface of the pterygoid 

and extends from the pterygoid hamulus forward to the anterior 

margin of the pterygoid where it continues as the palatal crest. 

The hamular crest is well developed in adult Tursiops and variable in other delphinids. It is well shown on ventral photographs 

of some delphinids (Fraser and Purves, 1960: pls. 43, 47).

= hamular fossa = pterygoid sinus fossa

The hamular fossa (Fraser and Purves, 1960:22) is the bilateral fossa for the hamular lobe of the pterygoid sinus. The 

hamular fossa is equivalent to the pterygoid sinus fossa (q.v.). 

The term has been used by de Muizon (1991:290) and Fordyce 

et al. (2002).

= hamular process (Schulte, 1917:375, 394, 399; Fraser and 

Purves, 1960:10, 44, 82) = pterygoid hamulus

= hamulus = pterygoid hamulus

= inferior lamina of the pterygoid = ventral lamina of the pterygoid

= inner lamina of the pterygoid = medial lamina of the pterygoid

pter y goid n u m b e r 6 2 7 • 8 5
= inner plate of the pterygoid (Owen, 1866a:28) = medial lamina 

of the pterygoid

= internal plate of the pterygoid = medial lamina of the pterygoid

− internal superior plate of the pterygoid (Anderson, 1879:506)

Anderson (1879:506) referred to the internal superior plate 

of the pterygoid in the following paragraph:

The posterior division of the wing of the orbitosphenoid articulates by its extremity with the frontal anteriorly, and by its outer and under surface (which is 

broadly and deeply grooved for the branches of the 

fifth nerve passing out by the sphenoidal fissure) with 

the outer extremity of the alisphenoid; this is overlapped by the pterygoid and by the under surface of 

the base of the wings with the internal superior plate 

of the pterygoid; the body of the bone being supported 

by the vomer (consult pl. XL, fig. 1, etc.)

Anderson’s plate XL shows two views of disarticulated 

pterygoid bones (figs. 13 and 14). The topography of those 

bones is extremely complicated and not adequately explained by 

the caption. We cannot locate the internal superior plate of the 

pterygoid.

− interpterygoid fossa = choanal fossa

McDowell (1958:125) described the interpterygoid fossa in 

insectivores as the “continuation of the choanal passage between 

the pterygoid laminae posterior to the false palate.” McDowell (1958:203) also used choanal fossa as a synonym. Novacek 

(1986:45) described the fossa in leptictids.

Tursiops and other delphinids have an interpterygoid fossa, 

sensu McDowell, formed by the nasopharyngeal surface, and 

comprising part of the basipharyngeal canal; the fossa continues posteriorly, without interruption, between the basioccipital 

crests. The term apparently has no past use for Tursiops.

See pharyngeal crest [new term] under “Basioccipital Bone” 

and see also “Basipharyngeal Canal” within “Multi-Element 

Complexes.”

= lamina of the pterygoid

The laminae of the pterygoid are the plate-like vertical parts 

of the pterygoid that connect the hamulus to the dorsal lamina 

of the pterygoid or to other dorsal structures such as the lateral 

lamina of the palatine. The medial wall of the medial lamina of 

the pterygoid is the nasopharyngeal surface. Fraser and Purves 

(1960:59) referred to the pterygoid laminae as the hamular 

laminae.

See also medial lamina of the pterygoid, lateral lamina of 

the pterygoid.

* lateral lamina of the pterygoid (Figure 21a–e)

In delphinids the lamina of the pterygoid is split by the 

development of the pterygoid sinus into a lateral lamina and 

a medial lamina (Fraser and Purves, 1960:19, 34, 35, 37–39, 

43–45, 47–52, 54–57, 59, 61–66, 68, 76, 82, 83, 84, 85, 87, 89, 

100, 102). Owen (1866a:37) referred to the lateral lamina as the 

outer or free lamellae, and Anderson (1879:507–509) referred 

to the lateral lamina as the external plate. Miller (1923:33) used 

the term “external reduplication of the pterygoid.” Fraser and 

Purves (1960:60) referred to the lateral laminae as outer laminae and used pterygoid plates (1960:6, 22, 42, 53, 81–85, 87, 

89, 102) to refer to the lateral lamina and medial lamina of the 

pterygoid bone.

medial flange of the pterygoid hamulus

Arnold and Heinsohn (1996:149, fig. 10) noted that in the 

delphinid Orcaella, a medial flange may extend from the pterygoid hamulus medially toward the contralateral element. Tursiops may develop a medial flange that becomes excavated by the 

hamular fossa. The medial flange of the hamulus should not be 

confused with the medial lamina of the pterygoid.

* medial lamina of the pterygoid (Figure 21a–e)

In Tursiops and other delphinids the lamina of the pterygoid

is split by the development of the pterygoid sinus into lateral and 

medial laminae. The medial lamina forms the ventrolateral wall of 

the nasal passage and part of the attachment of the palatal sphincter and carries the Eustachian notch. Owen (1866a:28) referred 

to the medial lamina as the inner plate of the pterygoid and Anderson (1879:508, 509) referred to it as the internal plate. Miller 

(1923:34) used the term “internal reduplication of the pterygoid.” 

See also Fraser and Purves (1960:31, 34, 39, 42, 43, 46, 47, 49–

51, 53, 56, 57, 60, 65, 66, 68–70, 73, 82, 83, 85, 89, 102).

− middle pterygoid sinus = pterygoid sinus

Luo and Gingerich (1999:28, 38, 40) proposed the term 

“middle pterygoid sinus” for part of the pterygoid sinus fossa

anteromedial to the path of the mandibular nerve in archaeocete 

whales. 

In Tursiops the equivalent structure appears homologous 

with part of the pterygoid sinus (sensu stricto). The middle pterygoid sinus is presumed not to be homologous with the basisphenoidal sinus in Phocoena and other Phocoenidae.

We recommend that the name “middle pterygoid sinus” not 

be used for part of the pterygoid sinus (sensu stricto) because 

of confusion with the middle sinus, which is a lateral extension 

from the tympanic cavity via the epitympanic hiatus into the 

tympanosquamosal recess (Fraser and Purves, 1960).

* nasopharyngeal surface of the pterygoid (facies nasopharyngea) (Figure 21a,b,d,e)

In Tursiops the nasopharyngeal surface of the pterygoid is 

the smooth concave medial surface of the bone that forms part 

of the lateral wall of the nasopharynx. 

See also interpterygoid fossa.

− orbital extension of the pterygoid (Fraser and Purves, 1960:45)

Fraser and Purves (1960:45, 49–51, 54, 56, 57, 59, 60) described the orbital extension of the pterygoid bone. An extension 

of the dorsal lamina of the pterygoid ventral to the optic canal

partly covers the contents of the optic canal ventrally. This situation is best seen in some specimens of Pseudorca (Fraser and 

Purves, 1960:50, pl. 29). In that species the dorsolateral wall of 

the hamular lobe of the pterygoid sinus is formed by the lateral 

lamina of the palatine. The orbital extensions of the pterygoid 

emerge onto the orbital region from the dorsal border of the 

lateral lamina of the palatine, as can be seen in Fraser and Purves 

plate 29 and USNM 484982. The orbital extensions of the ptery8 6 • smithsonian contributions to zoolog y pter y goid
goid extend anteriorly (preorbital extension, Fraser and Purves, 

1960:51–53, 56, 58 or pre-orbital part of the pterygoid sinus, 

1960:65) and posterior (postorbital extension Fraser and Purves, 

1960:51, 52) to the optic canal. Some specimens of Pseudorca

(USNM 208360) lack orbital extensions. The orbital extension 

should not be confused with the posterior wing of the lateral 

lamina of the palatine (q.v.) as seen in Orcaella.

− orbital lobes of the pterygoid sinus (Fraser and Purves, 1960:1, 

64, 70)

Fraser and Purves mentioned the orbital lobes in their discussion of the pterygoid sinus in Inia (1960:64) and Tursiops

(1960:70). They mentioned the orbital lobes in addition to the 

preorbital and postorbital lobes such that it is clear they were 

thinking of three separate structures, as can be seen in the following quotation: “The orbital, pre-orbital and post-orbital lobes are 

all well developed, the orbital lobe covering the orbito-sphenoid 

and forming a conspicuous laterally projecting ventral boundary 

to the optic infundibulum. The pre-orbital and post-orbital lobes 

are well extended and the latter spreads dorsally under the postorbital process of the frontal” (Fraser and Purves, 1960:70).

Fraser and Purves did not indicate the presence of orbital 

lobes in their plates of Tursiops (1960: pls. 43, 44), nor in their 

table of abbreviations (1960:137, 138), but they labeled orbital 

lobes in their illustration of Inia (1960:pls. 21, 22). It is clear that 

the structure labeled as orbital lobes in both plates 21 and 22 is 

the preorbital lobe of the pterygoid sinus.

In describing the situation in Globicephala melas, Fraser 

and Purves (1960:72) wrote: “This arrangement is well shown 

in Pl. 34 which figures the pterygoid sinus of Globicephala. The 

orbital portion is fairly prominent, covers the orbito-sphenoid 

and forms the ventral boundary of the optic infundibulum. 

The pre-orbital and post-orbital lobes are well extended laterally and unite above the optic infundibulum to form its dorsal 

boundary.”

Here they are using the orbital portion (orbital lobes) as that 

portion of the pterygoid sinus that covers the orbitosphenoids.

In view of this confusion we recommend using the term “orbital lobes” with care, including a statement of the context of use.

− orbitosphenoidal portions of the external plate of the pterygoid (Anderson 1879:509)

The orbitosphenoidal portions of the external plate of the 

pterygoid are those portions of the lateral plate of the pterygoid 

that lie external to the orbitosphenoid (Anderson, 1879:509).

Delphinids do not develop their lateral plate such that it 

extends over the orbitosphenoids.

− orifice for the inferior maxillary (mandibular) nerve

Anderson (1879:514) described the orifice for the inferior 

maxillary (mandibular) nerve as bounded by the pterygoperiotic 

plate in Platanista. In the specimen of Platanista available to us 

(USNM 172409) the orifice is bounded by the pterygoid not the 

falciform process of the squamosal bone. The exposure of the 

pterygoid is thin and could easily by hidden by the squamosal. 

In USNM 23456 the orifice is bounded by the pterygoid. The 

mandibular nerve normally emerges from the skull via the foramen ovale, but the modifications of the pterygoid and squamosal 

have hidden the foramen ovale in Platanista.

= palatine process of the pterygoid = lateral lamina of the pterygoid

Fraser and Purves (1960:13) paraphrased Boenninghaus 

(1904), who used palatine process of the pterygoid for the lateral 

lamina.

* palatine surface of the pterygoid (facies palatina) (Owen, 

1866a:39) (Figures 2, 21b,c)

The palatine surface is the surface of the palatine bone that 

is exposed on the palate of the skull (Evans and Christensen, 

1979:141, 143; Schaller, 1992:34.20, 36.17; Feneis, 1994:24.29). 

The expansion of the pterygoid in cetaceans (see general discussion under pterygoid bone) has resulted in exposure of the pterygoid on the palate.

The palatine surface of the pterygoid is formed by the ventral 

portion of the medial laminae of the pterygoid in odontocetes. 

Owen (1866a:39) referred to the palatine surface as the palatine 

plate of the inner portion (medial lamina). He also referred to 

the palatine portion of the pterygoid and made reference to plate 

13, figure 2, item 24, which illustrates the lateral lamina of the 

pterygoid. We prefer to think of this discrepancy as just a lapsus 

calami on Owen’s part and have interpreted the text as referring 

to the medial lamina.

* pharyngeal crest [new term under “Basioccipital Bone”] (Figure 2)

The pharyngeal crests in delphinids are the paired crests 

on the ventral surface of the skull that separate the pharyngeal 

region from the auditory region and optic regions. They consist of an anterior extension of the basioccipital crests onto the 

pterygoids. 

See further discussion under “Basioccipital Bone.”

− pharyngeal groove

Novacek (1986:45) described the pharyngeal grooves, or 

pharyngeal sulci (1986:6), as present, carrying nerves and vessels, along the internal base of the endopterygoid in leptictids.

Tursiops does not have recognizable pharyngeal grooves at 

the base (dorsal part) of the medial lamina of the pterygoid.

* posterior lamina (Owen, 1866a:39) (Figure 21a–c)

Owen, in his description of Kogia sima (1866a:39), referred 

to that portion of the pterygoid bone that forms the dorsolateral 

wall of the nasal passage as the posterior lamella. To keep our 

terms parallel, we have treated it as the posterior lamina. Delphinids have a similar conformation.

This structure is termed the medial pterygoid plate (lamina medialis) in humans (Gray, 1918:151; Feneis, 1994:3) and 

the nasopharyngeal surface of the pterygoid bone (facies nasopharyngea) in the dog (Evans and Christensen, 1979:145). 

It does not seem to have been recognized as a separate structure in most domestic animals since it is not found in Schaller 

(1992:20.25–29).

− postpalatine shelf

The postpalatine shelf extends along the inner edge of the 

descending laminae of the pterygoid, and is a feature in sloths 

that was mentioned by Gaudin (2004:267) in a list of cladistic 

characters without further amplification.

pter y goid n u m b e r 6 2 7 • 8 7
Tursiops and other cetaceans do not appear to have a structure that is homologous with the postpalatine shelf.

− pterygoid canal (canalis pterygoideus)

The pterygoid canal lies in the suture between the pterygoid 

and the pterygoid process of the sphenoid. It contains the autonomic nerve of the pterygoid canal (Gray, 1918:181; Evans and 

Christensen, 1979:145; Schaller, 1992:20.8; Feneis, 1994:12.12). 

Vesalius (1543:52; Vesalius et al., 1998:131) referred to the pterygoid canal (Vidian canal) as the aliud foramen inchoatur, recta 

antrorsum ion narium usque amplitudinem, meatus olongi modo 

protensum, and arteriae ramo viam exhibens, qui a soporalis arteriae surculis pulsum edens sensibilem.

Although we have not been able to visualize this canal in 

delphinids because the basisphenoid is not visible on the ventral 

portion of the skull, there is no reason to assume that the canal 

is not present in odontocetes in general.

− pterygoid crest

Andrews (1911:36, unnumbered tbl.) and Cowan (1944: 

tbl. 2), in accounts of Dall’s porpoise (Phocoenoides dalli), used 

the term “pterygoid crest” in a way that suggests they were referring to the pterygoid hamulus. Pterygoid crest should not be used 

for cetaceans in this context.

Pterygoid crest has been used for features of the insectivore 

basicranium (McDowell, 1958:169) and the mandible in Mesozoic mammals (e.g., Wible and Rougier, 2000:62).

Tursiops and other delphinids lack a pterygoid crest in these 

senses.

− pterygoid fossa (fossa pterygoidea) 

Pterygoid fossa, in the sense of McDowell (1958:128, a 

fossa for the origin of the pterygoid muscles on the skull base) 

and in the sense of Luo and Wible (2005, a fossa for insertion of 

pterygoid muscle on the mandible), should not be confused with 

the fossa for the pterygoid sinus. See further discussion under 

ectopterygoid fossa and ectopterygoid crest, above, and under 

pterygoid fossa of the palatine.

Tursiops and other delphinids do not have a pterygoid fossa 

in the sense of other mammals. For cetaceans, “pterygoid fossa” 

is an acceptable contraction for “pterygoid sinus fossa”; the term 

has had wide use in this context.

See also “Palatine Bone” and “Sphenoid Bone.” 

− pterygoid groove (sulcus n. canalis pterygoidei)

The pterygoid groove is a minute groove leading to the 

caudal opening of the pterygoid canal (Evans and Christensen, 

1979:154; Schaller, 1992:20.9).

In delphinids the ventral surface of the basisphenoid is covered by the vomer, and the pterygoid canal continues posteriorly. 

The pterygoid groove is absent.

* pterygoid hamulus (hamulus pterygoideus) (Figures 2, 21b–e)

The pterygoid hamulus is the posteroventral angle of the 

pterygoid that is hook-shaped in most mammals (Fraser and 

Purves, 1960:4, 19, 22, 35, 37–40, 43, 45–62, 64–66, 68–71, 

73, 82–85, 87, 89, 100, 102, 107). McDowell (1958:125, hamular process) described it as a hook-like process of the internal 

pterygoid lamina. The tendon of the m. tensor veli palatini

wraps around this hook. Fraser and Purves also referred to the 

pterygoid hamulus as the hamular part (1960:41, 54), hamular portion (1960:20,89), hamular process (1960:10, 44, 82), or 

hamular region (1960:42, 51, 59).

The pterygoid hamulus is well developed in Tursiops and 

other delphinids (Fraser and Purves, 1960:41, 42, 46, 48, 52–

60, 68, 73, 82–84, 89, 100, 102), albeit commonly modified 

through being expanded toward the midline and excavated by 

the hamular sinus. Each hamulus may develop a dorsoventrally 

flattened medial flange. Because of major changes in shape and 

proportion with development of the hamular sinus, the pterygoid hamulus in delphinids has become recognized more or less 

as that part of the pterygoid ventral to the level of the Eustachian notch. The primitive (relatively unmodified) state of the 

hamulus in odontocetes and mysticetes is probably represented 

by the structure in some balaenopterids (e.g., Balaenoptera acutorostrata) and certain fossil odontocetes (e.g., Simocetus rayi

of Fordyce, 2002).

= pterygoid lamina = entopterygoid

The pterygoid lamina in insectivores is the “downwardly 

projecting plate of bone from the sphenoid continuous anteriorly 

with the vertical lamina of the palatine” (McDowell, 1958:128). 

McDowell indicated (1958:127) that “internal pterygoid lamina” and “pterygoid lamina” are the same.

− pterygoid notch (incisura pterygoidea)

The pterygoid notch lies between the lateral and medial pterygoid plates in humans. It is occupied by the pyramidal process 

of the palatine (Feneis, 1994:12.4). It is also called the pterygoid 

fissure (Gray, 1918:151). In some artiodactyls it occurs between 

the pterygoid bone and the pterygoid process of the basisphenoid

(alisphenoid) (Schaller, 1992:20.26; not in Gray, 1918; Sisson, 

1910; Evans and Christensen, 1979). 

The cetacean pterygoid has been modified by the development of the pterygoid sinus fossa and the splitting of the pterygoid into the medial and lateral laminae. This has altered the 

relationship of the pterygoid and it no longer forms the pterygoid notch.

Fraser and Purves (1960:41, 43, 72) used “pterygoid notch” 

for the notch in the pterygoid through which the Eustachian tube

enters the nasopharynx (see Eustachian notch of the pterygoid).

See also ectopterygoid fossa.

− pterygoid plexus (Fraser and Purves, 1960:120)

The pterygoid plexus is the fibro-venous plexus that surrounds the accessory air sinuses (pterygoid sinus system). Fraser 

and Purves (1960:120) proposed that the pterygoid plexus acts 

to compensate for the decrease in volume of the accessory air 

sinuses caused by changes in pressure with diving.

− pterygoid ridge

The pterygoid ridge is an oblique ridge beginning at or near 

the posteromedial margin of the pterygoid and extending anterolaterally for nearly the entire length of the pterygoid in Mesoplodon europaeus, but not in M. mirus (Moore, 1960:18).

There is no pterygoid ridge in Tursiops.

8 8 • smithsonian contributions to zoolog y pter y goid
* pterygoid sinus (Figures 3, 29, 30)

The pterygoid sinus is a large air-filled diverticulum between 

the lateral lamina and medial lamina of the pterygoid and, in 

some cases, the palatine bones (Hanke, 1914; Fraser and Purves, 

1960:8, 14, 68). The sinus is unique to cetaceans and is an extension of the middle ear cavity. The relationship of the pterygoid 

sinus to the guttural pouches of the horse has yet to be elucidated. 

The guttural pouches arise from the Eustachian tube (auditory 

tube) and lie ventral to the skull (Sisson, 1910:756). The pterygoid sinus arises from the auditory tube near the opening of the 

tympanic bulla. The sinus then runs anteriorly along the dorsal 

aspect of the pterygoid bone to enter the space between the lateral lamina of the pterygoid and medial lamina of the pterygoid 

(pterygoid sinus fossa). In many odontocetes, but not in mysticetes, the sinus extends dorsally onto the frontal and sphenoid. The 

pterygoid sinus develops preorbital and postorbital lobes (q.v.). In 

Grampus and Tursiops two posteriorly projecting extensions of 

the sphenoidal portion of the pterygoid sinus surround the foramen ovale (Fraser and Purves, 1960:100). Fraser and Purves also 

referred to the pterygoid sinus as the hamular cavity (1960:57, 

59), hamular element (1960:89), hamular fossa (1960:22), hamular lobe (1960:64; but note the different sense of use by Fordyce 

et al., 2002), and hamular space (Fraser and Purves, 1960:22).

The entire complex of accessory air sinuses (q.v.) is sometimes referred to as the pterygoid sinus or the pterygoid sinus 

system. See Fraser and Purves (1960:1, 18, 22, 26, 30, 35, 37, 

62–74, 76, 81, 85, 86, 88, 101, 102, 120, 133, 140).

More study is needed to resolve the exact relationships of the lobes of the pterygoid sinus complex around the 

tympanoperiotic.

* pterygoid sinus fossa (Figures 18b–c,e, 21c–d)

The pterygoid sinus fossa is the space occupied by the 

pterygoid sinus in the pterygoid and sometimes adjacent bones, 

including the palatine, maxilla, and frontal. It is the cavity between the medial lamina and lateral lamina of the pterygoid. 

Fraser and Purves referred to this feature as the inter-laminar 

space (1960:40, 44, 45, 48, 50, 57) or the inter-laminar air space 

(1960:76).

In Tursiops, as discussed elsewhere under the pterygoid 

bone, the pterygoid sinus is elaborated to produce distinct hamular, postorbital, preorbital, and anterior sinuses (or lobes, or 

sacs, in the terminology of Fraser and Purves). These changes 

have greatly modified the primitive state of the pterygoid sinus 

fossa as seen in the simple subspherical fossa of basal odontocetes and mysticetes and of basilosaurid archaeocetes.

− pterygopalatine ridge

The pterygopalatine ridge in the fossil mammal Kryptobaatar delimits a lateral and medial pterygopalatine trough or fossa 

(Wible and Rougier, 2000:30, 83, 84). The pterygopalatine ridge 

is apparently not homologous with the mammalian pterygoid 

lamina or entopterygoid.

Tursiops and other Cetacea lack a pterygopalatine ridge.

− pterygopalatine trough

In the fossil mammal Kryptobaatar the pterygopalatine 

ridge of the pterygoid delimits a lateral and a medial pterygopalatine trough or fossa (Wible and Rougier, 2000:30, 83, 84). 

The former is perhaps unrelated to the Eustachian tube, and the 

pterygopalatine ridge is apparently not homologous with the 

mammalian pterygoid hamulus.

Tursiops and other delphinids lack a lateral and medial 

pterygopalatine trough.

= tubal notch (Schulte, 1917:374, 394) = Eustachian notch

− tympanic process of the pterygoid (Wible and Gaudin, 

2004:127)

Wible and Gaudin (2004:127) noted that in the yellow 

armadillo the tympanic process of the pterygoid is the feature 

that extends dorsolaterally from the posterodorsal corner of the 

pterygoid toward the ear region to contact the auditory bulla.

Tursiops and other Odontoceti lack a tympanic process of 

the pterygoid.

− ventral lamina of the pterygoid = inferior lamina (Fraser and 

Purves, 1960:37, 46, 138)

Fraser and Purves (1960:37, 46, 138) mentioned the ventral lamina as the inferior lamina but did not define it or give 

references to other anatomical works where it is defined. Fraser 

and Purves mentioned it in their discussion of the pterygoid of 

Caperea (1960:37) and Inia (1960:46; “fenestrated vestiges of 

the inferior lamina”) and illustrated the feature in plates 5 and 6 

(Caperea) and plate 21 (Inia).

We interpret the ventral lamina of the pterygoid as the portion of the bone that forms a ventral floor to the fossa between 

the medial and lateral laminae of the pterygoid. The ventral lamina is clear in balaenopterids such as Balaenoptera acutorostrata; 

there, the ventral lamina is a distinct area of bone that forms a 

floor to the pterygoid sinus fossa, lateral to the well-differentiated pterygoid hamulus, and ventrolateral to the Eustachian 

notch.

In Tursiops and other delphinids the pterygoid (including 

the hamulus) is heavily excavated by the pterygoid sinus fossa, 

with bone thinned or lost. Further, the pterygoid sinus fossa is 

laterally narrow, with the only major ventral surface being that 

of the excavated hamulus. It is debatable whether the ventral 

surface of the hamulus is homologous with the ventral lamina as 

seen in Balaenoptera acutorostrata; otherwise, Tursiops lacks a 

ventral lamina. The “fenestrated vestiges of the inferior lamina” 

in Inia (see Fraser and Purves, 1960:46, pl. 21) do not clearly 

represent the ventral lamina.

We have examined the USNM specimen of Caperea

(550146) and compared it to Fraser and Purves (1960: pls. 5, 

6). The bone labeled “inferior lamina” in plate 5 is clearly part 

of the squamosal in USNM 550146. Another specimen of Caperea (Otago Museum A81.2) has a prominent sulcus on the left 

squamosal where Fraser and Purves (pl. 5) indicated a suture. 

We think that they were working with an abnormal specimen. 

We feel that the ventral lamina in Caperea is the small thick 

shelf of the pterygoid that is immediately dorsal to the squamosal and exterior to the Eustachian notch. The notch is actually 

a groove prolonged anteromedially, associated with an indistinct hamulus at the medial end; the hamulus floors the choanae

rather than flooring the pterygoid sinus fossa. Fraser and Purves 

pter y goid n u m b e r 6 2 7 • 8 9
differentiated the ventral lamina and the pterygoid hamulus in 

their figures of Caperea (1960: pl. 6) and Inia (1960: pl. 21). We 

agree with their interpretation of Caperea but, as above, question the interpretation of Inia.

= ventral process = pterygoid hamulus

= Vidian canal = pterygoid canal

SEPTOMAXILLA

Os Septomaxilla

The septomaxilla (Parker, 1871) is an ossification that occurs in monotremes and edentates posterior to the nasal aperture 

and extends inward as a plate overlying the vomeronasal organ. 

It has also been termed the intranasal (Ecker et al., 1904) and the 

intranarial (Wegner, 1922).

Cetaceans do not have a septomaxilla.

SPHENOID BONE

Os Sphenoidale

Figures 6b,f, 8, 22, 28–32

The sphenoid bones form the middle part of the floor of 

the cranium (Schaller, 1992:18.9, 17, 20.12; Evans and Christensen, 1979:126–129; Feneis, 1994:10.1; Gray, 1918:147). 

Vesalius (1543:21–23, 25) referred to the sphenoid as the cuneiform os, the os cuneo (ibid., 21, 23, 25), and the os cuneiforme (ibid., 22, 23). Eustachius and Lancisius (1714:104, 

112) referred to the sphenoid as cuneiformia ossa, but they 

also referred to it as the osse sphaenoide or the sphaenoides os

(ibid., 112).

The sphenoid bones consist of a midline pair of bones and 

two lateral pairs of bones (Flower, 1885: fig. 47, 126, 127). The 

anterior midline ossification is termed the presphenoid and articulates anteriorly with the mesethmoid. The presphenoid articulates laterally with the first of the paired sphenoid ossifications, 

the orbitosphenoids. The presphenoid also articulates posteriorly 

with the basisphenoid, which in turn articulates with the basioccipital. The basisphenoid articulates laterally with the second 

pair of sphenoid ossifications, the alisphenoids or greater wings 

of the sphenoid. Because they form the base of the cranium, the 

sphenoid bones form the exits for cranial nerves II–VI (the optic, 

oculomotor, trochlear, trigeminal [ophthalmic, maxillary, mandibular], and the abducens nerves).

The base of the skull has been modified in cetaceans, principally in the posterior area where the tympanic and periotic parts 

of the temporal bone have been isolated from the rest of the skull. 

This, plus the elaboration of the air and vascular sinus systems 

(pterygoid, peribullary, etc.) has resulted in changes in detailed 

relationships of the sphenoid bones. The four elements of the 

sphenoid complex (basisphenoid, presphenoid, orbitosphenoid, 

alisphenoid) are still present.

= ala orbitalis = orbitosphenoid (Schulte, 1917:354, 394, under 

orbitosphenoid)

See “Ethmoid Bone.”

= ala parva = orbitosphenoid

= alar canal (canalis alaris) = alisphenoid canal

The alar canal runs through the anteromedial part of the 

alisphenoid. The anterior opening of the alar canal is known as 

the rostral alar foramen and the posterior opening as the caudal alar foramen (Evans and Christensen, 1979:128; Schaller, 

1992:20.2). The alar canal perforates the pterygoid process for 

passage of the maxillary artery in the dog and horse (Schaller, 

1992:20.2). The alar canal communicates with the foramen rotundum and transmits the maxillary branch of the trigeminal 

nerve (maxillary nerve), which exits via the rostral alar foramen 

(Evans and Christensen, 1979:914).

The alar canals are not developed in Cetacea.

= ala temporalis = alisphenoid (Evans and Christensen, 1979:128)

− alicochlear process (processus alicochlearis) (Kernan, 1916:623)

Schulte (1917:374) referred to a process in the sphenoid of 

Kogia that he thought was “probably the processus ali-cochlearis.” This structure was on the ventral part of the alisphenoid

close to the tympanoperiotic, on the margin of the posterior lacerate foramen (1917:379) and included that part of the alisphenoid or basisphenoid that carries the narrow groove leading to 

the carotid foramen of the sphenoid and the groove leading from 

the foramen ovale.

Kernan (1916:623, pl. 1, 3–6), in describing a 20 mm human 

embryo, used “processus ali-cochlearis” to mean a lateral part of 

the temporal wing of the sphenoid that continues posteriorly to 

contact the cochlea.

In mature Tursiops the region between the carotid foramen 

and foramen ovale is formed apparently by contributions of alisphenoid and basisphenoid. A discrete alicochlear process is not 

apparent.

* alisphenoid (temporal wing, greater wing) (ala temporale) (Figures 6b, 22a,b,d, 28, 29, 31b, 32)

The alisphenoids lie lateral to the basisphenoid (body of 

the sphenoid). They contain the foramen ovale, foramen rotundum, and foramen spinosum. The alisphenoids are also known 

as the ala temporalis (Owen, 1866a:26; Flower, 1885:120, 

211; Schulte, 1917:379, 392, 393; Ridewood, 1922; Fraser and 

Purves, 1960:35, 46, 47, 49, 51–53, 57, 59; Evans and Christensen, 1979:45, 128).

The alisphenoid is sometimes termed the pterygoid process 

of the basisphenoid (e.g., Schaller, 1992:20.1), or the auditory 

plates of the basisphenoid (Anderson, 1879:508), but we here 

follow literature on cetacean anatomy and mammalian phylogenetic anatomy in preferring use of “alisphenoid.”

The alisphenoid of Tursiops is a well-defined shelf of bone 

that is present lateral to the basisphenoid. The alisphenoid and 

basisphenoid centers of ossification are fused at birth in Tursiops. Owen (1853:447) referred to the alisphenoids as the great 

alae. Fraser and Purves (1960:87) referred to the alisphenoids 

9 0 • smithsonian contributions to zoolog y septomaxilla
in Monodon as the alar process (not to be confused with the 

alar process of the vomer) or the lateral wing of the sphenoid 

(1960:61).

− alisphenoidal infundibulum (Fraser and Purves, 1960:100)

Fraser and Purves (1960:100) mentioned the alisphenoidal 

infundibulum in this sense: “The osseous lateral lamina of the 

pterygoid is wanting, as in L. acutus, and the alisphenoidal infundibulum of the 5th nerve is much shorter than in either of the 

previous species (text-fig. 20e’).”

We presume that Fraser and Purves refer to the conical hollow formed in the alisphenoid by the passage of the mandibular 

branch of the trigeminal nerve and that it is the same feature 

referred to as the bony infundibulum of the foramen ovale

(1960:30, 35–40, 46, 53, 61, 87, 100, 102). Fraser and Purves 

also referred to a bony tube (1960:44, 45, 47–60, 85, 87, 89) 

or a bony channel (1960:89), which we have equated with the 

alisphenoidal infundibulum.

Fraser and Purves (1960) seemed to correlate the alisphenoidal infundibulum, falciform process, and the inter-laminar 

space. They stated (1960:34): “The splitting of the pterygoid, 

and sometimes of the alisphenoid and squamosal also, into lateral and mesial laminae, connected to a greater or lesser extent 

by superior and inferior laminae.”

We paraphrase that by saying that there existed a time when 

the pterygoid, alisphenoid, and squamosal had been split into lateral and medial laminae with the formation of an inter-laminar 

space. The mandibular branch of the trigeminal nerve traversed 

the inter-laminar space by sheathing itself in the alisphenoidal infundibulum. The falciform process is a remnant of this situation, 

being the residue of the lateral lamina of the squamosal bone.

− alisphenoidal region (Fraser and Purves, 1960:102)

The alisphenoidal region is that portion of the basicranium 

that lies ventral to the alisphenoid bone.

− alisphenoid canal (Flower, 1885:141)

The alisphenoid canal or alar canal in the dog (Evans and 

Christensen, 1979:128, 154) and other carnivores is a short horizontal canal that runs anteroposteriorly through the anteromedial part of the alisphenoid (canalis alaris of the pterygoid process 

of the sphenoid sensu Schaller, 1992:20.2, in dog and horse) on 

the ventral surface of the skull. The anterior opening of the alar 

canal is also known as the rostral alar foramen, and the posterior 

opening near the foramen ovale is the caudal alar foramen. The 

foramen rotundum opens into the dorsal part of the alisphenoid 

canal, and transmits the maxillary branch of the trigeminal nerve 

(maxillary nerve) into the canal; the maxillary nerve exits via 

the rostral alar foramen (Evans and Christensen, 1979:914). The 

canal also transmits the maxillary artery in the dog and horse 

(Schaller, 1992:20.2). Wible and Gaudin (2004:154) noted that 

the exit for the maxillary nerve may be separate from the alisphenoid canal, in which case the exit for the maxillary nerve 

is termed the foramen rotundum. The maxillary nerve may also 

exit via the sphenorbital fissure (q.v.). Wible (1987) discussed 

further details of the alisphenoid canal in Cetacea.

The external carotid artery does not penetrate the skull in 

Cetacea, and (Wible, 1987:130) there is no alisphenoid canal.

− alisphenoid portion of the lateral lamina (Fraser and Purves, 

1960:48)

Fraser and Purves (1960:48) referred to the lateral lamina in 

this sense as a structure composed of the lateral laminae of the 

palatine, of the pterygoid, and of the alisphenoid in monodontids (see their plate 13).

= anterior carotid foramen (MacPhee, 1981:46) = internal carotid foramen

− anterior lacerate foramen (foramen lacerum anterius) 

In the horse the anterior lacerate foramen is the large opening anterior and medial to the periotic bone (petrosal). It includes the following in its anterior border (Sisson and Grossman, 

1953:72, fig. 49): foramen spinosum, for passage of the middle 

meningeal artery; foramen ovale, for passage of the mandibular 

branch of trigeminal nerve; and internal carotid foramen (foramen lacerum medium), for passage of the internal carotid artery 

into the cranial cavity (McFarland et al., 1979:7).

In Tursiops the anterior lacerate foramen is confluent with 

the cranial hiatus and does not exist as a separate entity.

= auditory plates of the basisphenoid (Anderson, 1879:508) = 

alisphenoid

See alisphenoid.

* base of the alisphenoid (Owen, 1866a:28; pl. 9: fig. 3(6)) (Figure 22a)

Owen referred to the midportion of the alisphenoid as the 

base of the alisphenoid.

= basioccipitosphenoid (Owen, 1866a:39)

Owen (1866a:39; pl. 13: fig. 2(5)), in his description of the 

holotype of Kogia sima, referred to the fused basioccipital and 

basisphenoid as the basioccipito-sphenoid.

* basisphenoid (os basisphenoidale) (Figures 6b, 22a,b,d, 31a)

The basisphenoid lies posterior to the presphenoid and 

anterior to the basioccipital in the floor of the cranium. In humans the basisphenoid is referred to as the corpus (not corpus 

sphenoidale) (Feneis, 1994:10.2). MacPhee (1981:49) summarized the ontogeny of the basisphenoid and its fusion with the 

alisphenoid.

The basisphenoid is connected with the orbitosphenoids

anteriorly and the alisphenoids laterally (Schulte, 1917:374, 

379, 383, 384, 386, 394; McFarland et al., 1979:8; Schaller, 

1992:18.9).

− basisphenoidal sinus [new term]

Fraser and Purves (1960:49, 65, 92, 107) noted that, in 

Phocoena, the main part of the pterygoid sinus gives rise to a 

medially and posteriorly directed diverticulum in the basisphenoid. They referred to it as the “sphenoidal part of the sinus,” 

(1960:107) and otherwise did not name it.

The term “basisphenoidal sinus” is used here for that lobe 

of the pterygoid sinus. Sphenoidal sinus has already been used 

for one of the paranasal sinuses.

Tursiops lacks a basisphenoidal sinus.

s p h e n o i d n u m b e r 6 2 7 • 9 1
* basisphenoid–presphenoid fissure (Schulte, 1917:375, 386) 

(Figure 28)

The basisphenoid–presphenoid fissure is the space between 

the basisphenoid and the presphenoid that is occupied by the intersphenoidal synchondrosis. Schulte (1917:373, 378–380, 384, 

392, 394, 400) also referred to this as the sphenoid fissure or 

basisphenoid–presphenoid cleft.

Not mentioned in Sisson, 1910; Gray, 1918; Evans and 

Christensen, 1979; Schaller, 1992; or Feneis, 1994.

= body of the sphenoid = basisphenoid

− caroticotympanic canals (canaliculi caroticotympanici)

The caroticotympanic canals are small canals in the wall of 

the carotid canal of the sphenoid for arterial branches and neural 

branches of the internal carotid artery and internal carotid plexus. 

The caroticotympanic canals connect the carotid canal and the 

tympanic cavity (Schaller, 1992:24.11; Feneis, 1994:12.27).

We are unable to demonstrate the existence of the caroticotympanic canals in cetaceans.

* carotid canal of the sphenoid (Figures 22a, 28)

The carotid canal transmits the internal carotid artery to 

the cranial cavity. In the dog the carotid canal begins at the caudal carotid foramen of the sphenoid bone in the medial wall of 

the osseous bulla. The carotid canal terminates at the internal 

carotid foramen (Gray, 1918:143, 181; Evans and Christensen, 

1979:134, 156, 661, 676; McFarland et al., 1979; Schaller, 

1992:24.10; Feneis, 1994:12.26). Vesalius (1543:52; Vesalius et 

al., 1998:131) referred to the carotid canal as the insigne foramen maiori soporalis arteriae ramo calvaria ingredienti excavuatum. Eustachius and Lancisius (1714:105) referred to the 

ventral opening of the carotid canal as the foramen, per quod 

transit arteria carotis.

In Tursiops the external (ventral) opening of the carotid 

canal is formed by the anterodorsal portion of the basioccipital 

and the posteroventral portion of the basisphenoid. The carotid 

canal courses through the basioccipital to issue in anteriorly directed openings in the cranial surface of the basisphenoid. In the 

adult Tursiops the cranial openings of the carotid canal are immediately lateral to the sella turcica (McFarland et al., 1979: 

fig. 55). Owen, in his discussion of the cetacean skull in general 

(1866b–1868(vol. 2):420), said that “the basisphenoid . . . is 

perforated or grooved by the entocarotids.”

− carotid foramen of the sphenoid

The nomenclature associated with the extracranial course of 

the mammalian carotid artery (involving one or more foramina, 

canal, and sulci) is complicated and often confusing, as noted by 

Wible and Gaudin (2004:149). In contrast, the names applied 

to Cetacea seem reasonably straightforward and accordingly we 

discuss the cetacean situation first.

In Tursiops, as in other Cetacea, an osteological feature cited 

widely as the carotid foramen (here, ventral carotid foramen) 

opens medial to the pterygoid sinus fossa and tympanoperiotic, 

and transmits the usually vestigial internal carotid artery into the 

cranial cavity via the internal carotid canal of the sphenoid. No 

other bony pathway for a carotid vessel has been identified with 

any confidence in Cetacea.

In Tursiops the ventral carotid foramen is the ventral or external opening of the internal carotid canal, which is formed in 

the posteroventral portion of the basisphenoid.

The internal carotid canal courses through the basisphenoid 

to issue in an anteriorly directed dorsal carotid foramen in the 

cranial surface of the basisphenoid. The name “carotid canal” is 

not used for the cetacean structure because of possible confusion 

with the nonhomologous carotid canal of the dog and other carnivores, which is a structure associated with the medial margin 

of the tympanic bulla.

In the adult Tursiops the cranial openings of the internal 

carotid canal are immediately lateral to the sella turcica (McFarland et al., 1979: fig. 55). Owen (1866b–1868(vol. 2):420) 

said, in his discussion of the cetacean skull in general, that “the 

basisphenoid . . . is perforated or grooved by the entocarotids.”

In spite of the persistent carotid foramina and internal carotid canal, it appears that, at the level of the carotid foramina, 

the internal carotid artery is generally nonpatent in adult cetaceans; it is functional in fetal specimens but the lumen closes 

ontogenetically (McFarland et al., 1979:20). Kernan (1918:357) 

stated that the internal (here, dorsal) carotid foramen is more 

apparent in young Ziphius specimens. Mead (pers. obs.) has dissected the contents of the dorsal carotid foramen in specimens of 

Grampus (USNM 572267) and Mesoplodon europaeus (USNM 

571848) and found it to be traversed by a plexus of blood vessels. Walmsley (1938:141) summarized carotid circulation in 

some odontocetes and mysticetes. See McFarland et al. (1979) 

for a detailed discussion of cetacean endocranial circulation.

The situation may be more complicated in other Cetacea 

because in the archaeocete whale Dorudon atrox there appear 

to be no separate internal carotid canal or associated foramina 

(Uhen, 2004).

Wible and Gaudin (2004:149), in discussing carotid circulation, gave a useful interpretation of the account of Evans 

(1993), noting that the latter used two terms for the foramen in 

the braincase, internal carotid foramen, and foramen lacerum. 

Wible and Gaudin (2004:149) also noted that Evans (1993) used 

internal carotid foramen in two senses: for the foramen in the 

braincase and also for the rostral opening of the carotid canal as 

seen in carnivores.

− carotid notch (incisura carotica)

In some mammals the carotid notch occurs in the posterior 

margin of the alisphenoid and forms, with the squamosal, the foramen lacerum [jugular foramen] (Evans and Christensen, 1979:129, 

S18.25). The carotid notch transmits the internal carotid artery 

(Evans and Christensen, 1979: S18.25). The carotid notch is also 

known as the medial notch (Evans and Christensen, 1979:129).

In Tursiops the carotid notch is more medially located with 

respect to the alisphenoid, and the carotid canal of the sphenoid

transmits the internal carotid artery.

− carotid sulcus (sulcus caroticus)

The carotid sulcus lies on the cerebral surface of the basisphenoid posterior to the caudal clinoid process. The carotid sulcus contains the internal carotid artery (Evans and Christensen, 

1979:127). The carotid sulcus, in the sense of an endocranial 

structure in noncetacean mammals, lies on the cerebral surface 

of the basisphenoid posterior to the caudal clinoid process. The 

9 2 • smithsonian contributions to zoolog y s p h e n o i d
carotid sulcus contains the internal carotid artery (Evans and 

Christensen, 1979:127). In some armadillos (Wible and Gaudin, 

2004) a carotid sulcus is developed more externally in the basicranium, medial to the tympanic bulla and visible to ventral 

view. The carotid sulcus is also known as the carotid groove 

(McFarland et al., 1979:8). Vesalius (1543:51; Vesalius et al., 

1998:131) referred to the carotid groove as the ductus ucro and 

sinus non adeo commode.

A carotid sulcus is not developed in Tursiops or other delphinids either within the braincase (due to the lack of a cerebral portion of the internal carotid artery) or without, in the 

basicranium.

− caudal alar foramen (foramen alare caudale)

The caudal alar foramen is the posterior opening of the alar 

canal (Evans and Christensen, 1979:128; Schaller, 1992:20.4). The 

alar canal transmits the maxillary artery (Schaller, 1992:20.2).

Alar canals are not developed in delphinids.

− caudal carotid foramen of the sphenoid bone (foramen caroticum caudalis)

In the dog the carotid canal of the sphenoid begins at 

the caudal carotid foramen in the medial wall of the osseous 

bulla (Evans and Christensen, 1979:134, 156, 661, 676; not in 

Schaller, 1992). The caudal carotid foramen is also known as the 

posterior carotid foramen (MacPhee, 1981:59, 60).

The nomenclature associated with the bony path of the carotid foramen in mammals is complex. See discussion under carotid foramen of the sphenoid. 

In Tursiops we recognize the ventral carotid foramen, a synonym of the caudal carotid foramen. The ventral carotid foramen 

lies on the ventral surface of the basisphenoid just posteromedial 

to the oval foramen.

− caudal clinoid process (processus clinoideus caudalis)

The caudal clinoid process projects anteriorly from the dorsum sellae. Also known as the posterior clinoid process or the 

middle clinoid process (McFarland et al., 1979:10).

The caudal clinoid process in Tursiops and other delphinids 

is not developed.

* cerebral hollow (Anderson, 1879:504) (Figure 22a)

Anderson (1879:504) referred to the smooth dorsal surface 

of the alisphenoid in Platanista that houses part of the ventral 

surface of the brain as the cerebral hollow.

* cerebral surface of the sphenoid (facies cerebralis) (Figure 22d)

The cerebral surface of the sphenoid is the surface that is 

part of the cranial cavity (Schaller, 1992:18.18, 24.34).

* chiasmatic groove (sulcus chiasmaticus) (Figures 22a, 28, 31b)

The chiasmatic groove lies on the cerebral surface of the 

basisphenoid between the anterior edge of the basisphenoid 

and the tuberculum sellae (Schaller, 1992:15; Evans and Christensen, 1979:128, 155). The chiasmatic groove is continuous 

laterally with the optic foramen, through which the optic nerve 

is transmitted to the orbit. The chiasmatic groove contains the 

optic chiasma (Gray, 1918:147). Feneis (1994:10.4) referred to 

the sulcus chiasmaticus as the sulcus prechiasmaticus and Gray 

(1918:147) referred to it as the chiasmatic groove or the optic 

groove. Vesalius (1543:50; Vesalius et al., 1998:131) referred 

to the sulcus chiasmatis as the huic sinui cuneiformi ossi inciso, 

visoriorum nervorum coitus innititur.

The chiasmatic groove is faintly developed in Tursiops and 

has come to lie on the anterior portion of the basisphenoid.

= clinoid process = rostral and caudal clinoid processes

− craniopharyngeal canal (canalis craniopharyngeus)

The craniopharyngeal canal is the remnant in adults of the 

pharyngeal diverticulum from which the pars glandularis of the 

hypophysis develops (Evans and Christensen, 1979:128).

There is no record of a craniopharyngeal canal being present in delphinids.

* dorsal carotid foramen (Figures 22a, 28, 31b) 

The nomenclature associated with the bony path of the carotid foramen of the sphenoid in mammals is complex. Here, we 

recognize the dorsal carotid foramen in Tursiops as the internal opening of the internal carotid canal of the sphenoid, which 

marks the entry of the mostly vestigial internal carotid artery 

into the braincase.

The term “internal carotid foramen” should be avoided for 

Cetacea because of confusion between the general concept of foramina for the internal carotid artery and the foramen opening 

within the braincase.

See carotid foramen of the sphenoid.

= dorsal optic process

See metoptic process. 

* dorsum sellae (Figures 22a,c, 28)

The dorsum sellae is a flattened expanded process on the 

dorsal surface of the basisphenoid. It lies at the posterior border 

of the sella turcica (Evans and Christensen, 1979:128, 157).

The dorsum sellae in Tursiops is reduced to a low transverse ridge of bone that lies medial to the foramen rotundum. 

The dorsum sellae is a small conical tubercle in Kogia (Schulte, 

1917:383).

= entocarotids = internal carotid artery

− epitympanic wing

MacPhee (1981:53) identified an epitympanic wing as a general term for any outgrowth of a basicranial bone that contributes 

to the roof of the tympanic cavity, such as the epitympanic wing 

of the sphenoid or the epitympanic wing of the squamosal.

In Tursiops and other Cetacea the tympanic cavity is roofed 

by the periotic so that other skull bones do not have an epitympanic wing.

= ethmoidal foramen

See under “Frontal Bone.”

− ethmoidal spine

The anterior surface of the basisphenoid bone, in humans, 

presents a prominent spine, the ethmoidal spine, for articulation 

with the cribriform plate of the ethmoid (Gray, 1918:147).

s p h e n o i d n u m b e r 6 2 7 • 9 3
The ethmoidal spine is not developed in Tursiops and is 

probably lacking in other Cetacea.

− external carotid artery (Schaller, 1992:246.12)

In the dog the external carotid artery branches off the common carotid artery at the level of the occipital condyles (Evans 

and Christensen, 1979:656, figs. 11–16). The external carotid artery then follows a circuitous path along the basicranium and the 

tympanic bulla. The external carotid artery then bifurcates into 

the mandibular artery and the maxillary artery. The maxillary 

artery gives off the middle meningeal artery, which enters the 

cranial cavity via the foramen spinosum (Evans and Christensen, 

1979:666). The maxillary artery then enters the alar canal in the 

alisphenoid bone through the caudal alar foramen (Evans and 

Christensen, 1979:128, 665). No branches are given off from the 

maxillary artery while it is in the alar canal. The maxillary artery 

exits the alar canal through the rostral alar foramen.

Fraser and Purves (1960:14, 15, 23–26) described in detail 

the course of the external carotid artery and its branches. The 

maxillary artery does not enter the alisphenoid in Cetacea (Fraser and Purves, 1960:26) and no alar canals are present.

− false posterior clinoid process

The false posterior clinoid process lies on the dorsal surface 

of the basisphenoid and forms the posterior margin of the hypophyseal fossa in Platanista (Anderson, 1879:503). The process 

does not appear to occur in any odontocete other than Platanista, although further work is necessary to define what Anderson 

really meant by this term.

− foramen for the inferior petrosal sinus

The foramen for the inferior (ventral) petrosal sinus in the 

yellow armadillo lies in the medial portion of a gap between the 

promontory of the periotic, the alisphenoid and basisphenoid

anteriorly, and the basioccipital medially (McDowell, 1958:125; 

Wible and Gaudin, 2004:131).

This region has been incorporated into the cranial hiatus 

(q.v.) in odontocetes and the respective foramina are no longer 

visible.

− foramen for the lesser petrosal nerve

MacPhee (1981:54) identified the foramen for the lesser petrosal nerve as an aperture in the tympanic process of the alisphenoid of some mammals.

The foramen for the lesser petrosal nerve has not been identified in Tursiops.

− foramen for the ramus inferior of the stapedial artery

MacPhee (1981:54) identified the foramen for the ramus 

inferior of the stapedial artery as an aperture in the tympanic 

process of the alisphenoid next to the foramen ovale. Sometimes 

the feature may be an incisure rather than a foramen. The stapedial artery is vestigial in Tursiops, and a foramen for the ramus 

inferior has not been identified.

− foramen for the ramus superior of the stapedial artery

See “Periotic Bone.”

= foramen for zygomatic nerve = zygomatic foramen

− foramen of Vesalius (foramen Vesalii)

The foramen of Vesalius is a variable structure that sometimes occurs in humans medial to the foramen ovale, opposite 

the root of the pterygoid process, opening near the scaphoid 

fossa and transmitting a small vein from the cavernous sinus 

(Gray, 1918:150, 192). It is not mentioned in Evans and Christensen, 1979; Schaller, 1992; or Feneis, 1994.

Vesalius (1543:52; Vesalius et al., 1998:131) referred to the 

foramen Vesalii (emissary sphenoidal foramen) as the verum id 

in uno calvariae latere raro uisitur, atque adhuc multo rarius in 

utroque.

There does not appear to be a structure homologous with 

the foramen of Vesalius in the cetaceans.

* foramen ovale (oval foramen) (Figures 22a,b,d, 30, 31a,b)

In humans (Gray, 1918:150, 180, 192; Feneis, 1994:10.34) 

the foramen ovale opens in the wing of the sphenoid (alisphenoid) and transmits the mandibular nerve (mandibular branch 

of the trigeminal nerve) (McFarland et al., 1979:10), the accessory meningeal artery, and the lesser superficial petrosal nerve. 

In the dog (Evans and Christensen, 1979:128, 914; Schaller, 

1992:18.27) the foramen ovale is a large opening in the alisphenoid that leads directly through the cranial wall, posterior to the 

foramen rotundum. Vesalius (1543:51; Vesalius et al., 1998:131) 

referred to the foramen ovale as the non ad amussim orbiculare, 

sed circulo respondet utringue modice in longum compresso.

Many cetaceans, including Tursiops, have a single bony 

foramen that has been called the foramen ovale, but in some 

Cetacea the mandibular nerve is associated with two foramina 

in the skull. Ridewood (1922) and Fraser and Purves (1960:35) 

noted that when the mandibular nerve leaves the braincase in 

living Cetacea, the nerve passes through a notch or foramen in 

the posterior edge of the alisphenoid, forming the foramen ovale

as commonly recognized in Tursiops. From the notch or foramen 

in the posterior edge of the alisphenoid, the mandibular nerve 

may run externally in a groove or canal or “bony infundibulum” (sensu Fraser and Purves, 1960:35), which may be visible 

ventrally (e.g., Tursiops) or may be hidden from ventral view by 

development of adjacent bones, especially the pterygoid. In those 

cetaceans with a continuous bony lateral lamina to the pterygoid sinus fossa (namely, living Mysticeti, some Odontoceti, and 

basilosaurid Archaeoceti), the mandibular nerve exits toward 

the mandible through a second, external, foramen. Ridewood 

(1922) noted that, for mysticetes, the latter foramen is a “cleft 

between the squamosal and the pterygoid.” Fraser and Purves 

(1960) termed the latter cleft the “external opening of the foramen ovale,” and used the term “cranial aperture” (of the infundibulum) for the notch in the alisphenoid.

Fordyce (1994:175) used foramen ovale in the sense of Fraser and Purves for the internal notch or foramen in the posterior 

edge of the alisphenoid, and used the term “foramen ‘pseudoovale’” for what Fraser and Purves named the “external opening 

of the foramen ovale.” Luo and Gingerich (1999:49), conversely, 

identified the “external opening of the foramen ovale” as homologous with the foramen ovale in terrestrial mammals, and 

stated that “the foramen ovale of odontocetes has no equivalent 

in non-cetacean mammals.”

For Tursiops and other delphinoids, and for other odontocetes that lack a continuous bony lateral lamina to the pterygoid 

9 4 • smithsonian contributions to zoolog y s p h e n o i d
sinus fossa, we use the term “foramen ovale” for the structure 

located along the posteromedial margin of the alisphenoid. The 

foramen ovale is a notch in juveniles but is an enclosed foramen 

within the alisphenoid in adults; the adult foramen is commonly 

associated with a laterally directed groove on the ventral surface 

of the alisphenoid.

For cetaceans that have two foramina, as discussed above, 

a modification of the terminology of Fraser and Purves (1960) 

seems best: “cranial foramen ovale” for the notch or foramen in 

the alisphenoid that marks the exit of the mandibular nerve from 

the braincase, and “external opening of the foramen ovale” or 

“external foramen ovale” for the exit of the mandibular nerve 

toward the mandible.

See Schulte (1917:373, 374, 379, 400) and Fraser and 

Purves (1960:4, 30, 35, 37, 38, 40–54, 56, 65, 66, 68–71, 73, 

85, 87, 89, 100, 132) for a description of the foramen ovale in 

other species of cetaceans.

* foramen rotundum (round foramen) (Figures 8a, 22a, 28, 30, 

31b, 32)

The foramen rotundum lies in the lateral portion of the basisphenoid, just anterior to the foramen ovale (Gray, 1918:150, 

192; Schulte, 1917:373, 379, 384, 400; Evans and Christensen, 

1979:127; Feneis, 1994:10.33). The foramen rotundum transmits 

the maxillary nerve (maxillary branch of the trigeminal nerve) 

(Flower, 1885:123; Evans and Christensen, 1979:914; McFarland et al., 1979:11; Schaller, 1992:18.24). Vesalius (1543:50; 

Vesalius et al., 1998:131) referred to the foramen rotundum as 

the foramen orbiculare.

The foramen rotundum in Tursiops lies along the anteromedial border of the alisphenoid, in the suture between the alisphenoid and presphenoid, and is confluent with the sphenorbital 

fissure.

There is some confusion about the identity of the foramen 

rotundum. Fraser and Purves (1960:59) implied incorrectly that 

the foramen rotundum is confluent with the optic foramen; and 

Kellogg (1936:110) noted that, in the archaeocete Zygorhiza 

kochii, the maxillary nerve exited the sphenorbital fissure. See 

sphenorbital fissure for more comment.

* foramen spinosum (spinose foramen) (Figures 22b, 28)

The foramen spinosum is a variable structure that sometimes 

opens into the posterolateral border of the foramen ovale. The 

foramen spinosum serves to transmit the middle meningeal artery 

(Gray, 1918:150, 180, 192; Evans and Christensen, 1979:128; 

Schaller, 1992:18.29; Feneis, 1994:10.36). Vesalius (1543:52; 

Vesalius et al., 1998:131) referred to the foramen spinosum as 

the rursus ad externum foraminis Q indicati latus, aliud multo 

minus hoc, and exacte orbiculaltum, in cuneiforme osse cernitur, 

quo internae jugularis venae portio a soporali abscedens arteria, 

calvarium subintrat. Schulte (1917:374) identified a presumed 

foramen spinosum in Kogia, and Fordyce (1994) reported a possible foramen spinosum in the extinct odontocete Waipatia; see 

comments by Luo and Gingerich (1999:65, char. 54).

What could be the foramen spinosum in Tursiops lies in the 

sphenoparietal suture, just lateral to the foramen ovale. In old 

adults it lies lateral to the bony prominence that develops in the 

anteroventral edge of the bony tentorium. The identity of this 

feature has yet to be confirmed by dissection.

See also anterior lacerate foramen, vascular foramen (associated with the periotic), and foramen for the ramus superior of 

the stapedial artery.

* fossa for the postorbital lobe of the pterygoid sinus (Figures 

22b, 30)

The pterygoid sinus system is peculiar to cetaceans. The 

postorbital lobe of the pterygoid sinus is a lateral diverticula of 

the pterygoid sinus that arises between the falciform process and 

the orbital fissure (Beauregard, 1894; Fraser and Purves, 1960:8, 

25: fig. 8, 70, pl. 44). The fossa for the postorbital lobe of the 

pterygoid sinus lies over most of the anteroventral surface of the 

alisphenoid, anterior to the foramen ovale and a bony ridge that 

extends laterally from the foramen. The fossa passes over the 

anteroventral surface of the parietal near the suture between the 

parietal, frontal, and alisphenoid. The fossa for the postorbital 

lobe of the pterygoid sinus then extends anterolaterally onto the 

frontal, occupying a fossa that lies between the base of the postorbital process of the frontal bone and the crest that extends 

anterolaterally from the posterior margin of the orbital fissure. 

In adult Tursiops the anterolateral portion of the fossa 

can approach a centimeter in depth. This has been referred to 

as the postorbital smoothed area or recess (Fraser and Purves, 

1960:53,54ff.,60) or the post-orbital depression (Fraser and 

Purves, 1960:54), or the post-orbital recess (Fraser and Purves, 

1960:54).

* frontal border of the sphenoid (margo frontalis) (Figure 22a)

The frontal border of the sphenoid consists of that portion 

of the sphenoid that borders on (articulates with) the frontal.

In delphinids it is the anterior and lateral surfaces on which 

the frontal border occurs.

* frontal groove (Schulte, 1917:384) (Figure 30)

Schulte (1917:384) used the term “frontal groove” in Kogia to 

indicate a sulcus that was just posterior to a ridge (unnamed) that 

leads to the sphenoidal fissure (orbital fissure). That would make 

the frontal groove the lateral continuation of the optic canal.

In Tursiops the frontal groove is a major sulcus leading laterally from the optic canal on the orbitosphenoid.

* Glaserian process of the basisphenoid (Anderson, 1879:510) 

(Figure 30)

Anderson (1879:510) spoke of the Glaserian process in 

Platanista in this fashion: 

By its inward growth it also contributes to the division of this fissure in the cranial walls into two parts; 

one the foramen lacerum anterius . . . the other the 

foramen lacerum posterius, behind the two last-mentioned processes which define its anterior border, its 

inner margin being formed by a deep concavity lying 

between the Glaserian process of the basisphenoid and 

the strong, outward projection of the basioccipital 

which constitutes the anterior border of the precondyloid foramen [jugular foramen] of the occipital.

The Glaserian process of the basisphenoid is the projection 

on the posterolateral part of the basisphenoid that forms the posteromedial border of the endocranial sulcus / foramen for the 

vestibulocochlear nerve.

s p h e n o i d n u m b e r 6 2 7 • 9 5
= greater wing (ala major) = alisphenoid

* groove for mandibular nerve (sulcus n. maxillaris ) (Figure 22b)

The mandibular nerve lies in a sulcus on the cranial surface 

of the sphenoid, leading anteriorly toward the foramen ovale. 

The mandibular nerve is synonymous with the inferior maxillary 

nerve (Gray, 1918:893).

* groove for middle meningeal artery (sulcus arteriae meningea 

mediae) (Figures 22a, 31a)

The groove for the middle meningeal artery runs obliquely 

dorsolaterally from the aperture of the oval foramen on the cerebral surface of the alisphenoid. The groove continues on the 

cerebral surface of the squamosal and the cerebral surface of the 

parietal bones and carries branches of the middle meningeal artery (Evans and Christensen, 1979:129).

In Tursiops the groove for the middle meningeal artery runs 

from a fissure in the ventromedial cerebral surface of the parietal bone laterally along the cerebral surface of the alisphenoid. 

Branches of the groove for the middle meningeal artery continue 

dorsolaterally onto the cerebral surface of the parietal and cerebral surface of the frontal bones.

= groove for optic chiasm = chiasmatic groove

* hypophyseal fossa (fossa hypophysialis) (Figures 22a, 28)

The hypophyseal fossa lies in the center of sella turcica in 

the dorsal surface of the basisphenoid. The hypophyseal fossa 

is delimited anteriorly by the tuberculum sellae and posteriorly 

by the dorsum sellae. The hypophyseal fossa contains the hypophysis or pituitary gland (Evans and Christensen, 1979:128; 

Schaller, 1992:18.12; Feneis, 1994:10.8). Gray (1918:147, 190) 

referred to the hypophyseal fossa as the fossa hypophyseos. Vesalius (1543:51; Vesalius et al., 1998:131) referred to the hypophyseal fossa as the sinus in cuneiforme osse incisus, ac glandulam 

cotinens, cui ex cerebro defluens pituita instillat.

The hypophyseal fossa in Tursiops and other delphinids is 

very weakly developed. There exist two transverse ridges on the 

dorsal surface of the basisphenoid in adults, just medial to the foramen rotundum, that represent the tuberculum sellae and dorsum sellae. The hypophysis is contained within a pocket in the 

thick dura mater. The position of the hypophysis is immediately 

posterior to the optic chiasma (McFarland et al., 1979: fig. 44).

* inferior orbital fissure (fissura orbitalis inferior) (Figures 6f, 28, 

30, 31a,b, 32)

The inferior orbital fissure in humans is a cleft between 

the greater wing of the sphenoid (alisphenoid) and the orbital 

surface of the maxilla. The inferior orbital fissure transmits the 

zygomatic nerve plus the infraorbital nerve and infraorbital vessels (Gray, 1918:184; Feneis, 1994:32.24; not in Schaller, 1992). 

Vesalius (1543:50; Vesalius et al., 1998:131) referred to the inferior orbital fissure as the praesens foramen omnium quae in oculi 

sede conspiciuntur.

In Tursiops the inferior orbital fissure lies in the alisphenoid 

/ orbitosphenoid suture, just lateral to the optic canal and medial 

to the superior orbital fissure. The contents of the inferior orbital 

fissure in Cetacea have not been positively determined. See comments on orbital fissure.

* infratemporal crest / subtemporal crest (crista infratemporalis) 

(Figures 2, 10b)

The infratemporal crest in humans is a transverse ridge on 

the temporal surface of the alisphenoid that forms the ventral 

boundary of the temporal crest. The infratemporal crest divides 

the lateral surface into two portions, the vertically oriented superior portion or temporal portion and the horizontally oriented 

inferior portion or infratemporal portion (Feneis, 1994:10.32). 

The superior portion forms a part of the temporal fossa and gives 

rise to the m. temporalis. The inferior, together with the infratemporal crest, gives rise to the m. external pterygoideus (Gray, 

1918:150). The infratemporal crest is also known as the superior 

orbital ridge (crista orbitalis superior Davis, 1964:48).

The infratemporal crest is weakly developed in delphinids. 

The crest starts out posteriorly as the sphenoparietal suture, then 

deviates dorsally from that suture to follow the posterodorsal 

margin of the fossa for the postorbital lobe of the pterygoid 

sinus. The crest continues anteriorly and ends at the postorbital 

process of the frontal bone. Schulte (1917:384, 392, 393) described this crest similarly in Kogia.

= internal carotid foramen (foramen caroticum internum) = dorsal carotid foramen

See carotid foramen of the sphenoid. 

* intersphenoidal synchondrosis (synchondrosis intersphenoidalis) (Figure 28)

The basisphenoid articulates with the presphenoid anteriorly forming the intersphenoidal synchondrosis (synchondrosis 

intersphenoidalis) (Evans and Christensen, 1979:129; Schaller, 

1992:78.19). The presphenoid is united to the basisphenoid (postsphenoid) one month before birth in humans (Gray, 1918:153).

Owen (1866a:37) called the intersphenoidal synchondrosis 

the posterior fissure Kogia sima. In Tursiops it is open at birth 

(Figure 28) but is covered externally by the vomer and closes 

near the time that cranial maturity happens (Dailey and Perrin, 

1973:465; Walker, 1981:5).

− lateral lamina of the alisphenoid (Fraser and Purves, 1960:34, 

47–49, 51, 52, 56)

Fraser and Purves (1960:47, 48) described the most lateral 

extent of the alisphenoid as the lateral lamina of the alisphenoid 

in Monodon: “The lateral laminae of the alisphenoid, pterygoid 

and palatine on each side, form a bony bridge extending posteriorly from the anterior border of the orbital process of the frontal

to the squamosal. The greater part of the ventral portions of 

these laminae has disappeared leaving a wide, gaping, irregular 

concavity on the ventrolateral aspect of the skull.” Fraser and 

Purves (1960) illustrated that situation in plate 13 in which they 

labeled the lateral laminae of the palatine and pterygoid. Fraser 

and Purves (1960:35, 63) also referred to the lateral lamina of 

the alisphenoid and the lateral wings of the alisphenoid. The lateral part of the alisphenoid is continuous with the lateral laminae 

of the pterygoid and palatine but is not labeled as such.

Fraser and Purves (1960:56), in their description of the skull 

of Lagenorhynchus obscurus, state that “no part of the lateral 

lamina of the pterygoid and alisphenoid remains, and of the 

superior lamina (PT(SL)) only a small plate extends under the 

orbito-sphenoid.” Fraser and Purves illustrated that in plate 40, 

9 6 • smithsonian contributions to zoolog y s p h e n o i d
which shows the same relationship of those bones as their illustration of Tursiops (their plates 43 and 44).

In conclusion Monodon has a lateral lamina of the alisphenoid but delphinids do not. The increased development of the 

orbitosphenoid has taken the place of the lateral lamina of the 

alisphenoid in delphinids.

= lateral notch

See musculotubal canal of the sphenoid bone. 

= lesser wing of the sphenoid (ala minor) = orbitosphenoid (Feneis, 1994:10.19; not in Schaller, 1992)

See “Ethmoid Bone.”

− lingula (lingula sphenoidalis)

The lingula is a low ridge of bone separating the openings 

of the medial notch and the musculotubal canal of the sphenoid 

bone (Evans and Christensen, 1979:129).

The lingula is not developed in delphinids due to the lack of 

the musculotubal canal.

= mesial lamina of the alisphenoid = alisphenoid

Fraser and Purves (1960:34, 47, 48, 56) defined and illustrated (pl. 13) a lateral lamina of the alisphenoid (q.v.) in Monodon. They mention a mesial lamina in contradistinction to the 

lateral lamina only once on page 34. We assume that they meant 

the rest of the alisphenoid. This could conceivably be called the 

“body of the alisphenoid,” but that could generate confusion 

with the body of the sphenoid (basisphenoid).

Delphinids do not seem to have developed a lateral lamina 

of the alisphenoid. The alisphenoid in delphinids is entirely composed of what Fraser and Purves called the “mesial lamina.”

− metoptic foramen

According to Wible and Rougier (2000:33), the metoptic 

foramen is the foramen for the oculomotor nerve.

Tursiops does not have a separate foramen for the oculomotor nerve; the latter issues from the sphenorbital fissure.

* metoptic process (Figure 31b)

Schulte (1917:378) stated, for Kogia: “The optic foramen

is confluent with the sphenoidal fissure in the skull of the calf. 

In the adult it is on both sides separated by a very tenuous osseous lamella. In view of its late ossification the metoptic process 

would seem to be on the verge of disappearance.” Schulte here 

appeared to equate the metoptic process with the “tenuous osseous lamella” separating the optic foramen from the sphenorbital 

fissure. Metoptic process sensu Schulte seems to be equivalent 

to the embryological feature of mammals known as the pila 

metoptica (see Wible and Rougier, 2000:49): a bar separating 

the optic foramen from the metoptic foramen or exit for the oculomotor nerve. The term “metoptic process” seems useful for 

the bony equivalent of the embryological pila metoptica. The 

metoptic process is also known as the superoptic process (Owen, 

1866a:40).

Tursiops does have a metoptic process.

− musculotubal canal of the sphenoid bone (canalis musculotubarius)

The musculotubal canal is formed by the lateral notch of 

the sphenoid bone with its counterpart on the squamosal bone. 

This is a short canal that transmits the m. tensor veli palatini

and the auditory tube (Eustachian tube) (Evans and Christensen, 

1979:129). This squamosal portion in terrestrial mammals has 

been transferred to the tympanic bulla in cetaceans.

See musculotubal canal of the tympanic bulla.

− nasopharyngeal surface of the sphenoid (facies nasopharyngea)

The nasopharyngeal surface of the sphenoid is the surface 

that is in contact with the nasopharyngeal cavity.

The vomer and the pterygoid have expanded posteroventrally in delphinids and have covered the ventral surface (nasopharyngeal surface) of the sphenoid.

* optic canal (canalis opticus) (Figures 28, 30, 31a,b, 32)

The optic canals occur in the presphenoid bone and convey the optic nerves (Owen, 1866a:36; Evans and Christensen, 

1979:127; Schaller, 1992:20.20; Feneis, 1994:10.20;). Owen 

(1866a:36) also referred to the optic canal and the optic channel. Gray (1918:147) did not recognize the optic canal, merely 

the optic foramen. Vesalius (1543:50; Vesalius et al., 1998:131) 

referred to the optic canal as the qui venulae cum visorio nervo 

hac excidente paratur.

In Tursiops the anterior portion of the optic canals is formed 

by the orbital wings of the presphenoid (orbitosphenoid). The 

posterior portion of the optic canals is formed by the metoptic 

process (= optic process of the presphenoid) (Fraser and Purves, 

1960:51).

* optic foramen (foramen opticum) (Figure 31a)

The optic foramen lies on the lateral portion of the cranial 

surface of the presphenoid. It is continuous with the optic canal

and serves to transmit the optic nerve (Owen, 1866a:27, 30, 36; 

Gray, 1918:147, 151, 190; McFarland et al., 1979:10). Evans 

and Christensen (1979:128, 150), Schaller (1992:20.20), and 

Feneis (1994:10.20) did not recognize the optic foramen but referred instead to the optic canal without naming the entrance 

and exit foramina. Eustachius and Lancisius (1714:93) referred 

to the optic foramen as the foramen nervorum opticorum.

The optic foramen is usually distinct in adult delphinids, 

separated from the combined sphenorbital fissure and foramen 

rotundum by a fine metoptic process, and is well developed in 

cetaceans (Schulte, 1917:373, 378, 380, 384, 400; Fraser and 

Purves, 1960:29, 50, 57, 59, 85, 87).

Fraser and Purves (1960, e.g., many of plates 9–47) used 

optic foramen in a broader sense for the large bony opening that 

they elsewhere recognized as a “confluent aperture of the optic 

foramen, foramen rotundum and sphenoidal fissure” (Fraser 

and Purves, 1960:59, for Delphinus delphis). “Optic foramen” 

should not be used in this broader sense but should be restricted 

to the bony foramen for the optic nerve.

= optic groove = chiasmatic groove 

− optic infundibulum

Fraser and Purves (1960:30, 61, 68–70, 72, 73, 99, 100, 

102) used optic infundibulum without definition in text and illustrations. They stated that . . . 

s p h e n o i d n u m b e r 6 2 7 • 9 7
“the paths of the nerves concerned [on the skull base] 

are restricted [by soft tissues of the pterygoid sinus

system] to three exits, that associated with the optic 

infundibulum, that of the infundibulum of the foramen ovale and that of the ‘cranial hiatus’ in the vicinity of the periotic” (Fraser and Purves, 1960:30). 

In reference to Delphinus delphis (1960:59), Fraser and 

Purves mentioned a “confluent aperture of the optic foramen, 

foramen rotundum and sphenoidal fissure,” but they did not use 

the name optic infundibulum for any of these bony features. On 

skulls shown among plates 9–47, Fraser and Purves identified the 

large bony opening at the orbit as the optic foramen (in our terminology, optic foramen separate from confluent sphenorbital 

fissure and foramen rotundum), whereas for specimens shown 

on plates 9–47 in which air sacs are preserved on the skulls, the 

exit for orbital soft tissues was identified as optic infundibulum. In summary, optic infundibulum in the sense of Fraser and 

Purves (1960) apparently comprises the soft-tissue pathway, as 

constrained by the adjacent pterygoid sinus lobes, for nerves and 

vessels exiting the optic foramen, foramen rotundum, and orbital (sphenorbital) fissure. Contrary to past uses (e.g., Fordyce, 

1994, 2002), the term is not applicable to a bony feature.

* orbital fissure (fissura orbitalis) (Figure 6f)

The orbital fissure is located lateral to the body of the sphenoid in the sutures between the orbitosphenoid and alisphenoids. 

The orbital fissure is situated slightly posterolateral to the optic 

canals (Evans and Christensen, 1979:128; Schaller, 1992:14.30; 

Feneis, 1994:32.23). The orbital fissure contains the ophthalmic 

nerve (ophthalmic branch of the trigeminal nerve), the oculomotor nerve, the trochlear nerve, and the anastomotic artery. The 

orbital fissure has also been called the intersphenal fissure (Owen, 

1866a:30, 36, 40), the intersphenal fossa (Owen, 1866a:36), or 

the sphenofrontal fissure (Owen, 1866a:30). Owen (1866a:27) 

used the term “foramen lacerum anterius” as a lapsus calami 

for “fissura lacera anterior.” Schulte, 1917:384) referred to this 

structure as the orbital fissure.

The orbital fissure is only applicable in very young delphinids. The contents of the orbital fissure divide in adults into the 

superior orbital fissure and the inferior orbital fissure (q.v.). The 

exact contents of the superior orbital fissure and the inferior orbital fissure in Cetacea are not well known and it may be that the 

fissures are not homologous with other species.

The orbital fissure is also known as the sphenoidal fissure

(Whitney, 1889–1910:[vol. 3]2239; Fraser and Purves, 1960:59) 

and the sphenorbital fissure (Fraser and Purves, 1960:59).

Kellogg (1936:110) stated that, in the archaeocete Zygorhiza 

kochii, “the maxillary division of the trigeminal nerve leaves the 

cranial cavity through the sphenorbital fissure [orbital fissure].” 

We interpret Kellogg’s statement to mean not that the foramen 

rotundum is synonymous with the sphenorbital fissure [orbital 

fissure], but that the foramen rotundum, which in other mammals marks the exit for the maxillary nerve, is confluent with the 

sphenorbital fissure [orbital fissure].

= orbital infundibulum (Fordyce, 1994) = optic infundibulum

* orbital surface of the sphenoid (facies orbitalis) (Figure 8b)

The orbital surface of the sphenoid bone is that part of the 

sphenoid that borders the orbit. We have decided to use the definition of the orbital part of the frontal to define the orbit: the orbital 

part is a segment of a cone with the apex located at the optic canal

and the base forming the medial border of the infraorbital margin 

of the frontal bone (Evans and Christensen, 1979:125).

Thus defined, the orbital surface of the sphenoid bone in 

delphinids is confined to the lateral portion of the optic canals in 

the presphenoid (Schulte, 1917:384).

= orbital wing

See orbitosphenoid of the presphenoid.

* orbitosphenoid of the presphenoid (ala orbitalis) (Figures 6b, 

8a–e, 28, 31b)

The orbitosphenoids of the presphenoid lie anterior to the 

optic canal (Evans and Christensen, 1979:127).

The orbitosphenoids are strongly developed in Tursiops and 

other cetaceans (Schulte, 1917:373, 379, 384, 391, 392, 400). 

They form the anterior portion of the optic canal. Owen used the 

terms “orbitosphenoid” (1866a:26, 30, 36, 37, 39) and “orbitosphenoid” (1866a:27, 28, 30) interchangeably.

− orbitosphenoidal crest (crista orbitosphenoidalis)

The orbitosphenoidal crest lies dorsal to the optic canals on 

the presphenoid. It is formed by the sphenoidal yoke (Evans and 

Christensen, 1979:128).

The orbitosphenoidal crest is not developed in Tursiops due 

to the absence of the sphenoidal yoke.

* parafalciform fossa [new term] (Figure 30)

The parafalciform fossa lies on the posterolateral surface of 

the ventral aspect of the alisphenoid, directly dorsal to the falciform process in delphinids. The fossa extends posterolaterally 

from the foramen ovale, from which it is separated by a crest. 

The fossa terminates on the squamosal immediately dorsal to 

the attachment of the falciform process. The parafalciform fossa 

communicates laterally with the squamosal cleft.

* parietal border of the sphenoid (margo parietalis) (Figure 22a)

The parietal border of the sphenoid consists of that portion 

of the sphenoid that borders on (articulates with) the parietal.

In delphinids it is the posterior portion of the lateral surface 

on which the parietal border occurs.

− petrosal foramen (foramen petrosum)

In humans the petrosal foramen is a variable structure that lies 

between the foramen ovale and the foramen spinosum. The petrosal 

foramen transmits the lesser petrosal nerve (Feneis, 1994:10.37).

There is no evidence of the existence of a petrosal foramen 

in delphinids.

= pila metoptica

See metoptic process (Wible and Rougier, 2000:49). 

= posterior carotid foramen = caudal carotid foramen of the 

sphenoid bone

− posteroexternal process of the alisphenoid

In the fossil platanistoid Zarhachis, a posteroexternal process of the alisphenoid projects back to contact the squamosal 

near the periotic (Kellogg, 1926:16).

9 8 • smithsonian contributions to zoolog y s p h e n o i d
The homology of the posteroexternal process in Tursiops

is not clear.

* presphenoid (os presphenoidale [prae-]) (Figures 8a,b,d,e, 31b)

The presphenoid lies just posterior to the ethmoid and anterior to the basisphenoid. It houses the optic canals (Evans and 

Christensen, 1979:128).

In Tursiops the presphenoid is fused to the ethmoid at birth. 

The presphenoid forms the anterior half of the optic canal. It 

also consists of the body of the bone immediately posterior to 

the crista galli. The rostral clinoid process is developed faintly 

in adults. It is present in all cetaceans (Schulte, 1917:374, 378, 

384–386, 390, 392, 394).

= processus clinoideus medius (McFarland et al., 1979:10) = 

caudal clinoid process (Gray, 1918:147)

− pterygoid canal (canalis pterygoideus)

The pterygoid canal leads from the pterygoid groove through 

the pterygosphenoid suture and ends in the posterior part of the 

pterygopalatine fossa (antorbital fossa) (Evans and Christensen, 

1979:129, 127). The pterygoid canal carries the nerve of the 

pterygoid canal, which is a parasympathetic branch of the facial nerve destined for the pterygopalatine ganglion, and a variably developed Vidian artery (Evans and Christensen, 1979:145; 

MacPhee, 1981:61, 47).

The existence of the pterygoid canal does not appear to have 

been demonstrated in Tursiops, but we have seen what may be 

the pterygoid canal in a fossil cetacean.

− pterygoid crest (crista pterygoidea)

The pterygoid crest is a dorsal continuation of the pterygoid 

process of the sphenoid and borders the pterygopalatine fossa

(antorbital fossa) (Schaller, 1992:20.6). It is present in horses and 

pigs and absent in carnivores (Schaller, 1992:20.6). The pterygoid 

crest serves as the origin of the lateral pterygoid muscle (m. pterygoideus lateralis; Schaller, 1992:102.21; Feneis, 1994:80.16). The 

lateral pterygoid muscle is also known as the external pterygoid 

muscle (m. pterygoideus externus) (Gray, 1918:386; Fraser and 

Purves, 1960:6, 14, 17–19, 22, 24, 26, 29, 31, 76, 82).

The pterygoid process has been reduced in delphinids to the 

extent that it is just a small protuberance on the ventral surface 

of the basisphenoid. As a consequence the pterygoid crest has 

disappeared as a functional element.

− pterygoid fossa of the sphenoid (fossa pterygoidea)

The pterygoid fossa in humans lies in the lateral surface of 

the pterygoid processes of the sphenoid and contains the origins of the medial pterygoid muscle (m. pterygoideus medialis) 

and m. tensor veli palatini (McFarland et al., 1979:11; Feneis, 

1994:12.5).

In Tursiops the pterygoid process is not differentiated into 

separate fossae (pterygoid fossa and scaphoid fossa).

− pterygoid groove (sulcus n. pterygoidei)

The pterygoid groove is located in the pterygosphenoid suture. The pterygoid groove begins anterior to the small muscular 

process of the squamosal bone, leads into the pterygoid canal, 

which ends in the posterior part of the pterygopalatine fossa

(antorbital fossa) (Evans and Christensen, 1979:129, 127). This 

groove carries the nerve of the pterygoid canal, which is a parasympathetic branch of the facial nerve destined for the pterygopalatine ganglion.

The existence of the pterygoid groove has not been demonstrated in delphinids.

− pterygoid plate

The pterygoid plates (lateral pterygoid plate and medial 

pterygoid plate) in humans consist of ventral projections of the 

basisphenoid that form the pterygoid process of the sphenoid.

In Tursiops the pterygoid process is not differentiated into 

lateral and medial pterygoid plates. Fraser and Purves (1960:6, 

22, 42, 53, 81–85, 87, 89, 102) used “pterygoid plates” to refer 

to the lateral lamina and medial lamina of the pterygoid bone.

= pterygoid process of the basisphenoid (e.g., Schaller, 1992:20.1) 

= alisphenoid

See alisphenoid.

* pterygoid process of the sphenoid (processus pterygoideus) 

(Figure 22b–d)

The pterygoid process of the sphenoid bone is a ventrolateral 

process of the basisphenoid, consisting of a pair of lateral pterygoid plates and medial pterygoid plates, serving as attachments 

for the pterygoid bones (Evans and Christensen, 1979:129; McFarland et al., 1979:11; Schaller, 1992:20.1; Feneis, 1994:12.1). 

Vesalius (1543:21, 23, 25) compared the pterygoid process of 

the sphenoid to the wings of bats (quos vespertilionum alis comparabimus, vespertilionum alarum, and processus vespertilionum alis, respectively).

In Tursiops the pterygoid processes of the sphenoid are 

much reduced and are situated on the ventral surface of the basisphenoid just anterior to the caudal carotid foramen of the sphenoid bone.

− rostral alar foramen (foramen alare rostrale)

The rostral alar foramen is the anterior opening of the alar 

canal (Evans and Christensen, 1979:128) and transmits the maxillary nerve (maxillary branch of the trigeminal nerve) (Evans 

and Christensen, 1979:914).

Alar canals are not developed in Tursiops.

− rostral clinoid process (processus clinoideus rostralis)

The rostral clinoid process projects posteriorly from the 

posterolateral margin of the presphenoid, over the orbital fissure (Evans and Christensen, 1979:128, 157). The rostral clinoid 

process is also known as the anterior clinoid process (McFarland 

et al., 1979:7).

Tursiops does not develop a rostral clinoid process.

− scaphoid fossa (fossa scaphoidea)

The scaphoid fossa is a small oval depression that lies above 

the pterygoid fossa of the sphenoid on the basisphenoid. It is the 

origin of the m. tensor veli palatini.

Neither the pterygoid fossa nor the scaphoid fossa are developed in Tursiops.

* sella turcica (Figures 22a, 28)

The sella turcica lies on the dorsal part of the basisphenoid

and consists of the tuberculum sellae, the hypophyseal fossa, and 

s p h e n o i d n u m b e r 6 2 7 • 9 9
the dorsum sellae (Gray, 1918:147, 190; Evans and Christensen, 

1979:128, 155, 605; Schaller, 1992:18.11; Feneis, 1994:10.5.). 

The sella turcica is also known as the Turk’s saddle. Eustachius 

and Lancisius (1714:112) referred to it as the sella turcica.

Delphinids have a poorly developed sella turcica.

= small alar foramen (foramen alare parvum) = zygomatic 

foramen

= small wing = orbitosphenoid

− sphenoethmoidal suture (sutura sphenoethmoidalis)

The sphenoethmoidal suture lies between the presphenoid

and the cribriform plate of the ethmoid (Gray, 1918:190; Evans 

and Christensen, 1979:129, 138; Schaller, 1992:76.10; Feneis, 

1994:54.7). Vesalius (1543:51; Vesalius et al., 1998:131) referred to the sphenoethmoidal suture of the anterior cranial fossa 

as the quae durae cerrebri membranae hic firmadae extruitur.

The sphenoethmoidal suture closes in utero and no trace of 

it is evident in Tursiops neonates.

* sphenofrontal suture (sutura sphenofrontalis) (Figures 28, 30, 

31b)

The sphenofrontal suture is formed by the joining of the 

frontal to the sphenoid (alisphenoid) (Gray, 1918:182, 190; 

Evans and Christensen, 1979:126, 129; Schaller, 1992:76.9; Feneis, 1994:54.6). Vesalius (1543:23) referred to the sphenofrontal suture as merely the sutura.

In delphinids the sphenofrontal suture is formed on the 

frontal border of the alisphenoid (Figure 22a).

− sphenoidal concha (concha sphenoidalis)

The sphenoidal conchae are located at the anteroventral 

portion of the sphenoid bone. The sphenoidal sinus communicates with the nasal cavity via an aperture in the anterior wall 

of the conchae.

Sphenoidal conchae and the paranasal sinus system are not 

developed in cetaceans (Fraser and Purves, 1960:5, 75).

− sphenoidal crest (crista sphenoidalis)

The sphenoidal crest lies in the midline of the anterior surface of the sphenoid (presphenoid) in humans and articulates 

with the perpendicular plate of the ethmoid bone and forms part 

of the nasal septum (Gray, 1918:149).

The appearance of the sphenoidal crest in delphinids is moot. 

The presphenoid is already fused with the ethmoid in neonatal 

Tursiops, thereby obliterating any trace of the sphenoidal crest.

= sphenoidal fissure = sphenorbital fissure

Fraser and Purves (1960:59) said that in Delphinus delphis, 

“the confluent aperture of the optic foramen, foramen rotundum, 

and sphenoidal fissure was very much enlarged by resorption of 

the boundary margins of the orbitosphenoid and alisphenoid.” 

This use of sphenoidal fissure is equivalent to sphenorbital fissure or orbital fissure sensu Wible and Gaudin (2004:165).

− sphenoidal fossae

The sphenoidal fossa lies on the anteroventral surface of the 

presphenoid at the junction of the orbitosphenoids and the body 

of the presphenoid. It houses the posteroventral portions of the 

ethmoturbinates (Evans and Christensen, 1979:128, 158). The 

sphenoidal fossae are formed by a longitudinal septum that divides the hollow anterior portion of the presphenoid (Evans and 

Christensen, 1979:128).

The sphenoidal fossa is not developed in odontocetes due to 

the reduction in structures associated with olfaction.

= sphenoidal incisure

See “Vomer.”

− sphenoidal rostrum (rostrum sphenoidale)

The sphenoidal rostrum is a small median tubercle that 

projects from the anterior border of the sphenoidal yoke (Evans 

and Christensen, 1979:128).

The sphenoidal rostrum is not developed in Tursiops due to 

the absence of the sphenoidal yoke.

− sphenoidal sinus (sinus sphenoidalis)

The sphenoidal sinus lies within the presphenoid bone in 

dogs and is largely occupied by the fourth endoturbinate (Evans 

and Christensen, 1979:159; Schaller, 1992:20.10, 180.24). The 

extent of the sphenoidal sinus is variable in other animals. It also 

occupies the basisphenoid in pigs (Schaller, 1992:20.10).

The sphenoidal sinus is a paranasal sinus and as such is not 

developed in cetaceans (Fraser and Purves, 1960:5, 75).

− sphenoidal sinus septum (septum sinuum sphenoidalium)

The sphenoidal sinus septum separates the right and left 

paired sphenoidal sinuses (Schaller, 1992:20.11, 20.23, 180.25; 

Feneis, 1994:10.6).

The sphenoidal sinus is not developed in cetaceans.

* sphenoidal spine (spina angularis) (Figure 22b–d)

The sphenoidal spine in humans is a projection off the posterolateral part of the alisphenoids that fits into the angle between the squamosal and petrosal (Gray, 1918:150).

In Tursiops the sphenoidal spine has been modified into a 

rather blunt process that articulates with the squamosal and lies 

dorsal to the falciform process of the squamosal bone and ventral to the parietal bone.

− sphenoidal yoke (jugum sphenoidale)

The sphenoidal yoke is formed by the fusion of the orbital 

wings and forms the base of the anterior cranial fossae (Evans 

and Christensen, 1979:128). The sphenoidal yoke in delphinids 

is not developed due to the lack of fusion of the orbital wings.

− sphenoid sinus aperture (apertura sinus sphenoidalis)

The sphenoid sinus aperture is the opening into the sphenoidal sinus (Schaller, 1992:20.24, 20.22, 180.26).

The sphenoidal sinus is a paranasal sinus and is not developed in cetaceans (Fraser and Purves, 1960:5, 75).

= sphenomaxillary fissure = alar canal (Gray, 1918:184)

= sphenomaxillary fossa = pterygopalatine fossa = antorbital 

fossa

See “Maxilla.”

1 0 0 • smithsonian contributions to zoolog y s p h e n o i d
− sphenomaxillary suture (sutura sphenomaxillaris)

The sphenomaxillary suture lies between the pterygoid process of the basisphenoid (alisphenoid) and the maxilla in some 

mammals (e.g., the pig; Schaller, 1992:76.34) but in other mammals (e.g., the dog; Evans and Christensen, 1979:129) the basisphenoid does not contact the maxilla. In humans it is variable 

(Gray, 1918:183; Feneis, 1994:54.24), depending on the development of the basisphenoid and maxilla around the sphenomaxillary fissure. Vesalius (1543:23) referred to the sphenomaxillary 

suture merely as the sutura.

In delphinids, including Tursiops, the maxilla does not contact the sphenoid.

* sphenooccipital synchondrosis (synchondrosis spenooccipitalis) (Figures 6f, 28)

The sphenooccipital synchondrosis is the cartilaginous joint 

(synchondrosis) between the basisphenoid and the basioccipital bones (Evans and Christensen, 1979:45, 51, 129; Schaller, 

1992:78.16; Feneis, 1994:56.2). The sphenooccipital synchondrosis is also known as the occipitosphenoid synchondrosis (Gray, 

1918:284). Vesalius (1543:23) referred to the sphenooccipital 

synchondrosis as the transversam lineam or merely the linea.

Cetacea have a normal sphenooccipital synchondrosis, which 

fuses with age. In external views of adult Tursiops the sphenooccipital synchondrosis is hidden by the posterior part of the vomer.

− sphenoparietal suture (sutura sphenoparietalis) (Gray, 1918: 

182)

The sphenoparietal suture is the suture between the greater 

wing of the sphenoid (alisphenoid) and the parietal bone (Feneis, 1994:54.9). The point corresponding with the posterior end 

of the sphenoparietal suture is named the pterion. (Evans and 

Christensen, 1979:129; Schaller, 1992:76.12).

In Tursiops the sphenoparietal suture lies at the medial surface of the temporal fossa, where the alisphenoid meets the parietal (Fraser and Purves, 1960:61, 63).

= sphenorbital fissure (Kellogg, 1936) = foramen rotundum

* sphenosquamosal suture (sutura sphenosquamosa) (Figure 31b)

The sphenosquamosal suture lies between the alisphenoid (or 

presphenoid) and the squamosal in mammals (Gray, 1918:182; 

Evans and Christensen, 1979:129; Schaller, 1992:76.11; Feneis, 

1994:54.8). Vesalius (1543:23) referred to the sphenosquamosal 

suture as merely the sutura. Fraser and Purves (1960:39) referred 

to the sphenosquamosal suture as the alisphenoid–squamosal suture in reference to the pterygoid in Caperea.

In delphinids the alisphenoid contacts the squamosal and 

forms a sphenosquamosal suture just anterior to the falciform 

process. This suture lies on the sphenoidal margin of the squamosal (Figures 30, 31b).

− sphenozygomatic suture (sutura sphenozygomatica)

The sphenoid does not contact the zygomatic in most mammals, including the dog, cow, horse and pig (Evans and Christensen, 1979:129; Schaller, 1992:76). In humans the zygomatic 

(jugal) has expanded and contacts the alisphenoid in the orbit

(Gray, 1918:182; Feneis, 1994:54.23). Vesalius (1543:23) referred to the sphenozygomatic suture as merely the sutura.

In delphinids the zygomatic (jugal) does not contact the 

alisphenoid.

= spina ossis sphenoidalis = sphenoidal spine

− squamosal border of the sphenoid (margo squamosus)

The squamosal border of the sphenoid consists of that portion of the alisphenoid that borders on (articulates with) the 

squamosal.

Tursiops has a normal mammalian squamosal border.

− sulci for intracranial extensions of spinal meningeal arteries

See “Exoccipital Bone.”

= sulcus n. canalis pterygoidei = pterygoid groove

− sulcus tubae auditivae

The sulcus tubae auditivae is a groove in the lateral portion of the alisphenoid where it articulates by a synchondrosis 

with the petrosal. The sulcus tubae auditivae holds the cartilaginous part of the auditory tube (Eustachian tube) (Gray, 

1918: 150).

The auditory tube has moved ventrally with the auditory 

bulla and does not contact the alisphenoid in delphinids, hence 

the sulcus tubae auditivae is not developed.

* superior orbital fissure (fissura orbitalis superior) (Figures 28, 

30, 31a,b, 32)

The superior orbital fissure in humans is located in the posterior part of the lateral wall of the orbit between the greater and 

lesser wings of the sphenoid. It transmits the ophthalmic, oculomotor, trochlear, and abducens nerves as well as the superior 

ophthalmic vein (McFarland et al., 1979:11; Feneis, 1994:32.23). 

Vesalius (1543:50; Vesalius et al., 1998:131) referred to the superior orbital fissure as the praesens foramen caelatur gratia 

secundi [sic; third] paris nervorum cerebri.

In Tursiops the superior orbital fissure is located in the lateral part of the presphenoid–basisphenoid suture just lateral to 

the inferior orbital fissure. It is separated from the optic canal by 

the metoptic process. The contents of the superior orbital fissure 

in Cetacea have not been positively determined. See comments 

on orbital fissure.

− temporal surface of the sphenoid (facies temporalis)

The temporal surface of the sphenoid bone is that surface in 

contact with the temporal bone.

The temporal surface is not present in delphinids because 

the tympanic and periotic no longer contact the sphenoid.

= temporal wing = alisphenoid

− transverse canal foramen

Wible and Gaudin (2004:153, 166) identified the transverse 

canal foramen of the basisphenoid or alisphenoid basicranium 

as associated with the foramen ovale in a common depression 

on the alisphenoid of the [yellow] armadillo. In marsupials (e.g., 

Wible, 2003, Monodelphis), the transverse canal foramen opens 

laterally in the basisphenoid, anterior to the carotid foramen of 

the sphenoid.

s p h e n o i d n u m b e r 6 2 7 • 1 0 1
Tursiops does not appear to have a transverse canal foramen in the alisphenoid or adjacent basisphenoid.

The transverse canal foramen of the basisphenoid or alisphenoid should not be confused with the transverse canal (q.v.) at 

the internal occipital protuberance in mature Tursiops, or with 

the transverse canal of the vertebrae.

* tuberculum sellae (Figures 22a, 28)

The tuberculum sellae is a ridge of bone formed at the juncture of the presphenoid and basisphenoid. It serves as the anterior limit for the hypophyseal fossa (Evans and Christensen, 

1979:128).

In Tursiops the tuberculum sellae has moved posteriorly and 

occupies a position about 1 cm posterior to the presphenoid­–

basisphenoid suture (McFarland et al., 1979: fig. 44, related the 

pituitary to the optic chiasma).

− tympanic process of the alisphenoid (Wible and Gaudin, 2004: 

131)

Wible and Gaudin (2004:131) noted that in the yellow armadillo, the tympanic process of the alisphenoid is a low posterior 

ridge on the alisphenoid, which, as it runs from the posterolateral base of the entopterygoid crest to the entoglenoid process of 

the squamosal, abuts the tympanic bulla.

In Tursiops the alisphenoid does not abut the tympanic 

bulla, and a tympanic process is absent.

− vaginal process (processus vaginalis)

The vaginal process in humans consists of a thin lamina of 

the medial pterygoid plate that articulates with the sphenoid process of the palatine and the ala of the vomer.

The pterygoid process of the sphenoid of Tursiops is not differentiated into medial and lateral pterygoid plates, and, as such, 

a vaginal process is not developed.

* ventral carotid foramen (Figures 22b,c, 30)

The nomenclature associated with the bony path of the carotid foramen in mammals is complex (see discussion under carotid foramen of the sphenoid). Here, we recognize the ventral 

carotid foramen in Tursiops as the external or ventral opening 

of the carotid canal of the sphenoid, which marks the path of the 

mostly vestigial internal carotid of Cetacea into the braincase.

The term “external carotid foramen” should be avoided for 

Cetacea because of possible confusion with the external carotid 

artery of other mammals.

= wings of the sphenoid = alisphenoid

− zygomatic border of the sphenoid (margo zygomaticus)

The zygomatic border of the sphenoid consists of that portion of the sphenoid that borders on (articulates with) the zygomatic (Gray, 1918:148).

In delphinids the zygomatic border does not occur because 

the sphenoid does not contact the zygomatic (jugal).

− zygomatic foramen

The zygomatic foramen is a variable feature that lies on the 

anterodorsal surface of the basisphenoid. The zygomatic foramen lies on a ridge of bone between the orbital fissure and the 

rostral alar foramen. The zygomatic nerve passes through the 

zygomatic foramen on its route to the orbit (Evans and Christensen, 1979:127, 129, 914). The zygomatic foramen is also 

known as the foramen alare parvum (Evans and Christensen, 

1979:128).

The zygomatic foramen has not been reported in delphinids. 

Evidently the zygomatic branch of the maxillary nerve leaves the 

main root of the nerve in the orbit. The zygomatic nerve supplies 

the eyelid and some of the surrounding skin in most mammals 

(Evans and Christensen, 1979:916).

SQUAMOSAL BONE

Os Temporale / Pars Squamosa

Figures 1, 3–5, 6b,c, 23, 29–32

There is no single temporal bone in Cetacea. See discussions of the temporal bone in other mammals (Gray, 1918:138; 

Evans and Christensen, 1979:129; Schaller, 1992:22.1; Feneis, 

1994:12.14). Vesalius (1543:21–23) referred to the temporal as 

the temporis os. Temporal elements occur separately as ossified 

squamosal, periotic, tympanic bulla, and associated middle ear 

ossicles. Accordingly, we treat these elements separately. Some 

conventions follow widespread previous use in the cetacean literature; we use the terms “tympanic bulla” to refer to the ectotympanic bulla, and “periotic” for the periotic (or petrosal) 

bone. See ectotympanic part, below.

The squamosal bone consists of the squamosal plate, which 

extends dorsally over the parietal (Evans and Christensen, 

1979:134), and the glenoid process, which includes the zygomatic process, mandibular fossa (glenoid fossa), retroarticular or 

postglenoid process, and ear region.

The squamosal (squamous part of the temporal) in delphinids has, in addition to the anatomical relationships in terrestrial 

mammals, developed a large ventral process, the falciform process. See Schulte (1917:373, 375, 380–384, 392, 394) and Fraser 

and Purves (1960:9, 19, 34, 35, 37–39, 41–45, 47, 48, 55, 57, 

62, 77, 79, 80, 85, 115, 132, 135, 136).

− anterior angle of the tympanosquamosal recess (Fraser and 

Purves, 1960:45, 46)

Fraser and Purves (1960:45, 46) mentioned the anterior 

angle in the context of the anterior extremity of the tympanosquamosal recess, which they viewed as a triangular structure.

* anterior meatal crest (Figure 23c)

The anterior meatal crest lies posteromedial to the postglenoid or retroarticular process (Fordyce, 1994:156) and forms the 

anterior boundary of the external acoustic meatus sensu lato. 

Owen, when describing Orcaella (1866a:28, pl. 9: fig. 3(8), 

stated that the “mastoid part terminates below in a rough, flattened, triangular surface (figs. 3, 8), 5", 7''' [5 inches, 7 lines] 

in diameter, which is divided from the zygomatic or articular 

process of the squamosal (g) by a deep fissure.” (The lines symbol, ''', is an obsolete shorthand for measurement in lines—as in 

feet, inches, and lines; one line (1''') represents one-tenth or onetwelfth of an inch.) We feel that the “mastoid part” of Owen is 

1 0 2 • smithsonian contributions to zoolog y squamosal
synonymous with the anterior meatal crest. Owen (1866a:40, 

pl. 13: fig. 2, #8) reiterated this in his description of Kogia sima.

− anterior process of the tympanosquamosal recess (Fraser and 

Purves, 1960:47)

Fraser and Purves (1960:47) mentioned the anterior process 

of the tympanosquamosal recess in passing in their discussion 

of Inia: “The development of the tympano-squamosal recess 

(TSQR) shows a considerable advance on Inia, its anterior process projecting halfway along the mesial border of the zygomatic 

process of the squamosal (SQ).” We interpret “anterior” as a 

general orientation term, not a specific term of a process. 

See anterior angle of the tympanosquamosal recess.

The tympanosquamosal recess of delphinids does not have 

an anterior process.

= articular surface of the squamosal (facies articularis)

See mandibular fossa.

− articular tubercle (tuberculum articulare)

The articular tubercle is a rounded eminence anterior to the 

mandibular fossa on the zygomatic process of the squamosal

(Schaller, 1992:24.29; Feneis, 1994:16.20).

Delphinids do not develop an articular tubercle.

= dactyloid process (Kellogg, 1928:62) = falciform process

− entoglenoid process

MacPhee (1981:52) followed McDowell (1958) in recognizing this feature in eutherians as a descending process of the squamosal that may anterolaterally bound the tympanic region, but is 

distinct from the postglenoid or retroarticular process.

Luo (1998:287) mentioned the presence of an entoglenoid 

process on the squamosal of archaeocetes, and Luo and Gingerich (1999: fig. 1) indicated that the posterior falciform process

forms part of the entoglenoid region in archaeocetes. Geisler and 

Sanders (2003:48, 54) equated falciform process with entoglenoid process, and used both terms.

If the entoglenoid process and falciform process are homologous, then Tursiops has an entoglenoid process. The term “falciform process” (q.v.) has been used widely by cetologists for the 

feature that Luo and Gingerich (1999) termed the entoglenoid 

process, and we continue to use falciform process here.

* falciform process (processus falciformis) (Figures 6f, 23a–e, 

29, 30)

The falciform process of the squamosal bone (van Kampen, 1905, cited by Ridewood, 1922:262, fig. 15) is a unique 

development in Cetacea. It was first recognized by Beauregard 

in 1894 (Fraser and Purves, 1960:8). In delphinids it arises 

from the median dorsal border of the tympanosquamosal recess (which houses the middle sinus; Fraser and Purves, 1960:8, 

9, 13, 14, 33–35, 37–41, 43–61, 65–71, 73, 85, 87, 89) and 

extends medially to lie just ventral to the foramen ovale. The 

falciform process is crescentic, concave posteriorly. The distal 

(medial) end of the falciform process abuts the anterior end of 

the tympanic bulla at the anterodorsal crest anterior to the accessory ossicle (viz., with the dorsal lateral edge of the semicanal for the auditory tube of the tympanic bulla). The falciform 

process fits into the semicanal for the auditory tube (confirmed 

on USNM 504420).

Luo (1998:287) and Luo and Gingerich (1999:32; tbl. 3, 

#16a) noted that in some archaeocetes the anterior process (= 

processus tubarius of the bulla) of the tympanic bulla contacts 

the squamosal bullar process. We presume that the squamosal 

bullar process is the falciform process.

The falciform process in the ziphiids becomes long and thick 

and has been termed the dactyloid process by Kellogg (1928:62).

See also entoglenoid process. 

Schulte (1917:369) described the falciform process of the 

frontal in Kogia. It is a long slender process that lies dorsally 

between the maxilla and the supraoccipital. It is homologous 

with the external surface of the frontal bone that lies between 

the maxilla and the parietal in Tursiops.

− foramina for rami temporales

Wible and Gaudin (2004:154) used the term “foramina for 

rami temporales” for openings in the squamosal or parietal of 

armadillos that transmit the rami temporales of the stapedial artery and accompanying veins. They reported that such foramina 

are absent in the dog.

Tursiops has no significant supply from a stapedial artery 

(see sulcus for the internal carotid artery), and foramina for rami 

temporales are not identifiable.

− foveola suprameatica [suprameatalis]

In Nomina Anatomica (IANC, 1883:A14), under processus 

zygomaticus of pars squamosa of os temporale, there is an entry 

for foveola suprameatica [suprameatalis]. It is not in Whitney 

(1889–1910), Gray (1918), Sisson and Grossman (1953), Evans 

and Christensen (1979), Schaller (1992), or Feneis (1994). Foveola suprameatica translates as “small depressions above the 

(auditory) meatus.” 

See suprameatal fossa.

= glenoid cavity (Fraser and Purves, 1960:23,60)

See mandibular fossa.

= glenoid fossa = glenoid surface

See mandibular fossa. 

− glenoid plate

The glenoid plate extends from the postglenoid process of 

the squamosal bone to the falciform process of the squamosal in 

Platanista (Anderson, 1879:513). It forms the lateral border of 

the tympanosquamosal recess.

The glenoid plate occurs in delphinids.

* glenoid process (Figures 23a–e, 29)

The glenoid process is a strong quadrilateral mass of bone 

attached medially to the squamosal plate (Kernan, 1918:377). 

The glenoid process bears the zygomatic process, mandibular 

fossa, and the postglenoid or retroarticular process.

Delphinids have a well developed glenoid process (Fraser 

and Purves, 1960:38, 39, 44).

= glenoid surface = glenoid fossa

See mandibular fossa. 

squamosal n u m b e r 6 2 7 • 1 0 3
− groove for middle temporal artery (sulcus a. temporalis mediae)

The groove for the middle temporal artery lies on the dorsomedial portion of the external surface of the squamosal in humans (Feneis, 1994:16.16). The groove for the middle temporal 

artery does not seem to appear in other animals (equids, bovids, 

caprids, suids, and canids) (Sisson and Grossman, 1953).

The groove for the middle temporal artery is not present in 

delphinids.

* mandibular fossa (fossa mandibularis) (Figures 2, 23b–d, 29)

The mandibular fossa lies on the ventrolateral portion of 

the squamous part of the temporal and receives the condyloid 

process of the mandible (Gray, 1918:140, 180, 183; Evans 

and Christensen, 1979:134; Schaller, 1992:24.27; Feneis, 

1994:16.20). The mandibular fossa is also known as the glenoid 

fossa (Schulte, 1917:393) or the glenoid cavity, glenoid surface, 

mandibulo-articular surface, articular surface of the squamosal, 

articular cavity, or articular process of the squamosal (Owen, 

1866a:26, 29, 40, 43; pl. 9: fig. 3(g); Fraser and Purves, 1960:9, 

23, 41–43, 45, 49, 54, 56, 60, 67, 69, 71, 73, 77). Eustachius 

and Lancisius (1714:105) referred to the mandibular fossa as the 

sinus ossis ad excipiendum posterius caput madibulae inferioris.

The mandibular fossa in delphinids lies on the ventrolateral 

portion of the squamosal and receives the condyloid process of 

the mandible, forming the temporomandibular joint.

− mastoid diapophyses (Fraser and Purves, 1960)

Owen (1866b–1868(vol. 2):420) described the parietal in a 

skull of a fetal Physeter, using terms that implied serial homology of skull components with vertebrae: “the lower angles are 

confluent with the diapophyses, called ‘mastoids,’ which here, 

as in other Cetacea, are distinct from the petrosals, and chiefly 

support the squamosals . . . .” 

It is not clear what Owen meant by this use of the name 

mastoid. We cannot apply it in a useful way to Tursiops.

− mastoid portion of the squamosal (Fraser and Purves, 1960)

Owen (1866a:29), in his description of the skull of Orcaella, 

stated:

The rough posterior tract articulating with the parietal 

(7) and exoccipital (2), and contributing to the outer 

wall of the otocrane (fig. 3, or), I consider to be the 

“mastoid” confluent with the squamosal, together 

forming the bone which should be termed “squamomastoid.” The mastoid part terminates below in a 

rough, flattened, triangular surface (fig. 3, 8), 5" 7''' [5 

inches, 7 lines] in diameter, which is divided from the 

zygomatic or articular process of the squamosal (g) by 

a deep fissure. On the inner side of the base or back 

part of the mastoid, in the line of its suture with the 

parietal, is the (stylomastoid?) fossa.

Fraser and Purves (1960:77) identified in Caperea a “portion 

of the squamosal immediately anterior to the pars mastoidea, of 

a rugose and laminated appearance . . .”, which they interpreted 

as a mastoid component of tympanoperiotic fused to the squamosal posterodorsal to the external auditory meatus. This led 

to the suggestion that part of the mastoid process or posterior 

process of the periotic bone has lost its usual connection with 

the periotic, and has become fused to the squamosal (Fraser and 

Purves, 1960:5, 9, 34, 35, 37, 40–44, 47, 58, 77, 78: fig. 13, 79, 

80; Purves, 1966:340, Kasuya, 1973: fig. x). Oelschläger (1986a: 

fig. 6) provided a possible interpretation of mastoid–squamosal 

fusion in Tursiops.

Our studies of fetal and neonate skulls of modern species of 

Odontoceti and Mysticeti, and of skulls of fossil archaic Cetacea 

(Archaeoceti, Odontoceti, Mysticeti), provide no evidence that 

any mastoid component of the periotic fuses with the squamosal. 

The mastoid process of the periotic does fuse with the posterior 

process of the tympanic bulla (q.v.) in mysticetes but not in Tursiops. The mastoid portion of the squamosal bone in the sense 

of Fraser and Purves (1960:77) is identified here as the posttympanic process of the squamosal (q.v.).

See posterior process of the tympanic bulla for further 

discussion.

= medial sac (Beauregard, 1894; Fraser and Purves, 1960:8–10) 

= middle sinus

= medial sinus (Beauregard, 1894; Fraser and Purves, 1960:14) 

= middle sinus 

− middle sinus (Fraser and Purves, 1960:63–65)

The middle sinus is located in the tympanosquamosal recess. The middle sinus originates as a lateral projection from the 

tympanic cavity via the epitympanic hiatus (Fraser and Purves, 

1960:1, 63–65, 67–69, 71–74, 76).

= notch for external auditory meatus = groove for external auditory meatus (Kernan, 1918:359) = retroarticular notch

− occipital groove

The occipital groove in humans is medial to the origin of the 

digastric muscle (Gray 1918:179), on the posteroventral aspect 

of the external surface of the temporal. In the yellow armadillo 

(Wible and Gaudin, 2004:138) the groove is on the mastoid surface near the paroccipital process.

Due to the separation of the periotic from the skull in odontocetes, the mastoid process no longer contacts the squamosal 

and the occipital groove is absent.

* occipital margin of the temporal (margo occipitalis) (Figure 23c)

The occipital margin of the temporal bone is that portion of 

the squamosal that abuts the occipital.

The occipital margin in delphinids consists of the posterolateral portion of the squamous part of the temporal.

* occipital process (processus occipitalis) (Figure 23c)

The occipital process is the most posterior extension of 

the squamosal that fits between the parietal and the occipital 

(Schaller, 1992:24.21; not in Feneis, 1994).

The occipital process on the delphinid squamosal is the most 

posterior projection of that part of the temporal that overrides 

the parietal in a squamose suture.

− occipitosquamosal suture (sutura occiptosquamosa) (Schaller, 

1992:76.6)

The occipitosquamosal suture lies between the occipital and 

the squamosal bone (Feneis, 1994:76.6). In adult delphinids it 

1 0 4 • smithsonian contributions to zoolog y squamosal
runs from the ventral portion of the temporal crest anteriorly 

and then turns ventrally to follow the retroarticular notch. Fraser and Purves (1960:77) have named the portion of the occipitosquamosal suture that lies between the paroccipital process and 

the squamosal the “squamoparoccipital suture.”

* parietal margin of the temporal (margo parietalis) (Figure 

23a,c)

The parietal margin of the temporal bone is that portion of 

the temporal that abuts the parietal.

The parietal margin in delphinids consists of the dorsal portion of the squamous part of the temporal.

* parietal notch (incisura parietalis) (Figures 3, 23c)

The parietal notch lies on the dorsal margin of the external 

surface of the squamosal in the posteroventral part of the temporal fossa in humans where the squamosal, petrosal, and parietal 

bones meet (Feneis, 1994:16.12; not in Schaller, 1992).

In delphinids the periotic no longer contacts the parietal. 

Instead its place has been taken by the exoccipital. The parietal notch, as a feature of the external surface of the cranium in 

delphinids, consists of that place in the posteroventral part of 

the temporal fossa where the margins of the squamosal, parietal, 

and exoccipital meet.

= parietal plate (Anderson, 1879:514) = pars squamosa

* periotic fossa (Figure 2, 28, 30)

The periotic fossa is that area on the squamosal, exoccipital, 

and parietal that lies dorsal to the periotic and provides a fossa 

into which the periotic fits (Fordyce, 1994:156). 

In delphinids the anterior part of the periotic fossa bounds 

the alisphenoid and is largely occupied by the posterior lacerate 

foramen and the jugular foramen.

= petro-pterygo-tympanic plate = falciform process

The petro-pterygo-tympanic plate was used by Anderson 

(1879:513) for the medial process of the squamosal that contacted the anterior process of the periotic bone and the reduced 

lateral wall of the pterygoid. This is an extremely modified falciform process.

* posterior meatal crest (Figure 9b)

The posterior meatal crest lies at the posterior margin of the 

external acoustic meatus (Fordyce, 1994:158, 156). 

In Tursiops the posterior meatal crest is no longer identifiable because of changes around the external acoustic meatus.

= postglenoid border (Anderson, 1879:513) = retroarticular or 

postglenoid process

− postglenoid foramen

The postglenoid or retroarticular foramen in the dog lies 

on the lateral surface of the squamous part of the temporal just 

posterior to the retroarticular process (Evans and Christensen, 

1979:134, 152, 153; Schaller, 1992:24.31). The retroarticular 

foramen contains the retroarticular vein, which originates from 

the temporal sinus and drains into the maxillary vein (Evans and 

Christensen, 1979:793; Schaller, 1992:362.3). The canal that 

opens as the retroarticular foramen is the temporal meatus (meatus temporalis) (Schaller, 1992:24.31, 10.12).

In the literature on mammalian phylogenetic anatomy, the 

term “postglenoid” is used widely; thus, postglenoid foramen.

Wible et al. (2004), in their review of cranial drainage in 

the Cretaceous mammal Zalambdalestes, stated that an emissary 

vein exited the postglenoid foramen. They noted that elsewhere 

the vein was known as the capsuloparietal emissary vein.

Geisler and Luo (1998:188–191) gave detailed discussion 

of the postglenoid foramen and capsuloparietal emissary vein. 

They argued that in cetacean history the postglenoid foramen 

has moved from within the squamosal to the squamosal–petrosal

(periotic) suture; such a homology implies that the capsuloparietal emissary vein might traverse the lateral face of the periotic, perhaps associated with the anteroexternal sulcus of some 

Cetacea. However, the archaeocete Zygorhiza may have a nonpatent postglenoid foramen within the squamosal and also show 

a well-developed anteroexternal sulcus between the squamosal 

and periotic bones, suggesting that the postglenoid foramen (and 

capsuloparietal emissary vein) are not related to the anteroexternal sulcus.

Tursiops lacks a patent postglenoid foramen within the 

squamosal. Dissection is needed to determine whether Tursiops lacks an emissary vein (capsuloparietal emissary vein); 

similarly, the postglenoid foramen is absent in archaic odontocetes (Fordyce, 1994:157), archaic mysticetes, and some 

archaeocetes.

= postglenoid fossa = tympanosquamosal recess (Anderson, 

1879:512)

= postglenoid notch (Anderson, 1879:428) = retroarticular 

notch

= postglenoid process = retroarticular process

MacPhee (1981:60) identified the postglenoid process as any 

process receiving the mandibular condyle, noting that in some 

mammals the structure may be replaced by an analogue, the entoglenoid process (q.v.). Postglenoid process and retro­articular 

process (q.v.) are equally applicable in Cetacea. 

= postmeatal process or postmeatal apophysis = posttympanic 

process (de Muizon, 1987:3, 4)

= posttemporal fossa = temporal fossa (Fraser and Purves, 

1960:100, 108; Perrin, 1975:9)

− posttympanic process (Figure 23b,c)

MacPhee (1981:60) cited van Kampen (1905:353) that the 

posttympanic (or retrotympanic) process in mammals is a feature of the squamosal that lies next to or on the posterior margin of the external acoustic meatus. See also Wible and Gaudin 

(2004:133,176). In Cetacea, the posttympanic process (sensu 

Fordyce, 1994, following Pompeckj, 1922: pl. 2) is the posterolateral portion of the squamosal, just lateral to the suture for 

the tympanic bulla. Flower (1878:423) employed posttympanic 

process for both “mastoid and squamosal” in ziphiids, while 

de Muizon (1987:3, 4) used the terms “postmeatal process” or 

“postmeatal apophysis” for posttympanic process.

squamosal n u m b e r 6 2 7 • 1 0 5
− preglenoid process

The preglenoid process in some mammals is a transverse 

ventrally-directed ridge anterior to the glenoid fossa (e.g., 

Geisler, 2001). Kernan (1918:356) used preglenoid process 

for the anterior of the zygomatic process of the squamosal in 

Ziphius.

− pterygoid process of the squamosal (Ridewood, 1923:224–

226, 237, 259, 260)

The pterygoid process of the squamosal is that anterior 

part of the squamosal bone that lies dorsal to the foramen ovale

(Ridewood, 1923:224, fig. 15; Fraser and Purves, 1960:34, 35, 

37–39). The pterygoid process is developed in mysticetes, typically contacting the pterygoid (e.g., fin whale, Balaenoptera physalus), but sometimes reaching the palatine (e.g., blue whale, 

B. musculus, and bowhead, Balaena mysticetus).

= pterygoperiotic plate = petro-pterygo-tympanic plate = falciform process

The pterygoperiotic plate was apparently a slip-of-the-pen 

for the petro-pterygo-tympanic plate (Anderson, 1879:514).

= pterygotympanic process (Anderson, 1879:508) = falciform 

process

Anderson, in his description of the basicranium of Platanista, assigned several terms to what we consider the falciform 

process of the squamosal bone. One of these is the pterygotympanic process (1879:508).

* retroarticular notch (Figures 3, 23c)

The retroarticular or postglenoid notch marks the lateral 

end of the external auditory meatus (or external acoustic meatus) in the broad sense. A notch develops because the cetacean 

tympanic has become isolated from the squamosal bone and has 

moved medially away from the lateral end of the external auditory meatus, so that the meatus is not fully floored by bone.

The retroarticular notch in delphinids lies immediately 

posterior to the retroarticular or postglenoid process. The anterior border of the notch consists of the postglenoid process 

of the squamosal, and the posterior border consists of the posttympanic process of the squamosal. The cartilaginous external 

acoustic meatus sensu stricto lies ventral to the retroarticular 

notch.

* retroarticular process (processus retroarticularis) = postglenoid 

process (Figures 2, 23c)

The retroarticular process in mammals is a ventral extension 

of the squamous part of the temporal immediately posterior to 

the mandibular fossa (Evans and Christensen, 1979:134). This is 

not to be confused with the entoglenoid process (q.v.).

In Cetacea, the retroarticular or postglenoid process is a 

transverse crest immediately posterior to the mandibular fossa 

(Schulte, 1917:393; Fordyce, 1994:156, 157).

* retrotympanic process (processus retrotympanicus) (Figures 3, 

23c)

The retrotympanic process is a posterolateral process of 

the squamosal that passes posteriorly over the tympanic and 

articulates with the mastoid process of the petrosal (Schaller, 

1992:24.33; not in Feneis, 1994). Posttympanic process is an 

equally applicable synonym.

The retrotympanic process or posttympanic process (q.v.) in 

odontocetes is lateral to the bulla and posterolateral to the external auditory meatus, sensu lato. The process typically articulates 

with the bulla and exoccipital.

= sac moyen (Beauregard, 1894; Fraser and Purves, 1960:114) 

= middle sinus

* sphenoidal margin of the temporal (margo sphenoidalis) (Figures 23d, 30, 31b)

The sphenoidal margin of the temporal bone is that portion 

of the temporal that abuts the alisphenoid.

The sphenoidal margin in delphinids consists of the anteromedial portion of the squamous part of the temporal.

* spiny process (Figure 25v)

The spiny process (de Muizon, 1987; Fordyce, 1994:156, 

158) lies on the posteromedial corner of the squamosal bone, 

just posterior to the medial edge of the tympanosquamosal recess. In Platanista, the spiny process is a distinct medial projection of the squamosal that carries a transversely oriented groove 

(part of the external acoustic meatus in the broad sense) on its 

ventral surface, and that articulates with the hiatus epitympanicus of the periotic bone and with the posterior process of the 

tympanic bulla.

In Tursiops and other delphinids, the spiny process is generally indistinct or not developed in the adult. Occasional specimens have the spiny process articulated with the periotic.

− squamocranial notch (Fraser and Purves, 1960:46)

The squamocranial notch is the broad anterior notch formed 

by the glenoid process of the squamosal bone and the cranium 

(Fraser and Purves, 1960:46).

− squamosal bullar process

Luo and Gingerich (1999:32) equated the anterior process 

of the tympanic bulla with the processus tubarius, and noted 

that in some archaeocetes the latter structure contacts the squamosal bullar process.

See anterior process of the tympanic bulla.

* squamosal plate (Figure 23a–e)

The squamosal plate of the squamosal bone in odontocetes 

consists of that part of the bone that lies immediately medial to 

the glenoid process and that forms a squamous suture (squamosal suture) with the parietal (Kernan, 1918:377).

* squamosal suture (sutura squamosa) (Figure 32)

The squamosal suture is a squamose suture formed by overriding of the parietal by the squamosal part of the squamosal bone 

(Gray, 1918:183; Evans and Christensen, 1979:135; Schaller, 

1992:76.16; Feneis, 1994:54.10). Vesalius (1543) referred to the 

squamous suture as the conglutinationem squamaeformem (ibid., 

21), the glutinatio squamaeformis (ibid., 21), the squamaeformis 

conglutinatio (ibid., 23), the squamaeformis est conglutinataio

(ibid., 21), and the squamosa conglutinatio (ibid., 21, 25).

Cetaceans have a normal squamosal suture.

1 0 6 • smithsonian contributions to zoolog y squamosal
− squamous part of the temporal bone (pars squamosa)

The squamous part of the temporal bone consists of the portion of the temporal that forms the lateral part of the cranium. The 

squamous part comprises the glenoid process, the zygomatic process of the squamosal, and the squamosal plate (Gray, 1918:139; 

Evans and Christensen, 1979:134; Schaller, 1992:24.19; Feneis, 

1994:16.10). The squamous part is also known as the squama 

(squama temporalis) (Gray, 1918:139). The squamous part is differentiated from the petrous part, the mastoid part, the tympanic 

part, and the styloid process (Gray, 1918:138).

We have chosen to recognize the squamous part of the temporal bone in Cetacea as a separate ossification known as the 

squamosal bone (q.v.).

= subsquamosal foramina = foramina for rami temporales

The term “subsquamosal foramen” has been used in armadillos (Wible, 2003:183) for vascular apertures in the squamosal dorsal to the suprameatal bridge. Later, Wible and Gaudin 

(2004:154) used foramina for rami temporales as an alternative.

* subtemporal crest (Figures 3, 23c)

The subtemporal crest of the squamosal bone lies on the 

ventromedial surface of the zygomatic process of the squamosal, where it forms “the abrupt ventrointernal margin of the 

temporal fossa (here mainly formed by alisphenoid) which extends from near the choanae towards the squamosal, to separate 

the basicranium from the temporal fossa and orbit” (Fordyce, 

1994:154, 155). The subtemporal crest limits the temporal fossa 

anteroventrally.

In Tursiops the curve of the crest is continuous with the 

anterior curve of the falciform process.

= supramastoid crest (crista supramastoidea) 

The supramastoid crest is on the dorsal part of the zygomatic process of the squamous part of the temporal bone. It is 

attached to the temporal fascia (Schaller, 1992:24.25; not in Feneis, 1994). It is continuous with the nuchal crest (Evans and 

Christensen, 1979:131). This is also known as the temporal crest

(Evans and Christensen, 1979:134). Fordyce (1994:157) used 

the terms “crest of the zygomatic process” (of the squamosal) for 

a more-anterior structure, and “lambdoid crest” for the moreposterior structure.

= suprameatal bridge = supramastoid crest (Wible, 2003:183; 

Wible and Gaudin, 2004:132)

In the yellow armadillo the suprameatal bridge (Wible, 

2003:183; Wible and Gaudin, 2004:132) is a well-developed 

crest developed posterior to the dorsal margin of the zygomatic 

process of the squamosal; it presumably marks the lateral limit 

of the origin of the temporalis muscle.

See discussion under supramastoid crest.

− suprameatal foramen

Some mammals have a suprameatal foramen dorsal or anterodorsal to the external acoustic meatus (e.g., Ross and Covert, 

2000; Gabbert, 2004). In Monodelphis (see Wible, 2003:156) 

the foramen is associated with the postglenoid foramen. The relationship is not clear with the foveola suprameatica.

Tursiops lacks a suprameatal foramen.

− suprameatal fossa (Wang et al., 2004, 2005; Wesley-Hunt and 

Flynn, 2005:5)

The suprameatal fossa of some Carnivora is a depression 

immediately posterior to the bony external auditory meatus

on the lateral wall of the skull (Wang et al., 2004, 2005; Wesley-Hunt and Flynn, 2005:5). See also foveola suprameatica

[suprameatalis].

Tursiops lacks a suprameatal fossa in the sense of the structure in carnivores.

Suprameatal fossa in the sense of a feature on the lateral face 

of the squamosal should not be confused with the suprameatal fossa as recognized on the cetacean periotic (see suprameatal 

fossa of the periotic).

− suprameatal pit (Geisler and Sanders, 2003:50) 

Geisler and Sanders (2003:50) named the suprameatal pit 

of the squamosal bone for the feature described by de Muizon 

(1987) as the fossa that receives the hook-like articular process

of the periotic in Platanista. Geisler and Sanders considered the 

pit likely to house part of the peribullary sinus as well as the 

hook-like articular process of the periotic.

In Tursiops the periotic lacks a hook-like articular process, 

and there is no corresponding pit in the squamosal. The exact 

relationship between bone and soft tissue in Tursiops is uncertain for the fossae, pits, and ridges in the squamosal adjacent to 

the periotic.

− suprameatal spine (spina suprameatica [suprameatalis])

The suprameatal spine is a variable spinous process located at 

the root of the zygomatic process of the squamosal, posterodorsal 

to the external auditory meatus in humans (Feneis, 1994:16.5). It 

is located on the anterior border of the suprameatal triangle.

The suprameatal spine is not known in delphinids.

− supratubercular ridge (Fordyce, 1994:158) 

The supratubercular ridge divides the periotic fossa into an 

anterior and a posterior portion in Waipatia (fossil platanistoid; 

Fordyce, 1994:158). The supratubercular ridge lies lateral to the 

foramen spinosum and posteromedial to the falciform process. 

Geisler and Sanders (2003:48) commented further on this feature, associating it with the suprameatal pit.

The supratubercular ridge is not developed in delphinids.

* temporal arch (Figure 3)

The temporal arch in odontocetes is formed by the zygomatic process of the squamosal and the postorbital process of the 

frontal bone (Kernan, 1918:356). The temporal arch forms the 

anterior limit of the temporal fossa.

* temporal crest (Figures 3, 5)

The temporal crest lies on the dorsal surface of the zygomatic 

process of the squamous part of the temporal. The temporal crest 

is a continuation anteriorly of the nuchal crest (Evans and Christensen, 1979:134; Feneis, 1994:28.10a). Gray (1918:139) and 

Schaller (1992:24.25) referred to this as the supramastoid crest. 

Vesalius (1543:22) referred to the temporal crest as asperitas 

(slight roughness).

The temporal crest in adult delphinids is a well-defined crest 

that defines the lateral extent of the temporal fossa. The temporal 

squamosal n u m b e r 6 2 7 • 1 0 7
crest lies on the dorsal surface of the zygomatic process of the 

squamosal, where it is also known as the supramastoid crest. Posteriorly and dorsally the temporal crest is formed by the parietal. 

Anterodorsally it is formed by the frontal. Anderson (1879:428, 

501) referred to the temporal crest as the lambdoidal ridge.

See also supramastoid crest. 

* temporal fossa (Figures 3, 32)

The temporal fossa is the origin of the temporal muscle and 

consists of the lateral areas of the parietal, squamosal, frontal, 

and alisphenoid bones (Gray, 1918:183; Evans and Christensen, 

1979:124; Schaller, 1992:10.22; Feneis, 1994:30.11). Vesalius 

(1543:25) referred to the temporal fossa as the temporis. The 

temporal fossa is bounded by the temporal crest, orbitotemporal 

crest, infratemporal crest, and subtemporal crest. 

Tursiops has a normal temporal fossa that is representative 

for delphinids; the fossa is subcircular in lateral view, formed 

mainly in squamosal and parietal, and bounded by distinct nuchal and associated crests. In dorsal view, each fossa is formed 

by the laterally convex wall of the braincase. In contrast to archaeocetes and most other mammals, the temporal fossae do not 

meet medially, to separate the facial region from the supraoccipital region. 

The temporal fossa was mistakenly referred to as the posttemporal fossa (Fraser and Purves, 1960:100, 108; Perrin, 

1975:9). See Schulte (1917:369, 370, 375, 376, 381, 391–393, 

401), Fraser and Purves (1960:19, 22, 35, 100, 102, 106). 

Schulte also inadvertently referred to it as the zygomatic fossa 

(1917:373).

* temporal surface of the squamosal (facies temporalis) (Figures 

23c, 32)

The temporal surface of the squamosal bone is that portion 

of the external surface of the squamous portion that borders the 

temporal fossa (Schaller, 1992:24.24; not in Feneis, 1994).

The temporal surface of the squamosal lies dorsal to the 

zygomatic process of the squamosal.

− temporomandibular joint (articulatio temporomandibularis)

The temporomandibular joint is formed by the mandibular 

fossa of the squamous part of the temporal and the articular condyle of the mandible (Evans and Christensen, 1979:134). It is also 

known as the “jaw joint” and frequently abbreviated “TMJ.”

The temporomandibular joint in delphinids consists of the 

same elements as it does in terrestrial mammals. However, the 

temporomandibular joint in delphinids is a fibrous joint and the 

boundaries and surfaces of it are not as well defined as they are 

in terrestrial mammals, where it is a synovial joint. In mysticetes 

the fibrous joint has been called the interarticular fibro-cartilage 

(Fraser and Purves, 1960:22).

* temporozygomatic suture (sutura temporozygomatica) (Figure 

32)

The temporozygomatic suture lies between the jugal and 

the zygomatic process of the squamosal (Evans and Christensen, 

1979:135, 143; Schaller, 1992:76.35; Feneis, 1994:54.25). Gray 

(1918:182) referred to the temporozygomatic suture as the zygomaticotemporal suture. Vesalius (1543:23) referred to the temporozygomatic suture as the sutura ossi iugalis.

Most living cetaceans have a temporozygomatic suture that 

remains open throughout life.

* tympanosquamosal recess (Figures 23d, 30)

The tympanosquamosal recess (Fraser and Purves, 1960:9, 

19, 35, 38, 39, 41–61, 63–65, 67, 69, 71–74) is the smooth fossa 

just medial to the mandibular fossa of the squamosal bone. It 

contains the middle sinus.

* zygomatic process of the squamosal (processus zygomaticus) 

(Figures 23a–d, 29)

The zygomatic process of the squamous part of the temporal is a long, curved process that overlaps the posterior portion of the jugal bone and makes up the zygomatic arch. The 

zygomatic process comes laterally off the middle portion of the 

squamous part and is directed anteriorly (Gray, 1918:139; Evans 

and Christensen, 1979:134, 131; Schaller, 1992:24.26; Feneis, 

1994:16.16;). Vesalius (1543:22, 23) referred to the zygomatic 

process of squamosal as the temporis ossis processus, jutting out 

like a stylus for writing sciptorii stili.

The zygomatic process in delphinids is a triangular process 

that lies on the anteroventral portion of the glenoid process of 

the squamosal bone (Schulte, 1917:373, 375, 382, 390, 393, 

398, 401; Fraser and Purves, 1960:9, 13, 19, 26, 34, 37, 38, 

41–47, 50–57, 60, 61, 70, 77, 84). The base is immediately anterior to the mandibular fossa. The apex is directed anteromedially and articulates with the jugal. Owen (1866a:36) referred 

to this process at one point as just the zygoma, at others as the 

zygomatic part (1866a:29, 36), and at others as the zygomatic 

process (1866a:28, 39, 40).

SUPRAOCCIPITAL BONE

Os Supraoccipitalis

Figures 3–5, 6a,c,e, 12a–c,e, 24, 31a

The supraoccipital is one of the three bones that surround the 

foramen magnum and that form the occipital region of the cranium. The supraoccipital is the most dorsal of the three and forms 

the dorsal border of the foramen magnum and part of the roof of 

the cranium (Schulte, 1917:369–371, 375, 376, 382, 383, 401).

In cetaceans the occipital region has been evolutionarily 

modified by the process that has become known as “telescoping” (q.v.). In adult cetaceans the supraoccipital, together with 

the interparietal, forms the occipital shield. Schulte (1917:370) 

referred to the occipital shield as the occipital complex.

Owen (1866a) consistently referred to this bone as the 

superoccipital.

* cerebral fossa (fossa cerebralis) (Figure 31a)

Feneis (1994:8.34a) defines the cerebral fossa in humans 

as the depression for the occipital lobes of the cerebrum. Some 

authorities take a more general view, such as Whitney (1889–

1910:[vol. 3]2347): “cerebral fossae, one of three depressions, 

anterior, middle, and posterior, on each side of the floor of the 

cranial cavity, lodging respectively the frontal and temporal 

lobes of the cerebrum and the cerebellum.” It does not appear 

1 0 8 • smithsonian contributions to zoolog y supraoccipital
to have been used in describing nonhuman animals because no 

mention of it is found in Schaller (1992) or Evans and Christensen (1979).

Anderson (1879:511) used cerebral fossa to refer to that 

part of the cranial cavity that contains the cerebrum. In delphinids it is comprises portions of the exoccipital, supraoccipital, 

parietal, interparietal, frontal, ethmoid, and squamosal. The cerebral fossa is bounded posteroventrally by the tentorium and 

anteromedially by the basicranium.

* cruciform eminence (eminentia cruciformis) (Figure 24b)

The cruciform eminence is formed on the internal surface of 

the supraoccipital by the confluence of the sulci for the transverse 

sinus, sagittal sinus, and occipital sinus. The cruciform eminence 

centers on the internal occipital protuberance (Gray, 1918:130; 

Schaller, 1992:10.11; Feneis, 1994:8.28).

The cruciform eminence is developed in Tursiops but the 

lower limb of it (groove for the occipital sinus) is weakly developed. Owen (1866a:26) and Anderson (1879:501, 502) used the 

term “lateral sinus” instead of transverse sinus.

* dorsal sagittal sinus sulcus (sulcus sinus sagittalis dorsalis)

See “Interparietal Bone.”

* external occipital crest (crista occipitalis externa) (Figures 5, 

24a,c)

The external occipital crest is a smooth median ridge extending from the external occipital protuberance to the foramen magnum (Evans and Christensen, 1979:122; Schaller, 

1992:16.27; Feneis, 1994:8.24).

The external occipital crest is weakly developed in Tursiops

and most odontocetes (e.g., Anderson, 1879:501). It is more evident in the larger delphinids such as Globicephala and Orcinus.

− external sagittal crest (crista sagittalis externa)

The external sagittal crest is a median crest immediately anterior to the external occipital protuberance (Evans and Christensen, 1979:121; Schaller, 1992:16.30). It is not developed in 

humans (Feneis, 1994).

The external sagittal crest has become incorporated into 

the vertex in all living odontocetes and is not present as a recognizable feature. It is present in a number of fossil groups of 

cetaceans.

= foramen for the dorsal sagittal sinus (foramen sinus sagittalis 

dorsalis)

See foramen impar. 

− foramen impar

The foramen impar lies on the dorsal surface of the internal 

occipital protuberance. It contains the posterior end of the sagittal sinus as it joins with the transverse sinuses. It is also known as 

the foramen for the dorsal sagittal sinus (Evans and Christensen, 

1979:122, 157).

The foramen impar is present in odontocetes that have developed the internal occipital protuberance (i.e., older animals 

and large species).

= great occipital crest = external occipital crest

* groove for dorsal sagittal sinus (sulcus sinus sagittalis dorsalis) 

(Figures 12b, 24b)

The sagittal sinus drains the dorsal surface of the cranial 

cavity. It begins at the confluence of the rhinal veins, continues 

posteriorly in the attached edge of the falx cerebri. It terminates posteriorly in the transverse sinus (Evans and Christensen, 

1979:791; Schaller, 1992:10.9, 26.21, 28.6). In humans this feature is known as the groove for superior sagittal sinus (sulcus sinus 

sagittalis superior (Feneis, 1994:8.31, 16.26a, 18.16, 28.26).

In most mammals this sulcus lies along the sagittal suture of 

the parietals, but in cetaceans it lies along the median portion of 

the supraoccipital, interparietal, and may extend a bit onto the 

frontals. In Tursiops it does not occur on the frontals.

* groove for occipital sinus (sulcus sinus occipitalis) (Figure 24b)

The occipital sinus in humans is situated in the attached 

margin of the falx cerebelli. It commences around the margin of 

the foramen magnum and ends in the confluence of the sinuses. 

It runs dorsally from the foramen magnum to its termination 

in the internal occipital protuberance. The groove for occipital 

sinus forms the ventral limb of the cruciform eminence on the 

internal side of the supraoccipital bone. It is the smallest of the 

cerebral venous sinuses (Gray, 1918:658; Feneis, 1994:8.33a). It 

also occurs in the horse (Sisson, 1910:591) and the camel (Smuts 

et al., 1987:170) but not in the dog (Evans and Christensen, 

1979:791).

The occipital sinus occurs in delphinids and the groove 

for the occipital sinus is on the ventral side of the cruciate 

eminence.

= groove for sagittal sinus

See groove for dorsal sagittal sinus. 

* groove for transverse sinus (sulcus sinus transversi) (Figures 

24b, 31a)

The transverse sinus is a paired structure. It begins on the 

midline of the supraoccipital bone at the confluence of the sinuses (confluens sinuum). There, the sagittal sinus, transverse 

sinus, and sometimes straight sinuses (sinus rectus) (Schaller, 

1992:238.17) converge. The transverse sinus then runs laterally 

and anteriorly to terminate in the temporal sinus and sigmoid sinuses on the squamosal bone (Evans and Christensen, 1979:122; 

Schaller, 1992:16.37, 18.6; Feneis, 1994:8.32).

In Tursiops and other odontocetes the groove for transverse 

sinus begins medially at the internal occipital protuberance on 

the supraoccipital, and extends laterally across the dorsal portion of the exoccipital bone to the posteroventral part of the parietal bone.

− highest nuchal line (linea nuchae suprema)

The highest nuchal line in humans occurs on the dorsal 

portion of the supraoccipital bone in humans and is formed by 

the attachment of the galea aponeurotica to the skull (Gray, 

1918:129, 379). This thin broad sheet of connective tissue serves 

as the tendon of insertion for the occipital and frontal parts of 

the epicranius muscle. The galea aponeurotica serves as attachment to the scalp, permitting considerable movement.

This specialization does not occur in cetaceans, and the 

galea aponeurotica is absent.

supraoccipital n u m b e r 6 2 7 • 1 0 9
− inferior nuchal line (linea nuchae inferior)

The inferior nuchal line is the line on the supraoccipital between the insertions of the m. semispinalis capitis dorsally and 

the m. rectus capitis posterior and m. obliquus capitis superior

(Gray, 1918:129; Feneis, 1994:8.27).

The inferior nuchal line may be identifiable in cetaceans as 

the line on the supraoccipital bone ventral to the insertion of the 

m. semispinalis capitis.

− internal occipital crest (crista occipitalis interna)

The internal occipital crest sometimes consists of a pair of 

crests that bound the vermiform impression in the dog (Evans 

and Christensen, 1979:122) on the supraoccipital. The internal 

occipital crest extends posteroventrally from the internal occipital protuberance (Schaller, 1992:16.33; Feneis, 1994:8.30). In 

humans the internal occipital crest runs from the internal occipital protuberance to the foramen magnum (Gray, 1918:131, 

193). The internal occipital crest separates the inferior occipital 

fossae, which house the hemispheres of the cerebellum.

Anderson (1879:502) could find no trace of the internal occipital crest in Platanista, nor have we been able to find it in 

Tursiops or other delphinids.

* internal occipital protuberance (protuberantia occipitalis interna) (Figures 24b, 31a)

The internal occipital protuberance develops on the dorsal 

midline of the internal surface of the supraoccipital. It is closely 

associated with the posterior termination of the falx cerebri

(Evans and Christensen, 1979:122; Schaller, 1992:16.32; Feneis, 

1994:8.29).

In Tursiops and other odontocetes the internal occipital 

protuberance develops as the animal matures. It comes to contain the transverse canal and the posterior portion of the sagittal 

sinus. It forms the medial portion of the ossified tentorium.

= internal vertical ridge (Anderson, 1879) = internal sagittal crest

* keyhole notch (Figure 24e)

The keyhole notch (Evans and Christensen, 1979:121, 123) 

is a variable feature that lies dorsal to the foramen magnum. The 

ventral limits of the keyhole notch are the nuchal tubercles (Evans 

and Christensen, 1979:123; Schaller, 1992:16.4). The keyhole 

notch is formed by the supraoccipital ossification not extending 

ventrally to fill the gap between the exoccipital ossifications.

The keyhole notch is common in cetaceans.

* nuchal tubercles (tubercula nuchalia) (Figure 24a,e)

The nuchal tubercles are paired projections of the posterior 

limbs of the supraoccipital into the dorsal surface of the foramen 

magnum. The nuchal tubercles are developmental features that 

tend to be more apparent in young animals (Evans and Christensen, 1979:123; Schaller, 1992:16.4).

Nuchal tubercles are variable in Cetacea.

= occipital protuberance

See internal occipital protuberance or external occipital 

protuberance. 

= occipital shield = occiput

− occipital tuberosity (Barnes and McLeod, 1984:9, 17, fig. 2)

In the gray whale, bilateral occipital tuberosities occur on 

the supraoccipital, presumably forming the origin for some of 

the neck musculature (Barnes and McLeod, 1984:9, 17, fig. 2).

Occipital tuberosities are not developed in Tursiops.

* occiput (Figure 24c)

The occiput is the lower back of the head in newborn humans (Dox et al., 1979:341). The occiput lies between the foramen magnum and the vertex (Fraser and Purves, 1960:5). 

Vesalius (1543:21,23,25) referred to the occiput as the occipitis 

os; Eustachius and Lancisius (1714:28,111) as the occiput.

The occiput consists of the occipital ossification, which in 

cetaceans is the supraoccipital plus interparietal bones. In adult 

cetaceans, where the supraoccipital and interparietal are fused, 

the occiput has been referred to as the occipital shield.

* opisthion (Figures 5, 24d)

The opisthion is a craniometric point that occurs on the 

midpoint of the dorsal border of the foramen magnum (Gray, 

1918:181).

* parietal margin of the supraoccipital (margo parietalis) (Figure 

24a,c)

In noncetacean mammals the parietal margin of the supraoccipital bone is the entire anterior margin of that bone. Because 

of the inability in most mammals to differentiate the interparietal, it is assumed that the parietals make up 100% of the parietal ossification.

In delphinids the parietal is excluded from the midline by 

the extensive interparietal ossification. The parietal margin of the 

supraoccipital bone is therefore the anterolateral border of the 

supraoccipital.

= sagittal crest

See external sagittal crest, internal sagittal crest. 

= supraoccipital (squama occipitalis) = supraoccipital bone

= supraoccipital crest (Kernan 1918:383) = internal sagittal crest

− supraoccipital foramina

Wible and Gaudin (2004:166) mentioned the presence of 

small supraoccipital foramina in the dog and some armadillos, 

associated with the transverse sinus and occipital emissary vein.

Tursiops may have scattered small foramina on the supraoccipital bone but none is identifiable as supraoccipital foramina.

= supraoccipital shield (occipital shield) (Miller, 1923:5) = supraoccipital plus interparietal

* tentorium / bony tentorial ossification (tentorium osseum / 

processus tentoricus / tentorium cerebelli osseum) (Figure 31a,b)

The bony tentorium is an ossification that develops as a shelf 

in the cerebellar tentorium (tentorium cerebelli membranaceum). 

It spreads laterally from the internal occipital protuberance to 

the posterior edge of the parietal. The tentorium is formed by 

a leaf of bone that projects anteromedially from the dorsal part 

1 1 0 • smithsonian contributions to zoolog y supraoccipital
of the posterior border of the parietal and the internal occipital protuberance (Evans and Christensen, 1979:124; Schaller, 

1992:10.10; Feneis, 1994:268.25).

The anterolateral margin of the tentorial ossification in 

odontocetes ends on the most medial aspect of the internal surface of the parietal. The primary portion of the tentorium is on 

the supraoccipital and exoccipital bones. The tentorium is well 

developed in odontocetes, increasingly so in older animals. The 

development of the tentorium also seems to be correlated with 

overall size, that is, the tentorium is more developed in large species of delphinids than in small species.

* transverse canal (canalis sinus transversis) (Figure 31a)

The transverse canal lies on dorsal portion of the internal 

surface of the supraoccipital bone and penetrates the internal 

occipital protuberance. It is continuous laterally with the groove 

for transverse sinus (Evans and Christensen, 1979:122; Schaller, 

1992:10.13). The foramen impar opens dorsally into the transverse canal.

The transverse canal is not present in newborn Tursiops but appears upon development of the internal occipital 

protuberance.

− vermiform impression / vermiform fossa (impressio verminalis)

The vermiform impression lies between the internal occipital 

protuberance and the foramen magnum. It is bounded laterally 

by the paired internal occipital crests. The vermiform impression 

accommodates the vermis of the cerebellum (Evans and Christensen, 1979:154; Schaller, 1992:16.36).

The vermiform impression is very faintly developed in odontocetes because of the increased size of the foramen magnum to 

accommodate the vertebral vascular plexus. Most of the vermis 

abuts the vascular plexus instead of the supraoccipital bone. 

The vermiform impression is not expressed in Delphinids.

Tympanoperiotic COMPLEX

Periotic Bone

Os Temporale / Pars Petrosa

Figures 25, 28

The mammalian temporal bone (e.g., Evans and Christensen, 1979; Novacek, 1986) can be separated into petrosal, 

tympanic, and squamosal centers of ossification. The petrosal 

(pars petrosa, petrous temporal, or pyramid) contains the inner 

ear (cochlea and semicircular canals). The petrosal is bounded by 

the other elements of the temporal bone (tympanic and squamosal) and the basioccipital, exoccipital, basisphenoid, and parietal 

(Gray, 1918:142; Evans and Christensen, 1979:129; Schaller, 

1992:22.2; Feneis, 1994:12.15). Vesalius (1543:23) did not differentiate the petrosal, merely labeled it as temporis ossis, but 

Eustachius and Lancisius (1714:104, 107, 109, 112) referred to 

it as the os petrosum. Craigie (1831:46) referred to the periotic 

in cetaceans as the lithoid.

The cetacean ear is one of the most divergent regions of the 

skull. The tympanoperiotic in Tursiops is highly modified from 

the condition in many other mammals, and homologies are not 

always clear. Many of the identifications offered here should be 

investigated by detailed dissections and by embryological study. 

A complex anatomical terminology applies to the auditory region 

in mammalian embryos (e.g., Boenninghaus, 1904; MacPhee, 

1981). We have found it difficult to identify many embryonic 

features in adults, and generally have not included anatomical 

terms for those features that are apparent only in embryos.

In Tursiops the petrosal has been isolated from the rest of 

the skull; as in other Neoceti, it is now called the periotic. The 

periotic has most contact with the tympanic bulla, which lies 

ventral to it. It also is joined by delicate bony process to the squamosal just posterior to the retroarticular or postglenoid process. 

It lies on the ventral surface of the posterolateral margin of the 

skull, ventral to the jugular foramen and the bones that border 

it (alisphenoid, parietal, exoccipital, basioccipital) and dorsal to 

the tympanic bulla. Kellogg (1928:203, fig. 23) did a splendid 

figure of the tympanoperiotic of the narwhal.

= acoustic pore of the internal acoustic meatus

See internal acoustic pore and internal acoustic meatus.

− anterior bullar facet

In Neoceti the anterior bullar facet of the periotic bone lies 

on the ventral surface of the anterior process of the periotic bone. 

The anterior bullar facet is delimited posteriorly by the fovea epitubaria for the accessory ossicle (Fordyce, 1994:160) and, in many 

Odontoceti, it also receives the periotic facet on the convex elongate dorsal surface of the outer lip of the tympanic bulla. In Tursiops and other delphinids, the anterior bullar facet is lost because 

the accessory ossicle of the tympanic bulla is expanded to cover 

the ventral surface of the anterior process of the periotic bone.

Luo and Gingerich (1999: tbl. 2, #6b) stated that the bullar 

facet for the anterior process of the [ecto] tympanic (= anterior 

bullar facet of our use) is distinct from the fovea epitubaria, but 

it is only present in Odontoceti with a very elongate anterior 

process.

− anterior fissure of the facial foramen

Geisler and Luo (1996: fig. 3) used this term for the slit-like 

anterior opening of the petrosal canal in some Mysticeti.

See petrosal canal.

* anterior incisure [new term] (Figure 25d,m,v,x)

In Odontoceti, the cochlear process of the periotic is separated from the anterior process of the periotic bone by a “notch 

at the anterior border of the cochlea [sic; pars cochlearis]” (Anderson, 1879:514). This notch, although prominent, has escaped 

attention; it may be the feature identified in older literature as 

the groove for the tensor tympani muscle. We have named it the 

anterior incisure.

Tursiops has an anterior incisure.

* anterior keel (Figure 25c,d,n)

In Neoceti, the anterior keel is a crest located on the anterior 

process of the periotic bone and lies between the anteroventral

and anterodorsal angles (Fordyce, 1994:160). The anterior keel 

is a continuation of the dorsal crest. It is present in various archaic Odontoceti and in many Mysticeti.

p e r i o t i c n u m b e r 6 2 7 • 1 1 1
The anterior keel in Tursiops is transversely rounded and 

indistinct.

− anterior lamina

In some archaic terrestrial mammals the petrosal may have a 

three parts: a pars cochlearis, a pars canalicularis, and a prominent anterior lamina that forms part of the lateral wall of the 

braincase (Wible and Rougier, 2000:36).

Adult Tursiops and other delphinids lack an anterior lamina.

* anterior meatal pit [new term] (Figure 25c–u)

The anterior meatal pit in Tursiops is a small but distinct depression within the internal acoustic meatus, located on or near 

the transverse crest and posterior to the proximal opening of the 

facial canal. It is not obviously associated with a foramen, and 

does not occur in all specimens. The pit should not be confused 

with the foramen singulare or dorsal vestibular area.

* anterior process of the periotic bone (Figure 25a,m,n,p,t,w,x)

The anterior process of the periotic bone is the anterior eminence of the element that, in its elongate state, is a neomorph 

in Neoceti and many Archaeoceti; it is prominent in Tursiops. 

Studies of fossils, of embryos and of other mammals indicate 

that the anterior process is an anterior extension of the mammalian tegmen tympani (Luo, 1998:276).

The anterior process in the broad sense consists of everything anterior to a transverse line through the anterior margin of 

the cochlear portion / pars cochlearis (Kellogg, 1936; Yamada, 

1953; Kasuya, 1973); strictly, the anterior process should not 

include the superior process that is a development of the tegmen 

tympani (Luo, pers. comm.). For the ventral surface, Fordyce 

(1994) regarded the anterior process as that part of the periotic anterior to the mallear fossa, that is, anterior to the hiatus 

epitympanicus but including the fovea epitubaria. Dorsally, the 

anterior process in Tursiops merges posteriorly into the body of 

the periotic without any distinct boundary.

Synonyms include tuberosity of the tegmen tympani in the 

sense of Schulte (1917:397), prootic portion of the periotic bone

(Fraser and Purves, 1960:34), and tegmental process (Yamada, 

1953:20).

* anterodorsal angle (Figure 25c,d,m,n,p)

The anterodorsal angle of the periotic bone is the anterior 

curvature of the dorsal crest (Fordyce, 1994:160), as seen in 

many archaic Odontoceti and Mysticeti. The dorsal angle on 

the anterior process of the periotic bone in Tursiops is probably homologous with the anterodorsal angle of other Neoceti, 

although the anterior process of the periotic bone in delphinids 

is too modified to be sure.

− anteroexternal sulcus

The anteroexternal sulcus of the periotic bone lies on the 

lateral surface of the anterior process of the periotic bone, just 

lateral to the anterior bullar facet (Fordyce, 1983; 1994:149, 

160) in many Odontoceti, Mysticeti, and (but see below) Archaeoceti. It originates just anterior to the level of the mallear 

fossa, and rises toward the anterodorsal angle.

For some Archaeoceti, Luo and Gingerich (1999:45) named 

a comparable feature the transverse (or dorsoventral) vascular 

channel or vascular groove, and noted that when enclosed by the 

squamosal (e.g., in Dorudon atrox; their fig. 17) this structure 

forms a vascular foramen.

For the archaeocete Basilosaurus cetoides, Kellogg (1936:27, 

fig. 5) identified the ventral part of the anteroexternal sulcus (in 

our sense) as the fovea epitubaria, and described the sulcus on 

the periotic as “a deep dorso-ventrally curved furrow” (p. 27). 

We have examined this specimen and also isolated periotics of 

Basilosauridae and conclude that the structure discussed by Kellogg is what we term the “anteroexternal sulcus” of the periotic 

bone. We presume, therefore, that the feature in Basilosaurus 

cetoides is homologous with the structure in Dorudon atrox, 

namely the transverse (or dorsoventral) vascular channel or vascular groove of Luo and Gingerich (1999).

For some Mysticeti, Geisler and Luo (1996, 1998) identified 

a large depression here as the squamosal fossa (q.v.).

The anteroexternal sulcus probably marks the path of an 

artery across the lateral surface of the anterior process of the 

periotic bone; Fordyce (1994) suggested the middle meningeal 

artery. Alternatively, it could be associated with the retroarticular or postglenoid vein, although we consider this less likely. Dissection is needed to clarify the identity of the sulcus.

The anteroexternal sulcus is not present in Tursiops.

− anterointernal sulcus (Fordyce, 1994:158, 160)

The anterointernal sulci lie on the ventromedial surface of 

the anterior process of the periotic bone, medial to the anterior 

bullar facet and fovea epitubaria in some Odontoceti. One of the 

sulci may carry the lesser petrosal nerve. 

Tursiops does not have anterointernal sulci, but the sulci 

occur sporadically in other delphinids.

* anteroventral angle (Figure 25c,d,n–p,v)

In Neoceti, the anteroventral angle of the periotic bone is 

the angle that is made on the anteroventral surface of the anterior process of the periotic bone by a continuation of the anterior 

keel. The anteroventral angle lies anterior to the anterior bullar 

facet (Fordyce, 1983:30, 1994:160) or to the fovea epitubaria.

An anteroventral angle is very pronounced in Tursiops.

= antrum of the fenestra rotunda (Novacek, 1986:55)

See cochlear window (or round window).

* aperture for the cochlear aqueduct (Figure 25a,b,e,l,m,o,q,u–w)

In the dog, the aperture or external opening for the cochlear 

aqueduct lies on the medial wall of the petrosal, posteroventral 

to the internal acoustic meatus in the dorsolateral border of the 

jugular foramen, and just dorsal to the jugular incisure (Evans 

and Christensen, 1979:130, 133). The aperture is in the anterior 

edge of the jugular foramen (posterior lacerate foramen) (Evans 

and Christensen, 1979).

In Tursiops and other delphinids the aperture for the cochlear aqueduct (or cochlear canaliculus) lies posteriorly on the 

dorsomedial surface of the cochlear portion (process) of the periotic. The aperture for the cochlear aqueduct is posteromedial to 

the internal auditory meatus.

= aperture of the facial canal

See epitympanic foramen of the facial canal.

1 1 2 • smithsonian contributions to zoolog y p e r i o t i c
= aperture for the endolymphatic duct (Kellogg, 1936; Fordyce, 

1994: fig. 11)

See aperture for the vestibular aqueduct. 

* aperture for the vestibular aqueduct (Figures 25a–l,o,t,u, 28)

In the dog, the aperture for the vestibular aqueduct lies 

posterodorsal to the opening of the cochlear canaliculus on the 

medial surface of the petrosal bone (Evans and Christensen, 

1979:132). The vestibular aqueduct runs from the posterior medial side of the vestibule (Whitmore, 1953) posteroventrally to 

the posterior part of the cerebral surface of the petrosal. The 

vestibular aqueduct carries the endolymphatic duct.

The aperture is also known as the external aperture or foramen for the vestibular or endolymphatic duct or aqueduct, or 

the aquaeductus endolymphaticus (e.g., Kellogg, 1928: fig. 23; 

1936). Kellogg emphasized that in some Cetacea, the aperture is 

quite voluminous.

In Tursiops the opening of the vestibular aqueduct lies on 

the dorsal surface of the periotic just posterior to the internal 

acoustic meatus.

− apex pyramidalis (apex of pyramid) (apex partis petrosae)

The apex pyramidalis lies on the medial side of the petrous 

portion of the mammalian temporal. The apex forms the anterior termination of the petrosal crest in the dog (Evans and 

Christensen, 1979:132) or the anteroventral tip of the petrosal

in cattle (Schaller, 1992:22.9).

The apex pyramidalis cannot be identified with certainty in 

Tursiops.

See pyramid.

= aqueduct of Fallopius (aqueductus Fallopii) = Fallopian 

aqueduct

See facial canal. 

= aqueduct of the cochlea (aqueductus cochlearis)

See aperture for the cochlear aqueduct. 

= aqueductus cochleae

See cochlear aqueduct.

= aqueductus endolymphaticus

See aperture for the vestibular aqueduct.

− arcuate eminence (eminentia arcuata)

The arcuate eminence is an arched elevation on the anterior surface of the pyramid (petrosal) above the anterior semicircular canal in mammals (Feneis, 1994:14.3; not in Schaller, 

1992).

The semicircular canals are greatly reduced in size in the 

Odontoceti and do not present external signs of their presence.

− area cochleae (Figure 25u)

The area cochleae is the ventral or posterior part of the 

internal acoustic meatus into which opens the canal for the vestibulocochlear nerve in archaic artiodactyls (Whitmore, 1953: 

131).

In Tursiops the area cochleae merges without obvious 

boundary into the area nervus facialis.

* area cribrosa media (Figure 25a,u)

In the human petrosal, the portion of the internal acoustic meatus beneath (medial to) the crista falciformis has three 

sets of foramina: “one group, just below the posterior part of 

the crest, situated in the area cribrosa media, consists of several 

small openings for the nerves to the saccule” (Gray, 1918:143). 

Gray (1918:1058, 1059) also stated that the filaments of the inferior branch of the vestibular nerve traverse the foramina in the 

area vestibularis inferior, and end in the macula of the saccule; 

thus, the area cribrosa media and the area vestibularis inferior

appear to be the same.

Some specimens of Tursiops show what may be an area 

cribrosa media separate from the spiral cribriform tract, but in 

other specimens the distinction is not clear. Kellogg (1928: fig. 

23) showed the area vestibularis inferior for Monodon. Schulte 

(1917:396) identified the area cribrosa media in Kogia as a small 

foramen.

Further dissection is needed to confirm the identity of features discussed here.

− area nervus facialis (Figure 25u)

The area nervus facialis is the dorsal or anterior part of the 

internal acoustic meatus into which opens the dorsal foramen 

of the facial canal (Fallopian aqueduct) in archaic artiodactyls 

(Whitmore, 1953:131).

In Tursiops the area nervus facialis merges without obvious 

boundary into the area cochleae.

= area vestibularis inferior = area cribrosa media

Gray (1918:1058–1059) used area vestibularis inferior in 

a manner suggesting synonymy with the area cribrosa media

(q.v.).

− articular peg

De Muizon (1987:8) identified the articular peg as the projection found on the posterolateral face of the periotic in extinct 

eurhinodelphinid dolphins (formerly = rhabdosteid dolphins). 

De Muizon (1987:8) suggested that the articular peg may not be 

homologous with the articular process (q.v.).

The articular peg is absent in Tursiops.

− articular process

The articular process is one of an intergrading series of apparently homologous projections among a range of archaic platanistoids (de Muizon, 1987:8; Fordyce, 1994:149). The feature 

on some specimens was described by de Muizon as an articular 

rim, or small apophysis, or hook-like articular apophysis.

The articular process does not occur in Tursiops and appears to be restricted to the platanistoids (de Muizon, 1987:8).

− articular rim

In some Odontoceti, the articular rim of the periotic (de 

Muizon, 1987:7, 8) is the expanded margin immediately anterior, and dorsal-dorsolateral, to the base of the posterior process 

(Fordyce, 1994:160); in Platanistidae the articular rim is developed into the articular process.

The articular rim is not present in Tursiops.

= attic = epitympanic recess (Gray, 1918:142; Schulte, 1917:396)

p e r i o t i c n u m b e r 6 2 7 • 1 1 3
− auditory tube (tuba auditiva)

The auditory (Eustachian) tube communicates between the 

mammalian middle ear cavity and the nasopharyngeal cavity 

(MacPhee, 1981:48; Schaller, 1992:538.19). The auditory tube 

comprises part of the musculotubal canal of the tympanic (not 

a tympanic bulla; see Schaller, 1992:24.12) and is commonly 

known as the Eustachian tube.

The auditory tube in Tursiops runs from the tympanic opening of the auditory tube through the Eustachian notch in the 

pterygoid bone. 

See Eustachian tube and musculotubal canal of the tympanic 

bulla in “Tympanic Bulla.”

= basicapsular fissure = basicochlear fissure

− basicochlear fissure

MacPhee (1981:48, 49) stated that the basicochlear fissure 

or basicapsular fissure, which is a feature of embryonic mammals, 

may persist into some adult mammals as a space between the 

ventromedial edge of the auditory region and the basioccipital.

The cranial hiatus in Tursiops probably includes the basicochlear fissure. 

See cranial hiatus and jugular foramen.

− body of the periotic

The body of the periotic in Neoceti (e.g., Kellogg, 1931; 

Fordyce, 1994:161) is that part of the periotic bone other than 

the anterior process, posterior process, and pars cochlearis. It is 

thus roughly equivalent to the tegmen tympani (q.v.) of other 

mammals. Schulte (1917:396) used the term “pars vestibularis” 

for that part of the periotic in Kogia other than the pars cochlearis. Fraser and Purves (1960:34) used the term “otic portion” 

for this part of the periotic in Balaenoptera.

The body of the periotic is present in Tursiops.

= canal for the acoustic nerve

See internal auditory meatus. 

− canal for the auricular ramus of the vagus

For the armadillos Euphractus and Dasypus, Wible and 

Gaudin (2004:149) reported that a canal or small foramen for 

the auricular ramus of the vagus is associated with the facial 

canal or stylomastoid foramen in the petrosal (periotic bone).

We cannot identify in Tursiops a canal or foramen for the 

auricular ramus of the vagus.

= canal for the chorda tympani (canaliculus chordae tympani)

In mammals the canal for the chorda tympani arises from the 

peripheral turn of the facial canal (sensu lato) (q.v.) and passes 

through the wall of the facial canal to exit posterolateral to the 

vestibular window (Evans and Christensen, 1979:133, 931).

The canal for the chorda tympani is not developed in Tursiops, the chorda tympani leaving the facial nerve external to the 

facial canal. This is a result of the wall of the facial canal being 

absent distally (i.e., absent before the stylomastoid foramen), 

where a facial sulcus is present instead.

= canal for the facial nerve

See facial sulcus.

− canal for the lesser petrosal nerve (canalis n. petrosi minoris)

In mammals the lesser petrosal nerve in humans emerges 

from the tympanic plexus, pierces the anterior wall of the petrosal and exits the middle cranial fossa through the sphenopalatine fissure below the foramen ovale and joins the otic ganglion 

(Schaller, 1992:472.2, 474.21; Feneis, 1994:290.16). The lessor 

petrosal nerve bears parasympathetic fibers from the tympanic 

plexus to the otic ganglion (Feneis, 1994:294.15).

Dissection is needed to confirm that Tursiops has a lesser 

petrosal nerve and tympanic plexus. Fordyce (1994:158) implied 

that some Odontoceti have this nerve.

= canal for the major superficial petrosal nerve (canalis n. petrosi 

majoris) = petrosal canal

= canal for the stapedial muscle

See fossa for the stapedius muscle. 

− canal for the trigeminal nerve (canalis n. trigemini)

In the dog the short canal for the trigeminal nerve is located 

anterior to the internal acoustic meatus in the petrosal (Evans 

and Christensen, 1979:132). The trigeminal nerve passes through 

this canal, then forms the semilunar ganglion and separates into 

the ophthalmic nerve, maxillary nerve, and mandibular nerve 

(Evans and Christensen, 1979:912).

The canal for the trigeminal nerve is not developed in cetaceans due to the ventral movement of the periotic. This movement has resulted in further separation of the periotic from the 

central nervous system.

* caudal tympanic process (Figure 25o,q,w)

MacPhee (1981:50) identified the mammalian caudal tympanic process as arising primarily from the anteroventral part 

of the pars canalicularis (= tympanic process of Wible et al., 

2004:75).

Geisler and Luo (1996: fig. 3; see also Geisler and Sanders, 

2003: char. 225) used caudal tympanic process for a plate-like 

process that extends posteriorly off the pars cochlearis lateral 

to the fenestra rotunda and medial to the fossa for the stapedial 

muscle. Fordyce (2002) used the term “posterior cochlear crest” 

for this feature in the fossil dolphin Simocetus.

The caudal or posterior tympanic process is well developed 

in Tursiops.

− cerebellar fossa (fossa cerebellaris)

In the dog, the cerebellar fossa lies on the posteromedial 

surface of the petrosal and houses the paraflocculus of the cerebellum (Evans and Christensen, 1979:132).

In the horse, there is no subarcuate fossa; the cerebellar 

fossa houses the cerebellum (Schaller, 1992:22.21).

There is no cerebellar fossa in Tursiops. The cerebellar fossa 

is represented by the region medial to the superior process of the 

periotic bone in Archaeoceti and some basal Neoceti.

See also subarcuate fossa.

− cerebellar surface of the petrosal

The cerebellar surface of the petrosal in the dog consists 

of that portion of the petrosal that borders on the cerebellum 

(Evans and Christensen, 1979:132).

1 1 4 • smithsonian contributions to zoolog y p e r i o t i c
The periotic in delphinids has moved ventrally and no longer directly contacts the cerebellum. We use the term “cranial 

surface of the periotic” to refer to the surfaces that are known as 

cerebral surface and cerebellar surface in other mammals.

− cochlea

The mammalian cochlea is a part of the osseous labyrinth and 

is a spiral structure located in the periotic. The basal turn of the 

cochlea lies lateral to the ventral portion of the internal acoustic 

meatus, and it produces the bulk of the promontory of the petrosal (Gray, 1918:1050; Evans and Christensen, 1979:132, 1069, 

1070; Schaller, 1992:532.20; Feneis, 1994:376.18). Eustachius 

and Lancisius (1714:109) referred to this as the cochlea.

In Tursiops and other delphinids, the cochlea, spiral lamina, 

and associated structures bear the same anatomical relationships 

as they do in the dog. The apical turn of the cochlea lies just 

dorsal to the vestibular window and the basal turn of the cochlea lies next to the internal acoustic pore (Ketten and Wartzok, 

1990). The basal turn makes up the bulk of the promontory of 

the periotic bone.

− cochlear aqueduct (aqueductus cochleae)

The cochlear aqueduct in the dog runs ventrally from the 

ventral wall of the scala tympani near its origin to the external opening of the cochlear aqueduct. This canal contains the 

perilymphatic duct and provides communication between the 

subarachnoid space and the vestibule, cochlea, and semicircular canals (Evans and Christensen, 1979:1070, 1063). This 

canal is also known as the cochlear canaliculus (canaliculus cochleae) (Evans and Christensen, 1979:1063, fig. 19–3; MacPhee, 

1981:47, 51).

In Tursiops the opening or external aperture for the cochlear 

aqueduct lies on the dorsal surface of the periotic bone on the 

posteromedial aspect of the cochlear process / pars cochlearis.

= cochlear canaliculus (canaliculus cochleae)

See cochlear aqueduct.

− cochlear fossula

The cochlear fossula is a depression that, in some mammals, 

contains the cochlear window (round window, fenestra rotunda) 

(MacPhee, 1981:51).

The cochlear window in Tursiops may open in a slight 

depression in the profile of the pars cochlearis, forming an indistinct cochlear fossula. It is not known whether, as in some 

terrestrial mammals (Wible et al., 2004:75), the cochlear fossula 

in Tursiops contains a diverticulum of the tympanic cavity.

* cochlear portion

See pars cochlearis. 

− cochlear posterior pole

The cochlear posterior pole in mammals is the posterior part 

of the cochlear portion that contains the region of the cochlear 

fossula (MacPhee, 1981:51).

Tursiops lacks a cochlear fossula and does not have a distinct cochlear posterior pole.

= cochlear window = fenestra rotunda (Figure 25b,e,m,q,v–x)

* cranial surface of the periotic (Figure 25l)

The cranial surface of the periotic bone in delphinids is that 

surface that borders the cranial cavity and posterior lacerate foramen. The cranial surface is the dorsal surface of the periotic 

that bears the internal acoustic meatus.

= crista falciformis (Gray, 1918:143)

See transverse crest of the internal acoustic meatus.

− crista interfenestralis

The crista interfenestralis in many mammals (Wible and 

Gaudin, 2004) is a bridge or strut of bone separating the fenestra 

ovalis and fenestra rotunda. The fossa for the stapedial muscle 

may develop onto the crista interfenestralis.

In Tursiops the crista interfenestralis is a broad raised surface that is not particularly distinct from other parts of the pars 

cochlearis; it merges back into the indistinct caudal tympanic 

process.

= crista parotica = facial crest of the periotic bone (Wible and 

Gaudin, 2004:136, 174)

− crista vestibuli (Whitmore, 1953:132)

In archaic artiodactyls, a horizontal crest that separates the 

fenestra cochleae (= round window) from the vestibule.

We could not determine this internal feature in Tursiops.

− distal opening of the facial canal (Figure 25m)

See facial canal.

* dorsal crest (Fordyce, 1994:158,161) (Figure 25u)

In the sense of Whitmore (1953:131) the mammalian dorsal crest is synonymous with the petrosal crest of Evans and 

Christensen (1979:130) and the crista partis petrosae of Schaller 

(1992:22.16).

In the sense of Fordyce (1994:158,161), the dorsal crest of 

the periotic in archaic Odontoceti is the median dorsal elevation 

that extends from the anterodorsal angle posteriorly to a point 

lateral to the aperture for the endolymphatic duct. This crest is 

presumed to be the vestigial homologue of the superior process in 

the sense of Kellogg (1936) (Fordyce, 1994:158,160,161). Geisler 

and Luo (1996:1055) used the name dorsolateral ridge of the tegmen tympani, while Luo and Gingerich (1999:41) discussed it 

under the term “dorsal edge of the tegmen tympani.” It is not 

clearly homologous with the petrosal crest of the dog or deer.

In Tursiops and other delphinids, the dorsal crest is vestigial 

and indistinct, or absent. In some Archaeoceti and archaic Neoceti it is elevated into a plate-like process, the superior process of 

Pompeckj (1922) and others.

= dorsal ridge (Fordyce, 1994:149) = dorsal crest

* dorsal tuberosity (Figure 25t)

The dorsal tuberosity is a rounded eminence on the dorsolateral surface of the periotic in some Odontoceti. The dorsal 

tuberosity lies between the cochlear portion and the posterior 

process of the periotic bone (Fordyce, 1994:160, fig. 11b).

A moderately developed dorsal tuberosity is present in some 

Tursiops.

p e r i o t i c n u m b e r 6 2 7 • 1 1 5
* dorsal vestibular area (area vestibularis utriculo-ampullaris / 

foramen acusticum superius) (Figure 25u)

The dorsal vestibular area in mammals is located dorsal to 

the transverse crest of the internal acoustic meatus and contains 

the utriculus and the ampullae. Nerve fibers that come from the 

dorsal vestibular area leave in the vestibular nerve (Evans and 

Christensen, 1979:132).

In the extinct mammal Prokennalestes (see Wible et al., 

2001:8), the dorsal vestibular area [foramen acusticum superius

of their use] is a blind pit with tiny perforations for the vestibular nerve, lying posterior to the proximal opening of the facial 

canal within the superior or dorsal acoustic foramen / foramen 

acusticum superius.

The vestibular nerve in Tursiops exits via the foramen singulare, rather than by the pit-like feature noted by Wible et al. (2001). 

The anterior meatal pit (q.v.) of Tursiops should not be confused 

with the dorsal vestibular area in the sense of Wible et al.

= dorsolateral ridge of the tegmen tympani (Geisler and Luo, 

1996:1055)

See dorsal crest. 

= dorsoventral vascular channel (Luo and Gingerich, 1999:45)

See anteroexternal sulcus. 

− elliptical recess for the utricle

In mammals, the elliptical recess for the utricle lies in the 

posterodorsal part of the vestibule (Evans and Christensen, 

1979:1070). It is separated from the spherical recess (for the saccule) by the vestibular crus.

We could not confirm this feature for Tursiops.

= endolymphatic duct

See aperture for the vestibular aqueduct. 

* epitympanic foramen of the facial canal = aperture of the facial 

canal (apertura tympanica canalis facialis) (Figure 25x)

Kellogg (1936) used this term for the ventral or distal opening of the facial canal (q.v.) in the middle ear cavity of Archaeoceti. Foramen faciale (q.v.) is a synonym. All odontocetes have 

an epitympanic foramen.

See facial canal for further discussion of this matter.

* epitympanic hiatus (hiatus epitympanicus) (Figure 25n,t,v–x)

Evans and Christensen (1979:1063) summarized structures 

in this region of the dog as including the membrana shrapnelli

or pars flaccida of the tympanic membrane, which partly bounds 

the upper tympanic pouch, also known as Prussak’s pouch. All 

these are soft tissue structures.

In Tursiops the bony epitympanic hiatus is a transverse depression in the epitympanic recess, laterally on the ventral surface of the periotic. In the isolated periotic, it lies between the 

lateral tuberosity (q.v.; which in delphinids is integral with the 

parabullary ridge) and posterior process of the periotic bone. In 

the isolated periotic, the hiatus has two parts: an anterior smooth 

surface immediately posterior to the parabullary ridge marks the 

exit of the middle sinus, while, more posteriorly, a rough surface 

that extends onto the base of the posterior process marks a contact for the spiny process of the squamosal bone.

When the periotic is articulated, the hiatus is delimited ventrally by the sigmoid process and the tympanic notch (or tympanic incisure) of the bulla. Posteriorly, at least in the articulated 

periotic of young animals, the hiatus is limited by the spiny process, which is a medial extension of the squamosal; the spiny 

process is variably developed in adults. (See, e.g., Boenninghaus, 

1904; Kellogg, 1936:118; Yamada, 1953:20; Kasuya, 1973; 

Fordyce, 1994:160; Geisler and Luo, 1996:1053).

A crest is developed on the posterior surface of the sigmoid 

process and a corresponding crest on the posterior process of the 

periotic bone. These crests serve to limit the epitympanic hiatus 

ventrally; they also mark the tympanic notch.

Among living species this ventrally restricted aperture is peculiar to Odontoceti (Yamada, 1953:20), in which it is the site of 

exit of the middle sinus into the tympanosquamosal recess.

This feature was called the ductus petro-tympanicus by Beauregard (1893), the apertura petrotympanicus by Reysenbach 

de Haan (1957), the hiatus epitympanicus by Boenninghaus 

(1904), and the upper tympanic aperture by Kasuya (1973) and 

Yamada (1953).

In the dissected periotic of Delphinus delphis, the middle 

sinus arises at the epitympanic hiatus.

* epitympanic recess (recessus epitympanicus) (Figure 25v)

In mammals, the epitympanic recess forms the dorsal part 

of the tympanic cavity (Whitmore, 1953:133; Evans and Christensen, 1979:132, 134; MacPhee, 1981:52). In the dog the epitympanic recess has also been called the fossa for the head of 

the malleus (Evans and Christensen, 1979:1068) (but see mallear 

fossa). The incus, part of the stapes, and the head of the malleus 

lie in the epitympanic recess.

In humans, the tympanic antrum opens into the epitympanic 

recess (Gray, 1918:142).

In Tursiops this region is modified to form a distinct mallear 

fossa (q.v.) or fossa capitis mallei, and fossa incudis (q.v.). Laterally, the epitympanic recess passes into the hiatus epitympanicus. The fossa for the tensor tympani muscle (q.v.) is reduced 

and is no longer a useful landmark. The epitympanic recess is 

bounded ventrally by structures of the bulla at the tympanic 

notch (or incisure), specifically the posterior face of the apex of 

the sigmoid process and the bony shelf that projects anteriorly 

from the posterior process.

Luo and Gingerich (1999:30) indicated that in Archaeoceti 

the epitympanic recess may include part of the squamosal as well 

as periotic, but in Tursiops the epitympanic recess includes only 

the periotic.

Kellogg appeared to use recessus epitympanicus (e.g., 1936 

:27) in the sense of tegmen tympani (q.v.) of other authors, implying 

that it lies posterolateral to the fossa for the m. tensor tympani.

− epitympanic sinus

The epitympanic sinus (sensu van der Klaauw, 1931; as 

elaborated by Wible and Gaudin, 2004 for armadillos) is a diverticulum dorsal to the epitympanic recess, developed into the 

squamosal and the pars mastoidea of the petrosal.

The periotic in Tursiops lacks a distinct fossa for the epitympanic sinus. The soft tissues of the middle sinus, which issue 

dorsal to the epitympanic recess, are not clearly homologous 

with the epitympanic sinus of other mammals.

1 1 6 • smithsonian contributions to zoolog y p e r i o t i c
= Eustachian tube = auditory tube

= external aperture for the cochlear canaliculus (apertura externa 

canaliculus cochleae)

See aperture for the cochlear aqueduct. 

= external aperture for the vestibular aqueduct (apertura externa 

aqueductus vestibuli)

See aperture for the vestibular aqueduct. 

− external opening of the facial canal (Figure 25m)

See facial canal for further discussion.

= facet for the malleus = mallear fossa (Schulte, 1917:397)

* facial canal (canalis facialis) (Figure 25a,m,q,v)

The facial canal lies in the mammalian petrosal bone and 

transmits the facial nerve. In the dog and other mammals (Evans 

and Christensen, 1979:133,922; Schaller, 1992:22.6), the facial 

canal of the petrosal bone comprises the full route of the facial 

nerve from the internal acoustic meatus (proximally) to the stylomastoid foramen (distally) of the temporal on the skull surface. 

The more-distal path of the facial nerve is sometimes described 

as within the stylomastoid canal (q.v.). The facial canal is also 

known as the Fallopian aqueduct (Kellogg, 1936). The facial 

nerve at this point in the ear has also been termed the hyomandibular branch of the facial nerve (Wible et al., 2001:6, 14; Wesley-Hunt and Flynn, 2005:5). The distal opening or aperture of 

the facial canal is known as the facial sulcus.

The situation is modified in Tursiops and other Cetacea. 

The proximal (or cerebral, or internal, or dorsal) opening of the 

facial canal is in the area nervus facialis of the internal acoustic 

meatus, just dorsal to the transverse crest.

In Archaeoceti the opening has also been termed the internal 

facial foramen (Luo and Gingerich, 1999:45). For Cretaceous placental mammals, Ekdale et al. (2004:170) termed the opening the 

foramen acusticum superius. In Tursiops the distal opening is in 

the middle ear, lateral and slightly anterior to the fenestra ovalis. 

Synonyms for this foramen include epitympanic orifice (of 

Kellogg, 1936), foramen faciale, secondary facial foramen (e.g., 

Ross and Covert, 2000:243), or ventral or distal or external 

opening of the facial canal. This is not to be confused with the 

stylomastoid foramen of other mammals.

See also stylomastoid notch.

= facial canal within the tegmen tympani (Novacek, 1986:59)

See petrosal canal. 

* facial crest of the periotic (crista facialis petrosi) (Figure 

25m,o,v)

According to van der Klaauw (1931:239) the mammalian 

crista facialis petrosi is the crest to which fuses the tympanohyal. 

Wible and Gaudin (2004:136,174) indicated that the crista facialis is synonymous with crista parotica and stated: “the lateral 

wall of the facial sulcus [has] a lambdoidal bifurcation into medial and lateral arms . . . . The more anteroventrally projecting 

lateral arm borders the aperture connecting the tympanic cavity

proper and the epitympanic sinus; the medial arm is the crista 

parotica. Between these two arms is a small ovoid depression, 

the fossa incudis for the crus breve of the incus.” The fossa incudis in Tursiops is bounded medially by a facial crest that continues posteriorly toward the position of the variably developed 

tympanohyal.

See discussion under tympanohyal; see also processus cristae facialis.

= facial foramen (foramen faciale)

See foramen faciale and facial canal. 

= facial groove = facial sulcus

* facial sulcus (Figure 25e,m,o,q,r,u–w)

The mammalian facial sulcus (Whitmore, 1953:131) occurs 

on the ventral surface of the periotic posterior (distal) to the epitympanic foramen of the facial canal (or aperture of the facial 

canal) and the stylomastoid foramen.

The facial sulcus is well developed on the body of the periotic medial to the fossa incudis and on the medial face of the 

posterior process in Tursiops and other Odontoceti (Fordyce, 

1994:160).

See further discussion under stylomastoid foramen.

= facies encephalica (caudomedial part) (facies posterior partis 

petrosae) = medial surface of the petrosal

− facies encephalica (rostrodorsal part) (facies rostralis partis 

petrosae)

The facies encephalica (rostrodorsal part) is that part of the 

cranial surface of the mammalian petrosal that faces anterodorsally (Schaller, 1992:22.10). The rostrodorsal part lies on the 

anterior side of the crista partis petrosae. In humans it is known 

as the facies anterior partis petrosae (Feneis, 1994:14.1).

This part of the periotic is not distinct in Tursiops.

= Fallopian aqueduct (aqueductus Fallopii) = aqueduct of Fallopius

See facial canal.

= Fallopian foramen (Novacek, 1986:58)

See proximal opening of the facial canal.

= fenestra cochleae (Schulte, 1917:396; Whitmore, 1953:132)

See cochlear window and fenestra rotunda of “Periotic 

Bone.”

* fenestra ovalis (Figure 25m,v–x)

The mammalian vestibular window, vestibular fenestra, or 

oval window, which is occluded by the footplate of the stapes, 

lies just anterior and slightly dorsolateral to the cochlear window

(Evans and Christensen, 1979:132).

The fenestra ovalis in Tursiops and other delphinids opens 

lateral to the fenestra rotunda at the lateral edge of the pars 

cochlearis, just medial to the epitympanic orifice (or facial foramen, foramen faciale) for the facial nerve, and anterior to the 

fossa for the stapedial muscle.

The term “fenestra ovalis” has been used widely in cetacean 

osteological literature. Equally acceptable common synonyms include fenestra vestibuli, oval window, and vestibular window.

p e r i o t i c n u m b e r 6 2 7 • 1 1 7
* fenestra rotunda (Figure 25b,e,m,q,v–x)

The fenestra rotunda lies at the posterolateral end of the 

promontory of the mammalian petrosal. It is closed by the secondary tympanic membrane (Evans and Christensen, 1979:132). 

The cochlear window may lie within a cochlear fossula (MacPhee, 

1981:51).

The fenestra rotunda in Tursiops lies at the posterior edge of 

the pars cochlearis in an indistinct cochlear fossula.

Some Odontoceti carry a fissure between the fenestra rotunda and the aperture for the cochlear aqueduct that may reflect 

a common embryological opening (Kellogg, 1923:53, fig. 2).

The term “fenestra rotunda” has been used widely in cetacean osteological literature by Kellogg (e.g., 1936:116) and 

others. Equally acceptable common synonyms include fenestra 

cochleae, cochlear window, and round window. 

Not to be confused with the fenestra rotunda of tympanic 

bulla, of Boenninghaus (1904: fig. G, item 19).

= fenestra vestibuli

See vestibular window. 

= fissura petrooccipitalis

See fissura petrosoparoccipitalis.

− fissura petrosoparoccipitalis = fissura petrooccipitalis (Kellogg, 1936:114)

The fissura petrosoparoccipitalis is the fissure between the 

archaeocete periotic and the paroccipital process, into which 

may extend part of the posterior sinus and/or the peribullary

sinus (Pompeckj, 1922, as interpreted by Kellogg, 1936:114). 

We understand Kellogg to mean that the fissure developed posterior and dorsal to the periotic, in which case the structure possibly does not include a component of posterior sinus.

Luo and Gingerich (1999:20, tbl. 5, #34b) noted that the 

petrosoparoccipital fissure in Neoceti and some Archaeoceti 

comprises the enlarged basicapsular fissure plus jugular foramen. 

Enlargement was attributed to an expanded “medial pterygoid 

sinus” (sic). McPhee (1981), however, implied that the basicapsular fissure is medial, not posterior, to the periotic bone (petrosal), in which case the petroso-paroccipital fissure would not 

include the basicapsular fissure.

This region is so modified in adult Tursiops by the development of the cranial hiatus, and particularly by the large dorsally 

developed excavation in the anterior face of the paroccipital process, that the term is not easily applicable.

See also petrobasilar canal and ventral petrosal sinus.

= foramen faciale = epitympanic foramen

The foramen faciale of Denker was cited by van der Klaauw 

(1931:173) and identified by MacPhee (1981:55) as the apertura 

tympanica canalis facialis, or foramen through which the mammalian facial nerve enters the middle ear. Epitympanic foramen 

of the facial canal or aperture of the facial canal (q.v.) are preferred terms.

See also facial canal and stylomastoid foramen. 

= foramen for the facial nerve

See stylomastoid foramen.

− foramen for the greater superficial petrosal nerve (foramen n. 

petrosus major)

In mammals, the foramen for the greater superficial petrosal 

nerve is the opening of the petrosal canal in the petrosquamous 

suture just lateral to the canal for the trigeminal nerve.

See petrosal canal for discussion of the situation in Tursiops.

− foramen for the ramus superior of the stapedial artery

Various placentals have a foramen for the ramus superior of 

the stapedial artery as an aperture in the roof of the middle ear, 

such as in the tympanic process of the alisphenoid next to the foramen ovale, or between the petrosal and squamosal (Wible and 

Gaudin, 2004:153). Sometimes the feature may be an incisure 

rather than a foramen.

A foramen for the ramus superior of the stapedial artery 

has not been identified in Tursiops, and may not exist, given the 

likely vestigial nature of stapedial circulation. 

See section on arterial circulation and basicranial foramina 

in “Multi-element Complexes.”

* foramen singulare (singular foramen) (Figure 25a,u)

The foramen singulare is situated ventral to the transverse 

crest of the mammalian internal acoustic meatus. The vestibular nerve fibers from the ventral vestibular area (sacculus) 

pass through the foramen singulare (Evans and Christensen, 

1979:132). Gray (1918:143) said that the foramen singulare is 

the opening for the nerve to the posterior semicircular duct.

The foramen singulare in delphinids is located in the internal 

acoustic meatus, lateral to the transverse crest. We use the latinized term in preference to the ambiguous “singular foramen.”

= foramen stylomastoideum (stylomastoid foramen) = foramen 

faciale of Denker (cited by van der Klaauw, 1931:173)

See foramen stylomastoideum primitivum, foramen stylomastoideum tertium, and stylomastoid foramen. 

− foramen stylomastoideum definitivum

Novacek (1986:56; fig. 20) and MacPhee (1981:63) identified this as the definite bony aperture for the exit of the facial 

nerve from the mammalian middle ear.

Tursiops lacks a foramen stylomastoideum definitivum.

− foramen stylomastoideum primitivum

In some archaic artiodactyls (Whitmore, 1953) and archaic 

insectivores (Novacek, 1986 fig. 20) the distal path of the facial 

nerve as it exits the middle ear cavity is enclosed in a stylomastoid 

canal (q.v.), which starts proximally (internally) at the foramen stylomastoideum primitivum, and opens laterally at the stylomastoid 

foramen (q.v.) or the foramen stylomastoideum definitivum (reviewed by Van der Klaauw, 1931:171). MacPhee (1981:63) stated 

that the foramen stylomastoideum primitivum is strictly not a foramen at all but is the place where the facial nerve penetrates fibrous 

tissue adjacent to the tympanohyal on the way to the neck.

Tursiops lacks a foramen stylomastoideum primitivum.

– foramen stylomastoideum tertium

Wible and Gaudin (2004:154) reviewed the foramen stylomastoideum tertium of Patterson et al. (1989), noting that the 

1 1 8 • smithsonian contributions to zoolog y p e r i o t i c
latter proposed the term foramen stylomastoideum tertium for 

an aperture on the euphractine (armadillo) skull base, to distinguish it from the foramen stylomastoideum primitivum and the 

foramen stylomastoideum definitivum. The foramen stylomastoideum tertium is the exit for the facial nerve, which leaves the 

external acoustic meatus at a sizeable gap between the ectotympanic and the paroccipital process of the petrosal.

Tursiops lacks a foramen stylomastoideum tertium.

= fossa at the aperture for the ductus endolymphaticus (Kellogg, 

1936:116)

See aperture for the vestibular aqueduct. 

= fossa for the head of the malleus (fossa capitis mallei)

See mallear fossa. 

* fossa for the stapedius muscle (fossa m. stapedius) (Figure 

25b,e,m,o–q,u–w)

In mammals, the fossa for the stapedius muscle is located on 

the dorsal aspect of the facial canal just proximal to the stylomastoid foramen (Evans and Christensen, 1979:133).

In Tursiops the fossa for the stapedius muscle is located immediately posterior to the vestibular window or oval window

(fenestra ovalis), just dorsal to the facial sulcus, and between the 

pars cochlearis and the posterior process (Kasuya, 1973:2).

* fossa for the tensor tympani muscle (fossa m. tensor tympani) 

(Figure 25w)

The fossa for the mammalian tensor tympani muscle is a 

spherical depression that lies anterior to the vestibular window

and medial to the epitympanic recess (Evans and Christensen, 

1979:132; not in Schaller, 1992). In humans this feature is 

termed the semicanal for the tensor tympani muscle and includes 

part of the musculotubal canal of the sphenoid bone (Feneis, 

1994:12.29).

The tensor tympani muscle is minute but present in Neoceti 

(Yamada, 1953; Purves, 1966), in contrast to the large tensor 

tympani in many other mammals. The identity of the fossa for 

the tensor tympani muscle (fossa muscularis major of Reysenbach de Haan, 1957:42) has been confused. Schulte (1917:397) 

said that the region between the accessory ossicle (uncinate process [of the tympanic bulla] of Schulte) and pars cochlearis may 

correspond to the groove for the tensor tympani muscle. Kellogg 

(e.g., 1936) and later authors (e.g., Fordyce, 1994, Luo and Gingerich, 1999:45) also identified the fossa as formed by a groove 

(or, in Delphinidae, a narrow cleft) between the mallear fossa

and pars cochlearis, or alternatively on the “tympanic side of 

the periotic” (Luo and Gingerich, 1999:45). Yamada (1953), 

however, identified the muscle origin as the “medial side of the 

tubal tubercle” [= accessory ossicle of the tympanic bulla]. Fraser 

and Purves (1960:118, and fig. 27) indicated a similar origin for 

Globicephala, stating: “the tensor tympani arises from the dorsal 

wall of the tympanic cavity near that part which transmits the 

Eustachian tube.”

Tursiops lacks a clearly defined fossa for the tensor tympani 

muscle on the medial face of the accessory ossicle, but the ossicle 

may carry fine striations consistent with the origin of muscle fibers 

directed toward the muscular process of the malleus (Figure 25w).

* fossa incudis (Figure 25m,v)

In mammals, such as armadillos (Wible and Gaudin, 

2004:142), the crus breve of the incus is suspended from the 

skull by a ligament to a small pit-like fossa incudis, which is situated in the petrosal lateral to the crista parotica and the facial 

sulcus or facial canal.

In Cetacea, the fossa incudis lies posterolateral to the epitympanic foramen of the facial canal or aperture of the facial 

canal in Archaeoceti and many Neoceti. It receives the processus breve of the incus (Pompeckj 1922: pl. 1, fig. 1; Kellogg, 

1936:25).

The fossa incudis is distinct in Tursiops and other 

delphinids.

= fossa muscularis major (Reysenbach de Haan, 1957:42)

See fossa for the tensor tympani muscle. 

= fossa muscularis minor (Reysenbach de Haan, 1957:42; Novacek, 1986:56)

See fossa for the stapedius muscle.

* fovea epitubaria = fossa epitubaria (Kellogg, 1936:25, 27, fig. 

5) (Figures 5, 25m,s,v)

The fovea epitubaria (e.g., Pompeckj, 1922: Archaeoceti) is 

a concave depression on the ventral surface of the anterior process of the periotic bone, just posterior or posteromedial to the 

anterior bullar facet of some Odontoceti (Fordyce, 1994:160) 

and immediately in front of the mallear fossa. It receives the accessory ossicle of the tympanic bulla, which in Tursiops fuses 

with the periotic immediately in front of the mallear fossa. The 

fovea epitubaria is distinct from the anterior bullar facet. Kellogg (1936:27, fig. 5) stated that the fovea epitubaria lodges the 

processus tubarius (sic; accessory ossicle), but the feature that 

he labeled as fovea epitubaria is lateral to the fovea and instead 

represents the ventral part of the anteroexternal sulcus of the 

periotic bone.

In Tursiops and other delphinids the fovea epitubaria is 

so large as to obliterate the anterior bullar facet and occupies 

the ventrointernal surface of the anterior process of the periotic 

bone. In Odontoceti other than delphinoids, the depressed outline of the fovea epitubaria is visible laterally, but in Tursiops

and other delphinids the fovea is obscured by the enlarged parabullary ridge.

= fundus of the internal acoustic meatus

See internal acoustic meatus. 

− genu of the facial canal (geniculum canalis facialis)

The genu (knee) of the mammalian facial canal is the sharp 

turn that the facial canal makes in the petrosal in its course from 

the internal acoustic meatus to the stylomastoid foramen. The 

canal is slightly enlarged at the genu to accommodate the geniculate ganglion of the facial nerve. The genu may be enlarged to 

form a supracochlear cavity (q.v.).

In some cetaceans, a distinct canal for the greater superficial petrosal nerve arises at the genu, which probably is also the 

source of the minor superficial petrosal nerve; the condition in 

Tursiops is uncertain.

p e r i o t i c n u m b e r 6 2 7 • 1 1 9
There have been no reported deviations of the genu in delphinids from the situation seen in the dog.

− groove for caudal meningeal artery (sulcus a. meningea caudalis)

The groove for the mammalian caudal meningeal artery 

(posterior meningeal artery) occurs on the lateral surface of the 

petrosal in equids (Schaller, 1992:22.5; not in Feneis, 1994). 

This appears to be absent in humans (Gray, 1918:557) and the 

dog (Evans and Christensen, 1979:658).

There is no obvious groove for the caudal meningeal artery 

on the periotic in Tursiops, and a close relationship with the meninges is unlikely, given the separation of the ear from the brain. 

Vascular structure around the ear has yet to be determined by 

dissection.

− groove for dorsal petrosal sinus (sulcus sinus petrosi dorsalis)

The groove for the dorsal petrosal sinus (groove for the superior petrosal sinus) lies on the surface of the petrosal crest in 

some mammals (Schaller, 1992:22.17; Feneis, 1994:14.10).

The venous sinus system in the odontocete cranium is extremely complex. The dorsal petrosal sinus presumably exists 

(Boenninghaus, 1904: pl. 13, fig. 13, item 11; fig. 14, item 6) but 

does not leave a recognizable sulcus on the periotic in Tursiops. 

For Archaeoceti, Pompeckj (1922: figs. 3, 4, 6, 7) identified a 

groove for a sulcus peripetrosus superior on the wall of the squamosal immediately dorsal to the superior process, but the latter 

sulcus is not clearly for the dorsal (superior) petrosal sinus.

− groove for occipital artery (sulcus a. occipitalis)

The groove for the occipital artery in humans lies on the 

posteroventral external surface of the petrosal, medial to the 

mastoid process and mastoid notch of the temporal bone and 

lateral to the occipital margin (Feneis, 1994:12.20). This feature 

was not mentioned for equids, bovids, caprids, suids, and canids 

(Sisson and Grossman, 1953).

The groove for the occipital artery is not recognizable in 

Tursiops. Vascular structure around the ear has yet to be determined by dissection.

− groove for sigmoid sinus (sulcus sinus sigmoidei)

The groove for the sigmoid sinus in humans lies on the posterodorsal aspect of the cranial surface of the petrosal (Feneis, 

1994:12.19; not in Schaller, 1992). The sigmoid sinus passes 

over the posterior end of the petrosal in canids but does not leave 

an impression on that bone.

The venous sinus system in the odontocete cranium is extremely complex. The sigmoid sinus presumably exists but does 

not leave a recognizable groove on the periotic.

= groove for stapedial artery

See stapedial artery groove. 

= groove for tensor tympani muscle

See fossa for the tensor tympani muscle. 

− groove on ventral surface of the pars cochlearis

Schulte (1917:397) commented that the ventral surface of 

the pars cochlearis in Kogia becomes distinctly grooved toward 

the margin, anterior to the fenestra ovalis. Such a groove is 

readily apparent in the anterior view of the periotics of young 

K. simus (USNM 550472). Schulte related the groove to the 

structure of the osseous tuba. 

Tursiops periotics have an indistinct groove on the ventral 

surface of the pars cochlearis, but it is much less developed than 

in Kogia.

See musculotubal canal of the tympanic bulla.

= hiatus epitympanicus

See epitympanic recess. 

= hiatus Fallopii = aperture for the major petrosal nerve

The hiatus Fallopii is the anterior opening of the petrosal 

canal, and is widely recognized among eutherians (e.g., Novacek, 1986:59; Luo and Gingerich, 1999:42; Ross and Covert, 

2000:243; Wible and Gaudin, 2004:155). The foramen is the 

exit for the greater petrosal nerve (also known as the palatine 

ramus of the facial nerve, or superficial petrosal nerve of some 

authors; Sanchez-Villagra and Wible, 2002:35). The foramen 

has also been named the anterior fissure of the facial foramen, 

the hiatus of the facial canal (hiatus canalis facialis), the hiatus 

for the greater petrosal nerve, the opening for the major petrosal 

nerve (hiatus canalis nervi petrosi majoris), and hiatus Falopii

(which is a misspelling by Schulte, 1917). According to Wible 

(2003:172), Marshall and de Muizon (1995) used the term “median lacerate foramen” for the foramen for the greater petrosal 

nerve. Wible and Gaudin (2004:175) included Fallopian aqueduct as a synonym of hiatus Fallopii, citing McDowell (1958), 

but the latter identified the Fallopian aqueduct (McDowell, 

1958:124) correctly as the path of the facial nerve through the 

petrosal, or facial canal in our use.

For the situation in Tursiops, see discussion under petrosal 

canal and under aperture for the major petrosal nerve (the latter 

used here as an alternative to hiatus Fallopii).

= hiatus of the facial canal (hiatus canalis facialis) (Gray, 

1918:142; Whitmore, 1953)

See petrosal canal. 

* internal acoustic meatus (meatus acusticus internus) (Figures 

25c,e,l,o,p,t, 28)

The mammalian internal acoustic meatus lies just ventral to 

the cerebellar fossa on the posteromedial surface of the petrosal. 

Its opening is the internal acoustic pore. The internal acoustic 

meatus contains the transverse crest, the canal for the vestibulocochlear nerve, and the canal for the facial nerve (Whitmore, 

1953:131; Evans and Christensen, 1979:132). It is also known 

as acoustic foramen (Owen, 1866a:40). Vesalius (1543:52; 

Vesalius et al., 1998:131) referred to the internal and external 

acoustic meati as the quinti nervorum cerebri paris meatus, auditorius ve porus.

The internal acoustic meatus in delphinids is located near 

the middle of the dorsal surface of the pars cochlearis, at the 

base of the cochlea. Its opening is the acoustic pore. It contains 

the transverse crest, the canal for the vestibulocochlear nerve, 

the spiral cribriform tract (tractus spiralis foraminosus), the 

foramen singulare, and the ventral foramen of the facial canal

(internal aperture for the facial canal (Fallopian aqueduct)) (e.g., 

Kellogg, 1928: fig. 23; Kasuya, 1973; Fordyce, 1994:160).

1 2 0 • smithsonian contributions to zoolog y p e r i o t i c
− internal acoustic pore (porus acusticus internus)

The lip of the opening of the mammalian internal acoustic 

meatus is the internal acoustic pore. It lies on the posteromedial 

surface of the petrosal (Evans and Christensen, 1979:132).

The internal acoustic pore in delphinids is located near the 

middle of the dorsal surface of the pars cochlearis.

Yamagiwa et al. (1999:294) referred to the porus acusticus 

internus in Grampus in a different sense, as the “bony exit for 

the vestibulocochlear and facial nerves” formed by the basioccipital, parietal, and exoccipital.

Given the difficulty of differentiating between the internal 

acoustic meatus (canal) and the lip of the internal acoustic meatus 

(internal acoustic pore), plus the differing use of internal acoustic 

pore by Yamigawa et al., we do not recommend using it.

= internal auditory canal

See internal acoustic meatus. 

= internal auditory meatus (meatus auditorius internus)

See internal acoustic meatus. 

= internal auditory meatus (internal auditory foramen)

See internal acoustic pore. 

− intrajugular process of the periotic bone (processus intrajugularis)

In mammals, the intrajugular process of the periotic bone

divides the jugular foramen into a posterolateral portion for the 

jugular vein and an anteromedial portion for the glossopharyngeal 

nerve, vagus nerve, and accessory nerve (Feneis, 1994:14.20).

This is not to be confused with the jugular process of the occipital in the dog, which is a bony process projecting posteroventrally alongside the occipital condyles (Evans and Christensen, 

1979:151–153). The jugular process is also called the paracondylar or paroccipital process.

There is some question about the intrajugular process of the 

periotic bone in domestic animals. Schaller (1992:16.21) illustrated it as a process on the occipital bone (basioccipital) that 

divides the jugular foramen.

Due to the modification in the ear region of Neoceti, an intrajugular process of the periotic bone can no longer be recognized.

= labyrinthine part (pars labyrintha) (Turner, 1913:20)

See pars labyrintha.

− lateral groove

Fordyce (1994:160) labeled a shallow lateral groove located 

mid-length on the lateral surface of the periotic in archaic Odontoceti, between the lateral tuberosity and dorsal tuberosity.

The lateral groove is not present in Tursiops.

− lateral projection of the anterior process

Geisler and Luo (1996:1052) identified a lateral projection 

or ridge on the anterior process of the periotic bone in Mysticeti. 

The projection forms the ventral edge of the squamosal fossa. 

Geisler and Luo (1996:1054) stated that this process can become 

developed to resemble the ventrolateral tuberosity (= lateral tuberosity of Barnes, 1978), but that it is not homologous.

Tursiops lacks a lateral projection on the anterior process.

* lateral tuberosity (Figure 25n)

In many Odontoceti the lateral tuberosity (Barnes, 1978:5) 

of the periotic is located posterolaterally on the anterior process 

of the periotic bone, lateral to the vestibular window, and carries 

the mallear fossa medially.

In Tursiops and other delphinoids the lateral tuberosity is 

small, but in some other Odontoceti it is a well-formed subcircular to subquadrate to irregular projection. The lateral tuberosity is 

closely approached by the edge of the sigmoid process of the bulla.

Luo and Gingerich (1999:45, e.g., fig. 20) proposed the 

term “ventrolateral tuberosity” for this feature. They also identified the term “ventral tuberosity” as a synonym, ascribing it to 

Fordyce (1994:160) who, however, used lateral tuberosity in the 

sense of Barnes. De Muizon (1987) proposed the term “ventral 

tuberosity.”

See also prominentia canalis lateralis and ridge or lateral 

projection of the anterior process.

* mallear fossa (Figure 25m,v,x)

In the dog the head of the malleus lies in the epitympanic 

recess (Evans and Christensen, 1979:132, 1066, 1068), which 

is also called the fossa for the head of the malleus (Evans and 

Christensen, 1979:1068).

The mallear fossa (sensu Fordyce, 1994:160), or fossa (or 

fovea) capitis mallei of some authors (e.g., Pompeckj, 1922; 

de Muizon, 1987), or facet for the malleus (Kogia; Schulte, 

1917:397), is a hemispherical depression that receives the head 

of the malleus. The fossa lies on the ventral surface of the anterior process of the periotic bone, immediately behind the fovea 

epitubaria and just medial to the lateral tuberosity. It is part of 

the epitympanic recess (Fordyce, 1994:160). The mallear fossa 

receives the head of the malleus. 

In Tursiops the mallear fossa is small but well developed.

− mastoid canaliculus (canaliculus mastoideus)

The mastoid canaliculus is a small canal transmitting the auricular branch of the vagus nerve into the substance of the periotic 

in some mammals (MacPhee, 1981:57; Schaller, 1992:22.30; Feneis, 1994:14.25). In humans the mastoid canaliculus originates 

in the jugular fossa (Gray, 1918:144, 181). In horses it lies on the 

caudomedial aspect of the exoccipital margin of the petrous part 

of the temporal bone (Schaller, 1992:22.30).

The mastoid canaliculus has not been reported in Tursiops.

− mastoid cells

The mastoid cells or air cells in humans are cavities that 

occupy the mastoid process of the temporal bone and that communicate with the tympanic antrum (Gray, 1918:142; van der 

Klaauw, 1931:81ff.). The tympanic antrum in turn opens forward into the epitympanic recess.

The posterior process in Tursiops lacks mastoid cells, and 

there is no tympanic antrum.

− mastoid foramen (foramen mastoideum)

The mastoid foramen in mammals lies at the juncture of the 

exoccipital, supraoccipital, and the petrosal bones (Evans and 

Christensen, 1979:123, 133, 155; Schaller, 1992:10.29). This 

foramen appears to be variable in occurrence. In humans the 

mastoid foramen transmits a vein to the transverse sinus and a 

p e r i o t i c n u m b e r 6 2 7 • 1 2 1
branch of the occipital artery to the dura (Gray, 1918:141; Feneis, 1994:12.21). Vesalius (1543:53; Vesalius et al., 1998:131) 

referred to the mastoid foramen as the foramen id ad posteriorem regionem processus mammillaris.

In Tursiops a single foramen or several grooves may open 

immediately dorsal to the posterior process of the tympanic bulla

and at the anterolateral corner of the exoccipital. Its development varies ontogenetically. Study of soft tissues is needed to 

identify this foramen properly. A large foramen, perhaps the 

mastoid foramen, may open dorsal to the posterior process of 

the tympanic bulla in Kogia spp.

− mastoid notch (incisura mastoidea)

The mastoid notch in humans is a notch between the mastoid process of the temporal bone and the posterior portion of the 

squamosal (Feneis, 1994:12.18; not in Schaller, 1992), near the 

origins of the digastric muscle and longus capitis muscle (Gray, 

1918:179). Gray (1918:141) identified it as the origin for the 

digastric. The mastoid notch lies on the posteroventral aspect of 

the external surface of the temporal. Novacek (1986:56) named 

this the groove for the digastric muscle.

Due to the separation of the periotic from the skull in Odontoceti, the mastoid process no longer contacts the squamosal, 

and the mastoid notch is absent.

− mastoid process of the petrosal (processus mastoideus)

The mastoid process of the mammalian petrosal lies between 

the mastoid foramen in the exoccipital and the stylomastoid foramen in the petrosal. The mastoid process is at the posterolateral 

corner of the petrosal (Evans and Christensen, 1979:133; Schaller, 

1992:22.4; Novacek, 1986:54; 1993:462; Feneis, 1994:12.17). 

Vesalius (1543:22,23) referred to the mastoid process as the mammillaris processus, while Eustachius and Lancisius (1714:104, 

105, 109) referred to it as the processus mastoideus but later 

(1714:112) referred to it as the apophysis mammilaris. Wible and 

Gaudin (2004:138) elaborated on MacPhee’s (1981:57) concern 

that “mastoid process” is used with such variation in mammalian 

osteology that it is best avoided.

Past authors have used the term “mastoid” on the cetacean 

skull for features of the periotic bone, tympanic bulla, and squamosal bone. Because of such confused use in Cetacea, we use the 

terms posterior process of the periotic bone (q.v.) and posterior 

process of the tympanic bulla (q.v.), and recommend that “mastoid” not be used. 

For the homology and contact relationships of “mastoid” 

elements, and references to past use, see discussion under posterior process of the periotic bone and posterior process of the 

tympanic bulla in “Tympanic Bulla.”

= mastoid region

See posterior process of the periotic bone. 

− mastoid tubercle

The mastoid tubercle (Novacek, 1986:56, fig. 20) is that part 

of the mastoid process of the petrosal that contributes ventrally 

to the stylomastoid canal (q.v.) in mammals. Novacek speculated 

that the mastoid tubercle might be partly composed of the tympanohyal (q.v.). See also posterior process of the periotic bone.

The tympanohyal region of the posterior process of the periotic bone in Tursiops and other delphinids, ventral to the facial 

sulcus and the stapedial muscle fossa, may take the form of a 

minute tubercle.

− medial surface of the petrosal (facies medialis partis petrosae)

The medial surface of the petrosal bone is that part of the 

cranial surface that is located on the posteromedial side of the 

mammalian crista partis petrosae, including the area around the 

internal acoustic meatus (Schaller, 1992:22.18). In humans it is 

known as the facies posterior partis petrosae (posterior surface 

of the petrous temporal) (Feneis, 1994:14.11).

The periotic in Tursiops is modified significantly from the 

situation in other mammals, so that medial surface can be used 

only in a general sense.

= median petrosal crest (Novacek, 1986:42, fig. 15)

See petrosal crest. 

* median promontorial groove (Figure 25u,w)

In some Mysticeti and Archaeoceti (Geisler and Luo, 

1996:1054; Luo and Gingerich, 1999:30), a median promontorial groove arises near the fenestra rotunda and extends around 

the medial rim of the internal acoustic meatus.

A poorly developed groove is present on the medial face of 

the pars cochlearis in Tursiops, but we have not found reports of 

a promontorial artery in Tursiops, and the homology with median 

promontorial groove has yet to be confirmed by dissection. The 

groove seems equally likely to mark the dorsolateral limit of the 

soft tissues of the peribullary sinus on the surface of the periotic.

− modiolus

The modiolus is the cone-shaped bony core of the mammalian cochlea (Schaller, 1992:532.24; Feneis, 1994:342.22). It 

contains the ganglionic canal for the cochlear nerve and forms 

the medial wall of the spiral canal.

The modiolus in Odontoceti is larger than that of other 

mammals (e.g., Luo and Marsh, 1996).

− occipital surface (facies occipitalis)

The facies occipitalis is that portion of the mammalian petrosal facing the exoccipital (Schaller, 1992:22.3; not in Feneis, 

1994). Schaller illustrated it in the horse where it appears to be 

equivalent to the occipital margin. It is not illustrated elsewhere.

In Tursiops the periotic does not contact the exoccipital.

− opening for the lesser petrosal nerve (hiatus canalis nervi 

petrosi minoris)

In humans the opening for the lesser (or minor, or smaller) 

petrosal nerve is located on the anterolateral aspect of the cranial 

surface of the petrosal bone, just lateral to the opening for the 

greater petrosal nerve (Feneis, 1994:14.5; not in Schaller, 1992) 

and lateral to the opening of the facial canal (Gray, 1918:1047).

The lesser petrosal nerve in humans arises from the tympanic plexus, where it communicates with the tympanic branch 

of the glossopharyngeal (Gray, 1918:1047). It passes dorsally 

around the tensor tympani muscle, then anteriorly on the dorsolateral aspect of the auditory tube to the otic ganglion (Evans 

and Christensen, 1979:926). The nerve passes through the anterior part of the periotic just posterior to the foramen ovale (Feneis, 1994:290.16) and exits the middle cranial fossa through the 

sphenopalatine fissure below the foramen ovale to join the otic 

1 2 2 • smithsonian contributions to zoolog y p e r i o t i c
ganglion (Schaller, 1992:472.2, 474.21; Feneis, 1994:290.16). 

The lesser petrosal nerve bears parasympathetic fibers from the 

tympanic plexus to the otic ganglion (Feneis, 1994:294.15).

The opening for the lesser petrosal nerve has not been identified in Tursiops. It may be associated with one of the anterointernal sulci that lie on the medial surface of the anterior process 

of the periotic bone.

− opening for the major petrosal nerve (hiatus canalis nervi 

petrosi majoris)

In mammals the opening for the major petrosal nerve lies 

in the petrosquamous suture just lateral to the canal for the trigeminal nerve (Evans and Christensen, 1979:133). In humans 

the opening for the major petrosal nerve is located on the anterolateral aspect of the cranial surface of the petrosal just medial 

and posterior to the opening for the lesser petrosal nerve, lateral 

to the pyramid, and anterior to the arcuate eminence (Feneis, 

1994:14.4). The major petrosal nerve runs in the petrosal canal.

In some specimens of Tursiops the petrosal canal exits from the 

periotic in the groove (anterior incisure) between the pars cochlearis and anterior process of the periotic bone on the anterior aspect 

of the periotic. The opening for the major petrosal nerve is 2–3 mm 

ventral to the dorsal surface of the cochlear process. The proximal 

end of the petrosal canal is 1–2 mm within the facial canal. In other 

specimens of Tursiops, such as those that we have illustrated, the 

petrosal canal appears to be nonexistent, the major petrosal nerve 

branching off the facial nerve cranial to the facial canal.

See further comments under petrosal canal.

= opisthotic portion of the periotic

See posterior process of the periotic bone. 

− osseous labyrinth (labyrinthus osseus)

The mammalian osseous labyrinth consists of the cochlea, 

semicircular canals, and the vestibule and is contained in the 

petrosal (Gray, 1918:1047; Schaller, 1992:532.1; Evans and 

Christensen, 1979:132; Feneis, 1994:374.20). Eustachius and 

Lancisius (1714:107) referred to the osseous labyrinth as the labyrhinthi ductus. Eustachius and Lancisius (1714:107) referred to 

a part of the osseous labyrinth when they mentioned the spiralis 

labyrinthi ductus.

The osseous labyrinth in delphinids consists of the same elements as in the dog.

See pars labyrintha.

− otic capsule

The mammalian otic capsule consists of the cartilaginous 

structure that surrounds the inner ear in the embryo.

= otic portion

Fraser and Purves (1960:34) used the term “otic portion” 

apparently for the body of the periotic (q.v.) in Balaenoptera.

See body of the periotic. 

= oval window

See fenestra vestibuli. 

* parabullary ridge (Figure 25n,t,v,y)

The parabullary ridge (Fordyce, 1994:161) is a ridge on the 

periotic immediately lateral to the anterior bullar facet in some 

fossil Odontoceti. It may be equivalent to the “distinct ventral 

rim” or “ventral swelling” of de Muizon (1987:7).

Tursiops has a well-developed parabullary ridge, which is 

prominent especially on the lateral surface of the anterior process of the periotic bone about 5 mm dorsal and slightly lateral 

to the contact with the accessory ossicle of the tympanic bulla.

− pars canalicularis (canalicular part) = tympanic process (Wible 

et al., 2004:75)

MacPhee (1981:58) followed de Beer (1937) in recognizing 

the canalicular part as the posterodorsal portion of the mammalian otic capsule (of the periotic) that houses the utricle and 

semicircular canals. See also body of the periotic, pars cochlearis, and pars labyrintha.

The pars canalicularis is present but not distinct on the exterior of the periotic in Tursiops.

Luo and Gingerich (1999:45) observed that the pars 

canalicularis forms part of the cranial face of the periotic of 

Archaeoceti.

* pars cochlearis = cochlear part or cochlear portion (Figure 

25b,d,l,o–q,w)

The pars cochlearis or cochlear portion is a rounded medial 

eminence on the mammalian periotic that contains the cochlea.

The pars cochlearis in Tursiops is a rounded medial eminence on the periotic that contains the cochlea and, dorsally, 

the internal acoustic meatus and associated structures within the 

meatus, and the apertures for the cochlear aqueducts and vestibular aqueducts. The anterior limit is at the anterior incisure; 

medially and posteriorly, the pars cochlearis passes into the body 

of the periotic, the pars canalicularis / pars labyrintha, and the 

posterior process without obvious boundaries.

The term “cochlear portion” is an appropriate alternative.

− pars labyrintha (labyrinthine part)

The labyrinthine part of the mammalian periotic contains 

the cochlea, vestibule, and semicircular canals (Turner, 1913:20). 

This is in part synonymous with the pars canalicularis and with 

the pars vestibularis.

In adult Tursiops the pars labyrintha is present but not distinct from other parts of the periotic.

= pars mastoidea (Anderson, 1879:502) = mastoid process

In this sense, applied to the odontocete Platanista, the pars 

mastoidea is not to be confused with that ventral part of m. 

cleidocephalicus that attaches to the mastoid process (Schaller, 

1992:104.12).

See posterior process of the periotic bone, posterior process 

of the tympanic bulla.

= pars vestibularis (vestibular part or vestibular portion)

See vestibular part, body of the periotic. 

= perilymphatic foramen (Luo and Gingerich, 1999: fig. 19)

See cochlear aqueduct. 

* periotic bone (Figures 25a–e,l–q,t–x, 28)

The periotic bone (Mivart, 1892:69) in Cetacea is the 

equivalent of the petrous and mastoid parts of the temporal 

bone in other mammals. The petrosal part of the temporal bone 

p e r i o t i c n u m b e r 6 2 7 • 1 2 3
is spatially separated from the squamous part in delphinids and 

other Cetacea. 

We recommend the term “periotic bone” for Tursiops because of its long historical use for an element distinct from the 

temporal bone. The periotic contains the inner ear (cochlea and 

labyrinth), bounds the middle ear, serves as an origin for middle 

ear muscles, and transmits nerves and vessels.

The periotic bone also has been termed “cetotolite” (Owen, 

1846:527) or “cetolith” (Yamada, 1953:18; Reysenbach de 

Haan, 1957). In other mammals, the petrosal part of the temporal bone has sometimes been loosely termed the “pyramid.”

In Tursiops the periotic bone is sutured with the more ventrally placed tympanic bulla, but it has lost close sutural contact 

with the squamosal bone (squamous portion of the temporal of 

some other mammals). It lies on the ventral surface of the posterolateral margin of the skull, associated with but not contacting the alisphenoid, parietal, exoccipital, and basioccipital bones, 

and it lacks a mastoid exposure laterally on the skull wall.

Major parts of the periotic bone include the anterior process, the body of the periotic (including the pars vestibularis), 

the cochlear portion or pars cochlearis, and the posterior process 

(mastoid process of the periotic or pars mastoidea of past use). 

See also petrosal. 

− periotical processes

The periotical processes consist of both the anterior and posterior process of the cetacean periotic (Oelschläger, 1986a:353; 

not in Schaller, 1992; not in Feneis, 1994). We suggest that this 

term is of limited use.

− periotic canal (canalis perioticus) (McFarland et al., 1979:10) 

= internal acoustic meatus

The periotic canal is the passageway in the petrosal for the 

facial and auditory nerves and associated blood vessels (McFarland et al., 1979:10).

With the separation of the periotic from the tympanic portions of the temporal bone in Cetacea, the only place where the 

facial nerve and the auditory nerve run together through a bone 

is the internal acoustic meatus. The nerves do not run through 

a canal.

− periotic capsule

Not a postnatal term; not used by Schaller, 1992; or Feneis, 

1994.

− petrobasilar canal = petrooccipital canal

In the dog the petrobasilar canal is bounded laterally by the 

petrosal and tympanic bulla and medially by the basioccipital 

bone. It parallels the carotid canal of the sphenoid and lies medial to it. The petrobasilar canal lies in the petrooccipital fissure

and transmits the ventral petrosal sinus (Schaller, 1992:12.6; not 

in Feneis, 1994). It is also known as the petro-occipital canal 

(Evans and Christensen, 1979:134, 793).

The medial part of the petrobasilar canal in the mammalian basioccipital contains the ventral petrosal sinus (Evans and 

Christensen, 1979:134, 793) and has been termed the groove 

for the petrosal sinus, or sulcus sinus petrosi ventralis (Schaller, 

1992:16.6).

The petrobasilar canal is not developed in Tursiops due to 

the separation of the bulla and periotic from the basioccipital. 

The ventral petrosal sinus probably occurs in Tursiops and is 

present in Phocoena (Boenninghaus, 1902; Fraser and Purves, 

1960: fig. 2), but the anatomical situation with the ventral venous sinuses in delphinids is very complex and needs more descriptive work.

See also ventral petrosal sinus, cranial hiatus, and fissura 

petrosoparoccipitalis.

− petrobasilar foramen

The petrobasilar foramen is the anterior opening of the 

mammalian petrobasilar canal. It lies just posteromedial to the 

internal carotid foramen (Evans and Christensen, 1979:156).

The petrobasilar canal does not exist in delphinids due to 

the separation of the bulla and periotic from adjacent parts of 

the braincase.

− petromastoid bridge

The petromastoid bridge is the bony contact between the 

promontorium dorsal to the round window (cochlear window) and 

the mastoid process in archaic mammals (Novacek, 1986:56).

The petromastoid bridge is not distinct in Tursiops, in delphinids, or in other Cetacea.

− petrooccipital canal (canalis petrooccipitalis)

See petrobasilar canal.

= petrooccipital fissure (fissura petrooccipitalis) = petrosoparoccipital fissure

See fissura petrosoparoccipitalis, petrobasilar canal.

= petrosal (pars petrosa) = petrosal part of the temporal = periotic bone

The petrosal part of the temporal bone is located medially in 

the temporal complex and contains the inner ear. In some mammals it is slightly pyramidal in shape and is sometimes referred to 

as the pyramid (Evans and Christensen, 1979:129).

The petrosal part of the temporal bone is spatially separated from the squamous part in delphinids and other Cetacea 

and is widely known as the periotic bone (q.v.). This use, which 

we support for Tursiops, is historically widespread in cetacean 

literature.

* petrosal canal (canalis petrosus) (Figure 25a)

The petrosal canal or hiatus canalis facialis (Whitmore, 

1953) is a small canal that runs anteriorly from the genu of the 

facial canal to exit in the petrosquamous suture, just lateral to 

the canal for the trigeminal nerve in the dog (Evans and Christensen, 1979:133), or on the anterior face of the periotic in artiodactyls. See also hiatus Fallopii.

This appears to be the structure identified by Novacek 

(1986:59) for archaic mammals as the facial canal within the 

tegmen tympani, for the intermedius branch of the facial nerve. 

Novacek identified this canal as opening at the hiatus Fallopii. 

For some Mysticeti, Geisler and Luo (1996: fig. 3) noted that 

the canal is in the form of a fissure that they termed the anterior 

fissure of the facial foramen.

The mammalian petrosal canal carries a branch of the facial nerve, the major petrosal nerve (n. petrosus major) (Evans 

and Christensen, 1979:922). The major petrosal nerve or greater 

petrosal nerve carries fibers that are destined for the pterygo1 2 4 • smithsonian contributions to zoolog y p e r i o t i c
palatine ganglion. The major petrosal nerve is also known as the 

greater superficial petrosal nerve in humans (Gray, 1918:892).

In some specimens of Tursiops the petrosal canal exits from 

the periotic in the anterior incisure or groove between the pars 

cochlearis and anterior process on the anterior aspect of the periotic. The aperture for the petrosal canal is 2–3 mm ventral to 

the dorsal surface of the cochlear process. The proximal end of 

the petrosal canal is 1–2 mm within the facial canal. In some 

specimens of Tursiops the petrosal canal cannot be identified as 

a discrete structure. In other Odontoceti, the petrosal canal may 

form as a reentrant in the anterior border of the internal aperture 

for the facial canal. These inferred relationships have yet to be 

established by dissection.

− petrosal crest

The petrosal crest in mammals is a sharp crest that lies on the 

medial surface of the petrous part of the temporal, just dorsal to 

the internal acoustic meatus, cerebellar fossa, and the canal for the 

trigeminal nerve (Evans and Christensen, 1979:130, 132; Schaller, 

1992:22.16; not in Feneis, 1994). In the dog, the petrosal crest 

may be an anterior continuation of the tentorium cerebelli.

Whitmore termed this the “dorsal crest of the pars petrosa” 

in archaic artiodactyls: an elevated region that is posterior to and 

distinct from the superior process (Whitmore, 1953:131).

Novacek (1986:42, fig. 15) identified a median petrosal crest

in the archaic insectivore Leptictis. This crest lies anterior to the 

internal acoustic meatus and medial to the subarcuate fossa.

The petrosal crest has not been reported for Cetacea; it is 

not homologous with the dorsal crest (q.v.).

− petrosal fossula (fossula petrosa)

The mammalian petrosal fossula is a small fossa that holds the 

distal ganglion of the glossopharyngeal nerve (Schaller, 1992:22.34). 

The petrosal fossula is located on the posteromedial aspect of the 

cranial surface of the petrosal, just dorsal to the petrotympanic fissure and tympanomastoid fissure of the tympanic bulla. In humans 

the petrosal fossula lies in the bony crest between the carotid canal 

of the sphenoid and the jugular fossa and houses the tympanic ganglion of the glossopharyngeal nerve (Feneis, 1994:14.29).

Tursiops appears to lack a petrosal fossula.

= petrosal part of the periotic

See petrosal. 

= petrosal part of the temporal

See petrosal. 

− petrosal ridge

The petrosal ridge is a feature on the promontorium of archaic mammals that marks the contact with the underlying tympanic bulla (Novacek, 1986:55).

Tursiops and other Neoceti lack a petrosal ridge.

= petrosoparoccipital fissure (Luo and Gingerich, 1999:20, tbl. 

5, #34b)

See fissura petrosoparoccipitalis and cranial hiatus.

− petrosquamosal fissure (fissura petrosquamosa)

The petrosquamosal fissure lies on the dorsal surface of the 

petrosal and separates the latter from the squamosal in some mammals (goat, sheep, pig, horse; Schaller, 1992:22.37). In other species the petrosal and the squamosal are not separated by a fissure.

The contact between the periotic and squamosal has been 

greatly reduced in Tursiops and many other Odontoceti, so that 

the periotic is partly roofed dorsally by the squamosal and is 

loose in the macerated skull. The petrosquamosal fissure in the 

normal mammalian sense thus is absent.

− petrosquamosal suture

The petrosquamosal suture lies on the medial surface of 

the squamous part of the temporal bone and unites that with 

the petrosal (Gray, 1918:140:fig. 138, 142, 145). It is not given 

in Evan and Cristensen (1979:129–135), Nomina Anatomica

(IANC, 1983), Schaller (1992:23E), or Feneis (1994:12D).

In odontocetes the sutural connections between the squamosal and the periotic have disappeared and the petrosquamosal 

suture does not occur.

= petrotympanic bone (Flower, 1885) = petro-tympanic bone

See tympanoperiotic bone of “Tympanic Bulla.” 

= petrotympanic fissure

See petrotympanic fissure (fissura petrotympanica) of “Tympanic Bulla.” 

− piriform fenestra

According to MacPhee (1981:59), in fetal mammals and 

some adults, the piriform fenestra is the large gap between the 

auditory capsule and its dorsal outgrowths (such as the tegmen 

tympani and epitympanic wing of the petrosal) and the epitympanic wing of the squamosal and sphenoid. Wahlert (2000:8) reviewed previous uses of “piriform fenestra.” Wible and Gaudin 

(2004:162) noted that the piriform fenestra may be developed 

between the auditory capsule, basisphenoid, alisphenoid, and 

squamosal, and that it may be continuous with the carotid foramen of the sphenoid (see also Geisler, 2001: app. 2, 3); it is 

absent in the dog. Asher et al. (2003) stated that the piriform 

fenestra is present when the petrosal, alisphenoid, squamosal, 

and/or ectotympanic fail to ossify anterior to the promontory in 

the tympanic in fully grown individuals. See tympanic roof.

The piriform fenestra is present in young and adult Tursiops

and forms part of the cranial hiatus (q.v. for details).

* posterior bullar facet (Figure 25m–o,v)

The cetacean posterior bullar facet is the entire ventral surface 

of the posterior process of the periotic bone. It articulates with the 

posterior process of the tympanic bulla (Fordyce, 1994:160).

The posterior bullar facet is well developed in Tursiops.

= posterior cochlear crest (Fordyce, 2002)

See caudal tympanic process. 

= posterior division of the periotic (Anderson, 1879:515) = posterior process

− posterior margin of the petrosal bone (margo posterior partis 

petrosae)

The posterior margin of the petrosal bone is that portion of 

the posterior surface of the mammalian periotic that borders the 

occipital bone (occipital margin) (Feneis, 1994:14.17).

p e r i o t i c n u m b e r 6 2 7 • 1 2 5
Due to the change in relationship of the periotic to the surrounding bones in cetaceans, the posterior margin of the periotic 

is restricted to the posterior process of the periotic bone where it 

contacts the tympanic bulla.

* posterior process of the periotic bone (mastoid process, processus mastoideus) (Figure 25a,e,l,n,q,t,w,x)

In Neoceti and some Archaeoceti the posterior process of 

the periotic bone lies posterior to the pars cochlearis and mainly 

consists of the posterior bullar facet. The posterior process forms 

the lateral wall of the facial sulcus. In most Odontoceti, but generally not Delphinidae, the posterior process of the periotic bone 

articulates with (but is not fused with) the posttympanic process

of the squamosal. There is a wide body of literature about the 

process, its homology, and its relationships.

The posterior process of the periotic bone has often been 

discussed in the context of the mastoid process of other mammals. In mammals, the mastoid process forms the posterolateral corner of the petrosal (periotic bone) (Flower, 1885:131; 

Evans and Christensen, 1979:133); the mastoid has been defined 

as that portion of periotic bone posterior to a line joining the 

stylomastoid foramen and the posterior lacerate foramen (McDowell, 1958; Novacek, 1986). In noncetacean mammals, the 

term “mastoid” is applied to the periotic only, and generally is 

not used for the tympanic bulla. Following Flower (1868), Boenninghaus (1904), Pompeckj (1922), and others, we homologize 

the mastoid process in the traditional mammalian sense with the 

posteroventral eminence or posterior process of the periotic bone 

in Tursiops. The name “posterior process of the periotic bone” is 

used here, because the term “mastoid” also has been used previously for components of the squamosal bone and tympanic bulla

in Neoceti. MacPhee (1981:57) similarly cautioned on the use 

of “mastoid.”

The posterior process of the periotic bone has also been 

termed “processus tympanicus ossis petrosi” (Denker, 1902:429; 

Reysenbach de Haan, 1957). Lillie (1910:777) used the term 

“opisthotic portion of the periotic” for the posterior process of 

the tympanoperiotic of Balaenoptera musculus, but this process 

in B. musculus and other Mysticeti is formed mainly of tympanic 

bulla. Fraser and Purves (1960:77–80; e.g., pl. 8) used the term 

“mastoid process” for the posterior process of the tympanic bulla

in some Odontoceti. We cannot identify in Tursiops or other 

Odontoceti any mastoid component in the tympanic bulla, and 

recommend that the term “mastoid” not be used for components 

of the tympanic bulla. Fraser and Purves (1960:77–80; pl. 7) also 

used mastoid process for the fused posterior process of the tympanic bulla plus posterior process of the periotic bone, as seen in 

Mysticeti. We do not follow this use of mastoid. See posterior 

process of the tympanic bulla for discussion.

In Tursiops and all other Odontoceti, the posterior process 

of the periotic bone is tightly sutured to the posterior process of 

the tympanic bulla. The suture may be plane, serrate, or sometimes foliate (the latter giving an impression of fusion), but it 

is not known to fuse with the tympanic bulla. In contrast, the 

posterior process of the periotic bone and tympanic bulla do fuse 

in Mysticeti, which has led to the confused terminology reviewed 

under posterior process of the tympanic bulla.

Further, the posterior process of the periotic bone in Tursiops is not known to fuse with adjacent skull elements. Fusion between the posterior process and adjacent elements is not 

known for sure among other Odontoceti, except the fossil group 

Squalodontidae in which the posterior process of the periotic 

bone may fuse with the posttympanic process of the squamosal.

The mastoid process in many mammals contributes to the wall 

of the braincase between the mastoid foramen (at the junction of 

petrosal, exoccipital, and squamous temporal bones) and the stylomastoid foramen of the petrosal (Sisson and Grossman, 1953:37, 

71:fig. 48, 158:fig. 161; Evans and Christensen, 1979:133; Oelschläger, 1986b:fig. 6a; Novacek, 1993:472, 474). Archaeoceti 

show the expected mammalian condition, in which the posterior 

process of the periotic bone is exposed laterally on the skull wall, 

wedged ventrally between squamosal and exoccipital (Pompeckj, 

1922; Kellogg, 1936: fig. 5, fig. 28, pl. 15 fig. 1). In Archaeoceti, 

the posterior process of the tympanic bulla is visible here in lateral 

view of the skull wall, where it sutures with the squamosal at the 

postmeatal crest, but the tympanic bulla does not significantly fill 

in the space between the squamosal and exoccipital.

Sometimes in noncetacean mammals, the mastoid process 

may not be exposed laterally on the skull wall, producing an 

“amastoid” condition of the skull in, for example, some artiodactyls (Whitmore, 1953:135). We interpret Tursiops, all other 

Odontoceti, and all Mysticeti as amastoid, with the posterior 

process of the periotic bone not exposed laterally. The region 

between squamosal and exoccipital may be altered when the 

squamosal and exoccipital become sutured more ventrally, or it 

may be filled by an enlarged posterior process of the tympanic 

bulla in some Odontoceti (Ziphiidae, Physeteridae, Kogiidae), or 

by an enlarged posterior process of the tympanic bulla to which 

the periotic bone is fused dorsomedially in most Mysticeti. See 

posterior process of the tympanic bulla.

Fraser and Purves (1960:77) identified in Caperea a “portion of the squamosal immediately anterior to the pars mastoidea

[of tympanoperiotic], of a rugose and laminated appearance,” 

which they interpreted as “a mastoid element” fused to what 

we identify as post-tympanic portion of squamosal (q.v.). This 

interpretation of Fraser and Purves led others to accept that a 

mastoid component of periotic has lost its primitive connection 

with periotic, and has become fused to the tympanic bulla and/

or to the squamosal (Purves, 1966:340; Oelschläger, 1986a,b). 

However, we find no evidence among living or fossil mammals 

that any component of periotic or tympanic bulla loses its original connection through fusion with the squamosal bone.

* posteroexternal foramen (Figure 25c,e)

The posteroexternal foramen (Fordyce, 1994:161, 160) is 

located on the lateral surface of the posterior process of the periotic bone in some Archaeoceti and Neoceti. It is of uncertain 

function.

In Tursiops this part of the periotic carries many tiny foramina. The posteroexternal foramen was distinct in two of five 

periotics from different individuals. It is too small to be probed.

− postpromontorial tympanic recess = postpromontorial tympanic sinus (Wible and Rougier, 2000:94)

− postpromontorial tympanic sinus

In armadillos (Wible and Gaudin, 2004: fig. 4) the postpromontorial tympanic sinus is a depression between the fossa 

1 2 6 • smithsonian contributions to zoolog y p e r i o t i c
for the stapedial muscle and the fenestra ovalis, and lodges a 

diverticulum of the cavum tympani in life.

Tursiops lacks a postpromontorial tympanic sinus.

− posttemporal canal

The posttemporal canal is present in some mammals as a 

structure between the petrosal (periotic bone) and squamosal, 

associated with the stapedial artery. In some armadillos (Wible 

and Gaudin, 2004:163) it lies near the most dorsal part of the 

laterally exposed mastoid process. It occurs in the horse but 

not in artiodactyls or the dog (Geisler and Luo, 1998; Wible 

and Gaudin, 2004:163). Geisler and Luo (1998:187) stated 

that it is absent from Cetacea, except for possibly some basal 

archaeocetes.

Tursiops is not known to have a posttemporal canal.

= primary facial foramen = ventral foramen of the facial canal

Ross and Covert (2000:243) used primary facial foramen as follows: “The primary facial foramen carries the facial 

nerve from the internal acoustic meatus to the cavum supracochleare.” This is equivalent to the proximal (or cerebral, or 

internal, or dorsal) opening of the facial canal. Wible and Rougier (2000:118) attributed “primary facial foramen” to Wible 

(1990). 

See facial canal.

− processus cochleariformis

In humans (Gray, 1918:145) the processus cochleariformis, 

or septum canalis musculotubarii, is a thin plate of bone that 

separates two canals that lead into the tympanic cavity, namely 

the canal for the tensor tympani (semicanalis m. tensoris tympani) and the canal for the bony part of the auditory tube (semicanalis tubae auditivae).

In Kogia Schulte (1917:397) identified the processus cochleariformis as a thin ledge that lies medial to the accessory ossicle

(uncinate process [of the tympanic bulla] of Schulte) and projects medially and ventrally. The only structure apparent here in 

Kogia is the dorsomedial extremity of the anterior process of 

the periotic bone, which in turn is probably homologous with 

the anterodorsal angle (q.v.), which in Kogia is rotated medially 

and ventrally relative to the position in Tursiops. Dissection is 

needed to establish if a processus cochlearis is present.

− processus cristae facialis

Wible and Gaudin (2004:135), who attributed this term to 

Patterson et al. (1989), identified the processus cristae facialis as 

possibly the shelf that is continuous posteriorly with the crista 

facialis (here, facial crest of the periotic) or crista parotica.

There is no evidence that a processus cristae facialis is present in Tursiops.

= processus tubarius

See accessory ossicle and processus tubarius of the bulla in 

“Tympanic Bulla.”

− prominentia canalis lateralis

The prominentia canalis lateralis is an eminence that is 

closely applied to the squamosal in archaic artiodactyls (Whitmore, 1953:132). Its lower edge forms the tegmen tympani.

The prominentia canalis lateralis is not a discrete structure 

in Tursiops. Whether the prominentia canalis lateralis is homologous with the lateral tuberosity is uncertain.

See lateral tuberosity.

= promontorial groove, median

See median promontorial groove. 

− promontory of the pars cochlearis (promontorium)

See cochlear portion (pars cochlearis) in part.

The promontory of the mammalian petrosal is the eminence that forms the ventromedial part of the petrosal. It is 

directly medial to the fossa for the m. tensor tympani and the 

facial canal (Evans and Christensen, 1979:132). Whitmore 

(1953:132) and MacPhee (1981:61) stated that the promontorium is the bulge caused by the first turn of the cochlea. This 

structure is sometimes called the “promontory of the pyramid”; 

see pyramid.

For Archaeoceti, Luo and Gingerich (1999: fig. 19) identified the promontory as the ventromedial eminence of the pars 

cochlearis.

In Tursiops the promontory of the periotic forms part of 

the eminence comprising the ventral part of the pars cochlearis. 

It is medial to the vestibular window (oval window) and has the 

round window in its posterior wall. Because the promontory is 

not distinct from other parts of the ear, it is not easily identifiable, so we recommend use of the term “pars cochlearis” (or 

cochlear portion).

= prootic portion of the periotic bone (Fraser and Purves, 

1960:34)

See anterior process of the periotic bone. 

= pyramid

In terrestrial mammals, the term “pyramid” has been used 

both for the petrosal (periotic bone (q.v.) of our use) and for the 

pars cochlearis (q.v.).

See petrosal (Evans and Christensen, 1979:129) and periotic 

bone entries above. 

= pyramidal process of the periotic

Luo and Gingerich (1999: fig. 19) identified the pyramidal 

process of the periotic in Archaeoceti as the feature lateral to 

the aperture for the vestibular aqueduct and distinct from the 

superior process.

The indistinct dorsal crest of the periotic bone in Tursiops

may carry an eminence just lateral to the aperture for the vestibular aqueduct, but it is not certain if this is homologous with the 

structure in Archaeoceti. See also dorsal tuberosity.

Similarly, it is not clear if a dorsal structure of the pars 

cochlearis in some Mysticeti (Geisler and Luo, 1996: fig. 3) is 

homologous.

= pyramidal prootic portion (Fraser and Purves, 1960:34)

See anterior process of the periotic bone. 

= recessus epitympanicus

See epitympanic recess, body of the periotic, and tegmen 

tympani.

p e r i o t i c n u m b e r 6 2 7 • 1 2 7
= regio mastoidea = mastoid region

In Kogia Schulte (1917:396) described the “platelike processus tympanicus [of Denker] which Beauregard is no doubt 

right in interpreting as the regio mastoidea.”

See posterior process of the periotic bone. 

− rostral tympanic process

MacPhee (1981:63) identified the rostral tympanic process

in mammals as arising from the ventral surface of the pars cochlearis in mammals.

Tursiops lacks a rostral tympanic process.

= round window (fenestra rotunda)

See cochlear window (= fenestra cochleae).

− saccule (sacculus)

The saccule of the mammalian inner ear lies within the recessus sphericus or ventral vestibular area (q.v.). The saccule communicates with the cochlear duct, by way of the canalis reuniens, 

and the endolymphatic duct (Gray, 1918:1052).

Tursiops has a saccule.

= secondary facial foramen = stylomastoid foramen

Ross and Covert (2000:243) identified the secondary facial 

foramen as the epitympanic, ventral, distal, or external opening of 

the facial canal (Fallopian aqueduct). Sanchez-Villagra and Wible 

(2002:35) stated that almost all metatherians have a bony floor 

to the cavum supracochleare, and that the anterior and posterior 

edges of this floor have foramina that transmit the two major 

branches of the facial nerve. Sanchez-Villagra and Wible identified 

the anterior foramen as the hiatus Fallopii (for the palatine ramus 

or greater petrosal nerve), and the posterior foramen as the secondary facial foramen, which transmits the hyomandibular ramus.

= semicanal for the tensor tympani muscle (semicanalis m. tensoris tympani) = fossa for the tensor tympani muscle

See also processus cochleariformis and musculotubal canal 

of the tympanic bulla.

− semicircular canals

The mammalian semicircular canals are three in number 

and are designated the anterior canal, posterior canal, and lateral canal. The anterior semicircular canal is sometimes referred 

to as the superior semicircular canal. In the dog the semicircular 

canals lie in the petrosal, posterolateral and dorsal to the cochlea

and vestibule (Evans and Christensen, 1979:1069, 1070).

In Tursiops and other Odontoceti the semicircular canals 

bear the same anatomical relationships as they do in the dog 

(Yamada and Yoshizaki, 1959; confirmed on USNM 241288, 

241289).

− shallow lateral groove

Fordyce (1994:160) labeled a shallow lateral groove located 

midlength on the lateral surface of the periotic in archaic Odontoceti, between the lateral tuberosity and the dorsal tuberosity.

The shallow lateral groove is not present in Tursiops.

= singular foramen

See foramen singulare. 

= spherical recess (Evans and Christensen, 1979:1070)

See ventral vestibular area. 

− spiral canal

The spiral canal is a cavity within the mammalian cochlea

that is divided by the spiral lamina (q.v.).

* spiral cribriform tract (tractus spiralis foraminosus) (Figure 25a,u)

In mammals the spiral cribriform tract lies in the internal 

acoustic meatus, ventral to the transverse crest. The spiral cribriform tract passes the cochlear nerve (Evans and Christensen, 

1979:132).

The spiral cribriform tract in delphinids lies lateral to the 

transverse crest.

− spiral lamina (lamina spiralis ossea)

The spiral lamina is a shelf projecting from the modiolus into the spiral canal of the mammalian cochlea (Schaller, 

1992:532.29; Feneis, 1994:344.1). A secondary spiral lamina 

(lamina spiralis secundaria) projects from the opposite wall of 

the spiral canal of the cochlea on its basal turn only.

Odontoceti have a normal mammalian spiral lamina.

− squamosal fossa

Some Mysticeti have a squamosal fossa, which is a prominent groove on the lateral face of the periotic between the anterior process of the periotic bone and the body of the periotic

(Geisler and Luo, 1996:1052, fig. 3.6). The squamosal fossa may 

be homologous with the anteroexternal sulcus (q.v.). See Watson 

and Fordyce (1993) for comment.

Tursiops lacks a squamosal fossa.

− stapedial artery groove

In some mammals the stapedial artery runs in a groove on 

the promontorium of the petrosal (pars cochlearis of the periotic bone in the terminology used here for Tursiops), forming a 

promontorial stapedial artery groove (e.g., Wible and Gaudin, 

2004:165) or sulcus for the stapedial artery. 

Tursiops lacks a stapedial artery groove, and lacks grooves 

that in other mammals (e.g., Novacek, 1986:55) are attributable 

to carotid circulation through the middle ear. 

See also sulcus for the internal carotid artery.

− stylohyal fossa

Wible and Gaudin (2004:137) followed Patterson et al. (1989) 

in identifying, in the yellow armadillo, a shallow, round, depressed 

stylohyal fossa on the petrosal; they commented that the round 

structure within the fossa is the terminal end of the tympanohyal.

Tursiops sometimes has a tiny tympanohyal on the posteroventral side of the periotic at the posterior of the facial crest, which 

occasionally forms a projection in a larger fossa. We have noted a 

more-obvious circular stylohyal fossa in Physeter and Eubalaena.

= styloid process

See tympanohyal. 

− stylomastoid canal

In some archaic artiodactyls (Whitmore, 1953) the distal 

path of the facial nerve as it exits the middle ear cavity is en1 2 8 • smithsonian contributions to zoolog y p e r i o t i c
closed in a stylomastoid canal, which starts proximally (internally) at the foramen stylomastoideum primitivum and opens 

laterally at the stylomastoid foramen (q.v.), also known as 

the foramen stylomastoideum definitivum (Novacek, 1986: 

fig. 20). 

The stylomastoid canal is absent in Tursiops.

− stylomastoid foramen (foramen stylomastoideum)

In many mammals the stylomastoid foramen lies on the 

posterolateral surface of the petrosal posterior to the mastoid 

process of the petrosal. It marks the point where the facial nerve 

and stylomastoid artery (if present) pass onto the lateral face of 

the skull. The ventral margin of the stylomastoid foramen may 

be formed by the tympanic bulla (Gray, 1918:144,181; Schaller, 

1992:22.32; Feneis, 1994:14.27). Vesalius (1543:53; Vesalius 

et al., 1998:131) referred to the stylomastoid foramen as the 

foramen ex auditus organum amplitudinis medio exortu, ac illinc in posteriora porrectum . . . Paeparatur autem ramulo nervi 

quinti paris.

Evans and Christensen (1979:231, 133, 662) indicated that, 

in the dog, the stylomastoid foramen is the lateral opening of 

the facial canal (q.v.). Wible and Rougier (2000:119) interpreted 

Evans and Christensen’s definition of stylomastoid foramen to 

mean “the opening between the petrosal, the osseous bulla, and 

the tympanohyal (tympanohyoid) cartilage by which the facial 

nerve (hyomandibular branch) leaves the middle ear and the 

stylomastoid artery off the posterior (caudal) auricular enters.” 

Whitmore (1953) named the more-distal (more-lateral) canal for 

the facial nerve as the stylomastoid canal (q.v.).

The stylomastoid foramen is absent in Tursiops and generally in other Neoceti. The facial nerve passes onto the lateral wall 

of the skull via a shallow to indistinct facial sulcus. Occasionally 

in Neoceti the facial sulcus may end abruptly at a distinct lateral notch on the posterior process of the tympanic bulla, which 

we recognize as the stylomastoid notch, and which we regard as 

homologous with the stylomastoid foramen. In Kogia breviceps

(USNM 571648) a stylomastoid foramen is formed at the suture 

between the exoccipital and the posterior face of the posterior 

process of the tympanic bulla.

Van der Klaauw (1931:173) cited Hanke (1914:508) that 

the facial nerve in Odontoceti exits via the fissura tympano-periotica. The latter is not to be confused with the fissura petro-tympanica = petrotympanic fissure = fissura Glaseri, which serves 

as the exit from the bulla for the chorda tympani. See fissura 

Glaseri.

See also foramen stylomastoideum primitivum and foramen stylomastoideum definitivum.

− stylomastoid fossa

The stylomastoid fossa is a square-shaped depression on the 

posterior face of the cetacean pars cochlearis dorsal to the fossa 

for the stapedial muscle (Geisler and Luo, 1996:1054). In some 

Cetacea the fossa may involve the base of the posterior process. 

Fraser and Purves (1960:39) apparently referred to this structure 

when they noted a “concavity on the postero-dorsal face of the 

‘pars mastoidea’ of the tympano-periotic.” According to Fraser 

and Purves, the fossa is likely to accommodate a part of the peribullary sinus or the posterior sinus.

Tursiops lacks a stylomastoid fossa.

− stylomastoid notch

The stylomastoid notch is a semi-enclosed distal end of the 

facial sulcus on the lateral face of the skull, where the facial nerve 

exits the mammalian basicranium; it is regarded as homologous 

with the stylomastoid foramen (q.v.).

Geisler and Luo (1996:1054) and Luo and Gingerich 

(1999:45, and their fig. 2c) used stylomastoid notch for a feature 

on the periotic medial to the posterior process and between the 

posterior process and the pars cochlearis.

The stylomastoid notch is present in Tursiops; the term “facial sulcus” seems more applicable, while “stylomastoid notch” 

is retained for the appropriate feature on the lateral face of the 

mammal skull.

See facial sulcus.

− subarcuate fossa (fossa subarcuata)

The subarcuate fossa is a deep depression posterior to the 

internal acoustic meatus in carnivores (Schaller, 1992:22.22) and 

other mammals (Novacek, 1986; Whitmore, 1953). In humans it 

lies in the same position relative to the internal acoustic meatus 

(Feneis, 1994:14.14). The subarcuate fossa lies in the hollow medial to the petrosal crest and posterior to the internal acoustic meatus. In infants the subarcuate fossa extends posteriorly as a blind 

tunnel under the anterior semicircular canal (Gray, 1918:143).

The subarcuate fossa has also been termed the “cerebellar 

fossa” (Evans and Christensen, 1979:130). The cerebellar fossa lies 

on the posteromedial surface of the petrosal and houses the paraflocculus of the cerebellum (Evans and Christensen, 1979:132).

The subarcuate fossa is not present in adult Tursiops or 

other Neoceti, but de Burlet (1913: figs. 10, 13) reported a subarcuate fossa in an embryo of Phocoena phocoena.

− sulcus for the internal carotid artery

In some mammals one or more sulci for the carotid artery 

may course across the promontorium (Novacek, 1986:55). The 

sulci may branch to produce sulci for the stapedial artery and the 

promontory artery.

Tursiops and other Neoceti lack sulci for the carotid artery.

− sulcus medialis

In some archaic mammals the sulcus medialis courses along 

the medial intracranial edge of the petrosal; it is probably for the 

ventral or inferior petrosal sinus (Novacek, 1986:59).

The sulcus medialis appears to be absent in Tursiops and other 

Neoceti. Dissection is needed to establish the path of the inferior or 

ventral petrosal sinus relative to the periotic and other bones. 

See also median promontorial groove.

− superior margin of the petrosal (margo superior partis petrosae)

The superior margin of the mammalian petrosal bone is that 

portion of the dorsal cranial surface that borders the squamosal 

(Feneis, 1994:14.9). 

Due to the change in the relationship of the periotic to the 

squamosal with the isolation of the ear apparatus from the rest 

of the skull in Tursiops, only the posteroventral corner of the 

periotic borders the squamosal. The superior margin has disappeared; its homologue includes the dorsal crest of the periotic 

bone (q.v.). 

See also superior process.

p e r i o t i c n u m b e r 6 2 7 • 1 2 9
− superior process = petrosal crest

The superior process is that dorsal part of the periotic bone 

(petrosal) that extends dorsolaterally on the cranial wall of the 

squamosal (Pompeckj, 1922; Whitmore, 1953) in mammals, 

including archaic artiodactyls, some Archaeoceti, and some 

Neoceti. The process may project laterally, rather than dorsally 

(Whitmore, 1953), to floor the temporal venous sinus. It is apparently distinct from the petrosal crest. The superior process is 

part of the tegmen tympani (Luo and Gingerich, 1999:41).

In Tursiops and other living Odontoceti the superior process 

is not distinct, having become obliterated through changes in 

contact relationships with the squamosal (Fordyce, 1994: fig. 9). 

The former position of the superior process is perhaps indicated 

by the dorsal crest of the periotic bone (q.v. Fordyce, 1994).

Previously, Kasuya (1973:2) identified the superior process of the periotic bone as the rounded dorsolateral eminence 

that lies between the anterior process of the periotic bone and 

posterior process of the periotic bone, lateral to the cochlear 

portion. De Muizon (1987:8) also seemed to apply the term in 

this way.

− supracochlear cavity

In some mammals a supracochlear cavity or cavum supracochleare is well developed as a space that houses the geniculate ganglion of the facial nerve (Wible and Gaudin, 2004:151). 

The cavity arises from the medial part of, or lies internal to, the 

epitympanic recess and penetrates the pars cochlearis dorsally 

(MacPhee, 1981:64; Ross and Covert, 2000).

Tursiops lacks a supracochlear cavity but, like many other 

mammals (Wible and Gaudin, 2004:151), is presumed to have a 

genu of the facial canal.

− suprameatal area = suprameatal fossa of the periotic

Bisconti (2005) mentioned, for an extinct right whale (Balaenidae), the suprameatal area of the petrosal (periotic bone), 

referring to the work of Luo and Gingerich (1999) who showed 

that in basilosaurids the suprameatal area of the periotic is high 

and flat to slightly concave. Bisconti’s mention appears to refer to 

the suprameatal fossa of the periotic sensu Luo and Gingerich.

− suprameatal fossa of the periotic

Luo and Eastman (1995:436, fig. 1) proposed “suprameatal 

fossa” for the shallow depression between the internal auditory 

meatus and homologue of the superior process on the cranial 

face of the periotic bone in a squalodontoid odontocete. Previously, Fordyce (1994:161) referred to this feature through mention of the superior petrosal sinus or subarcuate (subfloccular) 

fossa, in turn influenced by Pompeckj (1922) and Kellogg (1936: 

figs. 5, 6). Kellogg (1936:117) did not name this area but identified it as the irregularly hollowed cerebral face of the periotic in 

the archaeocete Zygorhiza kochii. The suprameatal fossa of the 

periotic is well developed in Archaeoceti, forming much of the 

concave dorsal part of the periotic between the internal auditory 

meatus and the dorsal lip of the superior process (Luo and Gingerich, 1999:13, 26, 45, figs. 3, 19, item smf).

In Tursiops there is a variable and generally indistinct elongate depression lateral to the internal auditory meatus and medial to the vestigial dorsal crest; this might be the suprameatal 

fossa of the periotic.

The “suprameatal fossa of the cetacean periotic” should not 

be confused with the suprameatal fossa of some Carnivora, which 

is a depression immediately posterior to the bony external auditory meatus on the lateral wall of the skull (Wang et al., 2004, 

2005; see also suprameatal fossa under “Squamosal Bone”).

− tegmen tympani

The tegmen tympani in humans is a thin plate of bone 

(tegmen = roof) that separates the cranial cavity and tympanic 

cavity. It lies on the anterior surface of the petrosal close to its 

temporal margin. The tegmen is extended posteriorly to cover 

the tympanic antrum and anteriorly to cover the fossa for the 

tensor tympani muscle. It is limited laterally by the petrosquamous suture (Gray, 1918:1038). In the dog the tegmen tympani

is a region of thin bone immediately dorsal to the epitympanic 

hiatus and the fossa for the tensor tympani muscle. Whitmore 

(1953:132) identified the tegmen tympani as lying lateral to the 

fossa for the tensor tympani muscle.

The tegmen tympani is identifiable in embryonic Cetacea 

(Ridewood, 1922) and occurs in adults, albeit as a structure that 

is greatly thickened dorsoventrally in many Archaeoceti (e.g., 

Luo and Gingerich, 1999: fig. 2) and Neoceti. The tegmen tympani, in the sense of a thin roof to the middle ear, is not readily 

applicable in adult Tursiops.

For cetaceans Kellogg used “recessus epitympanicus” (e.g., 

1936:27) to refer to structures immediately ventral to the tegmen tympani of other authors, and (e.g., 1931) used “body of 

the periotic” to refer to that part of the periotic bone other than 

the anterior process of the periotic bone, pars cochlearis, and 

posterior process of the periotic bone.

Tuberosity of the tegmen tympani, as used by Schulte 

(1917:397, 398), referred to the anterior process of the periotic 

bone.

= tegmental process (Yamada, 1953:20)

See anterior process of the periotic bone.

= tractus spiralis foraminosus = spiral cribriform tract

* transverse crest of the internal acoustic meatus (crista transversa) (Figure 25t,u)

The transverse crest of the internal acoustic meatus separates the opening of the facial canal from the tractus spiralis 

foraminosus in the dog (Evans and Christensen, 1979:132). This 

is the crista falciformis of humans (Gray, 1918:143).

In Tursiops the transverse crest of the internal acoustic meatus separates the internal aperture for the facial canal (Fallopian 

aqueduct) from the foramen singulare and the spiral cribriform 

tract (tractus spiralis foraminosus) (Kellogg, 1928: fig. 23; Kasuya, 1973:2). The crest is directed anteroposteriorly, rather 

than transversely, across the meatus.

= transverse septum (Luo and Gingerich, 1999:45)

See transverse crest of the internal acoustic meatus. 

= transverse vascular channel (Luo and Gingerich, 1999:45, figs. 

1, 14, item vf)

See anteroexternal sulcus. Note that further work is needed 

to determine whether the latter is homologous with the trans1 3 0 • smithsonian contributions to zoolog y p e r i o t i c
verse (or dorsoventral) vascular channel or the vascular groove 

of Luo and Gingerich (1999:45).

− trigeminal impression (impressio n. trigemini)

The trigeminal impression is situated on the anterolateral 

portion of the cranial surface of the mammalian periotic, just 

posterior to the foramen ovale (Schaller, 1992:22.14; Feneis, 

1994:14.8). It may also develop on the contiguous portion of 

alisphenoid (MacPhee, 1981:64). The trigeminal impression 

contains the posterior part of the semilunar ganglion of the trigeminal nerve.

In Tursiops and other Odontoceti the contact with the trigeminal nerve is lost and the trigeminal impression is absent due 

to the separation of the periotic from the skull.

= tuberosity of the tegmen tympani = anterior process of the 

periotic bone (Schulte, 1917:397)

− tympanic antrum

The tympanic antrum in humans is a large irregular cavity 

that develops toward the mastoid process, is roofed by the tegmen tympani, and is continuous with the tympanic cavity (Gray, 

1918:142).

Tursiops lacks a tympanic antrum.

= tympanic aperture of the facial canal (Reysenbach de Haan, 

1957)

See facial canal.

− tympanic canaliculus (canaliculus tympanicus)

The mammalian tympanic canaliculus is a small canal for 

the tympanic branch of the glossopharyngeal nerve and inferior 

tympanic branch of the ascending pharyngeal branch of the external carotid artery (Schaller, 1992:22.33; Feneis, 1994:14.28). 

In humans the tympanic canaliculus lies between the jugular 

foramen and the carotid canal of the sphenoid. The tympanic 

branch of the glossopharyngeal nerve contributes to the tympanic plexus.

Presumably Tursiops has a tympanic nerve and tympanic 

plexus, but details have yet to be determined by dissection. 

See also opening for the lesser petrosal nerve.

= tympanic process = caudal tympanic process (Wible et al., 

2004:75)

− tympanic roof

“Tympanic roof” appears to be a general term for the roof 

of the middle ear, normally represented by the petrosal (periotic 

bone). See, for example, Wible and Rougier (2000:40), Asher et 

al. (2003), and Wible and Gaudin (2004).

Tursiops is inferred to have a tympanic roof, which, however, does not develop fully (see piriform fenestra). The term 

does not seem useful in describing adult specimens.

− tympanic surface of the periotic (facies tympanica) = tympanic 

surface of the petrosal

The tympanic surface of the petrosal bone in the dog is the 

ventrolateral surface that borders on the tympanic bone (Evans 

and Christensen, 1979:132).

In Tursiops the tympanic surface of the periotic bone is the 

ventral surface that faces the tympanic bulla. It bears the anterior 

bullar facet and posterior bullar facet and the oval window.

* tympanohyal (Figure 25k,m,o,t)

The tympanohyal cartilage is the most proximal of the 

hyoid elements. It runs between the stylohyoid and the petrosal (Evans and Christensen, 1979:148; Schaller, 1992:38.46; 

Sisson, 1910:64, figs. 27, 33). The tympanohyal is poorly developed in the dog. In humans the stylohyal fuses with the tympanohyal to form the styloid process or processus styloideus

(Gray, 1918:145). Van der Klaauw (1931:239) and Sisson and 

Grossman (1953:71) used the term “hyoid process” (processus 

hyoideus) for the tympanohyal as fused to the facial crest of the 

periotic (q.v.). Eustachius and Lancisius (1714:98, 104, 109, 

115) referred to the styloid process as the “processus styliformis” or “styloides processus.”

Van der Klaauw (1931:239) suggested that the styloid 

process as formed by co-ossified tympanohyal and stylohyal be 

termed “processus styliformis,” but this would introduce unnecessary confusion with the muscular process (styliform process) of 

the tympanic bone in some mammals.

In delphinids the base of the tympanohyoid is fused to the 

posteroventral side of the periotic (see Figure 25k,m,o,t,u). A 

vestigial tympanohyal is developed variably in Tursiops. Commonly, the tympanohyal in Tursiops and other Neoceti is 

marked by a small pit on the medial edge of the posterior bullar 

facet, immediately ventral to the facial sulcus. Van der Klaauw 

(1931:239) identified the point of fusion as the crista facialis 

petrosi or facial crest of the periotic. Occasionally the tympanohyal may be quite prominent (Owen, 1846:526, in Physeter; 

Oelschläger, 1986b; and our observations of Neoceti in the collections of the USNM).

The stylohyal has not been reported to fuse with the tympanohyal in Tursiops. Rather, in Odontoceti, the bony element 

usually identified as stylohyal articulates with the paroccipital 

process of the exoccipital. Dissection of Tursiops is needed to establish relationships between tympanohyal, paroccipital process, 

and stylohyal.

See also tympanohyoid under “Hyoid Apparatus.” 

− tympanomastoid fissure of the petrosal

Van der Klaauw (1931:174) stated that, in mammals, the 

common aperture for the facial nerve and the hyoid is termed the 

tympanomastoid fissure.

It seems unnecessary to apply this name to Tursiops.

= tympanoperiotic fissure (fissura tympano-periotica)

See petrotympanic fissure of “Tympanic Bulla” and stylomastoid foramen. 

= upper tympanic aperture (Kasuya, 1973: fig. 1)

See epitympanic hiatus. 

− utricle

The utricle is the cavity forming part of the labyrinth into 

which the semicircular canals communicate in humans (Gray, 

1918:1051, 1052). 

See pars canalicularis.

p e r i o t i c n u m b e r 6 2 7 • 1 3 1
− vascular foramen (associated with the periotic)

Luo and Gingerich (1999: fig. 18) showed a vascular foramen between the periotic and squamosal in Archaeoceti that is 

similar in position to that identified by Fordyce (1994) as perhaps for the middle meningeal artery.

See foramen spinosum.

− ventral border of the petrosal bone (margo ventralis partis petrosae)

The ventral border of the mammalian petrosal bone is the 

cranial margin of the petrosal that borders the tympanic bone 

(Schaller, 1992:22.25).

In delphinids the ventral border of the periotic is limited to 

the articular surface of the posterior process and the portion of 

the anterior process of the periotic bone on which the accessory 

ossicle lies. See also tympanic surface of the periotic.

− ventral foramen of the facial canal

The ventral foramen of the cetacean facial canal lies on the 

ventral surface of the petrosal, just lateral to the vestibular window (e.g., Fordyce, 1994:160). The ventral foramen is the epitympanic, distal, or external opening of the facial canal. 

See facial canal for further discussion.

− ventral petrosal sinus

The ventral petrosal sinus lies in the petrobasilar canal and 

connects the cavernous sinus with the sigmoid sinus in the dog 

(Evans and Christensen, 1979:793, 794). The feature is also 

termed the inferior petrosal sinus (e.g., MacPhee, 1981:56). It 

may be exposed ventrally in species in which the basicapsular 

fissure persists in adults.

The ventral petrosal sinus may exist in Tursiops, but the 

anatomical situation with the ventral venous sinuses in delphinids is very complex and needs adequate descriptive work. The 

petrobasilar canal is absent in Tursiops.

− ventral surface of the petrosal (facies ventralis partis petrosae)

The ventral surface of the mammalian petrosal is that 

portion of the external surface of the petrosal that is exposed 

ventrally (i.e., is not covered by the tympanic bulla) (Schaller, 

1992:22.29; not in Feneis, 1994).

None of the ventral surface is external in Tursiops, so that 

in this sense the ventral surface does not exist. The ventral aspect 

of the periotic is partly equivalent to the ventral border of the

petrosal bone and to the tympanic surface of the periotic.

= ventral tuberosity

Luo and Gingerich (1999:45) ascribed the term “ventral 

tuberosity” to Fordyce (1994), but it was used by de Muizon 

(1987:5).

See lateral tuberosity. 

* ventral vestibular area (area vestibularis saccularis or foramen 

acusticum inferius) (Figure 25t)

The ventral vestibular area in mammals is located ventral 

(anteroventral) to the transverse crest of the internal acoustic meatus and contains the sacculus. Nerve fibers that come from the 

sacculus pass through the foramen singulare (Evans and Christensen, 1979:132). The structure has also been called the spherical recess for the saccule (Evans and Christensen, 1979:1070). It 

is separated from the elliptical recess for the utricle by the vestibular crus. The term “ventral vestibular area” seems clearer 

than “spherical recess.”

Wible et al. (2001:8) used a broader definition for the extinct mammal Prokennalestes: the ventral vestibular area [foramen acusticum inferius of their use] is that part of the internal 

acoustic meatus that lies medial to the transverse crest, including 

the spiral cribriform tract and, although they did not mention it, 

the foramen singulare. 

In Tursiops the ventral vestibular area in the sense of Wible 

et al. (2001:8) includes the spiral cribriform tract and the singular foramen or foramen singulare.

− ventrolateral ridge of the anterior process

Some Mysticeti have a lateral projection on the anterior 

process of the periotic bone that forms part of the border of the 

squamosal fossa between the anterior process and the body of 

the periotic (Geisler and Luo, 1996:1052, fig. 3.6).

Tursiops lacks a ventrolateral ridge on the anterior process.

= ventrolateral tuberosity (Luo and Gingerich, 1999:45)

See lateral tuberosity. 

− vertical canal

The vertical canal in archaic Odontoceti opens dorsally into 

one of the anterointernal sulci (Fordyce, 1994:160). Its function 

is uncertain.

The vertical canal is not developed in Tursiops.

− vestibular aqueduct (aqueductus [aquae-] vestibuli)

The vestibular aqueduct in mammals runs from posteromedial side of the vestibule (Whitmore, 1953) posteroventrally to 

the posterior part of the of the cerebral surface of the petrosal. 

The vestibular aqueduct carries the endolymphatic duct (Evans 

and Christensen, 1979:133). It opens onto the surface of the petrosal in the aperture for the vestibular aqueduct.

The vestibular aqueduct in Tursiops bears the same anatomical relationships as in the dog. See aperture for the vestibular aqueduct.

= vestibular area

See dorsal vestibular area and ventral vestibular area. 

= vestibular fenestra (fenestra vestibuli)

See fenestra ovalis.

− vestibular fossa

The region adjacent to the mammalian vestibular region is 

sometimes termed the vestibular fossa (MacPhee, 1981:47).

− vestibular fossula

The mammalian vestibular fenestra, or fenestra ovalis for 

the footplate of the stapes, is situated in a shallow pit that is 

sometimes known as the vestibular fossula (MacPhee, 1981:47; 

Wible and Gaudin, 2004:134). There is an indistinct vestibular 

fossula in Tursiops.

1 3 2 • smithsonian contributions to zoolog y p e r i o t i c
− vestibular part (pars vestibularis)

The vestibular part is the dorsolateral part of the mammalian periotic that contains the semicircular canals (Whitmore, 

1953:131).

Schulte (1917:396) used the term “pars vestibularis” 

broadly, for that part of the periotic in Kogia other than the pars 

cochlearis.

In Tursiops and other Cetacea the vestibular part is continuous with other parts of the periotic, and is not recognized as a 

distinct structure.

See also body of the periotic.

= vestibular window = fenestra ovalis

Vestibular window is a common and equally acceptable 

synonym for fenestra ovalis (q.v.).

− vestibule (vestibulum)

The vestibule of the petrosal is the chamber where the three 

semicircular canals and cochlea join. The vestibule is located between the basal turn of the cochlea and the semicircular canals in 

the central portion of the petrosal in the dog (Evans and Christensen, 1979:133, 1069).

The vestibule in Odontoceti bears the same anatomical relationships as it does in the dog (Yamada and Yoshizaki, 1959; 

confirmed on USNM 241288, 241289.

Tympanic Bulla

Os Temporale / Pars Tympanica / Bulla Tympanica

Figures 3, 4, 6f, 25a–e, 25f–k, 25r,s,w,x,Y, 29

The tympanic bulla (bulla tympanica) is an inflated bone 

that lies directly ventral to the mastoid process. It is formed of 

the tympanic part of the temporal and contains the fundus of 

the tympanic cavity (Evans and Christensen, 1979:129, 133, 

134). The bulla was also referred to as the processus petrosus ossis tympani (sic) (Denker, 1902) or the tympanomastoid (Yamada, 1953:19; McFarland et al., 1979:7). Vesalius 

(1543:23) referred to the tympanic part of the temporal as 

merely the os.

The tympanic bulla in delphinids is a completely separate 

ossification consisting of the tympanic part of the temporal. It 

lies posterolaterally on the ventral surface of the skull, ventral 

to the periotic and ventromedial to the squamosal. It articulates 

with the periotic anteriorly and posteriorly.

* accessory ossicle (Figure 25a,d,f,g,I,j,r,w)

The term “accessory ossicle” as used in Tursiops follows 

Ridewood (1922:242), who cited van Kampen (1904:343, fig. 

4), and many later cetologists. In Odontoceti the accessory ossicle is an elongate nodule with rounded edges that is fused to the 

dorsal part of the outer lip of the bulla, anterior to the sigmoid 

process and petrotympanic fissure (fissura Glaseri). Its dorsal surface carries a gently undulating facet that makes a plane 

suture with the fovea epitubaria of the periotic. Ventrally, the 

rounded medial edge of the accessory ossicle descends into the 

tympanic cavity. 

In Tursiops the posterior quarter of the dorsal surface of the 

accessory ossicle is generally broken where the accessory ossicle 

fuses with the periotic just anterior to the mallear fossa; every 

specimen examined by microscope has shown fusion.

Luo (1998:276, 288) suggested that the accessory ossicle 

may be an evolutionary novelty for Odontoceti. All Odontoceti 

have an accessory ossicle, and the anterior of the periotic either 

lies close to the bulla or contacts the periotic facet of the bulla. 

Extant Mysticeti lack an accessory ossicle, and the periotic and 

bulla are separated widely but fused at a prominent anterior pedicle. We regard the accessory ossicle of Tursiops as partly homologous with the dorsal part of the anterior pedicle of Mysticeti, 

and note that a distinct accessory ossicle appears to be present 

in some extinct (stem-group) Mysticeti, in which it is extensively 

applied to the anterior bullar facet.

“Accessory ossicle” is preferred as a less ambiguous term 

than tubal tubercle (Yamada, 1953:20), uncinate process, unciform process (de Muizon, 1987, 1991), or processus tubarius

of the bulla. Boenninghaus’ (1904: fig. 10, item 3) label of the 

processus tubarius bullae shows that this term applies clearly to 

the accessory ossicle, but later use confused the nomenclature.

The accessory ossicle may be homologous with the wide 

massive portion of the anterolateral lip of the bulla (dorsal to the 

fissura Glaseri) in Odocoileus virginianus and Ovis aries.

= annulus (Fraser and Purves, 1960:65, 113)

See tympanic ring. 

= anulus tendineus

See tympanic sulcus. 

= anulus tympanicus

See tympanic ring. 

− anterior angle

The anterior angle is a projection from the dorsal part of the 

outer lip anterior to the accessory ossicle in some Archaeoceti 

(Luo, 1998: figs. 5, 6). It is not clearly the same as the structure 

that de Muizon (1987) termed the “anterolateral convexity” 

(q.v.).

The tympanic bulla in Tursiops lacks an anterior angle.

= anterior aperture (Fraser and Purves, 1960:65, 70)

See musculotubal canal of the tympanic bulla.

= anterior apophysis (de Muizon, 1988)

See muscular process of the tympanic bulla. 

= anterior bullar lip (Luo, 1998:288)

See musculotubal canal of the tympanic bulla. 

= anterior bullar process (Luo and Gingerich, 1999:36, tbl. 

4(16a))

See anterior process of the tympanic bulla. 

− anterior conical process (processus conicus anterior)

Denker (1902:428, pl. 14, fig. 2, “p.c.a.”) identified the 

processus conicus anterior in Odontoceti as the prominence at 

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 3 3
the distal (or anterolateral) end of the mallear process, adjacent 

to the lateral groove. (Beauregard, 1894:380, 381, fig. 2d, proposed the term as “apophyse conique anterieure.”) It is part of 

the anterior process of the tympanic bulla in the sense of Boenninghaus (1904), but should not be confused with the (posterior) 

conical process, which is a modified part of the tympanic ring

that lies posterior to the sigmoid process. We recommend using 

the term “anterior conical process.” The anterior conical process 

is present but indistinct in Tursiops.

Ridewood (1922:241, fig. 10) incorrectly used the term “anterior conical process” for the sigmoid process, while van der 

Klaauw (1931:262) equated the processus tubarius of the bulla

(“accessory ossicle” of our use) with the processus conicus anterior (“anterior conical process” of our use).

− anterior crus of the ectotympanic ring

The anterior crus is part of the primitive simple ring-shaped 

or horseshoe-shaped ectotympanic of eutherian mammals. (See, 

e.g., Ridewood, 1922:240; MacPhee, 1981; Novacek, 1986:51, 

52; Luo and Gingerich, 1999.)

The ectotympanic is highly modified in Tursiops and other 

Cetacea to form the tympanic bulla. The anterior crus is the embryonic precursor to the sigmoid process (Ridewood, 1922; Luo, 

1998:271, 284) and more-anterior structures, but it is not distinct in adult Tursiops.

= anterior entrance of the tympanic cavity (Fraser and Purves, 

1960:15)

See musculotubal canal of the tympanic bulla. 

= anterior opening of the tympanic cavity = anterior notch of the 

tympanic cleft, anterior notch for the Eustachian tube

See tympanic cavity. 

= anterior orifice of the bulla (Fraser and Purves, 1960:74) = 

musculotubal canal of the tympanic bulla

* anterior pedicle (Figure 25f,m)

The anterior pedicle of Carte and Macalister (1868:253; 

anterior osseous pedicle, which they also termed “processus anterior mallei”), Lillie (1910:778), and others is that anterior part 

of the tympanic bulla in balaenopterids that fuses with the periotic just anterior to the mallear fossa. In Mysticeti the pedicle 

is narrow laterally but dorsoventrally prolonged; judging from 

the situation in some fossil stem-Mysticeti, it seems to be at least 

partly a modification of the accessory ossicle.

In Tursiops and other Odontoceti, the bulla and periotic 

are partly fused and partly sutured at the accessory ossicle, and 

there is no dorsoventrally prolonged anterior pedicle. Fraser and 

Purves mentioned the pedicles only in passing (1960:133) and 

referenced Kellogg (1938).

= anterior process (conical) of the tympanic bulla (processus 

conicus anterior)

See anterior conical process. 

= anterior process of the external lip of the auditory bulla (Beauregard, 1894; Fraser and Purves, 1960:9) = anterodorsal crest of the tympanic bulla

− anterior process of the tympanic bulla

In reference to structures of the cetacean bulla, the term “anterior process” has had a history of ambiguous use. In noncetacean 

mammals, “anterior process” usually refers to structures associated with or arising from the anterior crus of the ectotympanic 

ring (q.v.). We recommend that the latter use be followed, noting 

that, if the components of the anterior crus are properly named in 

Tursiops, the term “anterior process” may be redundant.

In Tursiops, features of the more-dorsal part of the outer lip, 

from posterior to anterior, include the sigmoid process, petrotympanic fissure, mallear ridge, sulcus for the chorda tympani, accessory ossicle, and anterodorsal crest of the tympanic bulla (q.v.).

Several references illustrate the past state of nomenclature. 

Denker (1902) distinguished between the processus conicus anterior, the accessory ossicle, and the anterior process. Boenninghaus (1904: fig. 12) identified the anterior process of the bulla as 

including the sigmoid process and the processus tubarius of the 

bulla (or accessory ossicle).

Van der Klaauw (1931:262) stated that “the anterior process of the tympanic which is fused with the periotic is called 

the processus tubarius [or processus conicus anterior]. It forms, 

together with the processus sigmoideus, the processus ossis anterior tympanici.” Van der Klaauw (1931:263) then indicated 

uncertainty about the identity of the processus tubarius, the uncinate process of Schulte, and the processus conicus anterior. 

See anterior pedicle, processus tubarius of the bulla, and

accessory ossicle. 

Luo (1998:287) and Luo and Gingerich (1999:32; tbl. 4, 

#16a) equated the “anterior process” with the processus tubarius. They noted that in some Archaeoceti the anterior process 

(= processus tubarius) contacts the squamosal bullar process. 

See falciform process of “Squamosal Bone.”

− anterior spine

Kasuya (1973: fig.1) and de Muizon (1987:9, fig. 4) identified a prominent anterior spine of the tympanic bulla in fossil 

stem-Platanistidae and Platanista. The anterior spine is a prolonged muscular process. Tursiops lacks an anterior spine of the 

tympanic bulla.

Not to be confused with the anterior tympanic spine. 

See muscular process of the tympanic bulla.

− anterior tympanic spine (spina tympanica anterior) = greater 

tympanic spine (spina tympanica major)

Van der Klaauw (1931:204) stated that, as a rule in mammals, the tympanic crest ends with anterior and posterior tympanic 

spines (spina tympanica anterior and spina tympanica posterior), 

which lie near the top of the tympanic ring. A line connecting the 

anterior and posterior tympanic spines marks the lower margin of 

the membrana Shrapnelli or pars flaccida (Bondy, 1907, cited by 

van der Klaauw, 1931). The development of anterior and posterior tympanic spines varies among mammalian species.

In humans the greater tympanic spine is located on the anterodorsal border of the tympanic ring (Feneis, 1994:16.6); it is 

bordered dorsally by the tympanic notch or tympanic incisure of 

the squamosal.

An anterior tympanic spine is not developed in Tursiops; 

it is probably represented by part of the sigmoid process of the 

tympanic bulla.

1 3 4 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
* anterodorsal crest of the tympanic bulla [new term] (Figure 

25a,c,d,f,h,j,s)

The new term “anterodorsal crest of the tympanic bulla” is 

proposed here for the part of the outer lip of the cetacean tympanic bulla that lies anterior to the accessory ossicle.

In Tursiops and other delphinids the anterodorsal crest 

does not contact the periotic; it is thin-edged and descends toward the musculotubal canal of the tympanic bulla. In some 

other Odontoceti (e.g., Physeter, Platanista, many ziphiids), 

the anterodorsal crest is rounded transversely to form a periotic facet that is received by the anterior bullar facet of the 

periotic bone.

− anterolateral convexity

The anterolateral convexity is located on the anterolateral 

surface of the tympanic bulla in some species of Platanistoidea (de Muizon, 1987). It is most apparent in dorsal view. It is 

unlikely to be homologous with the similar structure that Luo 

(1998) termed the “anterior angle” (q.v.).

The anterolateral convexity does not occur in Tursiops.

= anteromedial angle of the involucrum (Luo and Gingerich, 

1999: fig. 11)

See anteromedial angle of the tympanic bulla. 

− anteromedial angle of the tympanic bulla

The anteromedial angle of the tympanic bulla of Luo and 

Gingerich (1999:31, also termed anteromedial angle of the involucrum of Luo and Gingerich, 1999: fig. 11) projects anteriorly or 

anteromedially from the anterior part of the involucrum in some 

Archaeoceti. This may be the same feature that Luo (1998:283) 

termed the medial angle of the involucrum. The homology is uncertain with the anteromedial process of the tympanic bulla of 

other mammals (See MacPhee, 1981:46).

The anteromedial angle of the tympanic bulla does not 

occur in Tursiops.

= anteromedial process of the tympanic bulla

This feature of some mammals (e.g., MacPhee, 1981:46) is 

probably the anteromedial angle of the tympanic bulla.

= antrum

MacPhee (1981:46, 57) equated the antrum of humans with 

the mastoid cavity of other mammals. 

See diverticulum anterior.

= aperture for the Eustachian tube

Kellogg (e.g., 1936:113) used this term for the musculotubal 

canal.

See musculotubal canal of the tympanic bulla.

= aperture for the paroccipital pneumatic sinus (apertura posterior sinus pneumaticus paroccipitalis) (van der Klaauw, 

1931:263, who also termed it apertura posterior)

See elliptical foramen. 

= ascial process (Ridewood, 1922: fig. 10C)

See mallear process and mallear ridge; see also anterior process of the malleus under “Malleus.”

− auditory aperture (Clarke, 1948:980)

Clarke (1948:980) used auditory aperture as the term for 

the surface opening of the ear canal (external auditory meatus) in 

Physeter (Fraser and Purves, 1960:111). There appears to be no 

comparable term in human anatomy (Gray, 1918; Feneis, 1994) 

or the anatomy of domestic animals (Evans and Christensen, 

1979; Schaller, 1992).

= basal pedicle

Kellogg (1936:114) mentioned the thin basal pedicle of the 

posterior process that originates just behind the median process

(or conical process) on the outer lip of the tympanic bulla in 

Archaeoceti.

See outer posterior pedicle. 

= bony tympanic tube (ostium tympanicum tubae) (Whitmore, 

1953)

See musculotubal canal of the tympanic bulla.

= bulla

See tympanic bulla.

= bullar cavity

See tympanic cavity. 

− bullar septum

One or more bullar septa may occur in mammals (van der 

Klaauw, 1931:209; MacPhee, 1981:63).

Tursiops has small anterior and posterior bullar septa associated with the conical process, tympanic ring, and hypotympanic sinus. 

See diverticulum anterior and diverticulum posterior for 

details.

− carotid canal (canalis caroticus)

The carotid canal in the dog lies in the medial edge of the bulla

(Evans and Christensen, 1979:134); it arises posteriorly at the caudal carotid foramen in the tympano-occipital fissure, and opens 

anteriorly at the rostral or cranial carotid foramen or foramen lacerum. Flower (1885:141) termed this the internal carotid canal.

Several synonyms are applicable; the anterior opening of 

carotid canal is known as the caudal carotid foramen, the rostral carotid foramen, or the foramen lacerum (Evans and Christensen, 1979:134); while the posterior opening of the carotid 

canal is also known as the caudal carotid foramen (Evans and 

Christensen, 1979:134).

The carotid canal is not present in Tursiops or other Neoceti. 

See also carotid canal of the sphenoid and carotid foramen 

of the sphenoid under “Sphenoid Bone.”

= caudal carotid foramen

The caudal carotid foramen is the posterior opening of the 

carotid canal in the dog (Evans and Christensen, 1979:134)

The caudal carotid foramen is not present in Neoceti.

See caudal carotid foramen of the sphenoid bone and carotid canal of the sphenoid under “Sphenoid Bone.” 

= caudal lip of tympanic bulla (Schulte, 1917:396)

See involucrum. 

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 3 5
− caudal ridge of sigmoid process

Schulte (1917:395) recognized two ridges arising from the 

apex of the sigmoid process in the bulla of Kogia. The caudal 

ridge, which becomes sharp toward the base of the sigmoid process, is homologous with the rounded external edge of the sigmoid process as seen in Tursiops and other odontocetes. 

Schulte used the term “caudal” to indicate his perceived orientation of the feature on the tympanoperiotic in the Kogia skull; in life, 

the “caudal” ridge is actually ventral and slightly anterior (rostral), 

while the “rostral” ridge is dorsal and slightly posterior (caudal).

The external or lateral margin of the sigmoid process in 

Tursiops is rounded and not produced as a sharp ridge. For cetaceans in which a ridge might be present, the name external or 

lateral ridge of the sigmoid process seems better in light of the 

standardized directional terminology for the tympanoperiotic.

See rostral ridge of sigmoid process. 

− caudal squamosal foot

The caudal squamosal foot is the anterior part of the mallear plate (q.v.) of the dorsal part of the ectotympanic in the 

archaic insectivore Leptictis (Novacek, 1986:51, fig. 19).

This structure cannot be homologized in Tursiops.

= cavum epitympanicum (Kellogg, 1936:113)

See tympanic cavity. 

− chordafortsatz

Van der Klaauw (1931:208; see also MacPhee, 1981:50) 

cited Bondy (1907:326), originator of the term, that the mammalian chordafortsatz is a small bony or cartilaginous process 

that conducts the chorda tympani nerve toward the malleus.

The term refers to a “continuation process” for the chorda 

tympani.

The chordafortsatz is not clearly distinguishable in Tursiops, but see sulcus for the chorda tympani.

− compound posterior process

In Mysticeti the posterior process of the tympanic bulla fuses 

with the posterior process of the periotic bone to form what Geisler 

and Luo (1996:1056) termed the compound posterior process.

Tursiops lacks a compound posterior process.

See posterior process of the tympanic bulla.

= concavity of the caudal lip of the bulla = concavity of the involucrum of the bulla (Schulte, 1917:397)

− concavity of the involucrum of the bulla

Schulte (1917:397) referred to the concavity of the caudal 

lip of the bulla, meaning a depression on the surface of the involucrum that is approached closely by the surface of the pars 

cochlearis of the periotic.

The ventral profile of the pars cochlearis of the periotic in 

Tursiops closely parallels the dorsal surface of the involucrum, 

resulting in a cavity or concavity similar to that of Kogia. 

See also medial petrotympanic fissure.

= conical apophysis (Kellogg, 1969:26; Luo and Gingerich, 

1999:36)

See conical process. 

* conical process (processus medius tympanici) (Figures 25c,g,h, 

r,x,y, 29)

The conical process of the tympanic bulla is a small dorsal 

projection of the lateral wall of the cetacean bulla that lies between the sigmoid process and the posterior process (Kasuya, 

1973:2). This structure is unique to Cetacea. The conical process, sigmoid process, and posterior process in part represent the 

highly modified tympanic ring of other mammals.

In Tursiops the conical process is excavated by the hypotympanic sinus, is associated with the anterior and posterior septa, 

and carries a ridge for the tympanic membrane.

According to Ridewood (1922:242), Beauregard (1894) 

proposed the term “apophyse conique postérieure.” The conical 

process has also been termed the “processus medius” of Boenninghaus (1904:221), “processus conicus posterior” or “processus medius bullae” of van der Klaauw (1931:262), and “median 

process” or “conical apophysis” of Kellogg (1936:113). Luo and 

Gingerich (1999:36) termed it the middle conical process, or the 

middle process.

− crista tympanica of the meatus (meatal tube, inner)

In mammals the crista tympanica of the meatus, or tympanic crest, is formed where the ectotympanic wall of the meatus

projects into the tympanic cavity (Whitmore, 1953:135). It is 

distinct from the tympanic ring (tympanic annulus). Luo (1998) 

termed this the “free inner end of the meatal tube.”

Tursiops lacks a crista tympanica of the meatus, not to 

be confused with the tympanic crest in the sense of MacPhee 

(1981:51) and others. 

See tympanic crest.

− distal plate of the posterior process of the tympanic bulla

Luo and Gingerich (1999: tbl. 3, #24) proposed the term 

“distal plate” for the cetacean homologue of the posterior wall 

of the external auditory meatus. For Odontoceti, Luo and Gingerich described it as the thick horizontal plate of the posterior process. The term is effectively synonymous with posterior 

process.

A distal plate is present in Tursiops.

* diverticulum anterior (Figure 25w)

The diverticulum anterior is also known as the antrum

or anterior chamber of the tympanic cavity (Luo, 1998:280). 

MacPhee (1981:46, 57) equated the antrum of humans with the 

mastoid cavity of other mammals. In some Archaeoceti the diverticulum anterior is expanded dorsolaterally anterior to the sigmoid process and is separated from other parts of the tympanic 

cavity by one or more septa (trabeculae) that are present ventral 

to the sigmoid process. 

In Tursiops a low anterior septum is identified provisionally 

on the medial face of the outer lip, extending anteroventrally 

from the base of the conical process; the diverticulum anterior is 

that part of the tympanic cavity anterior to the anterior septum.

See also diverticulum posterior.

− diverticulum posterior

The diverticulum posterior is also known as the posterior 

chamber of the tympanic cavity (Luo, 1998:281). In some Archaeoceti the diverticulum posterior is expanded posterodorsally 

1 3 6 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
into the base of the posterior process, posterior to the posterior 

septum. In turn, the posterior septum arises from the posterior 

part of the tympanic ring. 

In Tursiops the diverticulum posterior is that part of the 

tympanic cavity in the base of the posterior process or posterior 

pedicle; its anterior boundary is formed by a strong ridge that 

descends ventromedially from its origin on the posterior base of 

the conical process. The diverticulum posterior opens into the 

elliptical foramen.

See also diverticulum anterior. 

− ectotympanic part of the tympanic

The ectotympanic part of the tympanic bone represents the 

tympanic ring in many terrestrial mammals (Novacek, 1977). 

The element is incomplete dorsally at the tympanic notch or 

tympanic incisure (MacPhee, 1981:52). In Mysticeti (Ridewood, 

1922:242; van der Klaauw, 1931:261; de Beer, 1937:341ff.) 

and all other Cetacea for which we can find accounts (e.g., Luo, 

1998; Geisler, 2001; Geisler and Sanders, 2003; Uhen, 2004), 

the ectotympanic reportedly forms all of the tympanic bulla. Histological study of a range of living species would be helpful.

The auditory bulla of Tursiops is composed of the ectotympanic part of the tympanic bone.

* elliptical foramen (Figure 25e,k,w)

The elliptical foramen (vertical cleft or elongated aqueduct 

of Kellogg, 1936) is an opening in the wall of the cetacean tympanic bulla at its posterior end. It develops from the region of 

the diverticulum posterior. The elliptical foramen is just ventral 

to the posterior process and just dorsal to the outer posterior 

prominence of the tympanic bulla (Kasuya, 1973) and, when 

present, it divides the base of the posterior process into the 

inner and outer posterior pedicles. The elliptical foramen transmits the posterior sinus (Fraser and Purves, 1960) to the apex 

of the paroccipital process. For the elliptical foramen, van der 

Klaauw (1931:263) used the term “apertura posterior for the 

sinus pneumaticus paroccipitalis,” while Luo (1998:285) called 

it the “pedicular foramen,” and Luo and Gingerich (1999: fig. 

14) termed it the “posterior cleft.” Fraser and Purves (1960: 

e.g., fig. 1) used the term “posterior aperture of the tympanic 

cavity.”

The posterior sinus has also been termed the paroccipital 

pneumatic sinus (sinus pneumaticus paroccipitalis of van der 

Klaauw, 1931:37, 263), and the posterior pterygoid sinus (Luo, 

1998:285).

− endotympanic part (pars endotympanica)

The endotympanic part or entotympanic bulla is the one 

or more skeletal or cartilage elements that form independently 

from other bullar elements (Novacek, 1977; MacPhee, 1981:52), 

including the ectotympanic part.

The cetacean tympanic bone lacks an endotympanic part 

(Ridewood, 1922:242; Novacek, 1977).

− epitympanic crest

The epitympanic crest (MacPhee, 1981:53) is a septum that 

borders the epitympanic recess and is associated with the stapedial artery in some primates.

The epitympanic crest is not identifiable in Tursiops.

− epitympanic recess

The epitympanic recess is bounded ventrally by structures 

of the bulla at the tympanic incisure. Details are discussed under 

“Periotic Bone.”

= Eustachian cavity

See tympanic cavity. 

= Eustachian end of the tympanic cleft (Turner, 1913:13)

See these features of the tympanic bulla: musculotubal canal 

of the tympanic bulla, Eustachian notch, and Eustachian outlet. 

The term “Eustachian notch” should not be used for structures on the tympanic bulla because it also refers to a structure 

in the pterygoid. 

See Eustachian notch under “Pterygoid Bone.”

= Eustachian outlet (Kellogg, 1969:4)

Given that the term “Eustachian notch” is not appropriately 

applied to the cetacean bulla, the terms “Eustachian outlet” or 

“tympanic outlet” are appropriate alternative names for the musculotubal canal of the tympanic bulla. Kellogg (e.g., 1936:189, 

fig. 80) also used furrow or aperture for the Eustachian tube.

See musculotubal canal of the tympanic bulla.

= Eustachian tube (Luo, 1998; Luo and Gingerich, 1999:32)

See musculotubal canal of the tympanic bulla and Eustachian outlet.

The term “Eustachian tube” should be reserved for the soft 

tissue structure and not used for bony structures associated with 

the tympanic bulla.

= exoccipital contact (Luo and Gingerich, 1999)

See exoccipital protuberance of the tympanic bulla. 

− exoccipital protuberance of the tympanic bulla

Luo and Gingerich (1999:31, and fig. 11) identified in Archaeoceti a feature termed the exoccipital protuberance that they 

also termed the exoccipital contact and medial prominence. (Medial prominence in this sense should not be confused with medial 

process or conical process.) The exoccipital protuberance lies on 

the involucrum of the tympanic bulla, internal to the posterior 

pedicle.

Tursiops lacks an exoccipital protuberance of the tympanic 

bulla.

− external acoustic meatus (meatus acusticus externus) = external auditory meatus

The external acoustic meatus in mammals is the canal from 

the external ear to the tympanic membrane (MacPhee, 1981:53). 

Vesalius (1543:23) referred to the external acoustic meatus as 

the auditorii meatus in a portion of his work, while in another 

(Vesalius, 1543:52; Vesalius et al., 1998:131) he referred to the 

external acoustic meatus (auditory tube) as the “auditus organum petit, ac aer etiam in temporis ossis antrum auditus organo 

proprium, per id foramen sertur.” Eustachius and Lancisius 

(1714:105) referred to it as the “auditorius [externus] meatus dissectus.” In the dog all but the dorsal part of the external acoustic 

meatus is formed by the tympanic part of the bulla. The dorsal 

part is formed by the mastoid process of the petrosal (Evans and 

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 3 7
Christensen, 1979:134, 151). In the deer, Odocoileus virginianus, the dorsal part is formed by the squamosal (to the exclusion 

of petrosal), while the anterior, ventral, and posterior walls are 

formed by the tympanic bulla. In the sheep, Ovis aries, the external acoustic meatus is formed by a cylindrical tube of the bulla, 

with a small dorsal component of squamosal medially.

In some Archaeoceti the tympanic bulla forms a trough-like 

meatal tube that is part of the ventral wall of the proximal part 

of the external auditory meatus (Luo, 1998:278) and that may 

protrude internally into the tympanic cavity. In such whales the 

distal parts, and dorsal proximal parts, of the external acoustic 

meatus are formed by the squamosal.

The delphinid external acoustic meatus sensu stricto is 

mostly cartilaginous (e.g., Purves, 1966: fig. 4), with only a proximal bullar part formed by bone. It runs from near the dermis to 

the lower tympanic aperture of the bulla. In Tursiops the proximal bony bullar parts of the external acoustic meatus are the 

lateral part of the sigmoid process, conical process, and anterior 

face of posterior process.

For the external acoustic meatus, Luo and Gingerich (1999: 

fig. 21) used the name “opening for the tympanic ligament.”

In Tursiops the squamosal carries a prominent ventral 

groove, the [bony] external acoustic meatus, sensu lato. The bony 

meatus originates laterally at the postglenoid or retro­articular 

notch, and terminates medially at the spiny process.

− external acoustic pore (porus acusticus externus)

The external acoustic pore in mammals is the external 

opening of the bony external auditory meatus. The external 

acoustic pore lies laterally on the posteroventral surface of the 

skull. The ventral part of this opening is composed of the tympanic part of the temporal, and the dorsal part is composed 

of the squamous part of the temporal (Evans and Christensen, 

1979:150, 151).

Because the external acoustic meatus in delphinids is entirely 

cartilaginous, the external acoustic pore is not present.

= external auditory canal

See external acoustic meatus. 

= external auditory meatus

See external acoustic meatus. 

− external ridge

Luo and Gingerich (1999: tbl. 4, #15b) indicated that an 

external ridge is present on the anterior process of the ectotympanic of Archaeoceti and the extinct odontocete Xenorophus.

An external ridge cannot be identified in Tursiops.

= fenestra rotunda of the tympanic bulla

“Fenestra rotunda, of tympanic bulla” appears to be a mislabeling by Boenninghaus (1904: fig. G(19)).

See musculotubal canal of the tympanic bulla. 

= fissura Glaseri (van der Klaauw, 1931; Kellogg, 1936; Whitmore, 1953; Novacek, 1986)

The names fissura Glaseri (or Glaserian fissure; Wible and 

Gaudin, 2004:155) and petrotympanic fissure (q.v.) both have 

wide use for mammals. However, MacPhee (1981:55) observed 

that the name “fissura Glaseri” is more appropriate than “petrotympanic fissure” because the latter name does not properly describe the feature in some mammals. Vesalius (1543:23) referred 

to the petrotympanic fissure as merely the linea (line). In the dog 

the fissura Glaseri lies at the anterolateral end of the tympanic 

bulla, just posterior to the retroarticular process (or postglenoid 

process) of the squamosal. In artiodactyls, the fissura Glaseri 

may be bounded by the margo fissurae of the squamosal (Whitmore, 1953). The fissura Glaseri serves as the exit from the bulla

for the chorda tympani (Evans and Christensen, 1979:131, 133); 

in early ontogeny it serves as the exit for Meckel’s cartilage (van 

der Klaauw, 1931:164).

The fissura Glaseri or petrotympanic fissure is present in 

Tursiops and other Neoceti at the point of fusion of the malleus 

to the bulla immediately anterior to the sigmoid process.

The synonym “petrotympanic fissure” should be avoided 

because of confusion with the tympanoperiotic fissure.

− folian process of the malleus (processus folii or processus longus of the malleus)

Van der Klaauw (1931:235) discussed the manner in which 

the folian process or anterior process (or processus longus) of the 

malleus may contribute to the mammalian tympanic bulla. The 

anterior process of the malleus lies in the sulcus malleolaris of 

the tympanic bulla, and often fuses with the bulla. Homologies 

are uncertain for the sometimes associated accessory ossicle of 

the malleus (ossiculum accessorium malleoli).

In Tursiops and other Neoceti the anterior process of the 

malleus is fused to the tympanic bulla. 

See discussion under mallear ridge and malleolar process; 

see also “Malleus.”

= foramen lacerum

Vesalius (1543:51; Vesalius et al., 1998:131) referred to the 

foramen lacerum as the rimam hanc temporis ossi and occipitii 

communem.

See rostral carotid foramen, carotid canal of the sphenoid 

bone, and foramen lacerum anterius.

= foramen lacerum anterius (anterior lacerate foramen)

See anterior lacerate foramen under “Sphenoid Bone.” 

= Glaserian fissure (Luo, 1998)

See fissura Glaseri and petrotympanic fissure. 

= greater tympanic spine

See anterior tympanic spine. 

= groove for anulus tendineus (Kellogg, 1936)

See tympanic sulcus. 

* groove for facial nerve (Figure 25f,i)

A groove for the facial nerve may be present on the posterior process of the tympanic bulla in Cetacea (van der Klaauw, 

1931:263).

In Tursiops a groove is present variably on the posterior face 

of the posterior process of the tympanic bulla, just ventral to the 

suture with the posterior process of the periotic bone. Anteriorly, 

the groove passes into the facial sulcus of the periotic.

1 3 8 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
* hypotympanic sinus (Figure 25w)

Whitmore (1953:132) implied that this feature in archaic 

artiodactyls is broadly synonymous with the tympanic cavity. 

Earlier, van der Klaauw (1931:214) discriminated between the 

hypotympanic sinus and true tympanic cavity and indicated 

(1931:262) that the hypotympanic sinus is formed when the external acoustic meatus projects into the cavity of the bulla. It 

includes a lateral extension that excavates the median process or 

conical process (processus conicus posterior or processus medius 

bullae of van der Klaauw).

In Tursiops and other delphinids the conical process is excavated ventrally by a cavity that is continuous with the tympanic 

cavity and that is presumed to be the hypotympanic sinus.

= inner convexity (Kellogg, 1936:115)

See inner posterior prominence. 

= inner pedicle

See inner posterior pedicle. 

* inner posterior pedicle (Figure 25f,k,s,x)

The inner pedicle of the cetacean tympanic bulla is the medial support between the posterior process of the tympanic bulla

and the inner posterior prominence (Kasuya, 1973). It attaches 

to the involucrum. The inner posterior pedicle forms only when 

the base of the posterior process is split by the development of an 

elliptical foramen and posterior sinus. De Muizon (1987) termed 

this the “medial pedicle.”

The inner posterior pedicle is present in Tursiops.

* inner posterior prominence (Figures 25b,e,i,k,s, 29)

The inner posterior prominence (Kasuya, 1973) of the cetacean tympanic bulla is a ventral structure located on the medial 

side of the posterior surface of the tympanic bulla. In Odontoceti the feature is best seen in ventral view. Luo and Gingerich 

(1999:36, fig. 13) used the term “medial posterior prominence” 

for this feature.

In Tursiops the inner posterior prominence is the shorter of 

the two posterior prominences.

* interprominential notch (Figure 25e,k)

The interprominential notch (Kasuya, 1973) of the cetacean 

tympanic bulla lies on the posterior surface of the tympanic bulla 

between the outer and inner posterior prominences. It is continuous with the median furrow (Kasuya, 1973). For Archaeoceti 

Luo (1998:278, fig. 4) homologized the interprominential notch 

with the tympanohyal sulcus. Dissections of dolphins show that 

the path of hyoid elements is remote from this part of the bulla, 

so that we hesitate to accept this homology for Tursiops. 

Tursiops has an interprominential notch, visible from the 

posterior or ventral surfaces.

See sheath for the hyoid process.

* involucrum (Figures 25b,d,f,j,s, 28)

The involucrum of the tympanic bulla is the rounded, dorsoventrally thickened, medial part of the tympanic bulla. The 

involucrum extends between the inner pedicle and the most anterior point of the medial wall (Kellogg, 1928; Yamada, 1953:19; 

Kasuya, 1973). Schulte (1917:396) used the term “caudal lip” 

for the involucrum in Kogia, with “caudal” referring to the relative position of the involucrum when the tympanoperiotic is articulated in the skull.

= lacerate foramen (foramen lacerum)

In the dog the lacerate foramen is located at the anterior 

margin of the bulla, lateral to the occipitosphenoid suture and 

medial to the musculotubal canal of the tympanic bulla. It has 

also been called the external carotid foramen (Evans and Christensen, 1979:134; McFarland et al., 1979:9). Davis (1964:52) 

identified the foramen lacerum medium (or foramen lacerum anterius of some authors) in carnivores as transmitting veins associated with pharyngeal circulation and the cavernous sinus and 

the internal carotid artery. In carnivores the lacerate foramen 

contains a loop of the internal carotid artery.

It has also been termed the median lacerate foramen in 

many mammals, although it seems that foramen lacerum medium sensu Flower (1885:123) strictly refers to the foramen that 

transmits the internal carotid artery to the braincase (McFarland 

et al., 1979:9). According to Wible (2003:172), Marshall and 

de Muizon (1995) used the term “median lacerate foramen” in 

another context, namely for the foramen for the greater petrosal 

nerve; see hiatus Fallopii of “Periotic Bone.” See also comments 

under carotid canal of the sphenoid and carotid foramen of the 

sphenoid, under “Sphenoid Bone.” The term “lacerate foramen” 

also has been used, as posterior lacerate foramen, for the jugular 

foramen in Odontoceti (see “Exoccipital Bone”).

The lacerate foramen is not present in Neoceti.

* lateral furrow (Figure 25g,h,r)

The lateral furrow of the tympanic bulla in Odontoceti is 

a vertical feature located on the lateral surface of the bulla well 

anterior to the sigmoid process (Kasuya, 1973). It should not be 

confused with the groove that delimits the base of the sigmoid 

process. In some specimens the lateral furrow branches and becomes more complicated dorsally. Its function is not clear. The 

“lateral furrow” of Luo and Gingerich (1999:32) is a feature immediately anterior to the sigmoid process and may not be homologous with the lateral furrow in Odontoceti including Tursiops.

The lateral furrow is moderately developed in Tursiops, but 

more so in other nondelphinoid Odontoceti.

= lateral posterior prominence (Luo, 1998:34)

See outer posterior prominence. 

= lesser tympanic spine (spina tympanica minor)

See posterior tympanic spine. 

= lip-like process (Turner, 1913:16)

See sigmoid process. 

= longitudinal groove

See median furrow. 

* lower tympanic aperture (Figure 25h,s,w)

The lower tympanic aperture of the cetacean tympanic bulla

is the opening on the posterolateral surface of the bulla that is 

bounded by the sigmoid process, the conical process, and the 

outer posterior pedicle of the tympanic bulla. The aperture opens 

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 3 9
dorsally at the tympanic incisure. This is the bony part of the 

external acoustic meatus and is the tympanic aperture (Yamada, 

1953:20, Kasuya, 1973) or tympanic annulus.

Tursiops has a lower tympanic aperture.

See also tympanic aperture, external acoustic meatus.

− mallear plate

The dorsal part of the ectotympanic in the archaic insectivore 

Leptictis is flattened to form a mallear plate (Novacek, 1986:51, 

fig. 19). Anteriorly the mallear plate has a rostral squamosal foot; 

posteriorly it has a caudal squamosal foot. The rostral squamosal 

foot is probably homologous with the anterior process and anterior ossicle of the tympanic bulla, while the caudal squamosal foot 

is perhaps homologous with the posterior process of the bulla.

The term “mallear plate” is not applicable to Tursiops.

= mallear process (Turner, 1913:16)

The mallear process of the tympanic bulla in the sense of 

Luo (1998:275) referred to the structure in Cetacea that becomes 

fused to the anterior process of the malleus. That structure may 

be the mallear ridge (q.v.). For the anterior process of the malleus, Ridewood (1922: fig. 10C) named this the ascial process, 

and said that it is formed by the goniale. 

See anterior process of the malleus; sigmoid process.

* mallear ridge (Figure 25c,d,f,r,y)

The mallear ridge is located on the dorsolateral surface of 

the tympanic bulla immediately anterior to the sigmoid process, 

at least in Odontoceti (Fordyce, 1994:160). It descends obliquely 

laterally and ventrally from the medial part of the sigmoid process at the point of fusion of the malleus. Fordyce used the term 

for a surface feature without particular implications about embryonic origin; the feature is probably formed by the anterior 

process of the malleus (= ascial process of Ridewood, 1922:241). 

The sulcus for the chorda tympani lies medial and anterior to 

the ridge. The mallear ridge may be partly homologous with the 

malleolar sulcus. Luo and Gingerich (1999:18, tbl. 3, #20) referred to the mallear ridge as the malleolar accessory ossicle.

Tursiops has a well developed mallear ridge.

See malleolar process and malleolar sulcus.

= malleolar accessory ossicle

See mallear ridge. 

− malleolar process = mallear ridge

Luo and Gingerich (1999:18, 46, tbl. 3, #20) used the term 

“malleolar process” or ridge for the site of attachment of the 

processus gracilis of the malleus in Archaeoceti. Their illustration (fig. 21) and text identify the malleolar process as the horizontal feature on the crest of the outer lip of the tympanic bulla

medial to the groove or sulcus for the chorda tympani.

In Tursiops and other Neoceti the mallear ridge lies posterior and lateral to the groove for the chorda tympani. The feature 

identified by Luo and Gingerich (1999: fig. 21) may be related to 

the accessory ossicle (= processus tubarius of the bulla).

− malleolar sulcus (sulcus malleolaris)

The malleolar sulcus of the tympanic bulla (van der Klaauw, 

1931:235) carries the anterior process of the malleus, which in 

Tursiops and other Neoceti fuses with the bulla. The apparent 

region of fusion in Odontoceti is a ridge, rather than a sulcus, 

that Fordyce (1994) termed the “mallear ridge.”

MacPhee (1981:57) identified the malleolar sulcus as a feature at the apex of the anterior crus of the ectotympanic ring, 

associated with the chorda tympani, goniale, and Meckel’s 

cartilage.

= mastoid cavity

Mastoid cavity in the sense of MacPhee (1981:46, 57) 

matches the tympanic cavity as used herein.

See antrum, diverticulum anterior, and tympanic cavity. 

= mastoid process of the tympanic bulla

See posterior process of the periotic bone, posterior process 

of the tympanic bulla. 

− meatal tube, intrabullar part

In some Archaeoceti some of the tympanic bulla forms part 

of the ventral wall of the proximal part of the external auditory 

meatus. The resulting meatal tube is trough-shaped in dorsal 

view (Luo, 1998:278; Luo and Gingerich, 1999:32), and internally may protrude into the tympanic cavity. Other parts of the 

external auditory meatus are formed by the squamosal.

The projecting intrabullar part of the meatal tube may be 

supported by septa or trabeculae, and it carries the tympanic ring

(anulus tympanicus).

There is no intrabullar part of the meatal tube in Tursiops. 

The septa (or trabeculae) are subtle structures identifiable adjacent to the conical process (e.g., Figure 25w).

= meatus

See external acoustic meatus of “Tympanic Bulla”; spiny 

process of “Squamosal Bone.” 

= medial angle of the tympanic bulla

See anteromedial angle of the tympanic bulla. 

= medial conical process (Luo and Gingerich, 1999:18, tbl. 3, 

#20)

Also known as the median process. 

Not to be confused with the conical process. 

See anteromedial angle of the tympanic bulla.

− medial notch

In some Archaeoceti a medial notch is present on the medial 

and ventral surfaces of the involucrum, ventral to the musculotubal canal of the tympanic bulla (Luo and Gingerich, 1999:36, 

fig. 13).

The medial notch should not be confused with the lateral 

groove, nor the groove that delimits the base of the sigmoid process, nor the median furrow, all discussed elsewhere.

Tursiops lacks a medial notch.

= medial pedicle (de Muizon, 1987) = inner posterior pedicle

* medial petrotympanic fissure (Figure 25d,e)

Luo and Gingerich (1999: tbl. 4, #30) proposed the term 

“medial petrotympanic fissure” for the gap between the involu1 4 0 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
crum of the tympanic bulla and the promontorium (here, the pars 

cochlearis) of the petrosal (periotic bone). The feature should not 

be confused with the petrotympanic fissure (or fissura Glaseri).

Tursiops has a medial petrotympanic fissure.

= medial posterior prominence (Luo and Gingerich, 1999)

Luo and Gingerich (1999:36, fig. 13) used the term “medial posterior prominence” for what was earlier termed the inner 

posterior prominence (q.v.; Luo and Gingerich, 1999: fig. 10C, 

“mp”). They also termed it the medial prominence.

Luo and Gingerich (1999:29) discussed a tuberosity on 

the exoccipital that “serves to support the medial prominence of 

the bulla,” implying that a dorsal feature on the bulla also has the 

appellation “medial.” Elsewhere the dorsal feature of the bulla is 

termed exoccipital contact (their ‘eoc’, or exoccipital protuberance; 

Luo and Gingerich, 1999) on the dorsal side of the involucrum.

See inner posterior prominence. 

= medial prominence

See medial posterior prominence and inner posterior 

prominence. 

= medial prominence of the involucrum

In Archaeoceti (Luo and Gingerich, 1999:29) the medial 

prominence is dorsal to the posterior end of the involucrum and 

immediately internal to the posterior process. Luo and Gingerich 

also used the terms “exoccipital protuberance of the tympanic 

bulla” (Luo and Gingerich, 1999:31, fig. 11) and “exoccipital 

contact.” The medial prominence contacts the adjacent bullar 

process of the exoccipital bone in some Archaeoceti and contacts 

the basioccipital of others (Luo, 1998:286).

The feature is not identifiable in Tursiops.

* median furrow (Figure 25b)

The median furrow of the cetacean tympanic bulla lies on 

the ventromedial surface of the tympanic bulla and extends from 

the interprominential notch anteriorly until it disappears (Kasuya, 1973). The appearance of the median furrow depends on 

the definition of the posterior prominences, since it lies between 

them. The feature should not be confused with the medial notch

(q.v.) of Luo and Gingerich (1999). This has been also refered to 

as the longitudinal groove.

Tursiops has a well developed median furrow.

= median process (Kellogg, 1936) = conical process

= median ridge (Luo and Gingerich, 1999: tbl. 3, #29b)

See ventral keel. 

= middle conical process (Luo and Gingerich, 1999:36)

Not to be confused with the medial conical process. 

See conical process. 

= middle process (Luo and Gingerich, 1999:36)

See conical process. 

− muscular process of the tympanic bulla (processus muscularis) 

The muscular process (styliform process, or processus styliformis of van der Klaauw, 1931) of the mammalian tympanic 

bone projects anteroventrally from the anterior border of the 

tympanic bone (Schaller, 1992:24.7). It is strongly developed in 

ungulates. Whitmore (1953) identified it as forming part of the 

bony tympanic tube (ostium tympanicum tubae) and part of the 

origin for the m. levator veli palatini. MacPhee (1981:61) identified it as for origins of the m. tensor veli palatini and m. levator 

veli palatini.

In Neoceti, the muscular process is an anterior projection 

of the tympanic bulla that lies ventral to the auditory tube (Eustachian tube). It is variable in Tursiops and other delphinids, 

appearing with age (Kasuya, 1973). Fraser and Purves (1960:19) 

mentioned that in Delphinus delphis the m. tensor palati is “associated with the styloid near its contact with the bulla.” The 

latter use of styloid is not to be confused with the styloid process

or processus styloideus as formed by the fused tympanohyal and 

stylohyal of other eutherians.

The muscular process of the tympanic bulla has also been 

termed the anterior spine, anterior apophysis, and styloid apophysis (Kasuya, 1973; de Muizon, 1987, 1988). Where the muscular process is present as a marked projection, as in Platanista, the 

term “anterior spine” would seem appropriate.

* musculotubal canal of the tympanic bulla (canalis musculotubarius) (Figure 25c,d,s,y)

In some mammals the musculotubal canal is a double or 

joint canal for the auditory tube (Eustachian tube) and the m. 

tensor tympani (Schaller, 1992:24.12; Feneis, 1994:12.28). The 

musculotubal canal lies in the anteromedial portion of the tympanic bulla and the caudal portion of the temporal wing of the 

sphenoid (Evans and Christensen, 1979:129). The musculotubal 

canal is just lateral to the foramen lacerum (external carotid 

foramen).

See Whitmore (1953) = bony tympanic tube (ostium tympanicum tubae) and Wible and Gaudin (2004:160).

The musculotubal canal in delphinids and other Cetacea has 

been modified by the separation of the osseous ear components, 

so that it is not a canal but is a U-shaped depression or semicanal 

at the apex of the tympanic bulla, lacking a dorsal bony roof. It 

is represented by the semicanalis tubae auditivae of the tympanic 

bulla and reportedly the semicanalis musculus tensoris tympani

(Pilleri et al., 1987, pl. 16). However, the origin for the m. tensor 

tympani is on the accessory ossicle of the tympanic bulla, not on 

the thin outer lip. (See fossa for the tensor tympani muscle of 

“Periotic Bone.”)

The musculotubal canal of the tympanic bulla has also been 

named the anterior notch of the tympanic cleft (Turner, 1913:19), 

the anterior notch for the Eustachian tube (Luo, 1998:283), 

the Eustachian outlet, the Eustachian notch, the aperture for 

the Eustachian tube, the groove on the outer lip border for the 

Eustachian canal, and the anterior bullar lip. Possibly, Schulte 

(1917:397) referred to the musculotubal canal when he mentioned the osseous tuba. Boenninghaus (1904: fig. G) used the 

terms “fenestra rotunda” and “tympanicum tubae Eustachii.”

“Eustachian notch” should not be used, since it applies to a 

structure on the pterygoid bone.

In Tursiops the terms musculotubal semicanal, Eustachian 

outlet, and tympanic outlet are appropriate for what is elsewhere 

termed the “musculotubal canal.”

See also musculotubal canal of the sphenoid bone.

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 4 1
= opening for the tympanic ligament (Luo and Gingerich, 1999: 

fig. 21)

See external acoustic meatus. 

= opisthotic portion of the periotic (Lillie, 1910:777)

See posterior process of the tympanic bulla. 

= osseous tuba

Schulte (1917:397) identified the osseous tuba as formed by 

the articulated tympanic bulla and periotic, and probably therefore meant the musculotubal canal of the tympanic bulla.

See also groove on ventral surface of the pars cochlearis.

= outer convexity (Kellogg, 1936:115)

See outer posterior prominence. 

* outer lip (Figure 25b,g,j,r,x)

Outer lip is a general term for the thin-walled part of the 

cetacean bulla that forms the lateral (outer, external) wall to the 

bullar portion of the tympanic cavity. The outer lip in Odontoceti includes the anterodorsal crest of the tympanic bulla, anterolateral convexity, accessory ossicle, lateral furrow, sulcus for the 

chorda tympani nerve, mallear ridge, sigmoid process, and the 

conical process and associated sinuses and septa; the outer lip 

often passes imperceptibly into the outer posterior pedicle.

The bulla in Tursiops has an outer lip.

* outer posterior pedicle (Figure 25k)

The outer posterior pedicle of the posterior process of the 

cetacean tympanic bulla is situated at the posterolateral surface 

of the bulla, lying between the posterior prominence, the elliptical foramen, and the lower tympanic aperture. It has been called 

outer pedicle (Kasuya, 1973:2). It arises from the outer lip posterior to the conical process.

The outer posterior pedicle is present in Tursiops.

* outer posterior prominence (Figures 6f, 25b,e,g,i,k,y, 29)

The outer posterior prominence of the cetacean tympanic 

bulla is a rounded eminence that lies on the posteroventral surface 

of the bulla, and supports the posterior process. It is separated by 

the interprominential notch, when the latter is developed, from 

the inner posterior prominence (Kasuya, 1973). The outer posterior prominence is usually the highest and most striking of the 

topographic features of the bulla.

Tursiops has a well-developed outer posterior prominence.

− pedicle foramen

The pedicle foramen of Luo and Gingerich (1999: fig. 21d) 

was illustrated as a small opening between the inner and outer 

posterior pedicles of the archaeocete whale Saghacetus osiris that 

is shown as separate from a more-ventral elliptical foramen. On 

accompanying figures, however (Luo and Gingerich, 1999: figs. 

21c,e), the pedicle foramen is identified as the more-dorsal part 

of the elliptical foramen.

In Tursiops the elliptical foramen is the only major feature 

to pierce the posterior pedicles.

= pedicular foramen (Luo, 1998:285)

See pedicle foramen, elliptical foramen. 

− periotic facet [new term]

In many nondelphinoid Odontoceti (e.g., Physeter, Platanista, many ziphiids), the thin anterodorsal crest of the tympanic bulla is rounded transversely to form a periotic facet 

(new term) that is received by the anterior bullar facet of the 

periotic bone. Previously, Fordyce (1994:158,160) used the 

name processus tubarius for this part of the anterodorsal crest, 

but the processus tubarius or accessory ossicle is a more-posterior structure.

Tursiops lacks a periotic facet on the anterodorsal crest of 

the tympanic bulla.

= petro-tympanic bone (Flower, 1885) = petrotympanic bone

See tympanoperiotic bone.

= petrotympanic fissure (fissura petrotympanica)

Van der Klaauw (1931:160) cited Hanke (1914:507) as reporting that the fissura petrotympanica is broad, but this use of 

the term apparently refers to some other structure.

The petrotympanic fissure should not be confused with the 

medial petrotympanic fissure.

See fissura Glaseri. 

= petrotympanic fissure, medial (Luo and Gingerich, 1999: tbl. 

4, #30)

See medial petrotympanic fissure. 

= petro-tympanic orifice (Fraser and Purves, 1960:9)

See tympanic aperture (Flower, 1885). 

= posterior aperture (Fraser and Purves, 1960: e.g., fig. 1)

See elliptical foramen. 

= posterior cleft (Luo and Gingerich, 1999: fig. 14)

See elliptical foramen. 

= posterior conical apophysis

See conical process. 

− posterior crus of ectotympanic ring

The posterior crus is part of the primitive, simple, ringshaped or horseshoe-shaped ectotympanic of therian mammals; 

it articulates with the squamosal (see e.g., Ridewood, 1922:240 

ff.; Novacek, 1986:51–52; Luo and Gingerich, 1999).

The ectotympanic is highly modified in Tursiops and other 

Neoceti to form the tympanic bulla. The anterior crus forms the 

sigmoid process and more-anterior features, while the posterior 

crus forms the posterior process of the tympanic bulla.

The posterior crus is not identifiable in adult Tursiops.

= posterior pedicle

See inner posterior pedicle, outer posterior pedicle. 

* posterior process of the tympanic bulla (Figures 6f, 25b,c,e–

g,r,x,y)

We are not aware of an elongate posterior process of the 

tympanic bulla in noncetacean mammals, but bullar features homologous with those of cetaceans can be identified. For clarity, 

we detail Tursiops first, then other mammals.

1 4 2 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
In Tursiops the posterior process of the tympanic bulla lies 

at the extreme posterodorsal end of the bulla and articulates with 

the periotic by a facet for the posterior process of the periotic 

bone that sutures with the posterior bullar facet of the periotic. 

In Tursiops the posterior process of the tympanic bulla carries regions that can be homologized with the facet for the posterior meatal crest (q.v.) and the facet for the posttympanic process (q.v.) 

(sensu Fordyce, 1994: fig. 11) of archaic Odontoceti. In young 

Tursiops the facet for the posterior meatal crest on the bulla is 

loosely sutured with the posterior meatal crest of the squamosal (q.v.), while the facet for the posttympanic process is loosely 

sutured with the small posttympanic process of the squamosal 

(q.v.). These features are usually obscure in adult Tursiops.

The posterior process of the tympanic bulla is connected to 

the remainder of the bulla by the posterior pedicle. If an elliptical 

foramen is present, the posterior pedicle is divided into an inner 

pedicle (q.v.; inner posterior pedicle) that attaches to the involucrum, and an outer pedicle (q.v.; outer posterior pedicle) that 

attaches to the outer lip posterior to the conical process (Kasuya, 

1973). Yamada (1953) referred to the posterior process of the 

tympanic bulla as the mastoid process, but the bulla in Tursiops

and other Odontoceti apparently lacks any component of the 

mastoid process of noncetacean mammals. See discussion under 

mastoid process of the petrosal in “Periotic Bone.”

See also distal plate of the posterior process of the tympanic 

bulla.

Homologous features are seen in other mammals. In whitetailed deer (Odocoileus virginianus) and sheep (Ovis aries), such 

features occur in the posterior part of the tubular external auditory meatus, which is formed by the ectotympanic. In the deer 

(lateral view), the thin posterodorsal edge of the external acoustic meatus sutures with a thin plate of the retrotympanic process

of the squamosal, immediately anterior to the mastoid process. 

Here, the posterodorsal edge of the external acoustic meatus

probably represents the facet for the posterior meatal crest (q.v.) 

of the cetacean tympanic bulla, and perhaps also the facet for the 

posttympanic process. On the deer squamosal, the retrotympanic 

process is probably equivalent to the posterior meatal crest of 

the cetacean squamosal. Farther posteriorly, in deer, the bulla 

articulates narrowly with the mastoid process of the petrosal just 

lateral to the tympanohyal. In Tursiops this articulation is represented by contact of the posterior process of the tympanic bulla 

with the posterior bullar facet of the periotic.

The term “posterior process of the tympanic bulla” has had 

a confused history of use because of uncertain homology with 

the mastoid process or posterior process of the periotic bone. 

Flower (1872:218, 219, 234, pl. 29, caption) identified the 

large wedge-shaped posterior process of the tympanic bulla in 

Ziphiidae as comparable in position to the mastoid process of 

other mammals: “it differs from the ordinary mastoid in being 

united to the tympanic instead of the periotic.” Later, Flower 

(1885:216) clearly differentiated the mastoid process of the periotic from the enlarged posterior process of the tympanic bulla, 

which merely “resembles in its relations the mastoid of ordinary 

mammals. . . .”

Schulte referred to the posterior process of the tympanic 

bulla in Kogia as the “‘mastoid’ process of the tympanic.” 

(1917:392) or as the “tympano-mastoid” (1917:394). See also 

comment by Pompeckj (1922:63).

Van der Klaauw (1931:37) referred to the posterior process 

of the tympanic bulla as the processus petrosus [or processus 

posterior] of the tympanic.

Lillie (1910:777; see also Turner, 1913:14) used the term 

“opisthotic portion of the periotic” for the fused posterior process 

of the tympanic bulla plus periotic in Balaenoptera musculus.

Yamada (1953:19, fig. 17) and Fraser and Purves (1960: 

Caperea: pls. 5, 6; Balaenoptera: pl. 7; Ziphiidae: pls. 8–11) used 

the name “mastoid process” for the fused posterior process of 

tympanic bulla and periotic in Mysticeti. For Odontoceti Fraser 

and Purves (1960:77–80; e.g., pl. 8) also used “mastoid process” 

for the posterior process of the tympanic bulla and for the posterior process of the periotic bone.

We cannot identify in Tursiops or other Odontoceti any 

mastoid component in the tympanic bulla, and recommend that 

the term “mastoid” not be used for components of the tympanic 

bulla or, because of the above confusion, for components of periotic or squamosal.

Kellogg (e.g., 1928, 1931) identified the fused posterior 

process of tympanic bulla and periotic in Mysticeti merely as 

the “posterior process,” without indicating a component of 

periotic.

The structure in young animals helps resolve the homology 

of the posterior process of the tympanic bulla, particularly in 

Mysticeti. In fetal or neonate Tursiops and many other Odontoceti and some archaic Mysticeti, the posterior process of the 

periotic bone and the posterior process of the tympanic bulla are 

short and subequal in size, are relatively smooth rather than rugose, lie within a somewhat open region between squamosal and 

exoccipital, and are not exposed prominently on the skull wall. 

Both processes are similarly short in Archaeoceti, which differ, 

however, in having the posterior process of the periotic bone exposed laterally on the skull wall (see discussion under Periotic). 

In fetal and/or neonate modern specimens, the posterior suture 

between the tympanic bulla and periotic is clearly visible, and is 

not fused.

The situation in neonate Tursiops is shown in Figure 25a–e. 

For Mysticeti, Kasuya (1973: pl. 1, fig. 9) illustrated fetal Balaenoptera borealis. Lillie (1915: pl. III, fig. 1) illustrated the tympanoperiotic of Megaptera novaeangliae in which the suture is 

visible between the posterior process of the tympanic bulla and 

the periotic. Van Beneden and Gervais (1869–1879) provided 

lateral and medial views of tympanoperiotics of fetal and juvenile Balaena australis (pl. I, II, fig. 10) in which there is a distinct suture between the posterior process of the tympanic bulla 

and the periotic. Van Beneden and Gervais also showed older 

specimens of Balaena “antipodarum” (pl. II, fig. 12), Balaena 

mysticetus (pl. VI, fig. 5), and Megaptera “longimana” (pls. X, 

XI, fig. 7) in which the suture between the posterior process of 

the tympanic bulla and the periotic are fused anteriorly but are 

still open posteriorly (distally). In adult Mysticeti, periotic and 

tympanic bulla are fully fused posteriorly to form the structure 

that is usually termed the posterior process of the tympanic bulla 

despite the contribution from the periotic. Table 8 is a summary 

of homologies of some bullar and associated structures in Tursiops and Odocoileus.

* posterior tympanic spine (spina tympanica posterior) = lesser 

tympanic spine (spina tympanica minor) (Figure 25s)

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 4 3
The posterior tympanic spine is located on the posterodorsal border of the tympanic ring in mammals (Feneis, 1994:16.7; 

not in Schaller, 1992). The posterior tympanic spine, together 

with the anterior tympanic spine, marks the lower margin of the 

membrana Shrapnelli or pars flaccida (Bondy, 1907, cited by van 

der Klaauw, 1931). The development of anterior and posterior 

tympanic spines varies among mammalian species.

The tympanic ring or tympanic annulus is modified in cetaceans because of the development of the sigmoid process and 

conical process. A ridge that marks part of the tympanic ring was 

illustrated for Phocoena phocoena by Boenninghaus (1904: pl. 

13, fig. 12A), and comparable structures exist in Tursiops (Figure 

25w). A subhorizontal ridge extends posteriorly from the conical 

process and rises some way up the face of the outer pedicle of the 

posterior process. A projecting flange, originating from the outer 

pedicle of the posterior process, overhangs the ridge. The flange 

is probably homologous with the posterior tympanic spine.

Dissection is needed to identify the posterior boundary between the tympanic membrane and the membrana Shrapnelli

(pars flaccida).

= posteroexternal angle (Kellogg, 1936)

See outer posterior prominence. 

= posterointernal angle (Kellogg, 1936)

See inner posterior prominence. 

= processus conicus posterior

See conical process or median process. 

= processus conicus posterior sive lateralis (Schulte, 1917:395)

See conical process or median process. 

− processus perioticus

“Processus perioticus” was used by Schulte (1917:396) 

without clear definition. It appears to refer to that portion of the 

posterior process of the bulla in Kogia that carries the facet for 

the posterior process of the periotic bone. Because the original 

definition is not clear, we recommend the term “processus perioticus” not be used. Schulte (1917:394) apparently also equated 

the processus perioticus with the processus petrosus ossis tympanici (= processus conicus anterior of Denker, 1902:428; pl. 

14, fig. 2, “p.c.a.”).

See anterior conical process.

− processus petrosus of the tympanic

Schulte (1917:396) identified the processus petrosus of the 

tympanic as that part of the bulla contacted posteriorly by the 

periotic, but did not define the “processus petrosus.” He stated 

that “the processus petrosus [is reduced] to a plate of but moderate thickness,” implying that the processus petrosus is distinct 

from his “tympano-mastoid.” Because the original definition is 

not clear, we recommend the term “processus petrosus of the 

tympanic” not be used.

= processus petrosus ossis tympanici

See posterior process of the tympanic bulla (Denker, 1902: 

pl. 14; Schulte, 1917:394). 

= processus styliformis (van der Klaauw, 1931)

See muscular process of the tympanic bulla. 

= processus tubarius of the bulla = accessory ossicle

Boenninghaus (1904: fig. G(6)) clearly identified the processus tubarius as the nodular structure on the dorsal part of the 

outer lip, also known as the accessory ossicle or tubal tubercle. 

Subsequently, the term “processus tubarius” has had a confused 

use.

Van der Klaauw (1931:132) identified the processus tubarius for mammals generally as the attachment for the cartilaginous Eustachian tube and the m. tensor veli palatini, sometimes 

forming an inward-pointing hook. Van der Klaauw (1931) also 

equated the processus tubarius with the processus conicus anterior (q.v.), but Denker (1902) indicated that the latter is a separate structure.

Fordyce (1994:158, 160) used processus tubarius for the 

enrolled or subcylindrical part of the anterodorsal crest of the 

tympanic bulla that sutures with the periotic in the fossil dolphin 

Waipatia; here, we use the term “periotic facet” for the suture 

on the anterodorsal part of the outer lip on various Neoceti and 

Archaeoceti. In Tursiops there is no periotic facet on the enrolled 

or subcylindrical anterodorsal thin outer edge of the bulla beTable 8. A summary of homologies of some bullar and associated structures in Tursiops and Odocoileus.

Tursiops Odocoileus

Sigmoid process of the bulla = Anterodorsal part of ectotympanic in external acoustic meatus

Conical process of the bulla = Floor of ectotympanic in external acoustic meatus

Posterior process of the bulla = Posterodorsal part of ectotympanic in external acoustic meatus

Facet (on the posterior process of the = Suture, in part, on posterodorsal part of ectotympanic at external acoustic meatus, for 

tympanic bulla) for the posterior meatal crest contact with squamosal

Facet (on the posterior process of the tympanic bulla) = Suture, in part, on posterodorsal part of ectotympanic at external acoustic meatus, for

for the post-tympanic process contact with squamosal

Posterior meatal crest of the squamosal = Retrotympanic process in part, possibly the more medial portion

Post-tympanic process of the squamosal = Retrotympanic process in part, possibly the most lateral portion

1 4 4 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
cause this feature has been obliterated by an enlarged accessory 

ossicle.

Luo (1998:287) and Luo and Gingerich (1999:32, tbl. 4, 

#15, #16a) equated the processus tubarius with the whole of the 

anterior process of the tympanic bulla.

Van der Klaauw (1931:132) noted that Hanke (1914:508, 

509) reported the processus tubarius as absent in Mysticeti. The 

process is, however, present but altered to form the narrow elongate anterior pedicle of the tympanic bulla.

See accessory ossicle for discussion.

* recessus meatus (Figure 25w)

The recessus meatus in mammals is that part of the tympanic cavity that extends laterally beyond the crista tympanica

of the meatus (q.v.) (Whitmore, 1953:135).

Alternatively, van der Klaauw (1931:200) stated that the 

recessus meatus is the groove that sometimes occurs within 

the meatus lateral to the insertion of the tympanic membrane. MacPhee (1981:62) followed this definition; McDowell 

(1958:128) recognized the recessus meatus as the most proximal part of the bony external auditory meatus, set off from the 

meatus proper by its broader diameter In Tursiops a recessus 

meatus sensu Whitmore develops dorsolaterally via an excavation into the conical process. This recess is continuous with the 

tympanic cavity. In Tursiops the recessus meatus may be delimited by a bullar septum.

See hypotympanic sinus.

= rostral carotid foramen

The rostral carotid foramen or foramen lacerum is the anterior opening of the carotid canal in the dog (Evans and Christensen, 1979).

The rostral carotid foramen is not present in Neoceti.

See also carotid canal. 

= rostral lip

Schulte (1917:395; cited by van der Klaauw, 1931:29) appeared to use the term “caudal lip” for the involucrum in Kogia, 

and “rostral lip” for the opposite structure, which therefore 

could include the whole of the outer lip of the tympanic bulla.

See outer lip.

− rostral ridge of sigmoid process

Schulte (1917:395) recognized two ridges, caudal and rostral, arising from the apex of the sigmoid process in the bulla of 

Kogia. Of these, the rostral ridge “continues into the free margin 

of the bulla losing its identity at the point where the malleus is 

anchylosed.” The rostral ridge is thus homologous with the internal edge of the sigmoid process as seen in Tursiops and other 

odontocetes.

− rostral squamosal foot

The rostral squamosal foot is the anterior part of the mallear plate (q.v.) of the dorsal part of the ectotympanic in the 

archaic insectivore Leptictis (Novacek, 1986:51, fig. 19).

This structure cannot be homologized in Tursiops.

* semicanal for the auditory tube (semicanalis tubae auditivae) 

(Figure 25a)

The semicanal for the auditory tube lies at the anteromedial 

end of the tympanic bulla (Evans and Christensen, 1979:152, 

153; Schaller, 1992:24.14). The semicanal for the auditory tube 

accounts for part of the musculotubal canal of the tympanic bulla. 

In humans the semicanal for the auditory tube accounts for the 

ventral part of the musculotubal canal (Feneis, 1994:12.30).

In Tursiops and other Odontoceti the semicanal for the auditory tube (= musculotubal semicanal, Eustachian outlet, and 

tympanic outlet) has been relatively enlarged and occupies most 

of the lumen of the tympanic bulla.

− semicanal for the tensor veli palatini muscle (semicanalis m. 

tensoris veli palatini)

The semicanal for the tensor veli palatini muscle lies anterolateral to the semicanal for the auditory tube in the anteroventral 

portion of the pars tympanica (Schaller, 1992:24.13).

According to Fraser and Purves (1960:11, 19) the Odontoceti Phocoena phocoena and Delphinus delphis have an m. tensor veli palatini. We could not find published details of its origin 

at the tympanic bulla.

* septum bullae (Figure 25w)

The septum bullae in canids is a shallow transverse septum

in the ventral wall of the auditory cavity that divides the tympanic bulla (Schaller, 1992:24.9). It is also known as the septum 

of the meatal tube, and intrabullar part.

In some Archaeoceti the meatal tube protrudes into the 

tympanic cavity and is supported by septa or trabeculae (Luo, 

1998:278). Tursiops appears to have two indistinct bullar septa, 

associated with the conical process. An anterior septum descends 

obliquely forward ventral to the sigmoid process, while the more 

robust and lower posterior septum descends gently posteriorly, 

toward the inner posterior pedicle.

See diverticulum anterior and diverticulum posterior for 

discussion.

− septum of the musculotubal canal (septum canalis musculotubarii)

The septum of the musculotubal canal divides the lateral 

semicanal for the tensor veli palatini muscle from the medial 

semicanal for the auditory tube (Schaller, 1992:24.15; Feneis, 

1994:12.31).

It is not known if Tursiops has an m. tensor veli palatini

that originates in the wall of the auditory tube. There is no bony 

septum of the musculotubal canal. 

See semicanal for the tensor veli palatini muscle.

− sheath for the hyoid process (vagina processus hyoidei)

Schaller (1992:24.6) termed the sheath for the hyoid process 

the “vagina processus styloidei.” Van der Klaauw (1931) used 

the same term for the canal that encloses the “top of the stylohyal and the tympanostyloid cartilage.”

Schaller’s term seems inappropriate, given the homology of 

the hyoid components; see “Hyoid Apparatus.”

For archaic artiodactyls Whitmore (1953:134) identified the 

vagina processus hyoidei as the pit for the cranial end of the 

tympanohyal.

A small subcircular roughened surface is variably present in 

Tursiops; this is probably the vagina processus hyoidei.

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 4 5
− sheath for the styloid process (vagina processus styloidei)

Whitmore (1953) stated that, in archaic artiodactyls, the 

sheath for the hyoid process is the pit on the tympanic bulla

that surrounds the cranial end of the tympanohyal bone. (The 

latter is in part the styloid process.) This structure is present in 

ruminants and the horse (Schaller, 1992:24.6), where it is termed 

the “sheath for the styloid process” (vagina processus styloidei). 

The sheath for the styloid process is formed by a sheet of the 

tympanic bone reflected around the base of the styloid process 

(Schaller, 1992:24.6; Feneis, 1994:16.10).

Luo (1998:278, and fig. 4) identified this feature in Archaeoceti as the tympanohyal sulcus, and homologized it with 

the interprominential notch of the tympanic bulla. 

In Tursiops the tympanohyal, which in other mammals articulates with the stylohyal, is greatly reduced. Dissections have 

not shown that hyoid elements affect the surface topography 

of the tympanic bulla, and we hesitate to homologize the interprominential notch with the tympanohyal sulcus. However, the 

groove associated with the putative tympanohyal is reasonably 

homologized with the sheath for the hyoid process, for which 

“tympanohyal sulcus” is an appropriate alternative name. We 

cannot judge if the interprominential notch in Tursiops is functionally related to the sheath for the hyoid process.

* sigmoid process (Figures 25c–h,j,r,s,v–x,y, 29)

The sigmoid process of the tympanic bulla (Beauregard, 

1894:380, 381, fig. 2s) lies on the dorsal margin of the outer lip

of the bulla, anterior to the conical process and posterior to the 

fissura Glaseri. The sigmoid process extends dorsolaterally and 

is usually complexly concave on its posterior surface (Yamada, 

1953:20; Kasuya, 1973).

The tympanic membrane appears to insert subvertically in 

the middle of the posterior face of the sigmoid process. The lateral portion of the posterior face of the sigmoid process thus 

forms part of the anterior wall of the external acoustic meatus.

In the periotic of Delphinus delphis that we dissected, the 

laterally produced groove on the posterior surface of the apex of 

the sigmoid process seems to carry the start of the middle sinus.

Despite the suggestion of Hanke (1914:506, cited by van 

der Klaauw, 1931:37, 159), we know of no cetacean where the 

sigmoid process fuses with the periotic. In Tursiops the medial 

part of the sigmoid process closely approximates the periotic, to 

the extent that a gap cannot be seen between the elements, and 

thus might be said to suture, but the elements are not fused.

Turner (1913:16) named this the “mallear process” or “liplike process.” Van der Klaauw’s (1931:262) comment on Turner 

did not make it clear that sigmoid process and mallear process 

are the same structure.

The sigmoid process is homologous with part of tympanic annulus of other mammals (Doran, 1878; Ridewood, 1922). It represents the modified anterior wall of the external acoustic meatus, 

and Luo (1998:294) regarded it as arising from the embryonic 

anterior crus. Structures transitional between some land mammals 

and Tursiops are seen in some archaeocete whales (Luo, 1998).

See rostral ridge of sigmoid process.

= styliform process (van der Klaauw, 1931:133; Whitmore, 1953)

Van der Klaauw (1931:133) noted possible confusion between the term “processus styliformis” or “styloideus,” used 

here for the muscular process of the tympanic bulla, and the term 

“styloid process” or “processus styloideus,” used for the fused 

tympanohyal and stylohyal of other eutherians.

See muscular process of the tympanic bulla.

= styloid apophysis (de Muizon, 1988)

See muscular process of the tympanic bulla. 

* sulcus for the chorda tympani (sulcus pro chorda tympani) 

(Figures 25c,d,h,j, 26a)

In Tursiops and other Neoceti the chorda tympani lies 

in a sulcus that arises posteriorly at the petrotympanic fissure

(= fissura Glaseri) and runs anteriorly along the dorsal edge of 

the outer lip of the tympanic bulla (Kellogg, 1936:114; Archaeoceti: Pompeckj, 1922: pl. 2, fig. 8). The posteromedial part of the 

groove may be equivalent to the chordafortsatz. Relationships 

are not clear with the malleolar sulcus (in the sense of MacPhee, 

1981:57). The groove is bounded laterally and posteriorly by 

the mallear ridge and medially by the accessory ossicle. This interpretation differs significantly from that of Luo and Gingerich 

(1999: fig. 21).

= sulcus for the tympanohyal

See tympanohyal sulcus, sheath for the hyoid process, and 

interprominential notch. 

= sulcus malleolaris = malleolar sulcus

= trabeculae, of meatal tube, intrabullar part = septa of meatal 

tube, intrabullar part

− transverse ridges

Transverse ridges (Kellogg, 1969:25) sometimes occur on 

the dorsal surface of the involucrum in Neoceti.

They are indistinct in Tursiops.

* triangular opening (Figure 25y)

The triangular opening lies on the lateral surface of the articulated tympanic bulla and periotic between the sigmoid process of the tympanic bulla, the anterior process of the periotic 

bone, and the malleus (Kasuya, 1973: fig. 1).

The triangular opening in Tursiops is further subdivided into 

an anterior division and a posterior division by a transverse crest 

coming off the lateral surface of the bulla, anterior to the sigmoid process and posterior to the malleus. This crest articulates 

with the lateral tuberosity (Fordyce, 1994:160) of the periotic.

= tubal canal (tubal foramen, tubal groove) (MacPhee, 1981:64)

See musculotubal canal of the tympanic bulla. 

= tubal tubercle (processus tubarius)

See accessory ossicle.

= tympanic annulus (anulus tympanicus)

See tympanic ring. 

* tympanic aperture (apertura tympanica) (Figure 29)

The tympanic aperture in cetaceans (Denker, 1902) is 

bounded ventrally by the sigmoid process, conical process, and 

1 4 6 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
posterior process of the tympanic bulla. It is divided into the 

lower and upper tympanic apertures (Yamada, 1953; Kasuya, 

1973: fig. 1). We prefer to use “epitympanic hiatus” to refer to 

the structure that was known as the upper tympanic aperture. As 

it now stands, the tympanic aperture consists of the combined 

lower tympanic aperture and epitympanic hiatus (q.v.).

The tympanic aperture is present in Tursiops.

* tympanic bulla (bulla tympanica) (Figures 3, 4, 6f, 29)

The tympanic bulla, when present in mammals (van der 

Klaauw, 1931; Novacek, 1977), is an inflated bone that lies 

directly ventral to the mastoid process of the petrosal (periotic 

bone). It is formed of the tympanic part of the temporal and 

contains the fundus of the tympanic cavity (Evans and Christensen, 1979:129, 133, 134). The bulla was also referred to as 

the processus petrosus ossis tympani (Denker, 1902) or the tympanomastoid (Schulte, 1917; Yamada, 1953:19).

In Tursiops and other delphinids the tympanic bulla is a 

completely separate ossification formed by the embryonic ectotympanic (de Beer, 1937:341ff). It lies posterolaterally on the 

ventral surface of the skull, ventral to the periotic and ventromedial to the squamosal. It articulates with the periotic anteriorly 

at the accessory ossicle and posteriorly at the posterior process. 

Anteriorly, it is closely approached by the falciform process of 

the squamosal bone.

* tympanic cavity (cavum tympani) (Figure 25f,h,j,r)

The tympanic cavity contains the middle ear (Gray, 

1918:1037; Evans and Christensen, 1979:132; Schaller, 

1992:534.12; Feneis, 1994:378.16). Eustachius and Lancisius 

(1714:105) referred to the tympanic cavity as the cavitas tympani or the tympani cavitas.

The tympanic cavity in the dog is enclosed by the tympanic 

bulla and the periotic. It consists of three parts: the fundic part, 

which is the largest part and entirely contained within the tympanic bulla; the tympanic cavity proper, which is located dorsal 

to the fundic part and opposite the tympanic membrane; and 

the epitympanic recess, which is located dorsal to the tympanic 

cavity proper and contains the incus, part of the stapes, and 

the head of the malleus. In cetacean literature the fundic part 

has long been termed the “tympanic cavity,” without other 

qualification.

Whitmore (1953:132) used the term “hypotympanic sinus” 

for the tympanic cavity sensu lato of archaic artiodactyls. Van 

der Klaauw (1931:214) discriminated between the hypotympanic cavity and true tympanic cavity, but on page 262 implied 

that the hypotympanic sinus is a separate section of the tympanic 

cavity.

The tympanic cavity in Tursiops, other delphinids, and Neoceti in general is enclosed by the tympanic bulla and periotic. It 

communicates with the nasopharynx by means of the auditory 

tube (Eustachian tube).

The tympanic cavity has been termed the Eustachian cavity

(by various authors) and the bullar cavity (Luo, 1998:284). Luo 

and Gingerich (1999:41) used the term “tympanic cavity” (and 

also peribullar cavity) apparently to refer to the cranial hiatus.

= tympanic cleft (Turner, 1913:13)

See tympanic cavity. 

− tympanic crest (crista tympanica, or margo sulci tympanici)

MacPhee (1981:51) followed Bondy (1907) in recognizing the tympanic crest of mammals as a low semicircular ridge 

representing the dorsal margin of the tympanic sulcus. Van der 

Klaauw (1931:200) stated that occasionally the tympanic groove

or sulcus may be missing, in which case the tympanic membrane

attaches to the tympanic crest (crista tympanica, or margo sulci 

tympanici). The tympanic crest thus may be the same as the tympanic ring (q.v.) (= tympanic annulus).

Tursiops may have an tympanic crest. See tympanic sulcus.

= tympanic groove

See tympanic crest. 

= tympanic incisure

See tympanic notch. 

− tympanic membrane (eardrum) (membrana tympani)

The mammalian tympanic membrane (tympanum, tympanium) is not an osteological feature but is a membranous 

diaphragm that is supported by the tympanic ring (Evans and 

Christensen, 1979:134). The tympanic membrane intercepts airborne sounds and transmits them to the ossicular chain.

The tympanic membrane has been modified from a flat 

membrane in terrestrial mammals. In Mysticeti it forms an oval 

cone with the apex directed externally. This arrangement of the 

tympanic membrane has been termed the “glove finger” (Beauregard, 1894; Lillie, 1910:776, pl. lxxiv, fig. f; Fraser and Purves, 

1954, 1960:10; Purves, 1966:336). The situation in Odontoceti 

is less clear. For example, Fleischer (1975) stated that the tympanic membrane is absent in Kogia. Purves (1966:336) did not 

mention the shape of the membrane but said that its fibrous portion forms a broad flattened triangular [tympanic] ligament that 

inserts on the malleus. McCormick et al. (1970:1423) indicated 

that the tympanic membrane in Tursiops is a small planar feature. According to McCormick et al. (1970) the tympanic membrane is attached only to the lower tympanic aperture (in the 

tympanic bulla).

See also tympanic ring.

* tympanic notch (incisura tympanica) (Figure 25c,f,g,y)

MacPhee (1981:52) noted that the mammalian tympanic 

notch is the feature at the open dorsal part of the horseshoeshaped ectotympanic.

In many mammals the tympanic notch is bridged by part of 

the squamous part of the temporal where the zygomatic process 

of the squamosal is continued posterior to the mandibular fossa

(Schaller, 1992:24.32; Feneis, 1994:16.9; our observations on 

Odocoileus). Such uses indicate that the tympanic notch is the 

gap between parts of the bulla, and not a part of the periotic or 

squamosal. The tympanic notch lies on the ventral surface of 

the extension of the zygomatic process that forms the posterior 

limit of the supramastoid crest. In humans the tympanic notch 

and adjacent temporal form the dorsal surface of the external 

auditory meatus.

For Archaeoceti, Kellogg (1936:113) identified the tympanic 

notch, which he termed incisura Rivini, as the gap in dorsal edge 

of outer lip of the tympanic bulla, between the dorsal rim of 

the sigmoid process and the anterior edge of the outer pedicle 

t y m p a n i c b u l l a n u m b e r 6 2 7 • 1 4 7
of the posterior process. The incisura Rivini connects the lower 

tympanic aperture with the epitympanic hiatus. The tympanic 

notch in some Odontoceti other than delphinids is roofed by the 

spiny process of the squamosal bone, which occupies the hiatus 

epitympanicus of the periotic.

The tympanic notch is present in Tursiops.

See hiatus epitympanicus or epitympanic hiatus.

* tympanic opening of the auditory tube (ostium tympanicum 

tubae auditivae) (Figure 25a)

The tympanic opening of the auditory tube lies in the anteromedial aspect of the tympanic bulla (Schaller, 1992:538.20). 

The tympanic opening of the auditory tube is the opening for 

the semicanal for the auditory tube, which is part of the musculotubal canal of the tympanic bulla (Evans and Christensen, 

1979:152, 153).

In delphinids the tympanic opening of the auditory tube lies 

at the anteromedial end of the tympanic bulla.

= tympanic part of the temporal (pars tympanica)

The tympanic part of the temporal bone in mammals is that 

ossification that forms the tympanic bulla. The tympanic bulla

contains most of the tympanic cavity (Evans and Christensen, 

1979:134).

The term “temporal” is not appropriate for Tursiops because the squamosal, tympanic bulla (=tympanic part of the 

temporal), and periotic are separate elements; they are discussed 

separately here.

− tympanic plate of the bulla (Fleischer, 1978) (Figure 25g)

Fleischer (1975, 1978) used the term “tympanic plate” to 

refer to the thin ventrolateral portion of the tympanic bulla. Nummela et al. (1999a:63; 1999b: fig. 1) expanded the area. This is not 

to be confused with the tympanic plate of the basioccipital bone.

− tympanic ring (anulus tympanicus) (Figure 25w,x)

The tympanic ring in the dog is an annular-shaped process 

of the tympanic part of the temporal to which the tympanic 

membrane (q.v.) is attached (Evans and Christensen, 1979:134). 

In humans the tympanic ring is incomplete dorsally at the tympanic notch (Gray, 1918:146); it is the only portion of the tympanic part of the temporal in humans.

Van der Klaauw (1931:201) discussed the homology of 

parts of the tympanic ring, cautioning that the crista tympanica

is not the same as the tympanic ring.

The tympanic ring in Neoceti is open dorsally at the tympanic notch, but otherwise is highly modified and has lost its 

ring shape; the shape is probably related to the structure of the 

tympanic membrane (q.v.). Dissection of Delphinus delphis, and 

observation of the bulla, reveals that the tympanic membrane 

attaches to the middle of the posterior face of the sigmoid process, to the ventromedial edge of the conical process, and to the 

ridge that runs posterodorsally from the ventromedial edge of 

the conical process; these features are equivalent to the tympanic 

ring. A comparable structure may be expected in Tursiops.

− tympanic sulcus (sulcus tympanicus) 

The tympanic sulcus in mammals is a groove in the tympanic 

ring for the attachment of the tympanic membrane (Schaller, 

1992:24.3; Feneis, 1994:16.8; see tympanic ring). Schulte 

(1917:396) used the term “drum” for tympanic membrane in 

Kogia. Van der Klaauw (1931:200) stated that occasionally the 

tympanic groove or sulcus may be missing, in which case the tympanic membrane attaches to the tympanic crest (crista tympanica). 

He also discriminated between the tympanic sulcus and the groove 

that may lie lateral to the insertion of the tympanic membrane; 

this groove has sometimes been termed the “recessus meatus.”

The tympanic sulcus is poorly known in Neoceti (van der 

Klaauw, 1931:204). Archaeoceti show a grooved or depressed sulcus on the conical process, and the gray whale has a grooved sulcus 

at the base of the sigmoid process. Kellogg (1936) identified in Archaeoceti and in Monodon a groove on the conical process of the 

tympanic bulla as representing part of the groove for anulus tendineus, or tympanic sulcus. In Tursiops the position of attachment 

of the tympanic membrane is readily identifiable as a ridge in some 

individuals, but there is no obvious groove (tympanic sulcus).

= tympanohyal sulcus

“Tympanohyal sulcus” is an appropriate alternative name 

for the sheath for the hyoid process.

See sheath for the hyoid process and interprominential notch. 

= tympanomastoid (bone) 

See tympanic bulla. 

− tympanomastoid fissure of the tympanic bulla (fissura tympanomastoidea) 

The tympanomastoid fissure of the tympanic bulla is formed 

at the external contact of the tympanic part with the mastoid 

process of the mammalian petrosal (Schaller, 1992:22.38).

The tympanomastoid fissure is present in Odontoceti as the 

articular surface of the posterior process of the tympanic bulla 

and posterior process of the periotic bone.

− tympano-mastoid process or tympanomastoid process

The tympano-mastoid process described by Schulte 

(1917:393, 394, 396) in Kogia is the greatly inflated posterior 

process of the tympanic bulla that has come to articulate with 

the paroccipital process of the exoccipital and exoccipital process 

of the squamosal. This large process is likely to be mistaken for 

the mastoid process in humans but bears no relation to it. The 

tympano-mastoid process is also developed in Physeter (Flower, 

1868:321) and in ziphiids (Flower, 1872:218, pl. 29; Kernan, 

1918:358) but not in delphinids.

We cannot identify in Tursiops or other Odontoceti any 

mastoid component in the tympanic bulla, and recommend that 

the term “tympano-mastoid” not be used in this manner.

See posterior process of the tympanic bulla. 

− tympano-occipital fissure (fissura tympano-occipitalis)

In the dog the tympano-occipital fissure is formed by contact of the tympanic part of the temporal bone with the basioccipital (Evans and Christensen, 1979:135).

In Tursiops or other Odontoceti the tympanic bulla does 

not contact the basioccipital.

* tympanoperiotic bone

The tympanic and periotic portions of the temporal as seen 

in other mammals have become increasingly isolated from the 

cranium in cetaceans, much more so in Odontoceti than in Mys1 4 8 • smithsonian contributions to zoolog y t y m p a n i c b u l l a
ticeti. In many Odontoceti the tympanic and periotic bones are 

attached to the skull by a thin lamina of bone but are attached 

to each other by the articulation of the posterior bullar facet

of the periotic with the posterior process of the tympanic bulla. 

The tympanic and periotic form a functional unit that is referred 

to as the tympanoperiotic bone (Anderson, 1879:508; Flower, 

1885; Fordyce, 1994). It has also been called the petro-tympanic 

or petrotympanic bone (Owen, 1866a:30, 40), or the otocrane

(Owen, 1866a:26, 29, 30, 35).

− tympanosquamosal fissure (fissura tympanosquamosa) 

The tympanosquamosal fissure is the fissure formed where 

the tympanic bone contacts the squamosal bone on its cranial 

surface (Schaller, 1992:22.39). The tympanosquamosal fissure 

is present in sheep, goats, and horses, but is absent in other domestic animals.

The contact between the periotic and squamosal has been 

greatly reduced in delphinids, phocoenids, and iniids, and the tympanosquamosal fissure is absent (Kasuya, 1973:50, fig. 73). In other 

Odontoceti (e.g., the Ziphiidae, Platanistidae, Physeteridae) the 

tympanosquamosal fissure is present. Monodontids are equivocal.

There is no well-developed tympanosquamosal fissure in 

Tursiops, but sutures with the squamosal may occur in juveniles, 

between the anterodorsal crest of the tympanic bulla and the 

apex of the falciform process, and between the posterior process 

of the tympanic bulla and the posterior meatal crest. See tympanosquamosal suture.

− tympanosquamosal suture

The posterior process of the tympanic bulla in delphinids 

may suture with the squamosal via thin laminae of bone. These 

thin laminae go from the anterolateral margin of the posterior 

process to the posterior meatal crest of the squamosal. Because 

the posttympanic process is lost in Tursiops, there is no suture of 

squamosal and bulla here, contrasting with the situation in some 

nondelphinoid Odontoceti, e.g., Platanista.

= unciform process (de Muizon, 1987, 1991) 

This is presumably a lapsus calami for uncinate process. 

See accessory ossicle. 

= uncinate process

Schulte (1917 396; see also van der Klaauw, 1931) used 

“uncinate process” (i.e., hooked process) to refer to the accessory ossicle (q.v.) in Kogia and possibly also for the part of the 

outer lip of the bulla anterior to the accessory ossicle. For the latter we prefer the term “anterodorsal crest of the tympanic bulla” 

(q.v.). This feature of the tympanic bulla should not be confused 

with the uncinate process of the ethmoid bone (q.v.).

See accessory ossicle, tubal tubercle.

= vagina processus hyoidei

See sheath for the hyoid process. 

= ventral groove = median furrow (de Muizon, 1987; Fordyce, 

1994:149)

* ventral keel (Figure 25b)

The ventral keel of the cetacean tympanic bulla lies on the 

ventromedial margin of the tympanic bulla. The ventral keel is 

an anterior continuation of the eminence of the inner posterior 

prominence (Kasuya, 1973). The ventral keel commonly has a 

very rugose surface, but it is sharply developed only in a few species of Odontoceti. The structure in Tursiops is rounded.

Luo (1998:290) suggested that the ventral keel is present 

only in Mysticeti. Oishi and Hasegawa (1995) discussed the 

structures in mysticetes.

Luo and Gingerich (1999: tbl. 3, #29b) used the term “median ridge,” apparently for the ventral keel.

= vertical cleft (Kellogg, 1936: fig. 34)

See elliptical foramen. 

AUDITORY OSSICLES

Ossicula Auditus

With the evolutionary transition from reptiles to mammals, 

one of the elements that changed was the composition of the lower 

jaw and structure of the ear. The reptilian articular bone of the 

lower jaw became the incus and the quadrate bone of the skull 

became the malleus. The three bones are present in all mammals 

(Gray, 1918:1044–1046; Evans and Christensen, 1979:1065–1067; 

Schaller, 1992:536; Feneis, 1994:382). Eustachius and Lancisius 

(1714:10, 19, 20, 97) referred to these bones as the auditus ossicula; the malleus as the maleus os, the incus as the incudi os simile, 

and the stapes as the os stapedi simile or the stapedi os simile.

The three auditory ossicles, malleus, incus, and stapes, are 

considered separately below.

Malleus

Figures 25R,S, 26a–f

* anterior process of the malleus (processus gracilis, processus 

anterior, processus folianus) (Figures 25f, 26a,b,d,e)

In humans (Gray, 1918:1044; Feneis, 1994:382.17) the anterior process is a small projection that arises below the neck and 

is connected to the petrotympanic fissure by ligamentous fibers. 

This process in the dog (Evans and Christensen, 1979:1066) is 

largely embedded in the tympanic membrane. The anterior process is also called the rostral process (Evans and Christensen, 

1979:1066, fig. 19:6a) or long process; it is formed partly by an 

embryonic element, the goniale. The process contacts or is fused 

with the bulla in various groups of mammals (e.g., Novacek, 

1986:51, Luo and Gingerich, 1999: tbl. 3, #20, comment).

Van der Klaauw (1931:235) discussed the manner in which 

the anterior process (or processus longus) of the malleus may 

contribute to the tympanic bulla. The anterior process of the 

malleus lies in the sulcus malleolaris of the tympanic bulla and 

often fuses with the bulla. Homologies are uncertain for the 

sometimes-associated malleolar accessory ossicle (ossiculum accessorium malleoli).

In Tursiops and other Cetacea the anterior process (e.g., 

Kellogg, 1927) is an elongate robust projection that is fused with 

the outer lip of the tympanic bulla at the mallear ridge, where 

the medial part of the sigmoid process contacts the outer lip. The 

m a l l e u s n u m b e r 6 2 7 • 1 4 9
anterior process of the malleus carries a groove on its anterodorsal surface.

* articular surfaces of the malleus (Figure 26f)

The facet for the incus on the head of the malleus has two 

articular surfaces that contact the body of the incus at the incudomalleolar joint in the epitympanic recess (Gray, 1918:1044; 

Evans and Christensen, 1979:1066).

In Tursiops the articulation faces dorsomedially and posteriorly. As in other mammals, the upper facet is larger, the lower 

smaller.

* facet for the incus (Figure 26b)

The head of the malleus carries a facet for the incus. This 

facet faces dorsomedially and posteriorly and is divided into two 

articular surfaces.

* foramen for the chorda tympani (Figures 25r, 26a,b,e)

In the dog the nerve for the chorda tympani leaves the middle ear “under a fine bridge of bone of the tympanic ring” (Evans 

and Christensen, 1979:133), and continues through a canal in 

the lateral wall of the bulla.

In Tursiops and other Cetacea the nerve for the chorda tympani exits the middle ear via a small foramen for the chorda 

tympani in the malleus, just medial to the junction of the two 

articular surfaces of the facet for the incus.

= goniale

See anterior process of the malleus. 

* groove on the malleus (Figure 26f)

Delphinoids carry a prominent oblique groove that arises 

near the facet for the incus and traverses the dorsomedial face. 

Kellogg (1927:29) identified this groove as separating the tubercule of the malleus (with insertions for m. tensor tympani and 

the tympanic ligament) from the facet for the incus.

= handle of the malleus (Evans and Christensen, 1979:1066)

See manubrium of the malleus. 

* head of the malleus (caput mallei, capitulum mallei) (Figure 

26d)

In the dog (Evans and Christensen, 1979:1066), the head of 

the malleus (capitulum mallei) is one of three main parts of the 

malleus; it adjoins the neck. The head of the malleus carries the 

articular surfaces.

In Tursiops and other Delphinidae the dorsolaterally placed 

head of the malleus is subspherical and carries the facet for the incus. 

It articulates closely with the mallear fossa of the periotic. The head 

of the malleus merges indistinctly into the neck of the malleus.

* insertion for the tendon of the m. tensor tympani (Figure 26a,c)

The apex of the tubercule of the malleus, which in Tursiops

is the most anterior part of the malleus, carries a small oval pit 

that is the insertion for the tendon of the m. tensor tympani. In 

other Cetacea this insertion may lie more dorsally.

− lateral process (processus lateralis)

In humans (Gray, 1918:1044) the lateral process arises from 

the manubrium of the malleus, is directed laterally, and is attached to the upper part of the tympanic membrane at the position of the tympanomalleolar folds that border the pars flaccida

(membrana Shrapnelli). The lateral process in the dog (Evans 

and Christensen, 1979:1066) is the most dorsal attachment of 

the manubrium to the tympanic membrane. The lateral process is 

also known as the short process (processus brevis). The position 

of the lateral process in Tursiops is unknown.

= long process (Evans and Christensen, 1979:1066)

See anterior process of the malleus. 

* manubrium of the malleus (manubrium mallei) (Figures 25x, 

26b,c)

In humans (Gray, 1918:1044) and the dog (Evans and Christensen, 1979:1066) the manubrium of the malleus, or handle of 

the malleus, is an elongate process, the long lateral margin of 

which is connected with the tympanic membrane.

In Tursiops and other Delphinidae the manubrium of the 

malleus is an indistinct prominence marking the insertion of the 

tympanic ligament on the ventromedial border of the malleus. 

The position of the manubrium of the malleus is variable within 

the Odontoceti.

* muscular process of the malleus (processus muscularis) (Figure 

26a,c)

The muscular process carries the insertion for the m. tensor 

tympani (q.v.). In the dog (Evans and Christensen, 1979:1066) the 

small muscular process projects medially and rostrally from the 

base of the manubrium of the malleus. A small hook on the apex 

of the muscular process of the malleus forms the insertion for the 

tendon of the m. tensor tympani. In humans, the muscular process 

is on the medial side near the upper end of the manubrium.

In Tursiops the muscular process is the most apical part of 

the prominent and anteriorly prolonged tubercule of the malleus. 

The process carries a small pit, the insertion for the tendon of 

the m. tensor tympani, on the apex. In other odontocetes (e.g., 

Platanistoidea; de Muizon, 1987) the muscular process of the 

malleus may lie away from the apex of the manubrium.

− neck of the malleus (collum mallei)

In the dog (Evans and Christensen, 1979:1066) the neck of 

the malleus is an elongate region that links the head of the malleus with the muscular and lateral processes and the manubrium 

of the malleus. In humans (Gray 1918:1044) this is a narrow 

restricted region below the head of the malleus.

The neck of the malleus is not distinct in Tursiops or other 

Delphinidae.

= rostral process (Evans and Christensen, 1979:1066)

See anterior process of the malleus. 

* tubercule of the malleus (tuberculum mallei) (Figure 26a)

The tubercule of the malleus in Tursiops is the stout anterior 

end of the malleus that includes the manubrium of the malleus

and the muscular process of the malleus (see also Kellogg, 1927: 

fig. 13). Published literature gives the impression that “muscular 

process” and “tubercule” are used interchangeably. Among different groups of odontocetes the positions of muscular process 

and manubrium vary (de Muizon, 1987, 1991; Kellogg, 1927; 

and of Tursiops in this work).

1 5 0 • smithsonian contributions to zoolog y m a l l e u s
Incus

Figures 25W,X, 26g–l

* articular surfaces of the incus (Figure 26g,h,k)

Two articular surfaces on the body of the incus contact 

the malleus at the incudomalleolar joint in the epitympanic recess of the petrosal (Gray, 1918:1044; Evans and Christensen, 

1979:1066).

In Tursiops the articular surfaces are oriented anteriorly 

and slightly dorsolaterally. The upper facet is larger, the lower 

smaller.

* body of the incus (corpus incudis) (Figure 26g–j)

In humans (Gray, 1918:1044) the body of the incus is the 

main part of the incus. It carries two distinct projections, the crus 

breve and the crus longum, and has an articular surface that carries two facets for contact with the malleus.

In Tursiops the body of the incus is enlarged and merges 

with the indistinct crus longum.

* crus breve (processus brevis (Anderson, 1878:521)) (Figure 

26g,h,k,l)

In the dog (Evans and Christensen, 1979:1066) the short 

crus, or crus breve, of the incus points caudally into the fossa 

incudis of the petrosal.

In Tursiops the crus breve of the incus is a delicate lateral 

projection from the body of the incus.

* crus longum (processus longus (Anderson, 1878:521)) (Figure 

26i,j)

In humans (Gray, 1918:1044) the crus longum is a distinct 

projection from the body of the incus.

In Tursiops the crus longum is a short, robust posteromedial 

part that is not distinct from the body of the incus.

* facet for the malleus (Figure 26g,h,k)

In Tursiops the anterior part of the body of the incus carries 

a facet for the malleus. This facet faces anteriorly and slightly 

dorsolaterally and is divided into two articular surfaces.

* lenticular process (processus lenticularis, os lenticulare) (Figure 

26g–j,l)

In humans (Gray, 1918:1044) the lenticular process is a 

rounded projection on the end of the crus longum. The lenticular process articulates with the articular facet on the head of the 

stapes.

In Tursiops the lenticular process is a small dorsomedial 

projection on the posterior part of the body of the incus.

Stapes

Figures 25v,x, 26m–r

* anterior crus of the stapes (crus anterius) (Figure 26o–q)

The anterior crus of the stapes, or rostral crus of the stapes, 

is the more anterior of the two stapedial crura.

* articular facet (Figure 26n)

The head of the stapes carries an articular facet for contact 

with the lenticular process or crus longum of the incus (Kellogg, 

1927:29, 31).

* base of the stapes (basis stapedis) (Figure 26o,q,r)

The base of the stapes is the flattened oval plate of the stapes 

(Gray, 1918:1045) that articulates with the periotic at the fenestra vestibularis (fenestra ovalis, oval window). The base is also 

known as the “footplate of the stapes” (Kellogg, 1927:31).

= footplate of the stapes

See base of the stapes. 

* head of the stapes (caput stapedis, capitulum stapedius) (Figure 

26n,p,q)

The head of the stapes is at the opposite end to the base of 

the stapes. It carries the articular facet for contact with the lenticular process or crus longum of the incus (Gray, 1918:1045).

* muscular process of the stapes (Figure 26o,p,r)

In the dog (Evans and Christensen, 1979:1067) the muscular process on the posteromedial face of the neck of the malleus

marks the attachment of the stapedial muscle.

A muscular process of the stapes is well developed in 

Tursiops.

− neck of the stapes

In humans (Gray, 1918:1045) the neck of the stapes is the 

constricted part of the stapes between the head of the stapes and 

the stapedial foramen. It carries the muscular process of the stapes (q.v.) on the posterointernal face.

There is no obvious neck of the stapes in Tursiops.

* posterior crus of the stapes (crus posterius) (Figure 26o,p,r)

The posterior or caudal crus of the stapes is the more posterior of the two stapedial crura.

* stapedial foramen (Figure 26o,p)

The stapedial foramen is the foramen that opens, in humans 

(Gray, 1918:1045), between the two stapedial crura. The stapedial foramen is also known as the intercrural aperture or intercrural foramen (Kellogg, 1927:31).

In Tursiops the anterior and posterior crura are close together, and the stapedial foramen is vestigial.

* umbo (Figure 26m)

The umbo is the concavity on the vestibular face of the footplate of the stapes (Kellogg, 1927:31).

The umbo is well developed in Tursiops.

VOMER

Figures 27, 29, 31a

The vomer is the ventral midline portion of the rostrum and 

is the only unpaired bone in the rostrum. The vomer forms an 

important link between the facial bones of the rostrum and the 

v o m e r n u m b e r 6 2 7 • 1 5 1
mesethmoid of the cranium. The vomer also contributes to the 

ventral part of the nasal septum.

The vomer in cetaceans has taken over entirely the separation 

of the right and left nasal passages. The vomer forms the floor of 

the mesorostral canal, through which the mesorostral cartilage 

of the mesethmoid protrudes. In ziphiids, where the elements of 

the rostrum fuse, the vomer forms the mesorostral ossification 

(Schulte, 1917:374, 375, 378, 380, 381, 384–388, 400).

= alar process of the vomer (Anderson, 1879:511) = wings of 

the vomer

= aliform process (Owen, 1866b–1868(vol. 2):420) = alar process of the vomer

− base of the vomer (Evans and Christensen, 1979:146)

Evans and Christensen (1979:146) discussed the vomer as 

follows:

The sagittal part is formed of two thin, bony leaves, 

laminae laterales, which unite ventrally to form a 

sulcus, sulcus septi nasi, which in turn receives the 

cartilaginous nasal septum rostrally and the bony 

nasal septum, or perpendicular plate of the ethmoid 

caudally. It articulates ventrally with the palatine 

processes of the maxillae, with the caudal parts of the 

palatine processes of the incisive bones, and with the 

rostral parts of the horizontal portions of the palatine 

bones. This caudal articulation is at the palatine suture 

and the ventrorostral half of the base of the vomer. 

The sagittal part of the vomer is sharply forked at 

each end. The rostral notch is the incisive incisure (incisura incisiva); the caudal is the sphenoidal incisure

(incisura sphenoidalis).

Evans and Christensen did not identify the “base of the 

vomer” on any illustrations, although he labeled the articulation with the palatine on figure 4–34 (Evans and Christensen, 

1979:146). This articulation is on the posterolateral aspect of 

the wings (horizontal part) and not the sagittal part. Due to this 

inconsistency, we have not chosen to use the base of the vomer 

in this work.

− bony nasal septum (septum nasi osseum)

The bony nasal septum consists of the perpendicular plate

of the ethmoid bone (Gray, 1918:194; Evans and Christensen, 

1979:135; Schaller, 1992:14.2; Feneis, 1994:32.2;) and the sagittal part of the vomer. In many mammals, including humans and 

dogs, the cartilaginous nasal septum attaches to the anteroventral part of the bony nasal septum.

In delphinids the mesethmoid (perpendicular plate of the 

ethmoid bone) has come to lie internal to the nasal plate of the 

vomer, and the latter bone makes up the nasal septum.

− cartilaginous nasal septum (cartilago septi nasi)

The cartilaginous nasal septum is attached to the anterior 

margin of the perpendicular plate of the ethmoid bone and sagittal part of the vomer (Gray, 1918:194, 992; Evans and Christensen, 1979:158; Schaller, 1992:176.6; Feneis, 1994:134.22). 

The cartilaginous nasal septum separates the anterior part of the 

nasal cavity.

The entire nasal septum in delphinids is formed by the 

vomer, without cartilaginous component. The homologue of the 

cartilaginous nasal septum is attached to the mesethmoid as the 

mesorostral cartilage.

= choanal crest of the vomer (crista choanalis vomeris) = vomerine crest (crista vomeris)

= fusiform crest (Kernan, 1918:352) = mesorostral ossification

= groove for nasal septum = median vomerine groove (sulcus 

septi nasi / sulcus vomeris / sulcus septalis) = mesorostral canal

* horizontal part of the vomer (Figure 27b–d)

The vomer consists of two parts, the horizontal part and 

the sagittal part. The horizontal part of the vomer consists of the 

wings (ala vomeris) (Schaller, 1992:30.11).

The wings of the vomer are well developed in delphinids.

* incisive incisure (incisura incisiva) (Figure 27a,c,d)

The incisive incisure is a notch in the midline at the anterior 

end of the sagittal part of the vomer (Evans and Christensen, 

1979:146). This term is not in the Nomina Anatomica Veterinaria (Schaller, 1992:30.8).

The incisive incisure is present in some Tursiops.

* lateral sheet (lamina laterale) (Figure 27a,c)

The lateral sheets are composed of the sagittal part of the 

vomer. They unite ventrally to form the sulcus (groove) for the

nasal septum. This sulcus receives the cartilaginous nasal septum

anteriorly and the mesethmoid ossification posteriorly (Evans 

and Christensen, 1979:146). The vomer in humans and many 

other mammals is reduced and the lateral sheet is not differentiated (Schaller, 1992:30.8; Feneis, 1994:20.28). This term is not 

in the Nomina Anatomica Veterinaria.

In cetaceans the bulk of the vomer is composed of the lateral 

sheets.

= median vomerine groove = groove for nasal septum (sulcus 

vomeris / sulcus septi nasi / sulcus septalis) = mesorostral canal

= mesorostral bone = mesorostral ossification (Turner, 1872)

* mesorostral canal (Figures 1, 8a, 27a,d)

The mesorostral canal lies on the dorsal midline of the rostrum. It is bounded by the premaxillae laterally and by the vomer 

ventrally (Flower, 1878; Heyning, 1989a:5). The mesorostral 

canal is limited posteriorly by the mesethmoid. It has also been 

called the mesorostral furrow (Turner, 1880:5) or the vomerine 

gutter (Schulte, 1917:400).

The mesorostral canal is present in all cetaceans. It is homologous with the groove for nasal septum (sulcus vomeris

[sulcus septalis]), which is formed by the ventral fusion of the 

lateral sheets of the vomer (Schaller, 1992:30.9). In terrestrial 

mammals it receives the cartilaginous nasal septum anteriorly 

and the mesethmoid ossification posteriorly (Evans and Christensen, 1979:146).

1 5 2 • smithsonian contributions to zoolog y v o m e r
− mesorostral ossification

The mesorostral ossification occurs only in ziphiids and is a 

result of the dorsal expansion of the vomer (Fraser, 1942). It is 

usually found in adult males of the ziphiid genera, Mesoplodon, 

Ziphius, and Berardius (Heyning, 1984).

* nasal plates (Anderson, 1879:508, 521, 522) (Figure 27a–c)

Anderson described the vomer as follows:

Vomer (pl. XL, fig. 1, vo). – This is directed downwards and forwards, but has a twist to the left side. 

It may be resolved, into three portions: 1st, the expanded. plates which invest the under surface of the 

orbito-sphenoid and a portion of the basisphenoid; 

2nd, the thin nasal plate between them; 3rd, a division 

consisting of two wings, between which the mesethmoid cartilage (me) is received, the latter terminating 

below and anteriorly in a thin vertical plate wedged 

between the vertical plates of the maxillae, the posterior extremities of which are applied. to a lateral expansion on its posterior border. (Anderson, 1879: 521

Anderson’s plate XL is a disarticulated near-term fetus. Figure 1 of that plate is an oblique posteroventral view. We have 

interpreted the “nasal plate” in his description to mean that part 

of the lateral lamina that is exposed in the nasal passage.

* nasal septum (septum nasale) (Figures 1, 2, 27a,b)

The nasal septum serves to divide the right and left nasal 

cavities (Gray, 1918:194; Evans and Christensen, 1979:158; 

Schaller, 1992:176.6; Feneis, 1994:136.4). It comprises of the 

perpendicular plates of the ethmoid bone and vomer and the 

cartilaginous nasal septum. Vesalius (1543:23) referred to the 

nasal septum as the septum amplitudine narii. Eustachius and 

Lancisius (1714:112) referred to the nasal septum as the septo 

medio ipsius nasi.

In delphinids the mesethmoid (perpendicular plate of the 

ethmoid bone) has come to lie internal to the nasal plate of the 

vomer and the latter bone makes up the nasal septum. Schulte 

(1917:372, 373, 378, 384) referred to it as the internarial septum 

or the narial septum (Schulte, 1917:385).

* palatal part of the vomer (Owen, 1866a:27) (Figure 2)

The vomer is not present on the palatal surface of the skull 

in terrestrial mammals (Evans and Christensen, 1979:145, 146; 

Schaller, 1992:30.8) nor in humans (Gray, 1918:170; Feneis, 

1994:20.28, 25).

In cetaceans the rostrum has become extended anteriorly 

and the relationship of the bones has changed slightly. The vomer 

is exposed on the palatal surface of the skull and that portion of 

the bone is known as the palatal part of the vomer.

* prenarial process of the vomer (Schulte, 1917:385) (Figure 

27a–c)

The prenarial process is a midlateral process that occurs on 

the vomer just anterior to the bony nares (Schulte, 1917:385). 

The prenarial process was described in Kogia where it is very 

marked on the left. Schulte (1917:378, 384) also referred to the 

prenarial process as the tuberosity of the vomer or the prenarial 

tubercle.

Tursiops has a well-developed prenarial process.

* sagittal part of the vomer (Figure 27a,c)

The sagittal part of the vomer is composed of two thin 

plates, the lamina laterales, which unite ventrally to form the 

sulcus septi nasi. This sulcus receives the cartilaginous nasal 

septum anteriorly and the mesethmoid ossification posteriorly 

(Evans and Christensen, 1979:146). This term is not in the Nomina Anatomica Veterinaria.

In Cetacea the bulk of the vomer is composed of the sagittal 

part.

* sphenoidal incisure (incisura sphenoidalis) (Figure 27a,b,e)

The sphenoidal incisure of the vomer is a fork on the posterior end of the sagittal part of the vomer (Evans and Christensen, 

1979:146). This is contrary to the use of this term (incisura 

sphenoidalis) in the Nomina Anatomica Veterinaria (Schaller, 

1992:28.17), where it referred to a notch in the anteroventral 

portion of the frontal that receives the wing of the ethmoid in 

ruminants and horses.

The sphenoidal incisure is prominent in young delphinids, 

tending to change into a shallow concavity in older specimens. 

The sphenoidal incisure is visible on the ventral aspect of the 

skull.

* vomerine crest (crista vomeris) (Figures 2, 27b,c)

The vomerine crest is the ventral crest on the caudal part 

of the vomer (Evans and Christensen, 1979:146; Schaller, 

1992:30.10). It is homologous with the choanal crest of the 

vomer that separates the two nasal passages (choanae) in humans (Schaller, 1992:30.10; Feneis, 1994:20.30a).

The vomerine crest is readily seen on the ventral aspect of 

the skull of delphinids. The crest is better developed in adults.

− wedge-shaped part of the vomer (pars cuneiformis vomeris)

The wedge-shaped part of the vomer is the most anterior 

portion in humans that has a wedge-shaped form in lateral view 

(Feneis, 1994:20.30b). It forms the base of the cartilaginous 

nasal septum (Gray, 1918:194).

In odontocetes the vomer has changed its shape markedly, 

particularly with respect to the cartilaginous nasal septum. The 

part of the delphinid vomer that is homologous with the wedgeshaped part of vomer in humans is the entire dorsal aspect of the 

medial portion of the vomer that forms the floor of the mesorostral canal.

* wings of the vomer (ala vomeris) (Figure 27b–d)

The wings of the vomer, or ala vomeris, constitute the horizontal part of the vomer (Schulte, 1917:385, 392, 394; Evans 

and Christensen, 1979:146; Schaller, 1992:30.11). They lie at 

right angles to the sagittal part, flaring laterally and articulating 

with the sphenoid, ethmoid, and palatine bones. The wings of 

the vomer are also known as the alar process of the vomer or ala 

of the vomer (Schulte, 1917:374, 381, 385, 386, 393). Schulte 

(1917:394) referred to the wings of the vomer as the “processus 

alaris.”

In delphinids the wings of the vomer are paired lateral structures, at the posterior end of the vomer. The anterior surface of 

the wings of the vomer forms part of the posterodorsal wall of 

the nasal passage. The wings lie against the elements of the ethmoid posteriorly.

v o m e r n u m b e r 6 2 7 • 1 5 3
1 5 4 • smithsonian contributions to zoolog y the therian skull

MULTI-ELEMENT COMPLEXES:

STRUCTURES SHARED BY ADJACENT BONES

Topographic Features

The Rostrum

The term “rostrum” is derived from the Latin word for 

beak. The cetacean rostrum is defined generally as that portion 

of the skull that is anterior to the cranium. In terrestrial mammals, like the dog, the rostrum is formed principally by the nose. 

In cetaceans, where the skull has been subjected to “telescoping” 

(q.v.), the nasal passages have come to lie against the cranium 

and form the posterior boundary of the rostrum.

The odontocete rostrum consists of the maxilla, premaxilla, 

and vomer (Flower 1885:213).

The nasal bone, which in terrestrial mammals forms an important part of the rostrum, in odontocetes has become part of 

the anterior wall of the cranium.

The rostrum forms the upper jaw and functions primarily in 

feeding. The posterior portions of the rostrum, which form part 

of the facial region, function in the generation and modification 

of acoustic signals.

Antorbital Region

In strict morphometric terms, the rostrum is limited posteriorly by a line drawn between the apices of the antorbital notches

(see Appendix B). These notches contain the facial nerve where 

it emerges from the suborbital region and spreads out over the 

facial region of the skull.

The dorsal portion of the antorbital region blends into the 

facial region and consists of elements of the maxilla, premaxilla, 

frontal, and in some cases, the lacrimal. The dorsal portion bears 

a number of eminences, tubercles, crests, or ridges that have been 

given a variety of confusing names. We have grouped the names 

that pertain to the same structure in Diagram 2.

Facial Region

The face is defined in humans as the “front of the head from 

the top of the forehead to the bottom of the chin, and from ear to 

ear” (Webster’s New World Dictionary, College Ed., 1960:519). 

In cetaceans we have attempted to use the equivalent area of 

the skull and defined the facial region as the area into which 

the maxilla and premaxilla expand during telescoping. This area 

includes the entire dorsal surface of the rostrum (maxilla and 

premaxilla), the ascending process of the maxilla, the nasal process of the premaxilla, the external surface of the frontal, and 

the nasal bones. The facial region is bounded posteriorly by the 

nuchal crest and laterally by the orbitotemporal crest. The facial 

region includes the external nares.

Hinton and Pycraft (1922:233), in their treatment of the anatomy of Lipotes, described “a pair of large floating bones placed on 

each side of the subcutaneous narial slit, and forming together its 

posterior lip.” No further mention was made of these structures 

and the dissection material was ultimately lost. There seemed to 

be some doubt as to the nature of the “floating bones” because 

Hinton (1936:185) said, “The superficial valves are controlled by 

a pair of special ‘bones,’ which if not truly ossified are formed of 

very dense fibrous tissue.” Zhou and Qian (1981:120, 126) also 

treated Lipotes and found that the “floating bones” were the tendon of insertion of the m. maxillonasolabialis pars externa. That 

muscle had hypertrophied into what Zhou and Qian termed the 

“maxillonasalis tendinous plate”, and it was not bone.

The Palate and Pterygopalatine Fossa

The palatal area of the skull is expanded with the increase in 

relative size of the rostrum. The palate is primarily a surface feature that consists of the bones of the skull that form the mouth 

cavity. The palate ends at the posterior margin of the pterygoids 

where the pharynx begins. The palate consists of maxilla, premaxilla, vomer (in cases where the vomer has a palatal exposure), 

palatine, and pterygoid. The soft palate is the shelf of soft tissue 

that stretches between the pterygoid hamuli, in cases where the 

pterygoid hamuli are separated (e.g., the phocoenids). Tursiops

does not have a soft palate.

The pterygopalatine fossa (supermaxillary fossae of Schulte, 

1917:373; infratemporal fossa of Davis, 1964:48) is a complex issue 

in mammalian anatomy and is rendered more complex in odontocetes by the incursion of the anterior lobe of the pterygoid sinus.

The pterygopalatine fossa is bounded posteriorly by the orbital part of the frontal, from which it is separated by the ventral 

orbital crest. From the pterygopalatine fossa the pterygopalatine canal leads anteriorly via the pterygopalatine sulcus to the 

greater palatine sulcus.

The palatine canal in Tursiops lies along the palatomaxillary 

suture. It runs from the sphenopalatine foramen in the pterygopalatine fossa anteriorly to exit via the major palatine foramen

and minor palatine foramen.

The sphenopalatine ganglion (pterygopalatine ganglion) in 

humans is the largest of the four parasympathetic ganglia associated with the cranial nerves (Dox et al., 1979:177). The sphenopalatine ganglion sends postganglionic parasympathetic fibers 

to the lacrimal glands, the nasal and oral cavities, and the upper 

part of the pharynx.

The sphenopalatine foramen lies just anterior to the middle 

of the ethmoidal crest of the palatine on the medial (vomerine) 

surface of the palatine bone.

The concept of the pterygopalatine fossa seems to be the 

space bounded by the orbit, the palatine, and the area posterior 

to the ventral infraorbital foramen of the maxilla, into which 

space open the sphenopalatine foramen, the ventral infraorbital 

foramen, and the posterior palatine foramen. In Tursiops the 

pterygopalatine fossa is bounded by the low rounded ventral orbital crest dorsolaterally, the lateral lamina of the palatine bone 

medially, and the ventral infraorbital foramen anteriorly.

The pterygopalatine fossa contains the pterygopalatine ganglion (sphenopalatine ganglion), maxillary nerve, infraorbital 

nerve, maxillary artery and maxillary vein, and the origins of the 

m. pterygoideus.

The Cranium

The cranium is defined as the bones forming the enclosure 

of the brain. Vesalius (1543:25) referred to the cranium as the 

caput. The cranium consists of the occipital shield (exoccipital, 
a l e x i c o n n u m b e r 6 2 7 • 1 5 5

supraoccipital) posteriorly; the interparietal dorsally; the parietal 

and the squamosal laterally; the frontal and the ethmoid anteriorly; the basioccipital, tympanoperiotic, and sphenoid ventrally.

Internally the cranium consists of two major cavities or fossae, the cerebral fossa, which houses the cerebral hemispheres, 

and the cerebellar fossa, which lodges the cerebellum.

Vertex

The vertex has assumed a new role in the cetacean skull as a 

result of the posterior movement of the external nares. The vertex 

in terrestrial mammals was a craniometric point, defined as the 

most dorsal point on the skull, and did not have a definite function. In cetaceans, and particularly in some odontocetes such as 

the ziphiids, it serves as a nexus for many groups of muscles. The 

vertex serves as a foundation on which the muscles that control the 

movements of the nasal passage and associated diverticula rely.

The vertex is primarily centered on the nasal bones. In 

groups in which the vertex is more highly developed, such as 

the ziphiids, the vertex consists of the nasals and surrounding 

portions of the maxillae, premaxillae, and frontals. The vertex is 

surrounded by a dense matrix of connective tissue, so the bony 

elements are fused together and function as one.

Occipital Area

The occipital area has become more a part of the locomotor system of cetaceans and is the anterior insertion of the series 

of extremely well-developed epaxial muscles. The occipital area 

consists of the interparietal, supraoccipital, and exoccipital ossifications. The basioccipital forms part of the ventral surface of 

the skull and has not been considered part of the occipital area. 

The dorsal elements of the occipital area (interparietal, supraoccipital) have been termed the occipital shield or the occiput.

Zygomatic Arch and Temporal Fossa

The temporal fossa has been modified in its relationship to 

the zygomatic arch and the orbit. The primitive mammalian zygomatic arch consisted of the jugal (= malar, zygomatic), which 

spanned the ventral border of the temporal fossa. In the dog 

the zygomatic arch extends from the zygomatic process of the 

squamosal to the zygomatic process of the frontal bone and the 

maxilla. This bony bridge (the jugal) closes the temporal fossa 

ventrolaterally.

In the delphinids the ventrolateral border of the temporal 

fossa consists of the zygomatic process of the squamosal posteriorly and the postorbital process of the frontal bone anteriorly. The jugal has moved ventrally and runs from the zygomatic 

process of the squamosal to articulate with the lacrimal and the 

maxilla ventral to the preorbital process of the frontal. The jugal 

in odontocetes has been reduced to a slender rod that forms the 

ventral border of the orbit.

Orbit and Orbital Fissure

The orbit in generalized mammals is partially closed by the 

frontal, maxilla, and jugal. It is open posteriorly where it borders 

on the temporal fossa.

The orbit in cetaceans is open on the ventral portion. In delphinids the orbit is formed primarily by the frontal, with minor 

contributions by the jugal and lacrimal. The maxilla does not 

take part in formation of the orbit in odontocetes.

The orbital fissure in most mammals lies in the sphenoid in 

the sutures between the orbitosphenoid and the alisphenoid. The 

orbital fissure is located slightly posterolateral to the optic canal

and transmits the ophthalmic nerve, oculomotor nerve, trochlear 

nerve, and anastomotic artery.

The term “orbital fissure” is applicable only in young delphinids. In adults the orbital fissure is divided into the inferior 

orbital fissure, which transmits the zygomatic nerve, infraorbital 

nerve, and infraorbital vessels, and the superior orbital fissure, 

which transmits the ophthalmic, oculomotor, trochlear, and abducens nerves, as well as the superior ophthalmic vein.

In mammals, including delphinids, the optic canal transmits 

only the optic nerve and opens laterally by the optic foramen.

Basicranium

The most striking modifications have occurred in the ventral 

portion of the cranial vault, known as the basicranium. Vesalius 

(1543:25) referred to the basicranium as the calvariae basim. 

The basicranium is an inordinately complex area in vertebrates 

in general, but is extremely so in cetaceans.

The concept of the mammalian temporal bone has become 

modified in Cetacea (see introductory discussion under “Periotic 

Bone,” mastoid process of the petrosal, and introductory discussion under “Tympanic Bulla” in the preceding section of the 

Lexicon). This has resulted in our treating the temporal bone 

under “Tympanoperiotic Complex” (Periotic Bone and Tympanic Bulla) and “Squamosal Bone.”

Tympanoperiotic

Cetaceans have modified that portion of the temporal bone 

that deals with the ear into a single element, the tympanoperiotic. 

The tympanoperiotic is further broken down into the middle ear, 

which contains the tympanic cavity and auditory ossicles and is 

known as the tympanic bulla, and the inner ear, which contains 

the cochlea and semicircular canals and is known as the periotic 

bone. The periotic is homologous with the petrous temporal or 

petrosal of other mammals.

The tympanic bulla and periotic bone are joined by a complex interdigitation of their posterior processes. In odontocetes 

this joint is never fused. The tympanic bulla and periotic are also 

joined variably by their anterior processes. This joint is highly 

variable and details of its confused terminology are discussed 

under anterior process of both tympanic bulla and periotic in the 

preceding section of the Lexicon.

The functional reasons for this separation no doubt involve 

the increasingly complex sense of hearing, a topic that is still 

under theoretical discussion. In delphinids the only attachment 

remaining between the tympanic bulla and periotic bone is the 

delicate bony process that bridges the gap between the posterior 

process and the posttympanic process of the squamosal.

Cranial Hiatus

Another result of modifications associated with hearing in 

cetaceans is the isolation of the tympanoperiotic from the other 
1 5 6 • smithsonian contributions to zoolog y the therian skull

bones of the basicranium, resulting in an opening or cranial hiatus. The cranial hiatus is more complete in odontocetes than 

mysticetes and has resulted in skulls that frequently lose the tympanoperiotic elements on decomposition.

In delphinids the cranial hiatus is the confluence of the posterior lacerate foramen (jugular foramen) and the internal acoustic meatus.

Pterygoid Sinus Complex

One of the most striking modifications of the basicranium 

of cetaceans is the development of an anterior extension of the 

Eustachian tube (auditory tube). That extension has developed 

into a series of air sinuses known as the pterygoid sinus complex. 

In some delphinids the sinus system extends from the pterygoid 

hamulus (hamular lobe of pterygoid sinus), the posterior portion 

of the maxilla (anterior lobe of pterygoid sinus), through the orbital area (postorbital and preorbital lobes of pterygoid sinus), 

posterior to the nasal passage (basisphenoidal sinus in phocoenids), in the tympanosquamosal recess of the squamosal (middle 

sinus), around the tympanoperiotic (peribullary sinus), and into 

the paroccipital process (posterior sinus).

Venous Sinus System

Correlated with the development of the pterygoid sinus system is a complex system of venous sinuses. They have been described by Fraser and Purves (1960) as a system of fibro-venous 

plexuses associated with the entire air sinus system.

Mandible and Mandibular Foramen

The most striking change in the mandible is the development 

of a large mandibular foramen and mandibular canal in odontocetes. The lumen of this extends virtually the whole height of 

the mandible. The mandibular canal in mammals transmits the 

mandibular nerve and mandibular vessels, but in odontocetes the 

fatty material that is present in most foramina hypertrophies into 

the intra-mandibular fat body and occupies better than 95% of 

the lumen. The chemical composition of this fat body and the 

anatomical position have led researchers to hypothesize that it 

functions as a pathway for sound reception.

Transmission of Vessels, Nerves, and Passages

Infraorbital Complex

The nomenclature of the elements of the infraorbital complex have become extremely complicated, more as a function of 

historical lack of consensus than anything else (see earlier discussion under infraorbital canal of “Maxilla”).

The infraorbital complex consists primarily of the infraorbital 

nerves and vessels that supply the rostrum and facial areas. The 

nerves are infraorbital branches from the maxillary nerve and the 

vessels are infraorbital branches of the maxillary artery and vein.

Nasal Passages

Nares

Nares (naris) is a term used historically for both soft tissues 

and bones. In Cetacea it has been used for the external opening 

of the respiratory apparatus (blowhole), for the distal or external 

or facial bony openings associated with the nasals and premaxillae, and (generally with a qualifier) for the proximal or internal 

bony opening or openings associated with the palatines, pterygoids, vomer, and basisphenoid at the nasopharynx.

Table 9 shows the variation in terminology for the narial openings used in publications on Cetacea and some other 

mammals.

For Tursiops we use “external bony nares” for the distal 

or external or facial bony openings associated with the nasals 

and premaxillae, and “internal bony nares” or “choanae” for 

the proximal or internal bony opening or openings associated 

with the palatines, pterygoids, vomer, and basisphenoid at the 

nasopharynx.

One of the most obvious modifications in the delphinids is 

the movement of the external bony nares dorsally and posteriorly. This occurred while the rostrum was growing in relative 

length, resulting in heads with the external bony nares opening 

on top.

The rostral elements (premaxilla, maxilla, vomer) still bear 

the same relative relationship to the nasal passage, even though 

the relationship has shifted from a lateral to a vertical one (see 

Figure 31a). The anterior narial wall is formed by the premaxillae, vomer, palatine, and pterygoid. The posterior palatal elements (palatine, pterygoid) still form the bulk of the lateral walls 

of the nasal passage. The medial narial wall is the nasal septum, 

the bony element of which is the vomer. The posterior narial 

wall is formed by the nasals, mesethmoid, and vomer.

The nasal septum is formed principally by the vomer instead 

of the ethmoid. The ethmoid (mesethmoid) forms the dorsal margin of the nasal septum in very young animals but as the animal 

ages the vomer displaces the mesethmoid. In adults the mesethmoid is restricted to the posterodorsal wall of the nasal passage 

lying between the vomer ventrally and the nasals dorsally.

The internal bony nares (choanae) are formed by the pterygoids anterolaterally and the vomer posteriorly. Fraser and 

Purves (1960:20) used the term “posterior narial aperture” in 

speaking of the internal bony nares. The pterygoids have expanded to displace the palatines in forming the anterior border 

of the internal nares. Most of this pterygoid hypertrophy can 

be correlated with the development of the pterygoid sinuses. 

Fraser and Purves (1960:12) used the term “false choanae” in a 

discussion of Boenninghaus’ (1904) treatment of the naso-pharyngeal muscle mass that rises into the nose through the “false 

choanae,” which appear to be the internal bony nares. Anderson 

(1879:451) referred to the internal bony nares as the “internal 

nasal aperture.” Vesalius (1543:53; Vesalius et al., 1998:131) 

referred to the internal nares [posterior nares] as the “ampla 

narium foramina septo quodam insigni x notato interstinct, and 

in fauciam amplitudinem e naribus tedentia.”

The terms “spiracle” and “spiracular” have had ambiguous use in cetacean anatomy. Spiracle is an uncommon but occasionally used term for the cetacean blowhole. The spiracular 

plate of the premaxilla (premaxillary sac fossa of our use) is a 

bony structure associated with the bony external nares, with the 

implication that nares equate to spiracles. The term “spiracular 

surface of the vertex” as used in ziphiids (Heyning, 1989a) refers 

to the nasal process of the premaxilla or the posterodorsal portion of the premaxilla near the vertex of the skull. Spiracle is also 

applied to the first gill opening in fish (Romer, 1962). Accord-
a l e x i c o n n u m b e r 6 2 7 • 1 5 7

ingly, we consider the terms “spiracle” and “spiracular” to be 

too ambiguous to apply to Tursiops.

Nasal Cavity

The nasal cavity (cavum nasi) in mammals (Gray, 1918:994; 

Evan and Christensen, 1979:158; Schaller, 1992:14.1, 176.1; Feneis, 1994:32.1, 134.18) consists of the facial part of the respiratory tract. The nasal cavity is the space between the external 

nares and the choanae and is lined by the premaxillae, maxillae, 

frontals, nasals, vomer, ethmoid, palatine, and pterygoids. Vesalius (1543:25) referred to the nasal cavity as the narium.

The nasal cavity in odontocetes has moved posterodorsally 

in the skull in response to demands of an aquatic existence. In 

delphinids the external bony nares are formed of the premaxillae, maxillae, frontals, and nasals. The nasal passage is lined 

by the mesethmoid, palatines, vomer, and the pterygoids. The 

choanae consist of the posterior borders of the pterygoids and 

the vomer.

Basipharyngeal Canal

The basipharyngeal canal or choanal region in the dog 

(Evans and Christensen, 1979:153, 154) is the osseous part of 

the nasal pharynx that extends from the choanae to the caudal 

borders of the pterygoids, with contributions from pterygoid, 

palatine, vomer, basisphenoid, and presphenoid. Wible et al. 

(2005) stated that the basipharyngeal canal is the nasopharyngeal passage behind the choanae.

Tursiops has a basipharyngeal canal that is bounded dorsally and laterally by the pterygoids and vomer; the lateral borders of the basipharyngeal canal are the pharyngeal crests behind 

which lie the basioccipital crests. See also entopterygoid crest.

Paranasal Sinuses

Cetaceans have lost the paranasal sinus system (frontal, 

maxillary, and sphenoid sinuses). This may have been the result 

of the posterior movement of the nasal passages or the development of the pterygoid sinus system.

Arterial Circulation and Basicranial Foramina

In many mammals the internal carotid artery supplies the 

brain via the promontorial and stapedial arteries (McDowell, 

1958:122; Novacek, 1986; Wesley-Hunt and Flynn, 2005). Both 

the latter arteries traverse the middle ear and may leave distinct 

sulci on the periotic bone (petrosal), the tympanic bulla, and 

nearby bones (McDowell, 1958; Novacek, 1986). In contrast 

to many eutherian mammals, the internal carotid circulation 

in Odontoceti and Mysticeti is greatly reduced (Boenninghaus, 

1904; Walmsley, 1938:141), and the main supply to the brain is 

Table 9. Terminology for narial openings used by selected authors. Page numbers refer to the citation given in the first column; a dash 

(–) indicates opening not mentioned in the citation.

 Narial terminology

 External Bony opening at Bony opening at

Author, date opening premaxillae and nasals palatines and pterygoids

Bianucci, 2001 — External nares Internal nares

Evans and Christensen, 1979 Nostril or nares, p. 507 External nasal opening or piriform Choanae, p. 514; succeeded

aperture, p. 150; bony nasal posteriorly by basipharyngeal canal

aperture, p. 508 or choanal region, pp. 153–154

Flower, 1868, Physeter — Blowhole, p. 317 —

Flower, 1872 — Superior narial aperture, p. 217 —

Flower, 1885 — Anterior nares, p. 124 Posterior nares, p. 124

Fordyce, 1994 — Bony nares Choanae (posterior nares)

Fordyce, 2002 — External nares Internal nares (choanae)

Fraser and Purves, 1960 Blowhole Nares, p. 107 Bony nares, pp. 11, 20; bony 

nasopharynx, p. 12; choanae, p. 37; 

posterior nares, p. 68

Geisler and Sanders, 2003 Blowhole External bony nares, p. 36 Internal bony nares

Ichishima and Kimura, 2001 — Bony nares —

Lambert, 2005 Blowhole Bony nares Choanae

Luo et al., 2002 — — Internal choanae, char 241.

Morgane et al., 1980 Blowhole Bony nares, p. 15 —

de Muizon and Domning, 2002 — Bony nares Choanae

Schulte, 1917 Blowhole Nares, p. 371; nostril, p. 371ff. —

True, 1910 — Blowhole, p. 13; superior orifices of —

nares, p. 26; anterior nares, p. 50

Wible and Gaudin, 2004 — External nasal aperture, p. 119 Choanae or internal nasal aperture
1 5 8 • smithsonian contributions to zoolog y the therian skull

via spinal meningeal arteries (e.g., Viamonte et al., 1968:1233; 

Vogl and Fisher, 1981a). The internal carotid artery has been 

shown (Vogl and Fisher, 1981b) to be nonpatent in Monodon, 

while angiograms for Tursiops show that the internal carotid 

artery forms a truncated and atrophied system that extends to 

the base of the skull but does not supply the brain directly (Viamonte et al., 1968:1231). The internal carotid artery has not 

been shown, by corrosion casting or angiograms, to be patent 

in other living species. Nevertheless, the carotid foramen of the 

sphenoid is consistently patent in Neoceti, even in species (e.g., of 

Kogia) in which the skull base is modified to become extremely 

disparate from other eutherian mammals. Further, the internal 

carotid artery can sometimes be traced through the carotid foramen and into the braincase in Cetacea (J. G. Mead, pers. obs.), 

although it is not known if the internal carotid artery in such 

cases is patent.

Also of note, the stapedial foramen is reduced and often 

nonpatent in Odontoceti (Doran, 1878) and, in contrast to some 

other mammals (McDowell, 1958), is unlikely to transmit a stapedial artery. In Mysticeti the stapedial foramen is commonly 

patent but small (Doran, 1878). Stapedial circulation is relevant to endocranial supply, because, according to McDowell 

(1958:126), the mammalian stapedial artery may have a branch, 

the middle meningeal artery, that enters the braincase via the 

foramen spinosum. If the middle meningeal artery is a branch of 

the stapedial artery, it seems, given a reduced or absent stapedial 

artery in Cetacea, that the so-called foramen spinosum may be 

misidentified. However, Fraser and Purves (1960:26) noted that 

“in terrestrial mammals the middle meningeal artery is a conspicuous branch of the first portion of the internal maxillary, and 

anastomoses with the internal carotid. In at least one of the injected specimens evidence of an intra-cranial blood supply from 

this source has been established; and it cannot be assumed that 

this artery has atrophied, notwithstanding the apparent atrophy 

of the internal carotid.”
Figures
1 6 0 • smithsonian contributions to zoolog y the therian skull

Figure 1. Intact skull of adult specimen, dorsal view (USNM 550403).

vomer

premaxilla

maxilla

squamosal

supraoccipital

exoccipital

parietal

frontal

nasal

ethmoid

antorbital notch

dorsal infraorbital

foramen

premaxillary foramen

maxillary crest

mesorostral canal

porcelanous part

nasal fossa

frontal 

suture

external bony

 nares

frontomaxillary

suture

nuchal crest

nasal septum

5 cm
a l e x i c o n n u m b e r 6 2 7 • 1 6 1

Figure 2. Intact skull of adult specimen, ventral view (USNM 550403).
1 6 2 • smithsonian contributions to zoolog y the therian skull

Figure 4. Intact skull of adult specimen, anterior view (USNM 550403).

preorbital 

process of

lacrimal

frontal

ethmoid

nasal

premaxilla

maxilla

palatine

pterygoid

jugal

tympanic bulla

basioccipital

parietal

squamosal

exoccipital

ascending process 

of maxilla

orbit

vertex

temporal

arch

pyramidal process

pterygoid sinus 

supramastoid 

crest

retroarticular or 

postglenoid notch

temporal

crest

parietal

notch

supraoccipital

interparietal

maxilla

retrotympanic or 

postglenoid process

temporal 

fossa

preorbital 

process of

frontal

5 cm

Figure 3. Intact skull of adult specimen, lateral view (USNM 550403).
a l e x i c o n n u m b e r 6 2 7 • 1 6 3

external occipital 

protuberance

external occipital 

crest

opisthion

dorsal condyloid 

fossa

nuchal crest

parietal

squamosal

supraoccipital

temporal 

crest

occipital 

condyle

ventral condyloid 

fossa

intercondyloid 

notch/incisure

foramen 

magnum pterygoid

paroccipital 

process

exoccipital

basion

basioccipital

frontal

supraoccipital/

exoccipital suture

supraoccipitalinterparietal 

suture

interparietal

nuchal plane

parietosupraoccipital 

suture

5 cm

Figure 5. Intact skull of adult specimen, posterior view (USNM 550403).
1 6 4 • smithsonian contributions to zoolog y the therian skull

Figure 6a–f. Intact neonatal skull (USNM 550835). (a) dorsal view, (b) ventral view, (c) right lateral view, (d) anterior view, (e) posterior view, 

(f) ventral view with tympanoperiotics in place (USNM 500851).

b

a d

e

c f

lacrimal

parietal

supraoccipital interparietal

nasal

exoccipital

squamosal pterygoid

maxilla

premaxilla

frontal

palatine

supraoccipital

exoccipital

basioccipital

basioccipital

interparietal

interparietal frontal

maxilla

nasal

supraoccipital

parietal

exoccipital

squamosal

pterygoid

palatine

vomer

nasal frontal

premaxilla

tympanic 

bulla

pterygoid basioccipital

alisphenoid

orbitosphenoid

presphenoid

basisphenoid

outer posterior 

prominence

orbital fissure

antorbital 

fossa

falciform 

process

greater palatine 

foramen

palatine 

sulcus

posterior 

process of 

tympanic 

bulla

cranial hiatus

temporal

line

sphenoccipital 

synchondrosis

5 cm
a l e x i c o n n u m b e r 6 2 7 • 1 6 5

Figure 6g–i. Disarticulated neonatal skull (g), right lateral view; anterodorsal views showing some ontogenetic changes in (h) young and (i) 

adult skulls (from Kellogg, 1928, figs. 3, 22; specimen numbers not indicated). 
1 6 6 • smithsonian contributions to zoolog y the therian skull

Figure 7. Disarticulated neonatal skull, basioccipital (USNM 504560).
a l e x i c o n n u m b e r 6 2 7 • 1 6 7

Figure 8. Disarticulated neonatal skull, ethmoid (USNM 504560).
1 6 8 • smithsonian contributions to zoolog y the therian skull

Figure 9. Disarticulated neonatal skull, exoccipital (USNM 504560).

a

posterolateral 

sinus crest

sulcus for intracranial 

extension of spinal 

meningeal arteries

sulcus for the 

sigmoid sinus

c

e

jugular 

notch

foramen 

magnum

d

dorsal 

condyloid 

fossa

dorsal 

condyloid 

fossa

paroccipital 

process

ventral 

condyloid 

fossa

ventral 

condyloid 

fossa

hypoglossal 

foramen jugular 

notch

occipital 

condyle

paroccipital 

process

concavity for 

lobes of 

cerebellum

hypoglossal 

canal

tentorium

paroccipital 

concavity

cerebellar 

juga

jugular notch

tentorium

posterolateral 

sinus fossa

posterior 

sinus crest

hypoglossal 

canal

occipital 

condyle

posterolateral sinus crest

jugular notch

Medial 

exoccipital 

crest

medial 

exoccipital crest

posterolateral 

sinus crest

posterior 

sinus crest

posterolateral 

sinus fossa

paroccipital 

concavity

b

5 cm
a l e x i c o n n u m b e r 6 2 7 • 1 6 9

Figure 10. Disarticulated neonatal skull, frontal (USNM 504560).

a

external surface

ethmoidal 

margin

frontal 

eminence

interparietal 

margin

maxillary surface

nasal 

margin

orbitotemporal crest

parietal margin

postorbital process

preorbital process

supraorbital process

supraorbital margin

sagittal 

margin

b

cerebral 

juga

ethmoidal foramen

ethmoidal 

 margin

fossa for preorbital lobe

 of pterygoid sinus

internal 

surface

interparietal 

margin

ventral orbital 

 crest

temporal 

surface

sagittal 

margin

c

frontal 

eminence

external surface

interparietal 

margin

maxillary 

surface

preorbital process

postorbital 

process

parietal 

margin

temporal 

surface

orbitotemporal 

 crest

supraorbital 

process

d

ethmoidal foramen

ethmoidal margin frontal 

eminence

nasal margin

maxillary 

surface

postorbital process

supraorbital 

process

e

interparietal 

 margin

cerebral 

juga

internal surface orbitotemporal

crest

parietal 

margin

sagittal margin

 supraorbital 

margin

ventral orbital crest

infratemporal crest

infratemporal 

crest

preorbital 

process

orbital part

postorbital 

angle

preorbital angle

cerebronasal 

plate

temporoorbital plate

temporal 

plate

5 cm
1 7 0 • smithsonian contributions to zoolog y the therian skull

Figure 11. Disarticulated neonatal skull, hyoid (USNM 504560).
a l e x i c o n n u m b e r 6 2 7 • 1 7 1

Figure 12. Disarticulated neonatal skull, interparietal (USNM 504560).
1 7 2 • smithsonian contributions to zoolog y the therian skull

Figure 13. Disarticulated neonatal skull, jugal (USNM 504560).
a l e x i c o n n u m b e r 6 2 7 • 1 7 3

Figure 14. Disarticulated neonatal skull, lacrimal (USNM 504560).
1 7 4 • smithsonian contributions to zoolog y the therian skull

Figure 15. Disarticulated neonatal skull, mandible (USNM 504560).

pogonion

a

b

e

c

alveolar groove

dental 

alveolus

Interalveolar 

septa

coronoid 

crest

coronoid 

process

angle

angular 

process masseteric 

line

mandibular 

canal

coronoid 

crest

coronoid 

process

mandibular 

notch

mandibular 

foramen

pogonion

angle

mandibular 

canal

mandibular 

foramen

masseteric 

line

angle

angular 

process

condyloid 

crest

condyloid 

crest

coronoid 

crest

mandibular 

notch

masseteric 

line

mental foramina

buccal 

surface

labial 

surface

mandibular 

condyle

mandibular 

condyle

mandibular 

condyle

mandibular 

condyle

/ ramus

body

d

alveolar 

border

alveolar 

process

condylar 

articular surface

lingual 

surface

labial 

surface

mylohyoid 

groove

pterygoid 

fovea

mylohyoid 

line symphyseal 

surface

ventral 

margin groove 

for 

remains 

of 

Meckel's 

cartilage

base of the 

mandible

mandibular 

foramen

acoustic 

window

gnathion

alveolar 

margin

mandibular 

fossa

5 cm
a l e x i c o n n u m b e r 6 2 7 • 1 7 5

Figure 16. Disarticulated neonatal skull, maxilla (USNM 504560).
1 7 6 • smithsonian contributions to zoolog y the therian skull

Figure 17. Disarticulated neonatal skull, nasal (USNM 504560).
a l e x i c o n n u m b e r 6 2 7 • 1 7 7

Figure 18. Disarticulated neonatal skull, palatine (USNM 504560).

a

b

c

d

e

greater palatine foramen

lesser palatine foramen

maxillary process

nasal crest

nasal spine

ethmoidal crest

sphenoidal process

perpendicular 

lamina

greater palatine 

foramen

maxillary 

process 

nasal 

crest

ethmoidal crest

maxillary 

process

greater palatine foramen

lesser palatine foramen

perpendicular lamina

sphenoidal process

maxillary 

process

lesser palatine 

foramen

greater palatine 

foramen ethmoidal 

crest

ethmoidal crest

nasal crest

nasal spine

sphenoidal 

process

perpendicular 

lamina

sphenopalatine foramen palatine canal

perpendicular 

lamina

free margin

horizontal 

portion 

horizontal 

portion

posterior palatine 

foramen

palatine 

surface

palatine surface

sphenoethmoid 

lamina

nasal surface

orbital process

orbital process

orbital 

process

orbital process pyramidal process

pyramidal 

process

pyramidal process

pterygoid 

sinus 

fossa

pterygoid sinus 

fossa

pterygoid sinus fossa

orbital process

horizontal 

portion

base of 

palatine

lateral lamina

lateral 

lamina

lateral lamina

palatal 

crest

palatal crest

palatal 

crest

maxillary 

process

5 cm
1 7 8 • smithsonian contributions to zoolog y the therian skull

Figure 19. Disarticulated neonatal skull, parietal (USNM 504560).
a l e x i c o n n u m b e r 6 2 7 • 1 7 9

Figure 20. Disarticulated neonatal skull, premaxilla (USNM 504560).
1 8 0 • smithsonian contributions to zoolog y the therian skull

Figure 21. Disarticulated neonatal skull, pterygoid (USNM 504560).

a

c

d

e

b

nasopharyngeal 

surface

medial lamina

lateral lamina

Eustachian notch

medial 

lamina

nasopharyngeal 

surface

pterygoid 

hamulus

Eustachian notch

pterygoid 

hamulus

medial lamina

lateral lamina

pterygoid sinus 

fossa

pterygoid sinus 

fossa

lateral 

lamina

pterygoid hamulus

medial lamina

nasopharyngeal surface

lateral 

lamina

pterygoid 

hamulus

medial 

lamina

palatal 

surface

posterior lamina

palatal surface

dorsal lamina

posterior 

lamina

posterior lamina

dorsal lamina

dorsal 

lamina

5 cm
a l e x i c o n n u m b e r 6 2 7 • 1 8 1

Figure 22. Disarticulated neonatal skull, sphenoid (USNM 504560).
1 8 2 • smithsonian contributions to zoolog y the therian skull

Figure 23. Disarticulated neonatal skull, squamosal (USNM 504560).

a

b

c

d

e

falciform process

falciform 

process

falciform 

process falciform

process

glenoid process

glenoid 

process

mandibular 

fossa

mandibular fossa

mandibular fossa

zygomatic 

process

zygomatic process

zygomatic

process zygomatic 

process

squamosal plate/ temporal surface

squamosal 

plate squamosal 

plate

squamosal plate

tympanosquamosal 

recess

sphenoidal 

margin

retroarticular or postglenoid process

retroarticular or postglenoid notch

occipital margin

occipital process

parietal notch

parietal margin

supramastoid crest

parietal 

margin

retrotympanic process

squamosal 

plate

falciform 

process

glenoid 

process

anterior 

meatal crest

tympanosquamosal 

recess

posttympanic or 

retrotympanic process

5 cm
a l e x i c o n n u m b e r 6 2 7 • 1 8 3

Figure 24. Disarticulated neonatal skull, supraoccipital (USNM 504560).
1 8 4 • smithsonian contributions to zoolog y the therian skull

Figure 25a–c. Disarticulated neonatal skull, tympanoperiotic (USNM 504560).

aperture for cochlear aqueduct

sigmoid process

tympanic notch

conical process

outer posterior prominence

mallear ridge

posterior process of bulla

anterior opening of petrosal canal

posteroexternal 

foramen

cochlear portion

posterior 

process of 

periotic

epitympanic border of 

sigmoid process

accessory ossicle 

anteroventral angle

anterior keel

outer lip

involucrum

median furrow

aperture for 

cochlear aqueduct

musculotubal canal

inner posterior prominence

anterior process 

of periotic

internal acoustic meatus

fossa for stapedial muscle (obscured)

cochlear window (obscured)

anterodorsal angle

sulcus for chorda tympani

b

endocranial opening of 

facial canal

foramen singulare

spiral cribriform tract

aperture for the 

vestibular aqueduct a

c

posterior process of tympanic bulla

anterodorsal crest 

anterodorsal crest

tympanic bulla

area 

cribrosa 

media

semicanal for the

auditory tube

tympanic opening 

for the auditory tube

ventral keel

periotic

periotic

tympanic bulla

tympanic bulla

periotic

20mm
a l e x i c o n n u m b e r 6 2 7 • 1 8 5

Figure 25d,e. Disarticulated neonatal skull, tympanic, right (USNM 504560).
1 8 6 • smithsonian contributions to zoolog y the therian skull

Figure 25f–k. Skull of adult specimen, tympanic, right (USNM 550403).
a l e x i c o n n u m b e r 6 2 7 • 1 8 7

 Figure 25l–q. Skull of adult specimen, periotic, right (USNM 550403).
1 8 8 • smithsonian contributions to zoolog y the therian skull

 Figure 25r,s. Skull of adult specimen, tympanic and malleus, left (USNM 550403).
a l e x i c o n n u m b e r 6 2 7 • 1 8 9

Figure 25t–v. Skull of adult specimen, periotic, left (USNM 550403).

pars cochlearis

posterior process 

of periotic

aperture for cochlear aqueduct

anterior process 

of periotic

stapes in fenestra ovalis

 epitympanic hiatus 

median promontorial groove

anterior incisure

fovea epitubaria

anteroventral angle

fenestra rotunda

aperture for cochlear aqueduct (obscured)

posterior bullar facet

posterior part of facial sulcus

mallear fossa

fossa incudis

anterior part of facial sulcus

broken base of anterior 

pedicle of tympanic bulla

base of tympanohyal

fossa for stapedial muscle (obscured)

distal (external, epitympanic) 

opening of facial canal

internal 

acoustic 

meatus

proximal (internal, cranial) 

opening of facial canal

parabullary ridge

aperture for the 

vestibular aqueduct 

(endolymphatic duct)

parabullary ridge

approximate contact of sigmoid process

approximate contact of 

spiny process of squamosal

approximate position of 

epitympanic hiatus

presumed vestige 

of dorsal crest

foramen singulare

transverse crest

transverse crest 

(partly obscured)

facial crest of periotic

spiral cribriform tract

posterior part of facial 

sulcus (obscured)

base of tympanohyal

fossa for stapedial 

muscle (obscured)

central 

foramen

aperture for the 

vestibular aqueduct 

(endolymphatic duct)

t

u

v

area cribrosa 

media

position of dorsal 

tuberosity 

dorsal vestibular 

area

anterior meatal pit

ventral vestibular 

area

 epitympanic recess 

20 mm
1 9 0 • smithsonian contributions to zoolog y the therian skull

Figure 25w,x. Skull of adult specimen, sectioned tympanoperiotic, right (USNM 571017).
a l e x i c o n n u m b e r 6 2 7 • 1 9 1

y

sigmoid 

process

tympanic

bulla

musculotubal

canal

periotic

triangular 

opening

posterior process

outer posterior 

prominence

conical 

process

parabullary 

ridge accessory 

ossicle

mallear ridge

20 mm

Figure 25y. Disarticulated neonatal skull, tympanoperiotic, left (USNM 504560).
1 9 2 • smithsonian contributions to zoolog y the therian skull

Figure 26a–f. Skull of juvenile specimen, malleus, right (USNM 571036).
a l e x i c o n n u m b e r 6 2 7 • 1 9 3

Figure 26g–l. Skull of juvenile specimen, incus, right (USNM 571036).
1 9 4 • smithsonian contributions to zoolog y the therian skull

Figure 26m–r. Skull of juvenile specimen, stapes, right (USNM 571036).
a l e x i c o n n u m b e r 6 2 7 • 1 9 5

Figure 27. Disarticulated neonatal skull, vomer (USNM 504560).
1 9 6 • smithsonian contributions to zoolog y the therian skull

Figure 28. Disarticulated neonatal skull, basicranium, right, dorsal view (USNM 571622).
a l e x i c o n n u m b e r 6 2 7 • 1 9 7

Figure 29. Disarticulated neonatal skull, bulla, right, ventrolateral view (USNM 571622).

zygomatic process

mandibular 

fossa

falciform 

process

pterygoid

pterygoid

sinus

tympanic

bulla

outer

posterior

prominence

inner

posterior

prominence

basioccipital

exoccipital

squamosal

posterior 

process of 

tympanic alisphenoid

vomer

sigmoid

conical process

tympanic process

aperture

retrotympanic or 

posttympanic process

5 cm
1 9 8 • smithsonian contributions to zoolog y the therian skull

Figure 30. Skull of adult specimen, basicranium, right, ventrolateral view (USNM 501197).
a l e x i c o n n u m b e r 6 2 7 • 1 9 9

Figure 31. Skull of adult specimen, cranium, left, interior view; (a) medial view; (b) dorsomedial view (USNM 571695).
2 0 0 • smithsonian contributions to zoolog y the therian skull

Figure 32. Skull of adult specimen, orbit, left, lateral view (USNM 501197).

jugal

lacrimal

frontal

maxilla

optic canal

inferior orbital 

fissure

pterygoid

Eustachian 

notch

palatine

alisphenoid

foramen 

rotundum

parietal

temporal 

surface of 

squamosal

antorbital 

fossa

frontal groove

temporal

fossa

squamosal 

suture

temporozygomatic 

suture

superior 

orbital fissure

5 cm
Acknowledgments

This project stemmed from a suggestion made in the early 1970s to the senior author by Lawrence Barnes at the Los Angeles County Museum. Barnes suggested 

a detailed osteological study of Tursiops aimed at standardizing the anatomical 

terms.

This work began as a volunteer project for Terrell Stoessell Henke in 1993 while she 

was a student at the Thomas Jefferson High School for Science and Technology in Alexandria, Virginia. Terrell scanned into the computer the cranial osteology sections of the 

Nomina Anatomica and the Nomina Anatomica Veterinaria, put them in a spreadsheet 

and then correlated the terms with material from the anatomical literature.

The success of this work depends on the illustrations and we have been extremely 

fortunate to obtain illustrations and photographs. Trudy Nicolson began by illustrating 

the adult skull (Figures 1–5), and the disarticulated neonate skull (Figures 7–10, 12–24, 

27). Karolyn Darrow illustrated the tympanoperiotic, auditory ossicles, and detailed 

views of the sectioned skull (Figures 25f–q, 26, 28, 29). Both of these illustrators were 

extremely helpful in ensuring that the orientations of the material were correct. Mollie 

Oremland illustrated the medial view of the mandible (Figure 15d) and the hyoids (Figure 

11). John Steiner photographed the tympanoperiotic and the sectioned and intact skulls 

(Figures 6a–f, 25a–e,r–v, 30–32). Parts g–i of Figure 6 are from Kellogg, 1928).

We owe a great debt to the staff of the National Museum of Natural History, in 

particular the Division of Mammals, for the consideration given to this project. Early 

morning discussions with Richard Thorington, a fellow anatomist in the Division of 

Mammals, have proved invaluable. Mary Parrish, an illustrator in the Department of 

Paleobiology, gave us advice and access to the graphics computers in that department in 

the early phases of this project when we did not have our own.

The staff of the Marine Mammal Program, Charley Potter and Bernadette (Dee) 

Allen, provided invaluable support, ranging from assisting with specimens to the informal discussions of anatomical issues that made up the bulk of our work.

We owe a great deal to the rest of our anatomical and cetological colleagues, particularly John Geisler, John Heyning, Zhexi Luo, Ross MacPhee, Sentiel Rommel, Richard Thorington and his assistant James Whatton, Mark Uhen, and Allistair Watson, who 

reviewed all or portions of the manuscript. This work would not be as complete as it is 

without their efforts.

The Office of Fellowships and Grants provided air fare and per diem expenses for 

several visits by Ewan Fordyce to Washington, D.C. The Smithsonian Institution also 

made it possible for James Mead to visit New Zealand with money from the Research 

Opportunities Fund.
2 0 2 • smithsonian contributions to zoolog y the therian skull

The utility of a dictionary is dependent for a large part on 

its consistency. The authors, although they spoke the same language, were working in different dialects of it. We humbly appreciate the excellent editing that we received from the recently 

renovated Smithsonian Institution Scholarly Press under the able 

leadership of Publications Manager Ginger Strader. This work 

owes a lot to the hands-on editorship of Publications Specialist 

Meredith McQuoid and freelance copyeditor Fran Aitkens.

Lastly, the authors thank their wives, Rebecca Mead and 

Marilyn Fordyce, for putting up with this project for so long.
Appendix A

Historical Terminology of the Cranial Nerves

The cranial nerves are of historical and nomenclatorial significance because they 

have played a major role in determining the homologies and evolutionary development 

of the bony framework of the skull. It is helpful to review the historical nomenclature 

of the cranial nerves in order to understand their part in the overall naming of the bony 

structures surrounding them. In many cases the cranial nerves were given numbers according to their position in the longitudinal axis of the brain, and the original numbers 

are retained in this appendix.

Willis, Thomas. 1664. Cerebri anatome. Londini [London]: Tho. Roycroft for Jo. Martyn 

& Ja. Allestry.

1. Olfactory

2. Optic

3. Common motores oculorum

4. Pathetici

5. Trigeminal

6. Abducens

7. Facial + auditory

8. Glossopharyngeal + pneumogastric + accessory

9. Great hypo-glossal

A Society of Gentlemen in Scotland [Bell, A., C. Macfarquar, and W. Smellie]. 1771. 

“Anatomy.” Encyclopedia Britannica, 1st ed., 1:145–310, pls. xiii–xxi. [Cranial 

nerve data extracted from pp. 248–250, pl. xviii.]

First pair: Olfactory

Second pair: Optic

Third pair: Motor oculi

Fourth pair: Pathetici 

Fifth pair: [Trigeminal] (opthalmic, maxillaris superior, maxillaris inferior)

Sixth pair: [Abducens]

Seventh pair: (Portio mollis = vestibulocochlear, portio dura = facial proper)

Eighth pair: Vagus + [glossopharyngeal]

Ninth pair: [Hypoglossal]

Tenth pair: [Spinal accessory]

Handy, Washington R. 1854. “Nerves of Encephalon [Cranial Nerves]” in A Text Book 

of Anatomy, and Guide in Dissections for the Use of Students of Medicine and 
2 0 4 • smithsonian contributions to zoolog y the therian skull

Dental Surgery, pp. 420–425. Philadelphia: Lindsay & 

Blakiston. 

First pair, or Olfactory nerves

Second pair, or Optic

Third pair, or Motores Oculorum

Fourth pair, Pathetici or Trochleares

Fifth pair, Trifacial or Trigemini [opthalmic, superior and 

inferior maxillary]

Sixth pair, Motores Externi or Abducens Oculi

Seventh pair, Portio Dura [facial] and Portio Mollis [auditory]

Eighth pair, Glosso Pharyngeal, Pneumogastric or par 

vagum, Spinal accessory.

Ninth pair, Lingual or Hypoglossal

Chaveau, A., S. Arloing, and G. Fleming (eds.). 1885. The Comparative Anatomy of the Domesticated Animals. 2nd ed., revised and enlarged. New York: D. Appleton and Company, 

trans., ed. by Fleming from the French 2nd ed. of 1872. 

[includes man, horse, cow, sheep, dog; Fleming omitted rabbit and dromedary.]

1. Olfactory

2. Optic

3. Common motores oculorum

4. Pathetici

5. Trigeminal

6. Abducens

7. Facial 

8. Auditory

9. Glossopharyngeal

10. Pneumogastric

11. Accessory

12. Great hypo-glossal

Whitney, W. D. (ed.). 1889. The Century Dictionary and Cyclopedia, 2:1330. New York: The Century Co.

Olfactory

Optic

Motor oculi

Pathetic (trochlear)

Trigeminal (trifacial)

Abducent

Facial

Auditory

Glossopharyngeal

Pneumogastric

Spinal accessory

Hypoglossal

Testut, L. 1905. “Cranial Nerves” in Traite d’Anatomie Humaine

5th ed., 2:862–940. Paris: Octave Doin. [4 volumes: 1. Osteologie, arthrologie, myologie (vi + 1022 pp., 830 figs.); 

2. Angeiologie, system nerveux central (iv + 988 pp., 836 

figs.); 3. System nerveux peripherique, les organs des sens, 

l’appareil de la respiration et de la phonation.; 4. L’appareil 

de la digestion, l’appareil uro-genital, l’embryologie.]

1. Olfactif

2. Optique

3. Moteur oculaire commun

4. Pathetique

5. Trijumeau: trijumeau sensitif, trijumeau moteur

6. Moteur oculaire externe

7. Facial: nerf facial proprement dit, nerf intermediare de 

Wrisberg, 

8. Auditif (acustique): vestibulaire, cochleaire

9. Glosso-pharyngien

10. Pneumogastrique

11. Spinal

12. Grand hypoglosse

Kingsley, J. S. 1912. Comparative Anatomy of Vertebrates, pp. 

165–177. London: John Murray.

I. Olfactory

II. Optic

III. Oculomotorius

IV. Trochlearis

V. Trigeminal (opthalmic, maxillary, mandibular)

VI. Abducens

VII. Facial

VIII. Acustic [sic]

IX. Glossopharyngeal

X. Vagus 

XI. Accessory

XII. Hypoglossal

Parsons, Frederick Gymer. 1911. “Nerve.” Encyclopedia Brittanica, 11th ed., 19:394–400.

Olfactory

Optic

Oculomotor (motor oculi)

Trochlear (pathetic)

Trigeminal (trifacial)

Abducens

Facial

Auditory

Glosso-pharyngeal

Vagus (pneumogastric)

Spinal accessory

Hypoglossal

Hardesty, I. 1933. “The nervous system” pp. 1000–1038 in Morris’ Human Anatomy, 9th ed., Philadelphia: P. Blakiston’s 

Sons and Co. [ex Goss, 1959. p. 1088: Hardesty separated 

the masticatory nerve from the trigeminal, glossopalatine 

from the facial, equilabratory from the acoustic.]

Larsell, O. 1942. “The Nervous System,” in J. P. Schaeffer, Morris’ Human Anatomy, 11th ed., pp. 856–1178. Philadelphia: 

Blakiston Co. [Cranial nerve data is from pp. 1080–1081.]

I. Olfactorius

II. Opticus

III. Oculomotorius

IV. Trochlearis 

V. Trigeminus

VI. Abducens

VII. Facialis

VIII. Acusticus

IX. Glossopharyngeus

X. Vagus 

XI. Accessorius

XII. Hypoglossus
Appendix B

Skull Measurements for Delphinids

One of the reasons for defining skull landmarks is to provide the ability to take consistent measurements in morphometrics analysis. Over the years we have compiled a list 

of the measurements that have proved of value. This list is taken primarily from Perrin 

(1975:9–10).

1. Condylobasal length from tip of rostrum to hindmost margin of occipital condyles.

2. Length of rostrum from tip to line across hindmost limits of antorbital 

notches.

3. Width of rostrum at base along line across hindmost limits of antorbital 

notches.

4. Width of rostrum at 60 mm anterior to line across hindmost limits of antorbital 

notches.

5. Width of rostrum at midlength.

6. Width of premaxillaries at midlength of rostrum.

7. Width of rostrum at 3/4 length, measured from posterior end.

8. Distance from tip of rostrum to external nares (to mesial end of anterior transverse margin of right naris).

9. Distance from tip of rostrum to internal nares (to mesial end of posterior margin 

of right pterygoid).

10. Greatest preorbital width.

11. Greatest postorbital width.

12. Least supraorbital width.

13. Greatest width of external flares.

14. Greatest width across zygomatic processes of squamosal.

15. Greatest width of premaxillaries.

16. Greatest parietal width, within postemporal fossae.

17. Vertical external height of braincase from midline of basisphenoid to summit of 

supraoccipital, but not including supraoccipital crest (not illustrated).

18. Internal length of braincase from hindmost limit of occipital condyles to foremost limit of cranial cavity along midline.

19. Greatest length of left posttemporal fossa, measured to external margin of raised 

suture.

20. Greatest width of left posttemporal fossa at right angles to greatest length.

21. Major diameter of left temporal fossa proper.

22. Minor diameter of left temporal fossa proper.

23. Projection of premaxillaries beyond maxillaries measured from tip of rostrum 

to line across foremost tips of maxillaries visible in dorsal view.
2 0 6 • smithsonian contributions to zoolog y the therian skull

24. Distance from foremost end of junction between nasals 

to hindmost point of margin of supraoccipital crest.

25. Length of left orbit from apex of preorbital process of 

frontal to apex of postorbital process.

26. Length of antorbital process of left lacrimal.

27. Greatest width of internal flares.

28. Greatest length of left pterygoid.

29. Greatest width of anterior overhang of supraoccipital 

crest.

30. Greatest length of bulla of left tympanoperiotic.

31. Greatest length of periotic of left tympanoperiotic.

32. Length of upper left tooth row from hindmost margin 

of hindmost alveolus to tip of rostrum.

33. Number of teeth, upper left.

34. Number of teeth, upper right. 

35. Number of teeth, lower left.

36. Number of teeth, lower right.

37. Length of lower left tooth row from hindmost margin 

of hindmost alveolus to tip of mandible.

38. Greatest length of left ramus.

39. Greatest height of left ramus at right angles to greatest 

length.

40. Length of left mandibular fossa, measured to mesial 

rim of internal surface of condyle.

41. Deviation of skull from symmetry in dorsal view, in degrees.
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Index

A page number in bold type indicates the main entry for a headword in the lexicon. Latin 

terms appear before the identically spelled English terms.

Abducens nerve, 90, 101, 155

Accessory air sinus, 83, 88–89

Accessory meningeal artery, 94

Accessory nerve, 20, 21, 35, 121

Accessory olfactory bulb, 17

Accessory ossicle, 17, 103, 111, 119, 123, 127, 132, 133–135, 140–142, 144–147, 149

of the malleus, 138, 149

of tympanic bulla, 119

Accessory palatine foramen, 58, 71, 73

Accessory palatine foramina, 73

Acoustic foramen, 120

Acoustic pore, 120

of the internal acoustic meatus, 111

Acoustic signals, 154

Acoustic window, 42, 47

Ad palati sinem iuxta maxillae superioris sexta os, 58

Aditus nasomaxillaris, 49, 64

Air cells, 121

ethmoid, 14

Air sinus system, 90

Ala

cristae galli, 14

major, 96

minor, 97

orbitalis, 90, 98

palatina, 71

parva, 90

temporale, 90

temporalis, 90

vomeris, 102, 152–153

Alar canal, 90–91, 93–94, 99–100

Alar process, 11, 12, 91, 152–153

Alicochlear process, 90

Aliform process, 152

Alisphenoid, 11, 18, 24, 60–61, 66, 76, 78, 83, 90–98, 100–102, 105–108, 124–125, 

131, 138, 155
2 1 8 • smithsonian contributions to zoolog y the therian skull

Alisphenoid (continued)

base of, 91

basicranium, 101

border, 76

canal, 90, 91

lateral lamina, 96

portion of the lateral lamina, 91

Alisphenoid/orbitosphenoid suture, 96

Alisphenoidal 

infundibulum, 91

portions of the external plate, 83

region, 91

Aliud foramen inchoatur, recta 

antrorsum ion narium usque 

amplitudinem, 88

Alveolar 

border of the mandible, 42

canal, 49

foramina of the mandible, 42

foramina of the maxilla, 44, 49

groove of the mandible, 42

groove of the maxilla, 56–57

gutter, 42, 79

juga, 42

margin of the mandible, 42

margin of the maxilla, 49

nerve, 49

portion of the mandible, 42–43, 49, 

56

portion of the maxilla, 49, 56

process of the mandible, 42

process of the maxilla, 49

sulcus, 42, 49

vessels, 49

walls, 43

Alveoli dentales, 43

Alveolus, 43–44

Alveolus for the canine tooth, 79

Amastoid, 126

Ampla narium foramina septo quodam 

insigni x notato interstinct, 156

Ampullae, 116

Anastomotic artery, 98, 155

Angle

anterior, 133

basicoccipital, 17

tympanosquamosal recess, 102

anterodorsal, 112

anteromedial, of the tympanic bulla, 

135

anteroventral, of periotic, 112

external mandibular, 44

frontal, 77

inferior anterior external, 77

involucrum, anteromedial, 135

mastoid, 77

occipital of Broca, 77

occipital of Daubenton, 77

of the mandible, 43–44, 46, 47

of the mouth, 45

postorbital, 29

sphenoidal, 78

stylohyoid, 33

tympanic bulla, anteromedial, 135

Angular process, 43, 44, 46–48

external, 25

of the mandible, 43

Angular vein, 27

Angulus

frontalis, 77

mandibulae, 43–44 

mastoideus, 77

occipitalis, 77

sphenoidalis, 78

stylohyoideus, 33

Annulus

tendineous, 133

tympanicus, 133, 140, 146, 148

Anterior

air sinus system, 83

angle, 102, 133, 135

angle of the tympanosquamosal 

recess, 102–103

aperture, 133

apophysis, 133, 141

basi–occipital angle, 17

belly of the digastric, 44

border of the nasal, 68–69

bullar facet, 111–112, 119, 123, 131, 

133, 135, 142

bullar lip, 133, 141

bullar process, 133

bullar septa, 135

canal, 128

carotid foramen, 91

chamber of the tympanic cavity, 136

clinoid process, 99

condyloid foramen, 17

conical process, 133–134, 144

cranial fossa, 100

crus, 140, 142, 146, 

of the stapes, 151

of the tympanic ring, 134

diverticula, 135

division, 146

entrance of the tympanic cavity, 134

ethmoidal cells, 15

face, 69

face of nasal, 68

fissure of the facial foramen, 111, 

120, 124

incisure, 111, 122–123, 125

keel, 111–112

lacerate foramen, 23, 91, 95, 138

lacrimal crest, 5, 38, 41, 49, 62

lacrimal process, 38

lamina, 112

lobe, 49, 83, 84 154

lobe of pterygoid sinus, 156

maxillary sinus, 49, 63, 66

meatal crest, 102–103

meatal pit, 112

narial wall, 156

nasal spine, 79–80

notch for the eustachian tube, 134, 

141

notch of the tympanic cleft, 134, 141

opening 

infraorbital canal, 50

petrosal canal, 120

tympanic cavity, 134

orifice of the bulla, 134

osseous pedicle, 134

ossicle, 140

pedicle, 133, 134, 145

perforated substance, 17

pneumatic cavities, 83

process, 24, 36, 68, 70, 103, 111–

112, 114, 119, 121, 124–125, 

127–128, 130, 132, 134–135, 

138, 140, 146, 149–150, 155

(conical) of the tympanic bulla, 

134

ectotympanic, 111, 138

external lip of auditory bulla, 134

frontal, 28

jugal, 36–37, 39

malleus, 138, 140, 149

nasal, 68, 70

periotic, 105, 111, 112, 119, 

121–123, 127, 130, 132

tympanic bulla, 106, 111, 133, 

134, 145

tympanosquamosal recess, 103

zygomatic, 37

pterygoid sinus, 83

sac, 49, 83

septa, 136

septum, 136, 145

sinus, 41, 49, 64, 83, 89

sinus fossa, 41, 49–50, 58, 61, 64

spine, 134, 141

spine of the tympanic bulla, 134

surface of nasal, 68

surface of the maxilla, 49

tympanic spine, 134, 138, 144

Antero-internal facet, 37

Anterodorsal angle, 111, 112, 115, 127

Anterodorsal border of nasal, 68–69

Anterodorsal crest

nasal, 68

tympanic bulla, 103, 134, 135, 142, 

144, 149

Anterodorsal groove, 68

Anteroexternal sulcus, 105, 112, 116, 

119, 128, 130

Anterointernal sulcus, 112, 132
a l e x i c o n n u m b e r 6 2 7 • 2 1 9

Anterolateral convexity, 133, 135, 142

Anterolateral part of the frontal sinus, 24

Anteromedial 

angle of the involucrum, 135

angle of the tympanic bulla, 135, 

140

process of the tympanic bulla, 135

sulcus, 79, 81

Anteroventral 

angle, 111, 112

part of the nasal, 69

surface of the nasal, 69

Antorbital 

angle, 49

depression, 50

eminence, 51

foramen, 49, 50, 59, 67, 68

fossa, 27, 29, 32, 41, 50, 58–59, 

61–62, 65–67, 71–76, 89, 99, 

100

fossa of maxilla, 38

maxillary tuberosity, 50

notch, 36–39, 50–51, 56–57, 59, 

61–63, 65–68, 82, 154

external, 50

internal, 50

pit, 38–39, 50

pit of the lacrimal, 38

portion, 36

process, 36, 38, 39, 49, 50, 51–56, 

63

of the jugal, 36, 37, 38

of the lacrimal, 36, 37, 38–39, 

206

[new context], 38

of the malar, 36, 52

of the maxilla, 38, 50, 51, 56, 

prominence, 51, 66

protuberance, 51

region, 39, 154

sinus fossa, 41

tubercle, 50–51, 56, 61

tuberosity, 51

vacuity, 39

Antrum, 56, 135–136, 140

fenestra rotunda, 112

tympanicum, 131

Apertura

externa aqueductus vestibuli, 117

externa canaliculus cochleae, 117

nasalis anterior, 79

nasi ossea, 79

petrotympanicus, 116

piriformis, 79

sinus frontalis, 27

sinus lacrimalis, 39

sinus sphenoidalis, 100

tympanica, 146

tympanica canalis facialis, 116, 118

Aperture

anterior, 133

auditory, 135

cochlear aqueduct, 112–113, 117, 

118

endolymphatic duct, 113, 115

epitympanic, 116

Eustachian tube, 135, 137, 141

external for cochlear canaliculus, 117

external for vestibular aqueduct, 117

facial canal, 112

frontal sinus, 24, 28

lacrimal sinus, 39, 40

major petrosal nerve, 120

paroccipital pneumatic sinus, 135

posterior for the sinus pneumaticus 

paroccipitalis, 135, 137

sphenoidal sinus, 100

tympanic of facial canal, 131

upper tympanic, 131

vestibular aqueduct, 113, 116–117, 

119, 127, 132

Apex

partis petrosae, 113

pyramidalis, 113

Apex of 

pyramid, 113

manubrium, 150

tubercule of the malleus, 150

Apical turn of the cochlea, 115

Apophyse

conique anterieure, 134

conique postérieure, 136

mammilaris, 122

Apophysis

anterior, 133

conical, 136

postmeatal, 105

Apparatus hyoideus, 32

Aquaeductus [Aque-]

cochleae, 113

cochlearis, 113

endolymphaticus, 113

Fallopii, 117

vestibuli, 132

Aqueduct

cochlea, 113, 115

Fallopian, 117

Fallopius, 113

vestibular, 132

Arcade

laryngeal, 12

Arch

superciliary, 31

temporal, 107

Arcuate eminence, 113, 122

Arcus

alveolaris, 42

superciliaris, 31

Area

cochleae, 113

cribrosa media, 113

nervus facialis, 113, 117

vestibularis inferior, 113

vestibularis saccularis, 132

vestibularis utriculo-ampullaris, 116

Area

dorsal vestibular, 116

lacrimal, 61

suprameatal, 130

ventral vestibular, 132

vestibular, 132

Arterial circulation and basicranial 

foramina, 29

Artery

external carotid, 94

Articular, 42

bone, 149

cavity, 104

condyle, 45, 108

facet, 151

peg, 113

process, 45, 

periotic, 107, 113

squamosal, 102, 104

rim, 113

surface, 104, 132, 148, 151

ethmoid, 25

incus, 151

malleus, 150

squamosal, 103

Articular tubercle of the squamosal, 60, 

103

Articulating condylar process of the 

mandible, 43, 47

Articulatio temperomandibularis, 108

Ascending pharyngeal 

artery, 20

branch, 131

Ascending plates of the maxillaries, 56

Ascending process, 34, 36, 50, 56, 58, 

62, 65, 67, 79

jugal, 36

frontal, 24, 28

maxilla, 26, 28, 41, 48, 56, 58, 62, 

67, 154

palatine, 38

Ascending ramus, 47–48

Ascial process, 135, 140

Asperitas, 107

Asterion, 77

Attic, 113

Auditorii meatus, 137

Auditorius [externus] meatus dissectus, 

137

Auditory (Eustachian) tube, 114

Auditory 

aperture, 135
2 2 0 • smithsonian contributions to zoolog y the therian skull

Auditory (continued)

bulla, 101

capsule, 125

cavity, 145

nerve, 18, 124

nerves, 124

ossicles, 149, 155

plates of the basisphenoid, 91

region, 13, 87

tube, 83, 85, 89, 97, 101, 114, 117, 

122, 137, 141, 145, 147–148, 

156

Auditus organum petit ac aer etiam in 

temporis os, 137

Auditus ossicula, 149

Auricular branch of the vagus nerve, 

114, 121

Autonomic nerve of the pterygoid canal, 

88

Basal 

laminae, 15

pedicle, 135

process, 11–12

turn of the cochlea, 115, 133

Base, 71

alisphenoid, 91

mandible, 43

palatine, 71–72

stapes, 151

tympanohyoid, 33, 131

vomer, 152

Basicapsular 

fenestra, 19, 23

fissure, 19, 114, 118, 132 

Basicochlear fissure, 19, 23, 114

Basicranial region, 12

Basicranium, 18, 107, 109, 129, 155, 156

Basihyoid, 32–33

Basihyoideum, 3, 32

Basilar part, 11

Basin

circumnarial, 57

prenarial, 82

supracranial, 67

Basioccipital, 7, 11, 12, 17–21, 77, 83, 

86-87, 90–92, 94–95, 101, 111, 

121, 124, 141, 148, 155

arcade, 12

crest, 11–13, 18, 20–22, 86–87, 157

falcate process, 18

process, 11

ridge, 12

Basioccipitosphenoid, 91

Basion, 12, 18, 77–78

Basipharyngeal canal, 85–86, 157

Basirostral groove, 56, 62

Basis

mandibulae, 43

stapedis, 151

Basisphenoid, 11, 12, 14, 75–76, 82–83, 

88, 90, 91–97, 99–102, 111, 125, 

135, 156

pterygoid process, 90

Basisphenoid–presphenoid 

cleft, 92

fissure, 92

Basisphenoidal 

otocranial plate, 12

sinus, 83, 84, 86, 91, 156

Blowhole, 156

Body, 45

alisphenoid, 97

incus, 151

mandible, 43, 48

maxilla, 56

palatine bone, 71

periotic, 114, 117, 123–124, 

127–128, 130, 132–133

premaxilla, 79

sphenoid, 66, 92, 97

Bony 

external auditory meatus, 145

external nares, 156

infundibulum of the foramen ovale, 

91, 94

nares, 79

narial passage, 76

nasal septum, 70, 152

nasopharynx, 83, 85

palate, 75

part of the auditory tube, 127

tentorial ossification, 110

tentorium, 110

tympanic tube, 135, 141

Border, 

alisphenoid, of the parietal, 76

alveolar, of the mandible, 42

caudal, of the palatine, 71

choanal, 71, 73

exoccipital, of the parietal, 76

free, of the palatine, 71

free, of the parietal, 76

frontal, of the parietal, 77

frontal, of the sphenoid, 95

infraorbital, of the jugal, 36

infraorbital, of the maxilla, 59

interparietal, of the parietal, 77

lacrimal, of the jugal, 36

masseteric, of the jugal, 36

maxillary, of the jugal, 37

occipital, of the parietal, 77

parietal, of the sphenoid, 98

postglenoid, 105

rostral, of the lacrimal, 42

sagittal, of the parietal, 78

squamosal, of the sphenoid, 101

squamous, of the parietal, 78

supraoccipital, 78

temporal, of the jugal, 37

ventral, of the petrosal bone, 132

zygomatic, of the sphenoid, 102

Brain, 57, 154

Braincase, 27, 139, 158

Bregma, 31, 77

Bridge

petromastoid, 124

suprameatal, 107

Brow ridges, 31

Buccal surface of the mandible, 43–44

Bulla

ethmoidalis, 15

lacrimalis, 39

tympanica, 133, 147

Bulla, 116, 124, 133, 134, 135–149

ethmoid, 15

lacrimal, 39

Bullar 

cavity, 135, 147

facet, 111

process of exoccipital, 18–19, 103, 

141

septum, 135, 145

Calvariae basim, 155

Canal

acoustic nerve, 114

alar, 90

alisphenoid, 91

alveolar, 49

auricular ramus of the vagus, 114

caroticotympanic, 92

carotid, 92, 135

chorda tympani, 114

craniopharyngeal, 93

dental, 44

facial nerve, 114, 120

facial within tegmen tympani, 117

hypoglossal, 19

incisive, 79

incisivomaxillary, 59

inferior dental, 44

infraorbital, 59

internal auditory, 121

jugulo-acoustic, 21

lacrimal, 39, 61

lesser petrosal nerve, 114

major superficial petrosal nerve, 114

mandibular, 45

mesorostral, 80

minor palatine, 73

musculotubal, 97

optic, 97

orbitotemporal, 29

palatine, 74

palatine vessels and nerves, 65

periotic, 124
a l e x i c o n n u m b e r 6 2 7 • 2 2 1

petrobasilar, 124

petrooccipital, 124

petrosal, 124

posterior palatine, 75

posttemporal, 127

pterygoid, 88, 99

pterygopalatine, 75

secondary internal auditory, 23

sphenopalatine, 76

spiral, 128

stapedial muscle, 114

stylomastoid, 128

suborbital, 67

supraorbital, 31

tensor tympani, 127

transverse, 111

trigeminal nerve, 114, 118, 122, 

124–125

vertical, 132

vestibulocochlear nerve, 113, 120

Canales palatini minores, 73

Canalicular part, 123

Canaliculus

caroticotympanicus, 92

chordae tympani, 114

cochleae, 115

mastoideus, 121

tympanicus, 131

Canaliculus

cochlear, 115

mastoid, 121

tympanic, 131

Canalis

alaris, 90–91

alveolaris, 49

caroticus, 135

condylaris, 18

craniopharyngeus, 93

facialis, 117

hypoglossi, 19

incisivus, 79

infraorbitalis, 59

lacrimalis, 39, 61

mandibulae, 45

musculotubarius, 97, 141

n. hypoglossi, 19

n. petrosi majoris, 114

n. petrosi minoris, 114

n. trigemini, 114

nasolacrimalis, 41

opticus, 97

palatinus major, 74

perioticus, 124

petrooccipitalis, 124

petrosus, 124

pterygoideus, 88, 99

reuniens, 128

sinus transversis, 111

supraorbitalis, 31

Canine, 48, 79

alveolus, 59

eminence, 56

fossa, 56

tooth, 79

Capita occipitii ossis, 21

Capitis mallei, 121

Capitulum

inferioris maxillae, 45

mallei, 150

stapedius, 151

Capsule

otic, 123

periotic, 124

Capsuloparietal emissary vein, 105

Caput, 154

mallei, 150

mandibulae, 45

stapedis, 151

Caroticotympanic canal, 92

Carotid 

artery, 92, 129

canal, 92–93, 102, 124–125, 131, 

135, 138–139, 145

circulation, 92

foramen, 90, 92–93, 96, 101–102, 

125, 135, 139, 158

groove, 93

notch, 92

sulcus, 92–93

Cartilage

mesorostral, 16

Cartilaginous 

nasal septum, 16, 79, 81, 152–153

vomer, 16

Cartilago septi nasi, 152

Caudal 

alar foramen, 90–91, 93–94

border of the palatine, 71

carotid foramen, 92, 93, 98–99, 135

clinoid process, 92, 93, 99

crus of the stapes, 151

frontal sinus, 24

lateral nasal arteries, 71

lip of tympanic bulla, 135, 145

maxillary sinus, 56, 67

meningeal artery, 120

nasal nerve, 76

palatine foramen, 65, 76

ridge of sigmoid process, 136

squamosal foot, 136, 140

tympanic process of the periotic, 

114–115, 125, 131

Cavernous sinus, 95, 132, 139

Cavitas

inter duas frontis os, 27

tympani, 147

Cavities

anterior pneumatic, 83

Cavity

bullar, 135

for the zygomatic articulation, 57, 68

glenoid, 103

postnarial, 65

supracochlear, 130

Cavum

epitympanicum, 136

nasi, 157

supracochleare, 128

tympani, 147

Cecum

foramen, 25

Cells

mastoid, 121

Cellulae ethmoidales, 14

Central 

caudorostral ridge, 68–69

plate of the mesethmoid, 16

Ceratohyoid, 32, 33

Ceratohyoideum, 33

Cerebellar 

fossa, 19, 114, 120, 125, 129, 155

juga, 18, 24–25

surface of the petrosal, 114–115

tentorium, 110

Cerebellum, 18, 24, 108, 110, 111, 

114–115, 129, 155, 168

Cerebral 

area, 57

foramen of the facial canal, 127

fossa, 108–109, 155

hemispheres, 155

hollow, 93

juga, 18, 24–25

opening of the facial canal, 117

part of the periotic, 18

surface, 

alisphenoid, 96

basisphenoid, 92–93

frontal, 96

maxilla, 57

parietal, 96

petrosal, 113–114, 132

sphenoid, 93

squamosal, 96

Cerebronasal plate of the frontal, 

24–25, 32

Cerebrum, 24, 26, 108, 109

Cetolith, 124

Cetotolite, 124

Channel

dorsoventral vascular of periotic, 116

transverse vascular, 130

Charactibus, 21

Cheek bone, 35

Chiasmatic groove, 93, 96–97

Choana, 73, 83, 89, 107, 156, 157

border, 71–73
2 2 2 • smithsonian contributions to zoolog y the therian skull

Choana (continued)

crest of vomer, 152–153

false, 85

fossa, 83, 86

passage, 86

region, 157

Chorda tympani, 114, 129, 136, 138, 

140, 146

Chordafortsatz, 136, 146

Circumnarial basin, 19, 57, 67

Cirque faciale, 62

Cleft

premaxillary, 81

Clinoid process, 93

Clivus, 12

Cochlea, 90, 111, 115, 122–124, 128, 

133, 155

Cochlear 

aqueduct, 113, 115, 123

canaliculus, 112–113, 115

duct, 128

fossula, 115, 118

nerve, 122, 128

part, 123

portion, 112, 115, 123–124, 127, 130

posterior pole, 115

process, 111, 115, 125

window, 112, 115, 117–118, 124, 128

Collum

mallei, 150

mandibulae, 45

processus cornualis, 28

Common 

carotid artery, 94

inferior outlet, 59

Compound posterior process, 136

Concavity 

for lobes of cerebellum, 18, 23

caudal lip of the bulla, 136

involucrum of the bulla, 136

lobes of cerebellum, 18

paroccipital, 21

Conch

middle nasal, 16

Concha

nasalis dorsalis, 14, 16

nasalis media, 16

nasalis suprema, 17

sphenoidalis, 100

Concha

dorsal nasal, 14

sphenoidal, 100

supreme nasal, 17

ventral nasal, 17

Conchal crest, 57, 71

Condylar 

articular surface, 43

canal, 18

foramen, 18

plate, 43, 47

process of the mandible, 43, 45, 47

Condyle, 43, 47

mandibular, 45

occipital, 21

oval, 21

third, 13

Condyloid 

articular process, 43

canal, 18–20

crest, 43, 46

foramen, 18, 20

fossa, 18–19

process of the mandible, 43, 45, 104

Condylus

occipitalis, 21

tertius, 13

Confluence 

rhinal veins, 109

sinuses, 109

Confluens sinuum, 109

Conglutinationem squamaeformem, 

106

Conical 

apophysis, 136

process (of the tympanic bulla), 134, 

135, 136––146, 148

Convexity

anterolateral, 135

Cornu

majus, 33

minus, 33

Cornual process, 25

crown, 25

neck, 28

Corona processus cornualis, 25

Coronal suture, 25

Coronoid 

crest, 43, 46–48

process, 42, 43, 45, 47

Corpus, 32, 91

incudis, 151

mandibulae, 43

maxillae, 56

ossis incisivi, 79

Crêtes frontales, 62

Cranial 

aperture, 94

carotid foramen, 135

cavity, 18, 91–94, 108, 115, 130

foramen ovale, 95

hiatus, 12, 18-20, 22–23, 91, 94, 98, 

114, 124–125, 147, 156

margin, 132

nerve 0, 17

nerve VII, 18

nerve VIII, 18

nerve IX, 18–19, 22

nerve X, 19, 22

nerve XI, 19, 22

nerves, 18

surface, 57, 117

periotic, 115

petrosal, 120, 122, 125

wall, 18

Craniopharyngeal canal, 93

Cranium, 76, 90, 106, 108, 148, 152, 

154–155

lateral walls, 76

roof, 76

Crest

anterior meatal, 102

anterior lacrimal, 49

anterodorsal, 135

basioccipital, 11

conchal, 57, 71

condyloid, 43

coronoid, 43

dorsal, 115

ethmoidal, 57

ethmoidal of nasal, 69

ethmoidal of palatine, 71

external frontal, 25

external occipital, 109

external sagittal, 76, 109

facial, 58

facial of periotic, 117

falcate of exoccipital, 19

frontal, 26

great occipital, 109

incisor, 80

infratemporal, 27, 96

interfrontal, 27

internal frontal, 27

internal occipital, 110

internal sagittal, 34

lambdoid, 34

lateral nasal, 80

maxillary, 62

maxillofrontal, 41

median petrosal, 122

mylohyoid, 46

nasal, 64, 73

nasoturbinate, 70

nuchal, 34

occipital, 35, 64

orbital, 41

orbitosphenoid, 98

orbitotemporal, 29

palatal, 74

palatine, 74

petrosal, 125

pharyngeal, 13, 87

posterior 

cochlear, 125

lacrimal, 41

meatal, 105

posterolateral sinus, 22
a l e x i c o n n u m b e r 6 2 7 • 2 2 3

precoronoid, 47

premaxillary, 81

prominential, 66

pterygoid, 99

sagittal, 110

sphenoidal, 100

subtemporal, 96, 107

supramastoid, 107

supraoccipital, 110

supraorbital, 31

supratemporal, 67

temporal, 107

tentorial, 24

transverse, 130

ventral concha, 57, 71

ventral ethmoidal, 67

ventral orbital, 32

zygomatic process, 107

Cribri instar foraminibus, 14

Cribriform 

foramina, 14

plate, 13, 14–17, 25, 93, 100

Cribriformia ossa, 14

Crista

choanalis vomeris, 152

conchalis, 17, 57, 63, 71

ethmoidalis, 57, 69, 71

ethmoidalis dorsalis, 57

ethmoidalis ventralis, 67

facialis, 58, 117, 127

petrosi, 117, 131

falciformis, 113, 115, 130

frontalis, 26

externa, 25

interna, 27

galli, 13, 14, 99

infratemporalis, 96

interfenestralis, 115

lacrimalis

anterior, 49

posterior, 41

nasalis, 64, 73

nuchae, 34

occipitalis

externa, 109

interna, 110

orbitalis

inferior, 32, 60

superior, 29, 96

ventralis, 32

orbitosphenoidalis, 98

orbitotemporalis, 29

palatina, 74

parotica, 115, 117, 119, 127

partis petrosae, 115, 117, 122

periotica, 115

pterygoidea, 99

sagittalis

externa, 34, 76, 109

interna, 34

sphenoidalis, 100

supramastoidea, 107

tentorica, 24

transversa, 130

tympanica, 136, 145, 147, 148

vestibuli, 115

vomeris, 152–153

Cristati processus, 14

Crown, 32

cornual process, 25

Cruciate eminence, 109

Cruciform eminence, 109

Crus

anterius, 151

breve, 151

longum, 151

posterius, 151

Crus

ectotympanic ring, anterior, 134

Cuneiform os, 90

Dacryon, 39

Dactyloid process, 103

Dental 

alveolus, 42, 43, 48–49, 67

canal, 44–45

foramen, 44–45

furrow, 57

groove, 42, 79

portion of the maxilla, 56

sulcus, 42

Dentary, 42

Dentulous bones, 79

Descending 

laminae, 87

palatine artery, 58, 64, 79

process of the lacrimal bone, 15

ramus, 48

Dextrum uerticis os, 76

Diapophyses

mastoid, 104

Diastema, 57, 61

Diastemata, 44

Diastematic ridge, 44

Digastric, 44, 122

fossa, 44

muscle, 104

Digital impressions, 25

Diploe, 25

Distal ganglion of the glossopharyngeal 

nerve, 125

Distal opening 

facial canal, 115, 117, 128

respiratory passages, 156

Distal plate, 136, 143

Distinct ventral rim, 123

Diverticulum, 155

anterior, 135, 136–137, 140, 145

posterior, 136–137, 145

postorbital, 30

Division

posterior of periotic, 125

Dorsal 

acoustic foramen, 116

angle, 112

carotid foramen, 92, 93, 96

condyloid foramen, 18, 19

condyloid fossa, 18, 19

crest of the periotic, 111–112, 

115–116, 125, 127, 129, 

130

edge of the tegmen tympani, 115

ethmoid crest of the maxilla, 57

ethmoidal crest, 57

face of nasal, 68

foramen of the facial canal, 113

infraorbital foramen, 49, 57, 59, 62, 

65, 81

lamina of the ethmoid, 14

lamina of the pterygoid, 83–84, 86

nasal concha, 14, 16, 57, 69–71

nasal meatus, 69

optic process, 93

petrosal sinus, 120

pharyngeal region, 11

process of the jugal, 36

ridge, 115

sagittal sinus, 35

sagittal sinus sulcus, 34

sulcus of the premaxilla, 79, 81

surface of nasal, 68

surface of the maxilla, 57–58

temporal line, 76, 78

tuberosity, 115, 121, 127–128

vestibular area, 116, 132

Dorsolateral ridge of the tegmen tympani, 115, 116

Dorsoventral 

vascular channel, 112, 116, 131

vascular groove, 112, 131

Dorsum sellae, 12, 93, 96, 100

Drum, 148

Duct

endolymphatic, 116

nasopharyngeal, 73

Ductus

nasolacrimalis, 61

petro-tympanicus, 116

ucro & sinus non adeo commode, 93

Dura mater, 12

Eardrum, 147

Ectethmoid, 13, 14

Ectomaxillary groove, 57

Ectopterygoid, 85

crest, 84–85, 88

fossa, 75, 84, 85, 88
2 2 4 • smithsonian contributions to zoolog y the therian skull

Ectoturbinalia, 14

Ectoturbinate, 14

Ectotympanic, 119, 125, 134, 136–137, 

140, 142–143, 145, 147

bulla, 102, 137

part, 102

tympanic bone, 137

wall of the meatus, 136

Elevation

pterygoid, 66

Elliptical 

foramen, 22, 135, 137, 139, 

142–143, 149

recess, 116, 132

Elongated aqueduct, 137

Embryological terms, 4

Eminence

arcuate, 113

criciform, 109

frontal, 26

orbital, 37

parietal, 77

premaxillary, 81

Eminentia

arcuata, 113

cruciformis, 109

maxillae, 63

orbitalis, 37

Emissary 

sphenoidal foramen, 95

vein, 19, 105

Endocranial 

foramen, 95

sulcus of basioccipital, 19

sulcus/foramen for vestibulocochlear 

nerve, 12

Endolymphatic duct, 113, 116, 128, 132

Endopterygoid, 87

crest, 157

Endoturbinalia, 14

Endoturbinate, 14, 17, 100

Endotympanic part, 137

Entocarotids, 92, 93

Entoglenoid 

process, 102, 103, 105–106

region, 103

Entopterygoid, 85, 88–89

crest, 75, 84, 85, 102

Entotympanic bulla, 137

Entrance

tympanic cavity, anterior, 133

Epaxial muscles, 155

Epicranial sinus, 69, 82

Epicranius muscle, 34

Epihyoid, 32, 33

Epihyoideum, 33

Epitympanic 

aperture, 116, 118–119

crest, 137

foramen, 112, 116–119

hiatus, 86, 104, 116, 130–131, 

147–148

opening of the facial canal, 128

orifice, 117

recess, 113, 116, 119, 120–121, 127, 

130, 137, 147, 150–151

sinus, 116

wing,

petrosal, 125

sphenoid, 93, 125

squamosal, 93, 125

Eponymous terms, 5

Ethmoid, 7, 13–14, 17, 25, 57, 67, 

69, 71, 99–100, 109, 152–153, 

155–157

air cells, 14–15

bone, 13–14

foramina, 26

fossa, 69

incisure, 25

ossification, 16

perpendicular plate, 152

Ethmoidal, 57

bulla, 15, 17

conchae, 15

crest, 57, 65, 69, 71, 74, 76, 154

maxilla, 57

nasal, 69

palatine, 71

foramen, 25, 29

fossa, 69

incisure, 25

infundibulum, 15

labyrinth, 14, 15

margin, 25

margin of the frontal, 25

meatus, 15

nerve, 15, 25

notch, 25

process, 15

sinus, 29

spine, 93, 94

vessels, 25

Ethmoturbinal, 15

Ethmoturbinalia, 15

Ethmoturbinate, 13, 14, 15, 100

Eustachian 

apparatus, 83

canal, 141

cavity, 137, 147

end of tympanic cleft, 137

notch, 13, 85–86, 88–89, 114, 137, 

141

outlet, 137, 141, 145

sacs, 83

system, 83

tube, 85, 88–89, 97, 101, 114, 117, 

119, 137, 141, 144, 147, 156

Exoccipital, 7, 11, 12, 17–22, 24, 34, 

36, 76–77, 83, 104–106, 109–

111, 121–122, 124, 126, 129, 

131, 139, 141, 143, 148, 155

border of the parietal, 76, 78

contact, 18, 137, 141

contact of exoccipital, 19

crest, 13

margin, 121

plate, 19

process of the squamosal, 148

protuberance, 18, 19, 137, 141

Extension

lamelliform, 62

orbital of pterygoid, 86

External 

acoustic meatus, 105–107, 137–140, 

142–143, 146

acoustic pore, 138

angular process, 25, 32

antorbital notch, 50

aperture, 113

aperture for the cochlear aqueduct, 

115

aperture for the cochlear canaliculus, 

117

aperture for the vestibular aqueduct, 

117

auditory canal, 138

auditory meatus, 77, 104, 106–107, 

130, 137, 138, 140, 143, 147

bony nares, 26, 58, 64, 68, 70, 

79–82, 156–157

carotid artery, 91, 94, 102, 131

carotid foramen, 102, 139, 141

ear, 137

ethmoidal artery, 26

ethmoidal vein, 26

face of nasal, 68

foramen ovale, 95

frontal crest, 25

lacrimal fossa, 38, 39

lamina

ethmoid bone, 13, 15, 17

pterygoid bone, 85

mandibular angle, 44

nares, 154–155, 157

narial aperture, 79

nasal nerve, 15

occipital crest, 109

occipital protuberance, 34, 109

opening for the cochlear aqueduct, 

112

opening of the facial canal, 117, 128

opening of the foramen ovale, 94–95

opening of the respiratory apparatus, 

156

opening of the respiratory passages, 

156
a l e x i c o n n u m b e r 6 2 7 • 2 2 5

plate

maxilla, 57

maxillary crest, 62

pterygoid bone, 85–86

pterygoid muscle, 72, 74, 99

reduplication of the pterygoid, 85–86

ridge, 138

ridge of the sigmoid process, 136

sagittal crest, 25, 34, 76–77, 109

surface, 57–58, 60, 66, 69, 120

frontal, 25, 103, 154

maxilla, 57, 58

nasal, 68, 69

parietal, 76

petrosal, 132

premaxilla, 82

squamosal, 104

Extrinsic eyeball muscles, 39–40, 72 

Face, 154

posteroventral, 29

Facet

anterior, 111

posterior bullar, 125

Facet for the

incus, 150

malleus, 117, 121, 151

post-tympanic process, 143

posterior meatal crest, 143

posterior process 

tympanic bulla, 144

periotic, 143–144

Facial

area, 156

artery, 44

bones, 151

canal, 112–116, 117–120, 122, 

124–125, 127, 129–132

distal opening, 128

epitympanic opening, 128

external opening, 128

ventral opening, 128

within the tegmen tympani, 117, 

124

crest, 79

maxilla, 57, 58

periotic, 115, 117, 127, 131

foramen, 117

fossa, 16, 50, 58, 62, 65

groove, 114, 117

muscles, 50

nerve, 19, 36, 50–51, 99, 114, 

117–118, 122, 124, 128–129, 

131, 154

plate, 56

process, 58

region, 26, 61, 68, 108, 154

sulcus, 114, 117, 119, 122, 126, 129, 

131, 138

surface, 39–42, 44

lacrimal, 39

maxilla, 56, 58

tuberosity, 58

vessel notch, 44

Facies

anterior, 49

anterior partis petrosae, 117

buccalis, 43

cerebralis, 93

encephalica

caudomedial part, 117

rostrodorsal part, 117

externa, 25

facialis, 58

infratemporalis, 60

interna, 27, 77

labialis, 44, 80

lateralis, 36

lingualis, 45

maxillaris, 72

medialis partis petrosae, 122

nasalis, 41, 64, 73

nasopharyngea, 86–87, 97

occipitalis, 122

orbitalis, 29, 37, 41, 64, 98

palatina, 67, 74, 81, 87

posterior partis petrosae, 117, 122

pterygopalatina, 66

rostralis partis petrosae, 117

temporalis, 31, 37, 101, 108

tympanica, 131

ventralis partis petrosae, 132

Falcate 

crest of exoccipital, 12, 19

process, 11–12, 19

Falciform crest, 34

process, 12, 83, 87, 91, 95, 98, 

100–102, 103, 105–107, 134, 

147, 149

frontal, 103

squamosal, 103

Fallopian 

aqueduct, 113, 117, 120, 127–128, 

130

foramen, 117

False 

choanae, 83, 85, 156

palate, 86

posterior clinoid process, 94

Falx

cerebelli, 109

cerebri, 14, 30, 34–35, 109, 110

Fenestra

cochleae, 115, 117–118, 128

lacrimal, 40, 72

ovalis, 115, 117, 119, 127, 132–133, 

151

piriformis, 125

rotunda, 114, 115, 117, 118, 122, 

128, 138, 141

vestibularis, 132, 151

vestibuli, 117, 118, 123

Fibro-venous plexus, 156

Fibrous infraorbital arcade, 36

Fibrous joint, 108

First turn of the cochlea, 127

Fissura

Glaseri, 129, 133, 138, 141–142, 

146

lacera anterior, 98

orbitalis, 98

inferior, 96

superior, 101

palatina, 64, 80

petrooccipitalis, 118, 124

petrosoparoccipitalis, 118, 124–125

petrosquamosa, 125

petrotympanica, 125, 129, 142

tympanomastoidea, 148

tympanooccipitalis, 148

tympanoperiotica, 129, 131

tympanosquamosa, 149

Fissure

anterior of the facial foramen, 111

basicapsular, 114

basicochlear, 114

basisphenoid-presphenoid, 92

inferior orbital, 96

orbital, 98

palatine, 80

petrooccipital, 124

petrosoparaoccipitalis, 118

petrosoparoccipital, 125

petrosquamous, 125

petrotympanic, 125

sphenoidal, 100

sphenomaxillary, 100

sphenorbital, 101

superior orbital, 101

tympanomastoid, 131

tympanoperiotic, 131

Flange

basioccipital, 11

maxillary, 62

occipital, 11

prespiracular plate, 82

Floating bones, 154

Floor plate, 15, 67

Folian process of the malleus, 138

Fontanelle

frontal, 25–26

lateral occipital, 21

mastoid, 21

occipital, 21, 35

Foot

squamosal, caudal, 136

Footplate of the stapes, 117, 151
2 2 6 • smithsonian contributions to zoolog y the therian skull

Foramen, 19

acusticum inferius, 132

acusticum superius, 116–117

ad medium supercillii incisum, 31

alare caudale, 93

alare parvum, 100, 102

alare rostrale, 99

caecum, 25

caroticum

caudalis, 93

internum, 96

cecum, 25

condylar, 18

ethmoidale, 25

ex auditus organum amplitudinis 

medio exortu, 129

faciale, 116, 117, 118

frontale, 26

gingival, 44

hoc iuxta posteriorem dentium 

incisoriorum, 80

id ad posteriorem regionem processus mammillaris, 122

impar, 109, 111

in occipitii osse gratia ervi septimi 

paris nervorum cerebri incisum, 19

incisivum, 80

infraorbitale, 59

jugulare, 20

lacerum, 19, 92, 135, 138–139, 141, 

145

anterius, 91, 98, 138

basis cranii, 23

medium, 91, 139

posterius, 18, 20, 23, 95

posterius, nervous, 20

lacrimale, 40

magnum, 11–12, 18, 19–21, 23, 77, 

108–111

mandibulae, 45

mastoideum, 121

maxillare, 62

nervorum opticorum, 97

occipitis ossi & temporis ossi commune, 20

opticum, 97

orbiculare, 95

ovale, 19, 27, 30, 87, 89–91, 94–96, 

98, 101, 103, 106, 114, 122, 

131

palatinum

caudale, 65

majus, 58, 72

parietale, 35, 77

per quod transit arteria carotis, 92

petrosum, 98

quo dictae minoris tertii paris 

nervorum, 59

rotundum, 38, 66, 90–91, 93, 94, 

95–98, 100–101

singulare, 112, 118, 120, 128, 130, 

132

sinus sagittalis dorsalis, 109

sphenopalatinum, 76

spinosum, 90, 91, 94, 95, 98, 107, 

132, 158

stylomastoideum, 118, 129

definitivum, 118–119, 129

primitivum, 118–119, 129

tertium, 118–119

supraorbitale, 31

unicum, caterisque omnibus facile 

maximum, 19

Vesalii, 95

zygomaticofaciale, 38

zygomaticoorbitale, 38

zygomaticotemporale, 38

Foramen

accessory palatine, 71

alveolar, 42, 49

anterior 

carotid, 91

condyloid, 17

lacerate, 91

articular ramus vagus nerve, 114

carotid, caudal, 93, 135

caudal alar, 93

caudal carotid, 93, 135

condyloid, 18

dental, 44

dorsal 

condyloid, 19

infraorbital, 57

sagittal sinus, 109

epitympanic, 116

ethmoid, 25

facial, 117

canal, ventral, 132

nerve, 118

primary, 127

secondary, 128

Fallopian, 117

frontal, 26

diploic vein, 25

greater 

palatine, 58, 71

superficial petrosal nerve, 118

hypoglossal, 20

impar, 109

incisive, 80

inferior dental, 44

infraorbital, 59

internal 

carotid, 96

orbital, 72

jugular, 20

lacerate

anterior, 139

lacrimal, 40 

lesser 

palatine, 72

petrosal nerve, 94

magnum, 19

major palatine, 72

mandibular, 45

mastoid, 121

maxillary, 62

mental, 46

metoptic, 97

middle palatine, 73

minor palatine, 73

nasal, 70

nasal nerve, 15, 71

occipital, 21

olfactory, 16

optic, 97

ovale, 94

palatine, 74

parietal, 35

perilymphatic, 123

petrobasilar, 124

petrosal, 98

posterior 

ethmoid, 29

infraorbital, 65

lacerate, 20, 22

palatine, 65, 75

posteroexternal, 125

postglenoid, 105

postparietal, 78

precondyloid, 22

premaxillary, 81

pseudo-ovale, 94

ramus 

inferior of stapedial artery, 94

superior of stapedial artery, 94, 

118

temporale, 103

rostral alar, 99

rotundum, 95

singular, 128

small alar, 100

sphenopalatine, 76

spinosum, 95

stylomastoid, 129

subsquamosal, 107

suprameatal, 107

supraoccipital, 110

supraorbital, 31

transverse canal, 101

vascular (periotic), 132

ventral 

condyloid, 24

infraorbital, 67

Vesalius, 94

vestibulocochlear nerve, 12
a l e x i c o n n u m b e r 6 2 7 • 2 2 7

zygomatic, 102

zygomatic nerve, 95

zygomaticofacial, 38

zygomaticoorbital, 38

zygomaticotemporal, 38

Foramen . . . quod ex magno internove 

oculi angulo in narium cavitatum 

recta deorsum pertinet, 41

Foramen for the

auricular ramus of the vagus, 114

chorda tympani, 150

dorsal sagittal sinus, 109

facial nerve, 118

frontal diploic vein, 25–26

greater 

petrosal nerve, 120, 139

superficial petrosal nerve, 118

inferior (or ventral) petrosal sinus, 

12, 19, 94

lesser petrosal nerve, 94

nasal nerve, 15, 71

ramus 

inferior of the stapedial artery, 94

superior of the stapedial artery, 

94–95, 118

ventral petrosal sinus, 94

vestibular or endolymphatic duct, 113

zygomatic nerve, 94–95

Foramina

alveolaria, 49

laminae cribrosae, 14

mentalia, 46

palatina minora, 73

Foramina

cribriform, 14

in frontal

dorsal surface, 26, 31

ventral surface, 26

posterior condyloid, 22

rami temporales, 103, 107

Stenson, 79–80

terminal nerve, 17

Fossa

canina, 56

capitis mallei, 116, 119, 121

cerebralis, 108

condylaris dorsalis, 19

condylaris ventralis, 24

digastrica, 44

glandulae lacrimalis, 26

hypophyseos, 96

hypophysialis, 96

incudis, 116–117, 119, 151

infratemporalis, 60

lacrimalis externa, 39

m. obliqui ventralis, 39

m. stapedius, 119

m. tensor tympani, 119

mandibularis, 104

masseterica, 46

muscularis

major, 119

minor, 119

pterygoidea, 88, 99

pterygopalatina, 66

sacci lacrimalis, 39

scaphoidea, 99

subarcuata, 129

Fossa

anterior sinus, 49

antorbital, 50

aperture for ductus endolymphaticus, 

119

canine, 56

cerebral, 108

cerebellar, 114

digastric, 44

dorsal condyloid, 19

epitubaria, 119

external lacrimal, 39

facial, 58

glenoid, 103

head of malleus, 119

hypophyseal, 96

incudis, 119

infraorbital, 59

interorbital, 27

lacrimal gland, 26

mallear, 121

mandibular, 45–46, 104

maxillary, 16, 62

maxillary of palatine, 72

muscularis 

major, 119

minor, 119

nasal, 16

orbitotemporal, 29

parafalciform, 98

peribullary sinus, 13

periotic, 105

pituitary, 13

postglenoid, 105

postorbital lobe of the pterygoid 

sinus, 95–96

posttemporal, 105

premaxillary sac, 81

preorbital, 47

pterygoid, 99

pterygoid sinus, 89

postorbital lobe, 26

preorbital lobe, 26

pterygopalatine, 66, 75

scaphoid, 99

sphenoidal, 100

sphenomaxillary, 67, 100

squamosal, 128

stapedius muscle, 119

stylohyoid, 128

stylomastoid, 104, 129

subarcuate, 129

suprameatal, 107, 130

temporal, 108

tensor tympani muscle, 119

ventral condyloid, 24

ventral oblique muscle, 39

vermiform, 111

vestibular, 132

zygomatic, 32

Fossa for the 

anterior sinus, 41

hamular lobe, 70

hamular sinus, 72

head of the malleus, 116, 119, 121

lacrimal sac, 39–41, 49

lacrimal gland, 26

m. stapedius, 119

m. tensor tympani, 116, 119, 127, 

130, 141

postorbital lobe of the pterygoid 

sinus, 61, 95

preorbital lobe of the pterygoid 

sinus, 26

pterygoid sinus, 88

stapedius muscle, 114–115, 117, 

119, 127, 129

sublingual gland, 48

submaxillary gland, 48

tensor tympani muscle, 116, 

119–120, 128, 130

ventral oblique muscle, 39

Fossae for the olfactory lobes, 14

Fossula petrosa, 125

Fossula

cochlear, 115

petrosal, 125

vestibular, 132

Fovea

capitis mallei, 121

(fossa) epitubaria, 111–112, 119, 

121, 133

pterygoidea, 47

sublingualis, 48

submandibularis, 48

trochlearis, 32

Foveola

suprameatalis, 107

suprameatica, 103, 107

Free border, 71–72

of the palatine, 71, 74

of the parietal, 76

Free 

inner end of the meatal tube, 136

lamella, 86

lamina of the palatine, 71

Frons, 26

Frontal, 7, 14–16, 24–32, 34–36, 

38–41, 47, 50–51, 57–58, 62–63, 
2 2 8 • smithsonian contributions to zoolog y the therian skull

Frontal (continued)

66–70, 72, 76–77, 79–80, 83, 89, 

95–96, 100, 108–109, 154–155, 

157

angle, 77

ascending process, 24

bone, 24, 34, 40, 56, 78

border

of the parietal, 76, 77

of the sphenoid, 95, 100

crest, 25, 26

external, 2

diploic vein, 25, 26

eminence, 25, 26, 31

fontanelle, 25, 26

foramen, 26, 31

groove, 95

lobes of the cerebrum, 26

margin

frontal, 27

nasal, 69

maxillary surface, 24

notch, 26

plate, 56, 58

portion, 58

process, 36–37, 39, 41, 57–58, 61, 

64, 68–69, 79, 85

of the jugal, 36–38

of the lacrimal, 39, 41

of the maxilla, 28, 57, 58, 61, 

64, 68

of the nasal, 69

of the premaxilla, 79

of the pterygoid, 77, 85

protuberance, 51

sinus, 15, 24–25, 27–29, 63, 157

anterolateral part, 24

lateral part, 28

posterior portion, 24

septum, 30

squama, 25, 27–28

surface of the maxilla, 56, 58

suture, 27–28

vein, 27

Frontis os, 24

Frontomaxillary suture, 27

Frontonasal 

portion, 56

region, 56

surface, 56

suture, 28, 69–70, 77–78

Frontoparietal suture, 32

Frontosphenoidal suture, 25

Frontozygomatic suture, 27

Fundic part, 147

Fundus of the 

internal acoustic meatus, 119

nasal fossa, 15

tympanic cavity, 147

Furrow

dental, 57

for the Eustachian tube, 137

Fusiform crest, 152

Galea aponeurotica, 34, 109

Gap

internasal, 69

Geniculate ganglion of the facial nerve, 

119

Geniculum canalis facialis, 119

Genu of the facial canal, 119, 124, 130

Gingival foramen, 42, 44

Glabella, 27

Glaserian 

fissure, 138

process, 95

Glenoid 

cavity, 103, 104

fossa, 60, 102, 103–104

plate, 103

process, 103, 106, 108

surface, 103–104

Glossopharyngeal nerve, 20–21, 121, 

131

Glove finger, 147

Glutinatio squamaeformis, 106

Gnathion, 44

Goniale, 140, 149, 150

Gonion, 43, 44

Gonys, 44

Great 

alae, 91

flanges of the occipital, 11

lateral crests of the maxillary bones, 

62

occipital crest, 59, 64, 67, 109

transverse crest, 62

Greater 

palatine artery, 65

palatine canal, 64–65

palatine foramen, 58–59, 64–65, 71

palatine groove, 64–65

palatine nerve, 58, 64–65

palatine sulcus, 58, 65, 71

petrosal nerve, 120, 124, 128

superficial petrosal nerve, 119, 125

tympanic spine, 134, 138

wing of the sphenoid, 66, 90, 96, 

101

Groove

alveolar, 42

angularis oculi vein, 27

caudal meningeal artery, 120

chiasmatic, 93

dorsal petrosal sinus, 120

dorsal sagittal sinus, 109

ectomaxillary, 57

external auditory meatus, 105

frontal, 95

internarial, 69

lateral basirostral, 62

lateral of periotic, 121

mandibular nerve, 96

maxillary, 62

medial, 68

median promontorial, 122

middle meningeal artery, 96

middle temporal artery, 104

mylohyoid, 46

occipital, 104

occipital artery, 120

occipital sinus, 109

optic, 97

optic chiasm, 96

origin of ventral oblique muscle, 39

palatine, 64

prespiracular plate, 82

promontorial, 127

pterygoid, 88

pterygoid hamulus, 85

pterygoid of sphenoid, 99

shallow lateral, 128

sigmoid sinus, 120

sphenopalatine artery, 71

sphenopalatine canal, 71

stapedial artery, 120, 128

supraorbital, 31

tensor tympani muscle, 120

transverse sinus, 109

ventral petrosal sinus, 12

ventral surface of pars cochlearis, 120

Groove for the

angularis oculi vein, 27, 31

annulus tendineus, 138–139, 148

caudal meningeal artery, 120

chorda tympani, 140

digastric muscle, 122

dorsal petrosal sinus, 120

dorsal sagittal sinus, 109

external auditory meatus, 105

facial nerve, 138

mandibular nerve, 96

Meckel’s cartilage, 44

middle meningeal artery, 78, 96

middle temporal artery, 104

nasal septum, 152

nasociliary nerve, 69

occipital artery, 120

occipital sinus, 109

optic chiasm, 96

petrosal sinus, 124

pterygoid hamulus, 85

sagittal sinus, 109

sigmoid sinus, 120

sphenopalatine artery, 71

sphenopalatine canal, 71

stapedial artery, 120
a l e x i c o n n u m b e r 6 2 7 • 2 2 9

superior petrosal sinus, 120

superior sagittal sinus, 109

tensor tympani muscle, 111, 119, 

120

transverse sinus, 109, 111

ventral petrosal sinus, 12

Groove on the

malleus, 150

outer lip border, 141

ventral surface of the pars cochlearis, 

120, 142

Gutter

alveolar, 42

Guttural pouch, 83, 89

Hac sede in octavo capitis osse multa, 

sed exigua, 14

Hamular 

cavity, 89

crest, 85

element, 89

fossa, 72–73, 75, 85–86, 89

laminae, 86

lobe of the pterygoid sinus, 74, 83, 

84–86, 89, 156

part, 88

portion, 88

process, 85, 88

region, 88

sinus, 72–73, 88, 89

space, 89

Hamulus, 85–86, 89

lacrimalis, 40

pterygoideus, 88

Hamulus

lacrimal, 40

pterygoid, 85, 88

Handle of the malleus, 150

Hard palate, 59, 64–65, 70, 71–75, 82

oral surface, 71

ventral surface of, 67

Head 

malleus, 116, 121, 147, 150

mandibular, 45

stapes, 151

Hearing, 155

Hemi-mandible, 42

Hemispheres of the cerebellum, 110

Hiatus

canalis facialis, 120, 124

canalis nervi petrosi majoris, 120, 

122

canalis nervi petrosi minoris, 122

epitympanicus, 106, 112, 116, 120, 

147, 148

Fallopii, 120, 124, 128, 139

mandibularis, 45

maxillaris, 62

semilunaris, 17

Hiatus

cranial, 18

facial canal, 120

greater petrosal nerve, 120

Highest nuchal line, 34, 109

Highmore’s antrum, 56

Hollow

cerebral, 93

Hook-like articular 

apophysis, 113

process, 107

Hooked process, 149

Horizontal 

bodies, 43

lamina of the palatine, 70, 71, 73–75

part of the vomer, 152–153

plate, 74

portion of the palatine, 71–74

ramus, 43, 47–48

ventral plate, 64

Horn, 28

Huic sinui cuneiformi ossi inciso, visoriorum nervo, 93

Hyal, 32

Hyoid, 7, 32, 48, 131, 145

apparatus, 32–33

arch, 32

elements, 139, 146

process, 131

Hyoides os, 32

Hyomandibular 

branch of the facial nerve, 117

ramus, 128

Hypoglossal 

canal, 19–22

depression, 19

foramen, 17–19, 20, 24

fossa, 20

nerve, 20

notch, 11, 20, 22

Hypophyseal fossa, 13, 94, 96, 99, 102

Hypophysis, 24, 93, 96

Hypotympanic 

cavity, 147

sinus, 135–136, 139, 145, 147

Impressio

medullaris, 12

n. trigemini, 131

pontina, 13

verminalis, 111

Impression

digital, 25

medulla oblongata, 12

pontine, 13

ridge, 75

trigeminal, 131

vermiform, 111

Impressiones rugae, 75

Incisive 

canal, 65, 79, 80

foramen, 65, 79, 80

incisure, 152

portion of the mandibular body, 44

suture, 80

Incisivomaxillary canal, 59

Incisor, 79

crest, 79, 80

teeth, 44, 80

Incisura

basiparoccipitalis, 23

carotica, 92

ethmoidalis, 25

frontalis, 26

incisiva, 152

infratrochlearis, 39

intercondyloidae, 20

jugularis, 20

lacrimalis, 61

mandibulae, 45

mastoidea, 122

nasalis, 64

parietalis, 105

pterygoidea, 88

Rivini, 147–148

sphenoidalis, 153

sphenopalatina, 76

supraorbitalis, 31

tympanica, 147

uncinata, 17

vasorum facialium, 44

Incisure, 116

anterior, 111

ethmoid, 25

ethmoidal, 25

jugular, 20

Incudi os simile, 149

Incudomalleolar joint, 150–151

Incus, 9, 42, 116, 119, 147, 149–151

Inferior 

anterior external angle, 77

anterior external angle of the parietal, 77

border of the nasal, 68, 69

dental 

canal, 44

foramen, 44–45

lamina, 85, 89

maxillary nerve, 45, 96

maxillary nerve

orifice for, 87

maxillary sinus, 66

nasal concha, 15–16, 71

nuchal line, 34, 110

oblique, 40

occipital fossae, 110

orbital fissure, 66, 96, 98, 101, 155

orbital ridge, 32, 60
2 3 0 • smithsonian contributions to zoolog y the therian skull

Inferior (continued)

petrosal sinus, 129, 132

portion, 96

posterior external angle of the 

parietal, 77

sinuses, 12

temporal line, 78

tympanic branch, 131

vestibule, 80

Inferioris maxillae, 42

Infrafrontal 

arcade, 36

border 

maxilla, 59

jugal, 36–37, 39

branch of the trigeminal, 59

branches, 156

canal, 49, 50, 57, 59–60, 62–63, 65, 

67, 80–81

complex, 156

foramen, 50, 57, 59, 60, 67, 72

fossa, 59, 67

margin, 29

frontal, 98

maxilla, 59

nerve, 59, 60, 62, 81, 96, 154–156

notch, 50, 59

plates of the maxilla, 59–60, 64

process, 59, 64

sulcus, 60

vessels, 57, 59–60, 62, 80, 96, 155

Infraorbital 

border of the jugal, 36

border of the maxilla, 59

canal, 

(in maxilla), 59

(in premaxilla), 80

complex, 156

foramen, 59

fossa, 59

notch, 59

plates of the maxilla, 59

process, 60

sulcus, 60

Infratemporal 

crest, 26–27, 30, 96, 108

fossa, 27, 29, 32, 38, 60–61, 66, 74, 

154

portion, 96

surface of the maxilla, 60, 61, 66

Infratrochlear 

nerve, 39

notch, 39, 41

Infundibulum, 94

ethmoidale, 15

Infundibulum

alisphenoidal, 91

ethmoid, 15

foramen ovale, 18, 98

optic, 97–98

optic and oculomotor nerves, 29

Inner 

convexity, 139

ear, 111, 123–124, 155

lamina, 85

notch, 66

pedicle, 139, 143

plate

maxilla, 61

pterygoid, 86

posterior pedicle, 137, 139–140, 

142–143, 145

posterior prominence, 139, 141–142, 

144, 149

Insertion for the tendon of the m. tensor 

tympani, 150

Insigne foramen maiori soporalis 

arteriae ramo calvaria ingrediente 

excavatum, 92

Inter-laminar 

air space, 89

space, 89, 91

Interalveolar 

margin, 44, 61

septa, 43, 44, 61

Interarticular fibro-cartilage, 108

Intercondyloid notch, 12–13, 20

Intercrural 

aperture, 151

foramen, 151

Interdental space, 57, 61

Interfrontal 

crest, 27

suture, 27

Interincisive suture, 79, 82

Intermedius branch of the facial nerve, 

124

Internal 

acoustic meatus, 19, 111–119, 120–

125, 128–129, 130, 132, 156

acoustic pore, 111, 115, 120, 121

alveolar plate, 44, 48

antorbital notch, 50

aperture for the facial canal, 113, 120

auditory 

canal, 121

foramen, 121

meatus, 112, 114, 120, 121, 130

bony nares, 70–71, 83, 156

carotid 

artery, 29, 91–93, 102, 139, 

157–158

canal, 92–93, 135

circulation, 157

foramen, 91–93, 96, 124

plexus, 92

face of nasal, 68

facial foramen, 117

frontal crest, 27

jugular vein, 19

maxillary artery, 66

nares, 156

nasal 

aperture, 156

nerves, 15

occipital 

crest, 110–111

protuberance, 24, 34, 102, 109, 

110–111

ophthalmic rete mirabile, 24

orbital foramen, 72

plate 

pterygoid, 86

maxillary crest, 62

pterygoid lamina, 88

pterygoid muscle, 43, 72, 74–75, 

84–85

reduplication of the pterygoid, 86

sagittal crest, 27, 34, 110

superior plate of the pterygoid, 86

surface, 57, 69–70, 78

frontal, 27

nasal, 68, 69

parietal, 77

table of the frontal bone, 25

vertical ridge, 110

Internal-orbital foramen, 72, 76

Internarial 

groove, 69–70

septum, 152

Internasal

gap, 69–70

suture, 70

Interparietal

bone, 7, 24–25, 27, 30, 32, 33–35, 

56, 76–78, 108–110, 155

border of the parietal, 77–78

margin of the frontal, 27, 29

ossification, 34

process, 34

Interprominential notch, 139, 141–142, 

146, 148

Interpterygoid fossa, 83, 86

Interradicular septa, 44, 61

Intersphenal 

fissure, 98

fossa, 98

Intersphenoidal synchondrosis, 92, 96

Intramandibular fat body, 42, 45, 156

Intrabullar part of the meatal tube, 140

Intracondyloid closure, 77

Intracranial extensions for spinal 

meningeal arteries, 23-24

Intrajugular process 

exoccipital bone, 20

periotic, 121

Intramandibular fat body, 45, 47

Intranariale, 90

Intranasal, 90

Intraorbital fossa, 27
a l e x i c o n n u m b e r 6 2 7 • 2 3 1

Intraosseous passage, 20

Involucrum, 135–137, 139–141, 143, 

145–146

Jaw joint, 108

Joint

temporomandibular, 108

Juga alveolaria, 42

Juga

alveolar, 42

cerebellar, 18

cerebral, 24

Jugal (malar), 7, 27–30, 35–42, 47–51, 

58, 61, 68, 101–102, 108, 155

notch, 20

Jugalotemporal suture, 37

Jugular 

foramen, 12, 18, 19, 20–24, 92, 95, 

105, 111–112, 114, 118, 121, 

131, 139, 156

venous, 20

fossa, 121, 125

incisure, 20, 112

notch, 13, 18, 20–22

process, 20–22, 24, 33, 121

tubercle, 21

vein, 20, 22, 121

Jugulo-acoustic canal, 21

Jugulohyoideus muscle, 33

Jugum sphenoidale, 100

Juxtamastoid process, 22

Keel

anterior, 111

Keyhole notch, 110

Labial surface 

mandible, 43, 44–45

premaxilla, 80

Labyrhinthi ductus, 123

Labyrinth

ethmoid, 15

osseous, 123–124

Labyrinthine part, 121, 123

Labyrinthus

ethmoidalis, 15

osseus, 123

Lacerate foramen, 23, 139

Lachrymal, 38

Lachrymal 

area, 57, 61

bone, 57

Lachrymo-malar bone, 40

Lacrimal 

bone, 8, 24, 27–28, 30, 35–36, 

38–42, 47–51, 58, 61–62, 68, 

72, 83, 154–155

border of the jugal, 36

bulla, 39

canal, 39–41, 61, 63

canal of the maxilla, 61

duct, 38–40

fenestra, 40, 72

foramen, 38, 40, 49

fossa, 28, 38, 39, 40

gland, 38–40, 154

fossa, 26

hamulus, 40, 61

hook, 40

margin of the maxilla, 61

notch, 61

orifice, 40

pit, 40

process, 15

sac, 38–40, 61

fossa for, 39

sinus, 39, 40

aperture for, 39

sulcus, 38, 40, 61, 62

tubercle, 61

Lacrimojugal

bone, 27, 36–39, 40, 42, 50–51, 68

cleft, 36–38, 40, 41, 61

crest, 40, 49, 61–62, 68

fossa, 40

suture, 38, 40

Lacrimomaxillary fossa, 40–41

Lambda, 77

Graecorum mainsculae literae 

assimilatur, 34

Lambdoid 

crest, 34, 107

suture, 21, 34

Lambdoidal ridge, 34, 108

Lamelliform extension, 62

Lamina

basalis, 15

cribrosa, 13–14

externa, 13, 15

horizontalis, 71

laterale, 152–153

medialis, 87

orbitalis, 15, 17

perpendicularis, 16, 74

sphenoethmoidalis, 75

spiralis ossea, 128

spiralis secundaria, 128

tectoria, 17

Lamina

anterior of periotic, 112

dorsal, 14, 83

external, 15

palatine

free, 71

horizontal, 71

lateral, 72

perpendicular, 74

pterygoid, 86

external of pterygoid, 85

inner of pterygoid, 85

lateral of pterygoid, 86

medial of pterygoid, 86

posterior of pterygoid, 87

ventral of pterygoid, 89

sphenoethmoid, 75

sphenoid

lateral, 96

mesial, 97

spiral, 128

transverse, 15

ventral, 15

Large smooth tuberosity, 51

Laryngeal arcade, 12

Larynx, 85

Lateral 

atlantoccipital ligament, 22

basirostral groove, 62

border, 41

canal, 128

descending process, 12

ethmoid, 14

furrow of the tympanic bulla, 139, 

142

groove, 121, 134, 140

hyothyroid ligament, 33

lamina, 17, 57, 71–75, 83–86, 

87–89, 91, 94, 96–97, 99

alisphenoid, 96–97

ethmoid, 63

palatine, 72, 75, 86, 154

pterygoid, 72, 75, 86–87, 89, 91, 

96

squamosal, 91

lobe, 72–73

mass of the cribriform plate, 13, 15

nasal crest, 80

nasal diverticulum, 47

notch of the sphenoid, 97

occipital fontanelle, 21

palatal lobe of the palatine, 72–73

palpebral ligament, 37

part of the frontal sinus, 28, 40

plate, 83, 87

posterior prominence, 139

process, 17, 150

process of basioccipital, 11

process of the pterygoid, 83

projection of anterior process, 121

pterygoid muscle, 43, 47, 99

pterygoid plate, 60, 99

pterygopalatine fossa, 89

ridge of the sigmoid process, 136

sheet of the vomer, 152

sinus, 109

surface, 36, 41, 98

lacrimal bone, 39–40

lacrimojugal bone, 40

jugal bone, 36

nasal bone, 69

tuberosities of basioccipital, 11
2 3 2 • smithsonian contributions to zoolog y the therian skull

Lateral (continued)

tuberosity, 116, 121, 127–128, 132, 

146

tuberosity of Barnes, 121

wall of the maxillary sinus, 63

wing of the 

alisphenoid, 96

mesethmoid, 14

sphenoid, 91

Lenticular process, 151

Lesser 

cornua, 33

palatine foramen, 58, 72–73

petrosal nerve, 98, 112, 114, 122–123

superficial petrosal nerve, 94

tympanic spine, 139, 143

wing of sphenoid, 97

Levator rostri, 47

Ligamentum nuchae, 34

Line

highest nuchal, 34, 109

inferior nuchal, 34, 110

mandibular, 46

mylohyoid, 46

nuchal, 34

oblique, 47

of Daubenton, 77

superior nuchal, 35

temporal, 78

Linea, 101, 138

mylohyoidea, 46

nuchae, 34

nuchae inferior, 110

nuchae superior, 35

nuchae suprema, 109

obliqua, 47

temporalis, 31, 35, 78

temporalis inferior, 78

temporalis superior, 78

Lingual process, 33

Lingual surface of the mandible, 45

Lingula

mandibulae, 45

sphenoidalis, 97

Lip

bullar, anterior, 133

internal acoustic meatus, 121

tympanic bulla, caudal, 135

Lip-like process, 139, 146

Lithoid, 111

Lobe

orbital of pterygoid sinus, 87

postorbital lobe of pterygoid sinus, 30

preorbital of the pterygoid sinus, 30

Locomotor system, 155

Long process, 149, 150

Longitudinal 

groove, 139

sinus, 30

Longus capitis muscle, 13, 122

Lower jaw, 42

Lower tympanic aperture, 138, 139–

140, 142, 147–148

M. caninus, 56

M. cleidocephalicus, 123

M. epicranius, 109

M. external pterygoideus, 96

M. genioglossus, 46

M. geniohyoideus, 46

M. hyomandibularis, 48

M. levator labii superioris proprius, 47

M. levator veli palatini, 141

M. masseter, 36, 43, 46, 58

M. masseter lateralis, 27

M. maxillonasolabialis , 62, 66

M. maxillonasolabialis pars externa, 154

M. mylohyoideus, 46

M. obliqui ventralis, 39

M. obliquus capitis superior, 110

M. occipitofrontalis, 109

M. orbicularis oculi, 27

M. pterygoideus, 154

M. pterygoideus externus, 99

M. pterygoideus internalis, 47

M. pterygoideus internus, 43

M. pterygoideus lateralis, 99

M. pterygoideus medialis, 43, 47, 99

M. quadratus labii inferioris, 47

M. rectus capitis posterior, 110

M. rhomboideus

anterior portion, 35

M. semispinalis capitis, 35, 110

M. sternocephalicus, 48

M. sternocleidomastoideus, 35, 48

M. superior oblique, 32

M. temporalis, 43, 96

M. tensor palati, 141

M. tensor tympani, 141, 150

M. tensor veli palatini, 85, 88, 97, 99, 

141, 144–145

M. trapezius, 35

M. triangularis, 47

Major palatine 

branch, 74

foramen, 58, 65, 71, 72–74, 154

nerve, 72

sulcus, 71

vessels, 72

Major petrosal nerve, 122, 124–125

Malar 

bone, 35, 36, 155

foramen, 36, 38

process, 62, 68

Maleus os, 149

Mallear 

fossa, 112, 116–117, 119, 121, 

133–134, 150

plate, 136–139, 140, 145

process of the tympanic bulla, 

134–135, 140, 146

ridge of the tympanic bulla, 134–

135, 138, 140, 142, 146, 149

sulcus, 140

Malleolar 

accessory ossicle, 140

process, 138, 140

sulcus, 140, 146

Malleus, 9, 42, 135–136, 138, 140, 

145–146, 149–151

Malomaxillary 

fissure, 51, 62

fossa, 40–41, 50

Mammillaris processus, 122

Mandible, 8, 42–49, 56, 79, 88, 94–95, 

108, 156

angle, 43

body, 43

ramus, 47

ventral margin, 48

Mandibula, 42

Mandibular

artery, 94

body, 45

branch of the trigeminal nerve, 91, 94

canal, 44, 45, 49, 156

condyle, 43, 45, 48, 105

foramen, 42, 44, 45–47, 156

fossa, 43, 45, 102–103, 104, 106, 

108, 147

mandible, 45

small, 45

squamosal, 45

head, 45

hiatus, 45

neck, 43, 45, 47

nerve, 45, 86-87, 90, 94–96, 114, 156

nerve

orifice for, 87

notch, 43, 45, 47

ramus, 43, 45–46, 47–48

space, 45

sulcus, 45

symphysis, 46–48

torus, 46

vessels, 45, 156

Mandibulo-articular surface, 104

Manubrium mallei, 150

Manubrium of the malleus, 150

Margin

ethmoidal, 25

frontal of nasal, 69

infraorbital of maxilla, 59

interalveolar, 44

interparietal, 27

mastoid, 21

maxillary of nasal, 70
a l e x i c o n n u m b e r 6 2 7 • 2 3 3

mesethmoid, 70

nasal, 28, 70

occipital of squamosal, 104

parietal, 35

parietal of frontal, 29

parietal of squamosal, 105

parietal of supraoccipital, 110

posterior of petrosal, 125

sagittal, 30

sphenoidal of squamosal, 106

superior of petrosal, 129

supraorbital, 31

supraorbital of maxilla, 67

ventral of the mandible, 48

Marginal tubercle, 36

Margo

alveolaris, 42, 49, 79

ethmoidalis, 25

fissurae, 138

frontalis, 77, 95

infraorbitalis, 36, 59

interalveolaris, 44, 80

interparietalis, 77

lacrimalis, 61

liber, 71

mastoideus, 21

nasalis, 28

occipitalis, 77, 104

parietalis, 29, 35, 98, 105, 110

posterior partis petrosae, 125

sagittalis, 30, 78

sphenoidalis, 106

squamosus, 78, 101

sulci tympanici, 147

superior partis petrosae, 129

supraorbitalis, 31

ventralis, 48

ventralis partis petrosae, 132

zygomaticus, 102

Masseter, 46

lateralis, 38

Masseter muscle, 43

Masseteric 

border of the jugal, 36, 58

fossa, 46

line, 46

margin, 36

tuberosity, 46

Mastoid, 104, 105, 122, 126, 143, 148

angle, 77

canaliculus, 121

cavity, 135–136, 140

cells, 121

component, 104, 143

diapophyses, 104

fontanelle, 21

foramen, 121–122, 126

margin of the exoccipital, 21

notch, 120, 122

part, 102, 104, 106, 123

portion of the squamosal, 104

process, 20, 21, 104, 106, 120–124, 

126, 129, 131, 133, 137, 143, 

147–148

of the periotic, 104, 155

of the petrosal, 122

of the temporal, 21

of the tympanic bulla, 140, 143

region, 122, 128

surface, 104

tubercle, 122

Mastoid–squamosal fusion, 104

Maxilla, 8, 16, 24–28, 30–32, 35–41, 

47, 48–51, 56–59, 61–74, 76, 

79-83, 89, 101, 103, 154–157

body of, 56

facial process, 48

palatine process, 48

zygomatic process, 48

Maxilla–premaxilla suture, 57

Maxillary, 39, 48, 81

artery, 90–91, 93–94, 154, 156

bone, 48

border of the jugal, 37

branch of the trigeminal nerve, 

90–91, 95, 99

crest, 51, 59, 62–63, 67

division of the trigeminal nerve, 38, 98

flange, 62

foramen, 32, 57, 59, 62, 66–67

fossa, 16, 58, 62, 

ethmoid, 16

palatine, 72

groove, 54, 55, 62

hiatus, 62, 64

margin of the nasal, 70

nerve, 38, 58, 66, 74, 90–91, 95, 

98-99, 114, 154, 156

notch, 62

plate, 62–63

process, 16, 36–37, 41, 63, 68, 72

ethmoid, 16

jugal, 37, 41, 61, 63, 68

palatine, 72

zygomatic arch, 63

prominence, 62, 63, 66

protuberance, 63

recess, 63, 72

ridge, 53–55, 62–63

septum, 56, 66

sinus, 16, 27, 29, 39, 49, 56–57, 59, 

62, 63, 65, 71–72, 157

septum, 67

surface, 25, 28, 72

frontal, 24, 27, 28

jugal, 37

palatine, 72

tuber, 63

tubercle, 50–51, 62, 63

tuberosity of the maxilla, 63–64, 

66–67

vein, 105, 154, 156

Maxillo-frontal suture, 62

Maxillofrontal crest, 41

Maxillomesethmoid suture, 57

Maxillonasalis tendinous plate, 154

Maxillopalatine suture, 58, 63

Maxilloturbinal, 63–64

Maxilloturbinate, 17, 63

Maximo superioris maxillae ossi, 48

Meatal tube, 138, 140, 145

inner, 136

intrabullar part, 140

Meatus, 140

acusticus externus, 137

acusticus internus, 120

auditorius internus, 121

ethmoidales, 15

nasopharyngeus, 73

temporalis, 105

Meatus

dorsal nasal, 69

ethmoid, 15

internal acoustic, 120

internal auditory, 120–121

secondary internal auditory, 23

Meckel’s cartilage, 44, 138, 140

groove for remains of, 44

Meckelian 

cartilage, 48

ossicle, 64

Medial 

angle 

involucrum, 135

orbit, 27

tympanic bulla, 140

conical process, 140–141

exoccipital crest, 19, 21

flange of pterygoid hamulus, 86

lamina, 

palatine, 72–75

pterygoid, 13, 83–85, 86–89, 99

lobe, 72–73

margin of the nasal bone, 70

narial wall, 156

notch, 92, 97, 140–141

occipital crest, 19

palatal lobe of the palatine, 73

palatine suture, 73

pedicle, 139, 140

petrotympanic fissure, 136, 140–142

posterior prominence, 139, 141

process, 41, 137

of the lacrimal, 40, 41, 49, 62

prominence, 137, 141

involucrum, 141

tympanic bulla, 18, 141
2 3 4 • smithsonian contributions to zoolog y the therian skull

Medial (continued)

pterygoid 

muscle, 43, 47, 99

plate, 87–88, 99, 102

sinus, 118

pterygopalatine trough, 89

sac, 104

sinus, 104

surface 

nasal, 70

petrosal, 117, 122

wall of the maxillary sinus, 63

Median 

furrow, 139–140, 141, 149

lacerate foramen, 120, 139

palatal lobe, 73

petrosal crest, 122, 125

process, 135–136, 139–140, 141, 

144

promontorial groove, 122, 127, 129

ridge, 141, 149

vomerine groove, 152

Medulla oblongata, 12

Membrana

shrapnelli, 116, 134, 144, 150

tympani, 147

Mental 

foramina, 44, 46

nerve, 46 

point, 46

protuberance, 46–47

spine, 46

tubercle, 46–47

Mesethmoid, 13–15, 16, 30, 69–70, 

79–80, 90, 152, 156–157

cartilage, 16

margin of the nasal bone, 70

ossification, 152–153

ridge, 16

Mesial 

lamina, 91, 97

portion, 73

Mesorostral 

bone, 152

canal, 16, 64, 80, 152

cartilage, 16, 152

furrow, 152

groove, 15–16

ossification, 80, 152, 153

Metopic 

suture, 27, 28

foramen, 97

process, 28, 97–98, 101

Mid-facial 

crest, 58

sagittal crest, 58

Mid-frontal crest, 58

Midcrest, 58

Middle 

clinoid process, 93

conical process, 136, 141

cranial fossa, 114, 122

ear, 42, 118, 124, 155, 157

cavity, 89, 114, 118, 128

ossicles, 102

lacerate foramen, 19

meatus of the nose, 15

meningeal artery, 91, 94–96, 112, 

132, 158

nasal concha, 16

palatine foramen, 73

process, 136, 141

pterygoid sinus, 83, 84, 86, 103–104, 

106, 108, 116, 146, 156

sinus, 84, 104

Minor palatine 

branch, 74

canal, 73

foramen, 58, 65, 71, 72, 73, 154

nerve, 73

vessels, 66, 73

Minor superficial petrosal nerve, 119

Modiolus, 122, 128

Molar, 48

portion, 46

Mouth cavity, 154

Muscular 

process of the

malleus, 119, 150

squamosal, 99

stapes, 151

tympanic bulla, 133–134, 141, 

144, 146

tubercle, 12–13

Musculotubal canal, 97, 114, 119–120, 

128, 133–135, 137–140, 141–

142, 145–146, 148

Eustachian notch, 137

Eustachian outlet, 137

semicanal, 141, 145

Musculus obliquus, 72

Mylohyoid 

crest, 46

groove, 46

line, 46, 48

nerve, 46

vessels, 46

N. petrosus major, 124

Nares, 70, 156

external bony, 79

posterior movement, 48

Narial 

margin of the pterygoid, 12

passage, 25

process 

frontal, 24, 28

palatine, 73

prominence, 69

septum, 152

Naris, 156

Narium, 157

Nasal 

aperture, 90

bone, 8, 14, 16, 24, 28, 30, 32, 39, 

47, 58, 68, 69–70, 79, 81, 

154–157

branches of 

sphenopalatine ganglion, 60

ophthalmic nerve, 15

cavity, 15–16, 27–28, 38, 41, 48, 

58–59, 62–64, 66, 69–72, 73, 

75, 83, 100, 152, 154–157

concha, 15, 71

crest, 28, 75

maxilla, 64, 80

palatine, 73

diverticula, 69, 82

epithelium, 80

foramen, 70, 79

fossa,15, 16

margin of the frontal, 25, 28

nerve, 14–15

foramen for, 71

notch of the maxilla, 64

part of the frontal, 28

passage, 15–16, 28, 48–49, 70–75, 

79, 82, 86–87, 152–157

posterior movement, 68

posterior wall, 68

pharynx, 157

plate, 56, 58, 80, 153

maxilla, 49

vomer, 152, 153

plug muscle, 81–82

portion of the premaxilla, 80, 82

process, 58, 64, 68, 70, 80–82, 156

maxilla, 64

nasal, 70

premaxilla, 79, 80–81, 154

ridge, 25, 28

ridge of the frontal, 28

septum, 16, 30, 58, 70, 73, 100, 152, 

153, 156

spine 

frontal, 28

palatine, 73, 75

surface, 57

lacrimal, 41

maxilla, 64

palatine bone, 16, 71, 73

turbinate, 70

vessels, 80

Nasion, 77–78
a l e x i c o n n u m b e r 6 2 7 • 2 3 5

Nasociliary nerve, 15, 69

Nasofacial muscles, 58

Nasofrontal 

opening, 24, 27, 28

plate, 80

Nasolacrimal 

canal, 40, 41

duct, 40–41, 61

Nasomaxillary 

opening, 63, 64

suture, 70

Nasopalatine 

foramen, 76, 80

nerve, 65, 79–80

Nasopharyngeal 

cavity, 97, 114

duct, 73–76, 83

meatus, 73

muscle, 83

surface

pterygoid, 86–87

sphenoid, 97

Nasopharynx, 71, 83, 85–86, 88, 147, 

156

bony, 83

Nasoturbinal, 14, 16, 69

Nasoturbinate, 14, 16

crest, 41, 61, 70

Neck, 47

cornual process, 25, 28

malleus, 150–151

mandible, 45, 47

stapes, 151

Nerve 

chorda tympani, 150

pterygoid canal, 99

IX, 20

X, 20

XI, 20

Neural branch, 92

New 

context, 38

term, 12–13, 21–22, 30, 36–37, 

40–41, 42, 61, 66, 68, 71, 80, 

85, 87, 91, 98, 106

Non ad amussim orbiculare sed circulo 

respondet utrinque modice in 

longum compresso, 94

Non insigniter amplum foramen quod 

ab externa calvariae sede, 18

Nose, 154

Notch

antorbital, 50

at the anterior border of the cochlea, 

111

carotid, 92

ethmoid, 25

Eustachian, 85

external auditory meatus, 104–105

facial vessel, 44

frontal, 26

hypoglossal, 20

infraorbital, 59

infratrochlear, 39

intercondyloid, 20

jugal, 20

jugular, 20

keyhole, 110

lacrimal, 61

lateral of sphenoid, 97

mandibular, 45

mastoid, 122

maxillary, 62

nasal, 64

odontoid, 12

paraoccipital, 22

parietal, 105

postglenoid, 105

precondyloid, 22

prespiracular plate, 82

prominential, 66

pterygoid, 88

retroarticular, 106

sphenopalatine, 76

squamocranial, 106

stylomastoid, 129

supraorbital, 31

tubal, 89

uncinate, 17

Nuchal 

crest, 25, 34–35, 64, 67, 77, 102, 

107–108, 154

line, 34, 77

plane, 77

tubercle, 110

Nutrient foramina, 18

Oblique 

line, 47

muscle, 72

Occipital, 17, 19, 21–22, 35, 77, 104

angle, 77

of Broca, 77

of Daubenton, 77

area, 155

artery, 20, 35, 120, 122

bone, 21, 30, 34, 121, 125

border of the parietal, 76, 77

complex, 21, 108

condyle, 11–12, 17, 19, 20, 21–22, 

121

crest, 34, 35, 64, 67

emissary vein, 110

flange, 11

fontanelle, 21, 35

foramen, 19, 21

groove, 104

lobes of the cerebrum, 108

margin, 104, 120, 122, 125

temporal, 104

ossification, 110

process, 104

protuberance, 110

region, 108

shield, 22, 108, 110, 154–155

sinus, 109

surface, 122

tuberosity, 110

Occipitis os, 110

Occipitohyoid muscle, 48

Occipitomastoid suture, 21

Occipitosphenoid 

suture, 139

synchondrosis, 101

Occipitosquamosal 

suture, 21, 104–105

Occiput, 110, 155

Octavum capitis os, 13

Oculomotor nerve, 90, 97–98, 101, 155

Odontoid notch, 12, 20

Olfactory 

apparatus, 13, 15

bulb, 15, 17

chambers, 16

epithelium, 14

foramina, 16

nerve, 13–17

recess, 73

region of the nasal cavity, 17

sense, 25

tract, 17

Olivary 

eminence, 78

process, 78

Omohyoid muscle, 48

Opening for the 

greater petrosal nerve, 122

lesser petrosal nerve, 122–123, 131

major petrosal nerve, 120, 122

minor petrosal nerve, 122

nasofrontal, 24, 28

nasomaxillary, 64

smaller petrosal nerve, 122

tympanic cavity, anterior, 134

tympanic ligament, 138, 142

vestibular aqueduct, 113

Ophryon, 77

Ophthalmic 

division, 39

nerve, 90, 98, 101, 114, 155

nasal branches, 15

Opisthion, 77, 110

Opisthotic portion of the periotic, 123, 

126, 142–143
2 3 6 • smithsonian contributions to zoolog y the therian skull

Optic 

canal, 25–26, 28–29, 32, 86–87, 95, 

96, 97–99, 101, 155

channel, 97

chiasma, 17, 78, 93, 96, 102

foramen, 30, 72, 93, 95, 97–98, 100, 

155

groove, 93, 97

infundibulum, 18, 29, 87, 97–98

nerve, 90, 93, 97, 155

process of the presphenoid, 97

region, 13, 87

Oral 

cavity, 59, 71–74, 154

surface, 

maxilla, 59, 65

palatine, 70–72, 74, 76

Orbit, 24, 26, 27, 28, 29–30, 32, 36–39, 

41, 58–59, 61–64, 66–67, 75–77, 

84, 98, 101–102, 107, 154–155

Orbita, 28

Orbital 

border of jugal, 37

content, 36

contents, 61

crest, 32, 40–42

crest of the lacrimal, 39, 41

eminence, 37

extension of the pterygoid, 86–87

fissure, 26, 29, 60, 95–96, 98–102, 

155

fossa, 28

infundibulum, 98

lamina, 16–17

lobe, 87

lobes, 87

lobes of the pterygoid sinus, 87

margin, 31, 41

margin of the lacrimal, 39, 41

palate of the frontal, 28–29

part, 29, 31

part of the frontal, 25, 28–29, 98

plate, 60, 64, 68

plate of the frontal, 29, 32

plate of the maxilla, 64

plate of the palatine, 72

portion, 87

portion of jugal, 36

process, 31–32, 37, 48, 64, 74, 76, 96

frontal, 29–30

jugal, 37

maxilla, 63

palatine, 66, 74

region, 86

rim, 41

roof, 29, 31

surface, 26, 29, 37, 39, 41, 64

frontal, 29

jugal, 37

lacrimal, 41

maxilla, 64, 96

sphenoid, 98

Orbital wing 

frontal, 29

presphenoid, 97, 98, 100

Orbitalis

ala, 90

Orbitofrontal plate, 29

Orbitosphenoid, 13–15, 24, 29, 61, 84, 

87, 90–91, 95–97, 98, 100, 155

crest, 98

portions of the external plate of the 

pterygoid, 87

Orbitotemporal 

canal, 26, 29

crest, 26, 28, 29, 31–32, 108, 154

fossa, 29–30

Orientation terms, 4

Orifice

bulla, anterior, 134

inferior maxillary [mandibular] 

nerve, 87

Orificium (hiatus) tympanicum tubae 

Eustachii, 141

Oro-nasal passage, 74

Os

basioccipitalis, 11

basisphenoidale, 91

conchae nasalis ventralis, 17

cristatus, 13

cuneiforme, 90

cuneo, 90

ethmoidale, 13

exoccipitalis, 17

frontale, 24

hyoideum, 32

incisivum, 79

interparietale, 33

iugale, 35

jugale, 35

lacrimale, 38

lenticulare, 151

maxilla, 48

maxillae superioris ossium primum, 

35

nasale, 68

occipitale, 21

palatinum, 70

parietale, 76

petrosum, 111

presphenoidale, 99

pterygoideum, 82

rostrale, 80

septomaxilla, 90

sphenoidale, 90

stapedi simile, 149

supraoccipitalis, 108

temporale, 103

temporale-pars petrosa, 111

temporale-pars squamosa, 102

temporale-pars tympanica, 133

zygoma, 35

zygomaticum, 35

Osse sphaenoide, 90

Osseous 

bulla, 92–93

labyrinth, 115, 123

nasal septum, 13, 16

tuba, 120, 141, 142

Osseum palatum, 71

Ossicle

accessory, 133

auditory, 9, 149

Ossicula auditus, 149

Ossiculum accessorium malleoli, 138, 149

Ossification

tentorial, 24

Ostium tympanicum tubae auditivae, 

135, 141, 148, 

Otic 

capsule, 123

ganglion, 114, 122–123

portion, 114, 123

Otocrane, 12, 104, 149

Otocranial 

cavity, 19, 23

flange, 11

plate of the basioccipito-sphenoid, 11

plate of the basisphenoid, 11

process, 12, 20

process of Owen, 11

vacuity, 19, 23

Outer 

convexity, 142

facet, 36

facet of the malar, 41

lamella, 86

lamina, 86

lip of the tympanic bulla, 133–136, 

140, 141, 142–147, 149

pedicle, 142, 143, 144, 147

posterior pedicle, 135, 137, 139, 

142–143

posterior prominence, 137, 139, 142, 

144

surface of the nasal, 69

Oval 

condyle, 21

foramen, 90, 93–94, 96

window, 117, 119, 123, 127, 131, 151

Palatal 

area, 154

crest, 65, 71–72, 74, 85

exposure, 154

palatine, 72

face, 74
a l e x i c o n n u m b e r 6 2 7 • 2 3 7

fissure, 80

groove, 64

part of the vomer, 153

process of the maxilla, 65

process of the pterygoid, 75

ridge, 65, 71–72, 74–75

sinus, 74

sphincter, 85–86

surface, 153

maxilla, 64, 66

Palate, 48, 70, 73, 81, 87, 154

hard, 59, 71

orbital, 29

soft, 75

Palatine 

artery, 73

base of, 71

bone, 8, 39, 49, 58, 63–66, 70–75, 

76, 82–83, 85, 87–89, 91, 96, 

102, 153–154, 156–157

body of, 71

canal, 65, 73, 74, 76

crest, 74

dorsal surface of horizontal lamina, 

71

fissure, 64–65, 80

foramen, 74

grooves of the maxilla, 64–65

horizontal lamina, 71

lateral lamina, 96

medial surface, 76

nasal surface of horizontal lamina, 

70–71

nerve, 73

oral surface, 71

oral surface of horizontal lamina, 

70–71

plate of the inner portion of the 

pterygoid, 87

plate of the maxillary, 65

process, 59, 64–65, 79

maxilla, 59, 64–65, 67

premaxilla, 80

pterygoid, 87

prominence, 65, 66

ramus of the facial nerve, 120, 128

sinus, 65, 74

sinus septum, 74

spine, 65

sulcus, 58, 64, 65, 74

surface, 71, 87

of the palatine, 71, 74, 76

of the premaxilla, 81

of the pterygoid, 61, 87

vein, 73

vellum, 75

ventral surface, 71

ventral surface of horizontal lamina, 

71

vessels, 74, 80

vomerine surface, 76

Palatomaxillary 

articulation, 65

suture, 59, 65, 72–74, 154

Palatopharyngeal sphincter, 13

Palatum 

durum, 75

molle, 75

osseum, 59, 75

Palpebral ligament, 37

Pan bone, 42–43, 45, 47

Papyraceous portion, 47

Para-sympathetic ganglia, 154

Parabullary ridge, 116, 119, 123

Paracondylar process, 21–22, 121

Paracondyloid process, 21–22

Parafalciform fossa, 98

Paraflocculus, 114, 129

Parajugular process, 22

Paramastoid process, 21–22

Paranasal 

sinus, 14–16, 27, 28, 29, 39–40, 

48–49, 57, 62–63, 66–67, 74

sinus system, 24, 27, 29, 63, 157

Parasympathetic 

branch, 99

fibers, 114, 123

Parietal

bone, 8, 11, 17–19, 21, 24–27, 29, 

32, 34, 35, 76–78, 95, 98, 

100–101, 103–106, 108–111, 

121, 124, 155

border of the sphenoid, 98

eminence, 77

foramen, 35, 77

margin, 27, 76–78, 105

frontal, 27, 29

interparietal, 35

supraoccipital, 110

temporal, 105

notch, 105

ossification, 77

plane, 77

plate, 105

Parietointerparietal suture, 35, 77

Parietosupraoccipital suture, 77, 78

Paroccipital, 22

concavity, 21–22

fissure, 20

fossa, 22

notch, 20, 22

pneumatic sinus, 22, 137

process, 12, 20, 21, 22, 32–33, 

104–106, 118, 121, 131, 137, 

148, 156

of the petrosal, 119

Pars

alveolaris, 42, 49

anteroexternus, 62

anterointernus, 66

basilaris, 11

canalicularis, 112, 114, 123, 131

cochlearis, 111–112, 114–115, 

117–122, 123–130, 133, 136, 

141

cuneiformis vomeris, 153

endotympanica, 137

flaccida, 116, 134, 144, 150

frontalis, 58

glandularis, 93

horizontalis, 74

incisiva, 44

labyrintha, 121, 123

lateralis, 17

mastoidea, 123–124, 126

mastoidea of the petrosal, 116

molaris, 46

nasalis, 28

orbitalis, 28, 31

papyracea, 47

perpendicularis, 74

petrosa, 111, 124

posteroexternus, 62

posterointernus, 66

squamosa, 103, 105–106

tympanica, 145–148

vestibularis, 114, 123–124, 133

Part

labyrinthine, 121

nasal, 28

orbital of frontal, 28

petrosal, 124

porcelanous, 81

styliform, 37

vestibular, 133

Partes laterales, 17

Passage

interosseus, 20

Pedicle foramen, 142

Pedicle

anterior, 134

basal, 135

Pedicular foramen, 137, 142

Peg

articular, 113

Peribullar cavity, 19, 147

Peribullary 

sinus, 12–13, 18, 22, 83, 84, 107, 

118, 122, 129, 156

fossa, 13

system, 90

space, 13

Perilymphatic 

duct, 115

foramen, 123

Periotic, 9, 18, 21–22, 24, 32–33, 83, 

90–91, 93, 98, 101–102, 104–107, 
2 3 8 • smithsonian contributions to zoolog y the therian skull

Periotic (continued)

111–122, 123–135, 137–138, 

141–144, 146–149, 151, 155, 157

body, 114

canal, 124

capsule, 124

cerebral part, 18

facet, 111, 133, 135, 142, 144

fossa, 105, 107

Periotical processes, 124

Perpendicular 

lamina, 

ethmoid, 13

palatine, 49, 71–73, 74–75

plate, 

ethmoid, 13, 16, 100, 152

palatine, 66, 72, 74, 

process, 71

Petro-occipital 

canal, 124

fissure, 20, 23

synchondrosis, 24

Petro-pterygo-tympanic plate, 105–106

Petro-tympanic, 149

bone, 142

orifice, 142

Petrobasilar 

canal, 12, 118, 124, 132

foramen, 124

Petromastoid bridge, 124

Petrooccipital 

canal, 124

fissure, 124

Petrosal, 18, 21–22, 91, 94, 100–102, 

111–114, 117–118, 124–132, 

137, 141, 147, 151, 155, 157

canal, 111, 114, 117–118, 120, 122, 

124–125

crest, 113, 115, 120, 122, 125, 

129–130

foramen, 98

fossula, 125

part, 124, 125

part of the temporal, 123, 124

ridge, 125

sinus, 19, 120

Petrosoparoccipital fissure, 19, 118, 

124, 125

Petrosquamosal 

fissure, 125

suture, 125

Petrosquamous 

fissure, 125

suture, 118, 122, 124, 130

Petrosum, 124

Petrotympanic, 149

bone, 125

fissure, 125, 129, 131, 133–134, 

138, 141, 142, 146, 149

medial, 142

Petrous, 123

part of the temporal, 106, 121, 125

temporal, 111, 155

Pharyngeal 

canal, 66

crest, 11, 12, 13, 19, 21, 86, 87, 

157

groove, 87

raphe, 13

region, 12–13, 87

sulci, 87

tubercle, 13

Pharynx, 154

Pila metoptica, 97, 98

Piriform 

aperture, 79

fenestra, 19, 23, 125, 131

Pit

anterior meatal, 112

lacrimal, 40

reception of zygoma, 29

suprameatal, 107

trochlear, 32

Pituitary, 102

body, 24

fossa, 13, 78

gland, 96

Plane

nuchal, 77

parietal, 77

temporal, 78

Planum 

nuchale, 77

parietale, 77

temporale, 78

Plate

basisphenoid otocranial, 12

cerebronasal, 24

cribriform, 14

exoccipital, 19

external, 57

external of pterygoid, 85

floor, 15

frontal, 58

glenoid, 103

infraorbital, 59

inner, 61

inner of pterygoid, 86

internal alveolar, 44

internal of pterygoid, 86

internal superior of pterygoid, 86

maxillary, 62

orbital, 64

orbitofrontal, 29

parietal of squamosal, 105

perpendicular, 16

petro-pterygo-tympanic, 105

posteroexternal, 81

posterointernal, 81

posterolateral, 81

prespiracular, 82

pterygoid, 99

pterygoperiotic, 106

roof, 17

side, 17

spiracular, 82

squamosal, 106

supraorbital, 31, 67

symphyseal, 48

temporoorbital of frontal, 32

tympanic, 13

vertical, 32

Plexus

pterygoid, 88

Pogonion, 47

Pole

cochlear posterior, 115

Pons, 12–13

Pontine impression, 13

Porcelanous part, 81–82

Pore

acoustic, 111

internal acoustic, 121

Portion

alisphenoid of external plate, 83

alisphenoid of lateral lamina, 91

alveolar, 42, 49

cochlear, 115

incisive, 44

mastoid of squamosal, 104

mesial of palatine, 73

molar, 46

nasal of premaxilla, 80

opisthotic of periotic, 123

orbitosphenoid of the external plate, 

87

otic, 123

prootic of periotic, 127

pyramidal prootic, 127

rostral of maxilla, 66

rostral of premaxilla, 82

styliform, 37

Porus

acusticus externus, 138

acusticus internus, 121

Postalveolar tubercle, 47

Posterior 

aperture, 142

aperture of the tympanic cavity, 137

bullar facet, 125, 126, 131, 143, 

149, 189

bullar septa, 135

canal, 128

carotid foramen, 93, 98

chamber of the tympanic cavity, 136

cleft, 137, 142

clinoid process, 93

cochlear crest, 114, 125

condyloid foramina, 22

conical apophysis, 142
a l e x i c o n n u m b e r 6 2 7 • 2 3 9

crus of ectotympanic ring, 142

crus of the stapes, 151

diverticulum, 135

division (of triangular opening), 146

division of the periotic, 125

division of the wing of the 

orbitosphenoid, 86

ethmoidal foramen, 29

falciform process, 103

infraorbital foramen, 60, 65

lacerate foramen, 18–19, 20, 22, 23, 

76, 90, 105, 112, 115, 126, 

139, 156

lacrimal crest, 40, 41

lacrimal process, 41

lamella, 87

lamina, 87

margin of the periotic, 126

margin of the petrosal bone, 125

maxillary sinus, 56, 63, 65

meatal crest, 105, 143, 144, 149

meningeal artery, 120

nares, 156

narial aperture, 156

narial wall, 156

nasal spine, 75

palatal elements, 156

palatine canal, 75

palatine foramen, 65–66, 75, 154

pedicle, 137, 142–143

process, 21, 113–114, 116–117, 

119, 121, 123–126, 129–

130, 132, 135–144, 147–149, 

155

of the periotic, 104, 115–116, 

122–123, 125, 126, 128, 

130, 136, 138, 140, 143

of the tympanic bulla, 21, 104, 

106, 122–123, 125–126, 

129, 136, 139–140, 

142–144, 147–149

of the tympanoperiotic, 126

prominence, 139, 141–142

pterygoid sinus, 22, 137

semicircular duct, 118

septum, 136–137, 145

sinus, 22, 83, 84, 118, 129, 137, 

139, 156

crest, 22

fossa, 22

surface 

nasal, 69

petrous temporal, 122

swelling of the premaxilla, 81

tympanic process, 114

tympanic spine, 134, 139, 143–144

wall 

external auditory meatus, 136

lateral lamina, 75, 87

wing of the lateral palatine, 75

Posteroexternal 

angle, 144

foramen, 126

plate, 81

process of the alisphenoid, 98–99

Posterolateral 

extension of the peribullary sinus, 

12, 22

lobe of the peribullary sinus, 84

palatine foramen, 58

plate of the premaxilla, 80, 81

sinus, 12, 22

crest, 22

fossa, 12, 22

 sulcus, 80, 81

 vacuity, 58

Posteromedial 

process, 41

process of the lacrimal, 40, 41

splint of the premaxilla, 81

sulcus, 81, 82

Posteroventral 

eminence, 126

face, 29

Postfrontal, 29, 30

process, 30

Postganglionic parasympathetic fibers, 

154

Postglenoid 

border, 105

foramen, 105, 107

fossa, 105

notch, 105

process, 103, 105–106, 111, 138

process of the squamosal, 22

vein, 112

Postmeatal 

apophysis, 105

crest, 126

process, 105

cavity, 65

process, 80

prominence of the frontal bone, 32

tract, 65

Postnasal passage, 74, 75

Postorbital, 30

angle, 29

bar, 29, 36

diverticulum, 30

extension, 87

ligament, 36

lobe, 30, 83, 87, 89

lobe of the pterygoid sinus, 30, 84, 

95, 156

part, 36

process, 25, 29–32, 36, 78, 96

of the jugal, 37

of the frontal bone, 25, 29, 30–32, 

37, 78, 87, 95, 96, 107, 155

recess, 95

ridge, 30

sinus, 89

smoothed area, 95

Postpalatine 

foramen, 58

shelf, 87–88

sinus, 83

spine, 73, 75

torus, 75

Postparietal foramen, 35, 78

Postpromontorial 

tympanic 

recess, 126

sinus, 126–127

Postsphenoid, 96

Posttemporal 

canal, 127

fossa, 105, 108

Posttympanic 

portion of squamosal, 126

process of the squamosal, 104, 105, 

126, 143, 144, 149, 155

Praesens foramen caelatur gratia 

secundi [sic: third] paris nervorum 

cerebri, 101

Praesens foramen omnium quae in oculi 

sede conspiciuntur, 96

Precondyloid 

foramen, 22, 95

notch, 22

Precoronoid crest, 47

Prefrontal bone, 16, 30

Preglenoid process of the squamosal, 

103, 106

Preinterparietal, 35

Premaxilla, 8, 16, 26, 32, 58–59, 65, 

68–71, 79–82, 152, 154–157

Premaxillary, 50, 79

boss, 81

cleft, 80, 81

crest, 70, 81

eminence, 81–82

foramen, 57, 59, 79, 80, 81

ossification, 79

sac, 80–81

fossa, 79, 80, 81–82, 156

sulcus, 82

surface of the maxilla, 65, 67

tubercle, 82

Premolar, 48

Prenarial 

basin, 82

fossa, 82

plate, 81

process, 153

triangle, 81, 82

tubercle, 153

Prenasal 

fossa, 82

protuberance, 81, 82
2 4 0 • smithsonian contributions to zoolog y the therian skull

Preorbital 

angle, 51

apophysis, 51

concavity, 66

depression, 26

extension, 87

extension of the smoothed area, 26

extensions of the pterygoid sinus, 30

foramen, 67

fossa, 40, 47

lobe of the pterygoid sinus, 26, 30, 

49, 83, 84, 87, 156

notch, 65

part of the pterygoid sinus, 87

process, 30–32, 41–42, 51

frontal, 30, 32, 38–39, 41, 155

lacrimal, 39, 41–42

recess, 26, 50, 66

ridge, 30, 41, 42, 50

sinus, 89

smoothed area, 26, 50

Presphenoid, 13–14, 82–83, 90–92, 

95–98, 99, 100–102

Presphenoid–basisphenoid suture, 

101–102

Prespiracular plate, 82

flange, 82

groove, 82

notch, 82

Primary facial foramen, 127

Process

alicochlear, 90

annular, 43

anterior, 112

lacrimal, 38

tympanosquamosal recess, 103

tympanic bulla, 134

anteromedial of tympanic bulla, 135

antorbital, 51

jugal, 36

articular of periotic, 113

ascending, 56

frontal, 24

ascial, 135

basal, 11

basioccipital, 11

bullar, 18

anterior, 133

caudal 

clinoid, 93

tympanic of periotic, 114

clinoid, 93

cochleariformis, 127

condyloid, 43

articular, 43

conical

anterior, 133

tympanic bulla, 134

cornual, 25

coronoid, 43

dorsal optic, 93

entoglenoid, 103

ethmoid, 15

external angular, 25

external lip of auditory bulla, 134

facial, 58

falcate, 12

falciform, 103

frontal, 79

jugal, 36

maxilla, 58

pterygoid, 85

Glaserian, 95

glenoid, 103

hamular, 85

interparietal, 34

intrajugular, 20, 121

jugular, 20

lacrimal, 15

lingual, 33

malar, 62

mastoid, 122

maxillary, 16

jugal, 37

palatine, 72

medial of lacrimal, 41

metoptic, 97

narial, 28

nasal of premaxilla, 80

occipital, 104

orbital, 29, 37, 74

otocranial, 12

palatine, 64

premaxilla, 80

paracondylar, 21

paramastoid, 21

paroccipital, 22

periotic, 124

perpendicular, 71

posterior lacrimal, 41

posterior of periotic, 126

posterior of tympanic bulla, 142

posterior, compound, 136

postglenoid, 105

postmeatal, 105

postorbital, 30

posttympanic, 105

preglenoid, 106

preorbital, 30

pterygoid, 106

maxilla, 66

sphenoid, 99

squamosal, 106

pterygotympanic, 106

pyramidal, 75, 127

retroarticular, 106

retrotympanic, 106

rostral 

clinoid, 99

tympanic, 128

septal, 30, 70

sphenoidal, 75

spiny, 106

squamosal bullar, 106

styloid of periotic, 128

superior of periotic, 130

suprafrontal, 67

supraorbital, 31, 67

tegmental, 130

temporal of jugal, 37

tentorial, 24

tympanic 

alisphenoid, 102

periotic, 131

pterygoid, 89

uncinate, 17

vaginal, 102

ventral of pterygoid, 90

zygomatic, 32

maxilla, 68

jugal, 38

Processus

alaris, 11, 153

alicochlearis, 90

alveolaris, 42, 49

angularis, 43

anterior, 135, 149

mallei, 134

breve, 119

brevis, 150, 151

clinoideus

caudalis, 93

medius, 99

rostralis, 99

cochleariformis, 127–128

cochlearis, 127

condylaris, 45

conicus

anterior, 133–134, 144

posterior, 136, 139, 144

posterior sive lateralis, 144

cornualis, 25

coronoideus, 43

cristae facialis, 117, 127

cristatus, 13–14

ethmoidalis, 15

falciformis, 103

folianus, 135, 149

Folii, 138

frontalis, 36, 39, 58

gracilis, 135, 149

gracilis of the malleus, 140

hyoideus, 131

interparietalis, 34

intrajugularis, 20, 121

jugularis, 20

lacrimalis, 15

caudalis, 41

rostralis, 38

lateralis, 150
a l e x i c o n n u m b e r 6 2 7 • 2 4 1

lenticularis, 151

lingualis, 33

longus, 138, 149, 151

malleus, 138

mastoideus, 122, 126

maxillaris, 16, 72

medius

bullae, 136, 139

of Boenninghaus, 136

tympanici, 140–142

muscularis, 141, 150

nasalis, 80

occipitalis, 104

orbitalis, 74

ossis anterior tympanici, 134

palatinus, 64, 80

papillares, 14

paracondylaris, 21

paramastoideus, 21

perioticus, 144

petrosus

of the tympanic, 143, 144

ossis tympani [sic], 133, 147

ossis tympanici, 144

posterior, 143

pterygoideus, 66, 99

pyramidalis, 75

retroarticularis, 106

retrotympanicus, 106

septalis, 30, 70

sigmoideus, 134

sphenoidalis, 75

styliformis, 131, 141, 144, 146

styloideus, 131, 141, 146

temporalis, 37

tentoricus, 24, 35, 110

tubarius, 103, 106, 119, 127, 

133–134, 140, 142, 144–146

tympanicus, 128

ossis petrosi, 126

uncinatus, 17

vaginalis, 102

vespertilionum alis, 99

zygomaticus, 32, 68, 103, 108

Projecting plate of the palatine, 72, 75

Projection

lateral of anterior process, 121

Prominence

maxillary, 63

palatine, 65

Prominentia canalis lateralis, 121, 127

Prominential 

crest of the maxilla, 66

notch, 50, 53–56, 63, 66

Promontorial 

artery, 157

groove

median, 127

stapedial artery groove, 128

Promontorium, 124–125, 127–129, 141

Promontory, 118, 125, 127

artery, 129

pars cochlearis, 127

periotic, 94, 115, 127

petrosal, 115, 128

pyramid, 127

Prootic portion of the periotic bone, 

112, 127

Prosthion, 82

Protuberance

external occipital, 34

internal occipital, 110

mental, 46

occipital, 110

prenasal, 82

Protuberantia

mentalis, 46

occipitalis

externa, 34

interna, 110

Proximal 

infundibular cavity, 45

opening of the facial canal, 116

Prussak’s pouch, 116

Pterion, 78, 101

Pterygoid 

air sinus, 66

bone, 8, 11, 49, 61, 66, 70–75, 77, 

80, 82–85, 87–89, 91, 94, 

96–97, 99, 105, 114, 141, 154, 

156–157

canal, 66, 88, 90, 99

crest, 88, 99

elevation, 65, 66

eminence, 65

fissure, 88

fossa, 85, 88

palatine, 75

sphenoid, 75, 99

fovea, 47

groove, 88, 99, 101

hamulus, 49, 71–72, 74, 85–86, 

88–90, 154, 156

hypertrophy, 156

inner plate, 86

internal plate, 86

lamina, 85–86, 88–89

lateral lamina, 96

medial lamina, 86

muscle, 43, 47, 49, 61, 74–75, 88

notch, 88

plate, 86, 99

plexus, 88

process, 66, 75, 88, 90, 95, 99, 106

basisphenoid, 90, 99. 101

maxilla, 66

sphenoid, 66, 82, 88, 91, 99

squamosal, 106

ridge, 88

sac, 49

sinus, 12, 26, 30, 50, 70, 75, 83, 84, 

85–87, 89, 91, 95, 98, 154, 156

complex, 83, 89, 156

fossa, 63, 75, 83–86, 88, 89, 92, 

94–95

system, 12, 49, 83, 88–90, 98, 

156, 157

postorbital lobe, 30

preorbital lobe, 30

tubercle, 47

tuberosity, 47

Pterygomaxillary 

fissure, 27, 66

region, 66

Pterygopalatine 

canal, 58, 66, 75

fossa, 41, 61, 66–67, 71, 75, 76, 89, 

99, 100, 154

ganglion, 99, 125, 154

ridge, 89

sulcus, 58, 154

surface of the maxilla, 66

trough, 89

Pterygoperiotic plate, 87, 106

Pterygosphenoid suture, 99

Pterygotympanic process, 106

Pyramid, 111, 113, 122, 124, 127

pars cochlearis, 127

Pyramidal process, 88, 

palatine, 75

periotic, 127

Pyramidal prootic portion, 127

Quadrate bone, 42, 149

Quae durae cerrebri membranae hic 

firmadae extruit, 100

Quartum maxillae superioris os, 48

Qui venulae cum visorio nervo hac 

excidente paratur, 97

Quinti nervorum cerebri paris meatus, 

auditorius ve porus, 120

Quos vespertilionum alis 

comparabimus, 99

Rami temporales

of the stapedial artery, 103

foramina for, 103, 107

Ramus, 43, 45–48

mandibulae, 47

nasalis medialis, 15

Ramus of the mandible, 47

Recess

elliptical, 116

epitympanic, 116

postpromontorial tympanic, 126

spherical, 128

tympanosquamosal, 108

zygomatic, 68

Recessus

epitympanicus, 116, 127, 130
2 4 2 • smithsonian contributions to zoolog y the therian skull

Recessus (continued)

maxillaris, 63

meatus, 145, 148

sphericus, 128

Rectus capitis

lateralis muscle, 21–22

posterior, 34

ventralis muscle, 12

Regio mastoidea, 128

Regio pterygomaxilaris, 66

Region

alisphenoid, 91

mastoid, 122

Renflement postérieur du prémaxillaire, 

81

Respiratory passages

distal opening, 156

external opening, 156

facial bony openings, 156

internal bony opening, 156

proximal bony opening, 156 

Retroarticular 

foramen, 105

notch, 102, 105, 106

process, 102–103, 105, 106, 111, 

138

vein, 105, 112

Retrotympanic process, 106, 143

Rhinal veins, 30, 35

Rhomboideus, 35

Ridge

basioccipital, 12

caudal rostral, 68

caudal, sigmoid process, 136

dorsal, 115

dorsolateral of tegmen tympani, 116

impression, 75

internal vertical, 110

mesethmoid, 16

nasal, 28

on the anterior process, 121

palatal, 74

parabullary, 123

petrosal, 125

postorbital, 30

pterygoid, 88

supratemporal, 67

supratrabecular, 107

trans-basicranial, 13

ventrolateral, anterior process, 132

Rim

articular of periotic, 113

Rimam hanc temporis ossi & occipitii 

communem, 138

Roof 

of mouth, 71

orbital, 29

plate, 14, 17

tympanic, 131

Rostral 

alar foramen, 90–91, 94, 99, 102

border 

of the jugal, 37

of the lacrimal, 42

carotid foramen, 135, 138, 145

clinoid process, 99

crest, 51, 63

crus of the stapes, 151

elements, 156

lip, 145

maxillary crest, 51

maxillary sinus, 66–67

part of the maxilla, 56

portion

maxilla, 66

premaxilla, 80, 82

process, 79, 81, 149, 150

ridge, 63

of sigmoid process, 136, 145–146

squamosal foot, 140, 145

surface 

maxilla, 66

premaxilla, 82

tympanic process, 128

Rostrale

os, 80

Rostrodorsal part, 117

Rostrum sphenoidale, 100

Rostrum, 15, 28, 48–50, 58, 62–64, 66, 

82–83, 151–152, 154, 156

sphenoidal, 100

Round 

anterior extremity, 51

foramen, 90, 95

window, 112, 115, 118, 124, 127, 

128

Rursus ad externum foraminis Q 

indicati latus, 95

Sac moyen, 106

Sac

anterior, 83

medial, 104

Saccule, 116, 128

Sacculus, 118, 128, 132

Sagittal 

border of the parietal, 78

crest, 58, 78, 110

facial crest, 58

margin of the frontal, 30

part of the vomer, 152, 153

sinus, 25, 30, 34, 35, 109, 110

sulcus, 27

suture, 27, 30, 32, 34, 78, 109

Sagittalis sutura, 78

Salivary gland, 48

Scala tympani, 115

Scaphoid fossa, 95, 99

Sciptorii stili, 108

Sclera, 14

Secondary 

facial foramen, 117, 128

internal auditory 

canal, 19, 23

meatus, 19, 23

spiral lamina, 128

tympanic membrane, 118

Sedis oculorum, 28

Sella turcica, 13, 78, 92–93, 96, 99, 

100

Semicanal 

auditory tube, 103, 145, 148

tensor tympani muscle, 119, 128

tensor veli palatini muscle, 145

Semicanalis

m. tensoris tympani, 127–128

m. tensoris veli palatini, 145

musculus tensoris tympani, 141

tubae auditivae, 127, 141, 145

Semicircular canals, 111, 113, 115, 123, 

128, 133, 155

Semilunar ganglion, 114, 131

Semilunar hiatus, 17

Septa

interalveolaria, 44

interradicularia, 44

Septa, 145

of meatal tube, intrabullar part, 146

Septal 

cartilage, 16

process

frontal, 30

nasal, 70

Septo medio ipsius nasi, 152

Septomaxilla, 90

Septum

amplitudine narii, 152

bullae, 145

canalis musculotubarii, 127, 145

nasale, 152

nasi osseum, 152

sinuum frontalium, 30, 35

maxillarium, 67

palatinorum, 74

sphenoidalium, 100

Septum

bullar, 135

frontal sinus, 27, 30

interalveolar, 44

interradicular, 44

maxillary sinus, 67

meatal tube

intrabullar part, 145

musculotubal canal, 145

palatine sinus, 74

sphenoidal sinus, 100

transverse, 130
a l e x i c o n n u m b e r 6 2 7 • 2 4 3

Septum . . . quae cerebri processibus 

parantur, 14

Sextis superioris maxillæ ossibus, 70

Shallow lateral groove, 128

Sheath 

hyoid process, 139, 145–146, 

148–149

styloid process, 146

Shelf

supravomerine, 67

vomerine, 67

Shield

occipital, 110

supraocciptal, 110

Short 

crus, 151

process, 150

Side plate, 17

Sigmoid process, 116, 121, 133–134, 136, 

138–140, 142, 144, 145, 146–149

conical process, 146

sinus, 109, 120, 132

Sinciput, 31

Singular foramen, 118, 128, 132

Sinstrum uerticis os, 76

Sinus, 45

condylaris, 18

frontalis, 27

caudalis, 24, 27, 35

intermedius, 27

lateralis, 27–28

medialis, 27

rostralis, 27

rostralis

lateralis, 24, 27

medialis, 27

in cuneiforme osse incisus, 96

lacrimalis, 40

maxillaris, 63

caudalis, 56, 63, 65

rostralis, 49, 63, 66

ossis ad excipiendum posterius 

caput madibulae inferioris, 

104

palatinus, 65, 74

paranasales, 29

pneumaticus paroccipitalis, 22, 137

rectus, 109

sagittalis, 30, 35

sphenoidalis, 100

Sinus

anterior, 49, 83

maxillary, 49

pterygoid, 83

basisphenoidal, 91

caudal maxillary, 56

epitympanic, 116

ethmoid, 29

frontal, 27, 29

lacrimal, 40

maxillary, 29, 63

medial, 104

middle, 104

pterygoid, 86

palatine, 65, 74

paranasal, 29

paroccipital pneumatic, 22

posterior, 22

maxillary, 65

pterygoid, 22

postpromontorial tympanic, 126

pterygoid, 89

rostral maxillary, 66

sagittal, 30, 35

sphenoid, 29

sphenoidal, 100

ventral petrosal, 132

Sixth bone of the upper jaw, 70

Small 

alar foramen, 100

apophysis, 113

mandibular fossa, 45

wing, 100

Socket, 48, 67

Soft palate, 71, 74, 75, 82, 154

Sound reception, 156

Space

interdental, 61

mandibular, 45

Spermaceti 

organ, 65

cavity, 65

Sphaenoides os, 90

Sphenethmoid recess, 73

Spheno-occipital suture, 13

Sphenoethmoid lamina, 75

Sphenoethmoidal suture, 100

Sphenofrontal 

fissure, 98

suture, 100

Sphenoid, 9, 66, 76, 78, 89, 90, 98, 

100–102, 141, 153, 155

body of, 92

complex, 90

fissure, 92

lesser wing, 97

ossifications, 90

process, 66, 102

of the palatine, 66

sinus, 100, 157

aperture, 100

Sphenoidal 

angle, 78

concha, 100

crest, 100

fissure, 95, 97–98, 100

fossa, 100

incisure of the vomer, 100, 153

margin 

squamosal, 101

temporal, 106

part of the sinus, 91

portion of the pterygoid sinus, 89

process, 75–76

rostrum, 100

sinus, 29, 91, 100

sinus septum, 100

spine, 100–101

yoke, 98, 100

Sphenomandibular ligament, 45

Sphenomaxillary 

fissure, 100–101

fossa, 67, 100

suture, 101

Sphenooccipital synchondrosis, 101

Sphenopalatine 

artery, 60, 71, 76

canal, 76

fissure, 114, 122

foramen, 63, 65–66, 71–72, 74, 76, 

80, 154

ganglion, 66, 154

lamina, 76

notch, 76

opening, 76

Sphenoparietal suture, 95–96, 101

Sphenorbital fissure, 91, 95, 97–98, 

100, 101

Sphenosquamosal suture, 101, 106

Sphenotympanic fissure, 23

Sphenozygomatic suture, 101

Spherical recess for the saccule, 116, 

128, 132

Spina 

angularis, 100

mentalis, 46

nasalis, 73

anterior, 79

ossis sphenoidalis, 101

palatinae, 65

suprameatica [suprameatalis], 107

trochlearis, 32

tympanica

anterior, 134

major, 134

minor, 139, 143

posterior, 134, 143

Spinal cord, 19

Spinal meningeal arteries, 158

sulcus for, 23–24

Spine

anterior 

nasal, 79

tympanic bulla, 134

ethmoidal, 93

frontal, 28

mental, 46
2 4 4 • smithsonian contributions to zoolog y the therian skull

Spine (continued)

nasal, 28, 73

palatine, 65

posterior nasal, 75

sphenoidal, 100

suprameatal, 107

trochlear, 32

tympanic

anterior, 134

greater, 134

Spinose foramen, 90

Spiny process, 106, 116, 138, 140, 148

Spiracle, 156–157

Spiracular, 156–157

plate, 82, 156

sac, 81

surface of the vertex, 80, 82, 156

Spiral 

canal, 122, 128

cribriform tract, 113, 120, 128, 130, 

132

lamina, 115, 128

Spiralis labyrinthi ductus, 123

Splint

posteromedial, 81

Squama, 106

frontalis, 27

occipitalis, 110

temporalis, 106

Squamaeformis conglutinatio, 106

Squamo-mastoid, 104

Squamocranial notch, 106

Squamomastoid groove, 106

Squamoparoccipital suture, 105

Squamosa conglutinatio, 106

Squamosal 

articulation, 37

bone, 9, 12, 17–19, 21, 24, 30, 

34–37, 42–43, 45, 68, 76–78, 

83, 89, 91, 94, 96–98, 100, 

101, 102–109, 111–112, 116, 

120, 122, 124–127, 129–130, 

132–134, 138–140, 142–143, 

147–149, 155

border of the sphenoid, 101

bullar process, 103, 106, 134

cleft, 98

fossa, 112, 121, 128, 132

part, 106

plate, 103, 106

suture, 106

Squamosal–petrosal (periotic) suture, 

105

Squamose suture, 106

Squamoso-alisphenoidal suture, 106

Squamous 

border of the parietal, 78

part of the temporal bone, 24, 37, 

102, 106, 107–108, 124–125, 

138, 147

portion of the temporal, 108, 124

suture, 27, 106

temporal, 126

Stapedi os simile, 149

Stapedial 

artery, 29, 94, 129, 137, 157, 158

groove, 120, 128

rami temporales, 103

circulation, 29

crura, 151

foramen, 29, 151, 158

muscle, 151

muscle fossa, 122

Stapes, 9, 116, 147, 149, 151

Sternohyoid muscle, 48

Sternomandibular 

muscle, 48

tuberosity, 48

Sternum, 48

Straight sinus, 109

Styliform 

part, 36, 37–38, 68

portion, 37

process, 131, 141, 146

Styloform 

part, 36-37

posterior half, 37

process, 37

Stylohyal, 22, 33, 131, 141, 145–146

fossa, 128

Stylohyoid, 32, 33, 131

angle, 33

ligament, 33

Stylohyoideum, 33

Stylohyoideus muscle, 33

Styloid, 141

apophysis, 141, 146

process, 33, 106, 128, 131, 141, 

146

Styloides processus, 131

Stylomastoid 

artery, 129

canal, 117–118, 122, 128–129

foramen, 114, 117, 118–119, 122, 

126, 128, 129, 131

fossa, 104, 129

notch, 117, 129

Subarachnoid space, 115

Subarcuate fossa, 114, 125, 129

Sublingual 

depression, 48

fovea, 48

salivary gland, 48

Submandibular 

fovea, 48

salivary gland, 48

Submaxillary 

depression, 48

gland, 48

triangle, 48

Suborbital 

arch, 35

bar of the malar, 35, 37

canal, 67

foramen, 59

region, 154

Subsquamosal foramen, 107

Substantia perforata anterior, 17

Subtemporal crest of the squamosal, 96, 

107–108

Subvomerine shelf, 67

Sulcus

arteriae meningea caudalis, 120

arteriae occipitalis, 120

arteriae temporalis mediae, 104

arteriae meningea mediae, 96

alveolaris, 42

caroticus, 92

chiasmaticus, 93

chiasmatis, 93

ethmoidalis, 69

hamuli pterygoidei, 85

infraorbitalis, 60

lacrimalis, 40, 61

malleolaris, 138, 140, 146, 149

medialis, 129

mylohyoideus, 46

nervus canalis pterygoidei, 88, 101

nervus maxillaris, 96

nervus pterygoidei, 99

palatinus, 64–65

palatinus major, 58, 64, 65

peripetrosus superior, 120

prechiasmaticus, 93

pro chorda tympani, 146

pterygopalatinus, 58

septalis, 152

septi nasi, 79, 152, 153

sinus occipitalis, 109

sinus petrosi dorsalis, 120

sinus petrosi ventralis, 12, 124

sinus sagittalis dorsalis, 34, 109

sinus sagittalis superior, 109

sinus sigmoidei, 24, 120

sinus transversi, 78, 109

supraorbitalis, 31

tubae auditivae, 101

tympanicus, 148

vomeris, 152

Sulcus

alveolar, 42

anteroexternal of periotic, 112

anterointernal of periotic, 112

anteromedial, 79

brain, 18

carotid, 92

cerebellum, 18

chorda tympani, 134, 136, 140, 142, 

146

dorsal, 79
a l e x i c o n n u m b e r 6 2 7 • 2 4 5

facial, 117

greater palatine, 58

infraorbital, 60

internal carotid artery, 103, 128, 129

intracranial extensions of the spinal 

meningeal artery, 23, 78

lacrimal, 61

mandibular, 45

medialis, 129

middle meningeal artery, 78

middle temporal artery, 104

mylohyoid nerve, 46

nasal septum, 152

palatine, 65, 74

posterolateral, 81

posteromedial, 81

sigmoid sinus, 24

spinal meningeal arteries, 23–24

stapedial artery, 128

supraorbital, 31

transverse, 79

transverse sinus, 18, 24, 35, 78, 79

tubae auditivae, 101

tympanohyal, 146

vestibulocochlear nerve, 12

Supaoccipital border, 78

Superciliary 

arch, 25, 27, 31

arches, 31

Superficial petrosal nerve, 120

Superior 

alveolar canal, 59

alveolar foramina, 62

lamina 

pterygoid, 83–84, 96

pterygoid hamulus, 83

pterygoid plate, 83

margin of the petrosal, 129

maxillary sinus, 57

nasal concha, 17

nuchal line, 35

ophthalmic vein, 101, 155

orbital, 

crest, 29

fissure, 96, 98, 101, 155

ridge, 60, 96

petrosal sinus, 120

portion, 96

process, 115, 120, 125, 127, 129, 130

Pompeckj, 115

periotic, 114, 130

ramus for the stapedial artery, 118

semicircular canal, 113, 129

temporal line, 78

Superiori maxillae, 48

Supermaxillary fossa, 154

Superoccipital, 108

Superoptic process, 97

Superorbital 

fossa, 66

plate, 56

process, 31

ridge, 31

Supracochlear cavity, 119, 130

Supracranial basin, 19, 57, 62, 64, 67

Suprafrontal 

extension, 56

process, 56, 67

Supramastoid crest, 107–108, 147

Suprameatal 

area, 130

bridge, 107

crest, 29

foramen, 107

fossa, 103, 107, 130

pit, 107

spine, 107

triangle, 107

Supraoccipital

bone, 9, 17, 19, 21, 33–35, 76–78, 

103, 108–109, 110–111, 121, 

155

border of the parietal, 78

crest, 110

foramina, 110

region, 108

shield, 110

Supraorbital 

artery, 31

canal, 31

crest, 51, 52, 57, 62, 67

foramen, 59

foramen of the frontal bone, 26, 31

groove, 31

line, 77

margin, 26, 27, 29, 31–32, 58

frontal, 26, 28, 31

maxilla, 67

nerve, 26, 31

notch, 31

part of the maxilla, 62

plate, 31, 67

process 

frontal, 28–30, 31, 32, 59, 64, 67

maxilla, 67

ridge, 51, 57, 67

sulcus, 31

vein, 27, 31

wing, 31

Supratemporal 

crest, 29, 31, 64, 67, 78

ridge, 67

Supratrochlear artery, 26

Supratubercular ridge, 107

Supreme nasal concha, 17

Surface

anterior of the maxilla, 49

articular of squamosal, 103

buccal, 43–44

cerebral

maxilla, 57

petrosal, 114

sphenoid, 93

condylar articular, 43

cranial of periotic, 115

external, 25

maxilla, 57

facial, 44

lacrimal, 39

maxilla, 58

frontal of maxilla, 58

glenoid, 103

infratemporal, 60

internal 

frontal, 27

nasal, 69

parietal, 77

labial 

mandible, 44

premaxilla, 80

lateral of jugal, 36

lingual, 45

maxillary, 28

frontal, 24

palatine, 72

medial of petrosal, 122

nasal 

lacrimal, 41

maxilla, 64

palatine, 73

nasopharyngeal, 86

sphenoid, 97

occipital of petrosal, 122

orbital, 29, 37

lacrimal, 41

maxilla, 64

sphenoid, 98

palatine 

palatine, 74

premaxilla, 81

pterygoid, 87

premaxillary of maxilla, 65

pterygopalatine, 66

rostral 

maxilla, 66

premaxilla, 82

spiracular of vertex, 82

symphyseal, 48

temporal 

frontal, 31

jugal, 37

sphenoid, 101

squamosal, 108

tympanic, 131

ventral

palatine, 74, 76

petrosal, 132

premaxilla, 82

Sutura, 27, 68, 100–101

coronalis, 25
2 4 6 • smithsonian contributions to zoolog y the therian skull

Sutura (continued)

frontomaxillaris, 27

frontozygomatica, 27

incisiva, 80

interfrontalis, 27

{lambda} exprimens, 34

{lambda} imitantis, 34

{lambda} literam, 34

{lambda} referentis, 34

{lambda} simili, 34

occipitomastoidea, 21

occipitosquamosa, 104

ossi iugalis, 108

sagittalis, 78

sphenoethmoidalis, 100

sphenofrontalis, 100

sphenomaxillaris, 101

sphenoparietalis, 101

sphenosquamosa, 101, 106

sphenozygomatica, 101

squamosa, 106

temporozygomatica, 108

zyomaticomaxillaris, 67, 68

Suture

frontal, 27

frontonasal, 69

incisive, 80

internasal, 70

lambdoid, 34

maxillopalatine, 63

metopic, 28

nasomaxillary, 70

occipitosquamosal, 104

parietointerparietal, 77

parietosupraoccipital, 77

sphenoparietal, 101

sphenosquamosal, 106

zygomaticomaxillary, 67

Symphyseal 

end, 48

part, 48

surface, 42, 48

plate, 48

Symphysis mandibulae, 46

Symphysis, 42, 44, 46–48

mandibular, 46

Synchondrosis

intersphenoidalis, 96

sphenooccipitalis, 101

Synchondrosis

intersphenoidal, 96

Syncipite, 31

Synciput, 31

Syndesmosis, 42

Synovial joint, 108

Synvertex, 32 

Tegmen tympani, 112, 114, 116, 

124–125, 127, 130–131

Tegmental process, 112, 130

Telescoping, 26–27, 56–57, 59–60, 108, 

154

Temporomandibular joint, 108

Temporoorbital plate of the frontal, 25, 

32

Temporozygomatic suture, 108

Temporal 

arch, 107

bone, 21, 35, 90, 101–102, 104, 

106–107, 111, 117, 122–125, 

147–148, 155

border, 37, 77

jugal, 37

crest, 26, 29, 34, 77–78, 105, 106, 

107–108

fascia, 78, 107

fossa, 27, 29–32, 35–37, 60–61, 63, 

66, 68, 76–78, 96, 101, 105, 

107, 108, 155

line, 26, 31–32, 35, 77, 78

lobes of the cerebrum, 108

meatus, 105

muscle, 36, 78, 108

part, 102

plane, 78

plate of the frontal, 31–32

portion, 96

jugal, 36

process of the jugal, 37

sinus, 105, 109

squamous part, 102

surface, 78

alisphenoid, 96

frontal, 29, 31–32

jugal, 37

sphenoid, 101

squamosal, 108

venous sinus, 130

wing, 90, 101

sphenoid, 90, 141

Temporale

ala, 90

Temporalis muscle, 26, 36, 107

Temporalis

ala, 90

Temporis, 108

os, 102

ossis, 111

processus, 108

Temporomandibular joint, 42, 45, 104, 

108

Temporoorbital plate, 32

Temporozygomatic suture, 108

Tendon of the m. tensor tympani, 150

Tensor

tympani muscle, 119, 122

veli palatini muscle, 85, 145

Tentorial 

crest, 24

ossification, 24, 111

process, 24, 35, 78

Tentorium, 24, 95, 109, 110–111

cerebelli, 24, 125

cerebelli membranaceum, 110

cerebelli osseum, 24, 110

osseum, 110

Tenuous osseous lamella, 97

Terminal nerve, 17

foramina, 17

Third occipital condyle, 13

Thyreohyoid, 33

Thyrohyal, 33

Thyrohyoid, 32, 33

muscle, 33

Thyrohyoideum, 33

Thyrohyoideus muscle, 33

Thyroid cartilage, 33

TMJ, 108

Torus

frontalis, 26

mandibularis, 46

Torus

mandibular, 46

Trabeculae, 145

Tract

spiral cribriform, 128

Tractus spiralis foraminosus, 120, 128, 

130

Trans-basicranial ridge, 13

Transversam lineam, 101

Transverse 

canal, 102, 110, 111

foramen, 101–102

crest, 62, 112, 115–118, 120, 128, 

130, 132, 146

lamina, 15

ethmoid, 67

occipital crest, 62

ridges, 146

septum, 130

sinus, 18–20, 30, 35, 78, 109–110

sulcus, 78–79

vascular channel, 112, 130–131

vascular groove, 112, 131

Trapezius, 35

Triangle

prenarial, 82

Triangular opening, 146

Trigeminal 

impression, 131

nerve, 39, 57, 90, 114, 131

Trochlear 

nerve, 90, 98, 101, 155

pit, 32

spine, 32

Trou

dentaire superior, 59

sous orbitaire, 59

True tympanic cavity, 147

Tuba auditiva, 114
a l e x i c o n n u m b e r 6 2 7 • 2 4 7

Tubal 

canal, 146

foramen, 146

groove, 146

notch, 85, 89

tubercle, 119, 133, 144, 146, 149

Tube

auditory, 114

bony tympanic, 135

Eustachian, 117

Tuber

faciale, 58

frontale, 26

maxillae, 63

parietale, 77

Tubercle

antorbital, 56

articular, 103

jugular, 21

lacrimal, 61

marginal, 36

mastoid, 122

maxilla, 63, 67

mental, 46

muscular, 12

nuchal, 35, 110

pharyngeal, 13

postalveolar, 47

premaxilla, 82

Tubercula nuchalia, 110

Tubercule of the malleus, 150

Tuberculum

articulare, 103

jugulare, 21

mallei, 150

marginale, 36

mentale, 46

musculare, 12

pharyngeum, 13

sellae, 78, 93, 96, 99, 102

Tuberositas

m. sternomandibularis, 48

masseterica, 46

pterygoidea, 47

Tuberosity

dorsal, 115

facial, 58

lateral of periotic, 121

masseteric, 46

maxillary, 63

occipital, 110

premaxilla, 82

pterygoid, 47

sternomandibular, 48

tegmen tympani, 112, 130, 131

ventral, 132

ventrolateral, 132

vomer, 153

Turbinal, 14–16, 17, 64

Turbinate complex, 70

Turk’s saddle, 100

Tympani cavitas, 147

Tympanic, 90, 101, 106, 111, 124–125, 

143, 148–149

annulus, 136, 140, 144, 146–147

antrum, 116, 121, 130, 131

aperture, 139, 140, 142, 146–147

facial canal, 131

bone, 131–132, 137, 141, 146, 149

branch, 131

branch of the glossopharyngeal, 

122

bulla, 9, 12–13, 17–18, 21–22, 33, 

83, 89, 91–94, 102–103, 105, 

111, 119, 124–126, 128–129, 

131, 133–146, 147–149, 155, 

157

canaliculus, 131

cavity, 19, 49, 83, 84, 86, 92–93, 

104, 115–116, 119, 127, 

130–131, 133–140, 142, 145, 

147–148, 155

cavity proper, 147

cleft, 147

crest, 134, 136, 147–148

ganglion of the glossopharyngeal 

nerve, 125

groove, 147–148

incisure, 116, 134, 137, 140, 147

ligament, 150

membrane, 116, 136–137, 144–146, 

147–148, 149–150

nerve, 131

notch, 106, 116, 134, 137–138, 

147–148

opening of the auditory tube, 114, 

148

outlet, 137, 141, 145

part, 106, 137, 148

temporal, 133, 138, 147, 148

plate, 13, 148

plexus, 114, 122–123, 131

process, 114, 131

alisphenoid, 94, 102

pterygoid, 89

region, 103

ring, 133–137, 140, 144, 146, 147, 

148

roof, 125, 131

sulcus, 133, 139, 147, 148

surface of the periotic, 131–132

Tympanicum, 148

Tympanohyal, 33, 117–118, 122, 128, 

131, 141, 143, 145–146

cartilage, 131

sulcus, 139, 146, 148

Tympanohyoid, 32, 33, 131

cartilage, 33

Tympanohyoideum, 33

Tympanomalleolar fold, 150

Tympanomastoid, 133, 143–144, 147, 

148

fissure, 125, 131, 148

process, 148

Tympanooccipital fissure, 23, 135, 

148

Tympanoperiotic, 9, 12, 18, 89–90, 92, 

104, 111, 125–126, 136, 143, 

148–149, 155, 156

bone, 142

fissure, 131, 138

hiatus, 19, 23

region, 11

Tympanosquamosal 

fissure, 149

recess, 86, 102–106, 108, 116, 156

suture, 149

Tympanostyloid, 145

Umbo, 151

Unciform process, 133, 149

Uncinate 

notch, 17

process, 15, 17, 119, 133–134, 149

of Schulte, 127

Upper jaw, 48

Upper tympanic 

aperture, 116, 131, 147

pouch, 116

Utricle, 123, 131, 132

Utriculus, 116

Vacuity

antorbital, 39

Vagina processus

hyoidei, 145, 149

styloidei, 145–146

Vaginal process, 102

Vagus nerve, 20–21, 121

Vascular 

channel, 112, 131

foramen, 132

foramen associated with the periotic, 

95

groove, 112, 131

sinus system, 90

Vein to the transverse sinus, 121

Velum palatinum, 75

Vena angularis, 27

Venous sinuses, 156

Ventral 

border 

periotic, 132

petrosal bone, 132

carotid foramen, 13, 92–93, 102

condyloid, 19

foramen, 24

fossa, 20, 22, 24

cranial venous sinuses, 12

ethmoidal crest of the maxilla, 67
2 4 8 • smithsonian contributions to zoolog y the therian skull

Ventral (continued)

foramen of the facial canal, 120, 

127, 132

groove, 149

infraorbital foramen, 32, 40, 49–50, 

58–59, 62, 64, 67, 76, 81, 

154

keel, 141, 149

lamina, 15, 85, 89–90

pterygoid, 89

margin of the mandible, 48

nasal concha, 17, 63

oblique muscle, 39

fossa for, 39

occipital condyle, 20

opening of the facial canal, 117, 128

orbital crest, 25–26, 32, 66, 154

petrosal sinus, 12, 20, 118, 124, 129, 

132

process, 90

surface, 74

frontal, 26

hard palate, 67

nasal, 69

palatine, 76

pars cochlearis, 120

petrosal, 132

premaxilla, 82

swelling, 123

temporal line, 78

tuberosity, 121, 132

vestibular area, 118, 128, 132

Ventrolateral 

crest of lacrimal, 41–42

crest of lacrimojugal, 42

ridge, 132

tuberosity, 121, 132

Vermiform 

fossa, 111

impression, 110, 111

Vermis of the cerebellum, 111

Vertebral vascular plexus, 19, 111

Vertex, 26, 28, 32, 58, 68–70, 81, 

109–110, 155

Vertical 

canal, 132

cleft, 137, 149

lamina, 75

plate, 25, 32

Verticis ossi, 32

Verticis sinistrum os, 76

Verum id in uno calvariae latere raro 

uisitur, 94

Vestibular 

aqueduct, 113, 123, 132

area, 132

crus, 116, 132

face, 151

fenestra, 132

fossa, 132

fossula, 132

nerve, 116, 118

part, 123, 133

portion, 123

window, 114–115, 117–119, 121, 

127, 132, 133

Vestibule, 113, 115–116, 123, 128, 

132, 133

Vestibulocochlear nerve, 12, 19, 95

Vestibulum, 133

Vidian 

artery, 99

canal, 88, 90

Vomer, 10, 14, 16, 64, 70, 73, 75, 79–

80, 82–83, 91, 96–97, 100–101, 

151–154, 156–157

perpendicular plate, 152

Vomerine 

crest, 152, 153

gutter, 152

shelf, 65, 67

Vomeronasal 

nerve, 17

organ, 17, 80, 90

Vomeropalatine suture, 75

Walls

alveolar, 43

Wedge-shaped part of vomer, 153

Window

acoustic, 42

cochlear, 115

oval, 123

round, 128

vestibular, 133

Wing

epitympanic, 93

greater, of sphenoid, 90, 96

orbital, 98

orbital of frontal, 29

small, of sphenoid, 100

sphenoid, 94, 102

supraorbital, 31

temporal, 90, 101

vomer, 153

Wing-like 

posterior extension, 75

process, 75

Wormian ossicles, 35

Yoke

sphenoidal, 100

Zygoma, 108

os, 35

Zygomatic, 35, 62, 68, 101–102, 155

arch, 27, 30, 35–38, 48, 63, 108, 

155

articulation

cavity for, 57

bone, 30, 35, 38, 68, 106

border of the sphenoid, 102

branch of the maxillary nerve, 102

foramen, 95, 100, 102

fossa, 60, 66, 108

frontal, 27, 32

jugal, 38

nerve, 38, 96, 102, 155

part, 108

process, 29–32, 36, 58, 60, 62, 68, 

78, 95, 102–103, 106–108, 

147

jugal, 38, 60

frontal, 25, 30, 31, 32, 155

lacrimal, 41

malar, 37, 38

maxilla, 37, 68

squamosal, 29–32, 36–37, 107, 

108, 155

recess, 57, 61, 68

maxilla, 37

root of the maxilla, 68

style, 37

Zygomaticofacial 

foramen, 36, 38

nerve, 38

Zygomaticofrontal suture, 27

Zygomaticomaxillary suture, 67, 68

Zygomaticoorbital foramen, 38

Zygomaticotemporal 

foramen, 38

nerve, 38

suture, 108
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