Observations on the Myology

of Dugong dugon (Miiller)

*

DARYL P. DOMNING

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 226
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SMITHSONIA N CONTRIBUTION S T O ZOOLOG Y • NUMBE R 226

Observations on the Myology

of Dugong dugon (Miiller)

Daryl P. Domning

SMITHSONIAN INSTITUTION PRESS

City of Washington

1977
ABSTRAC T

Domning, Daryl P. Observations on the Myology of Dugong dugon (Muller).

Smithsonian Contributions to Zoology, number 226, 57 pages, 54 figures, 2 tables,

1977.—The form and gross relations of the dugong's skeletal muscles are

described, illustrated, and compared with published descriptions of manatee

muscles. Maps of muscle attachments to the bones and data on skin thickness

are included.

Though closely paralleling cetaceans in swimming adaptations, sirenians are

much less specialized in this regard, since they are not active predators. Manatees

show less anatomical specialization and presumably less efficiency and endurance

in swimming than dugongs because manatees are less active and inhabit more

protected waters. The structure of the shoulder region is quite different in the

two sirenian families and may reflect the requirements of maneuvering in more

or less open habitat. Other muscle systems, however, are not notably different

in the two families.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The coral Montastrea

rrrurrnmn cavernosa t\ (Linnaeus) inn3ptie\ .

Library of Congress Cataloging in Publication Data

Domning, Daryl P.

Observations on the myology of Dugong dugon (Mullet)

(Smithsonian contributions to zoology ; no. 226)

Bibliography: p.

Includes index.

1. Dugong. 2. Manatees. 3. Muscles. 4. Mammals—Anatomy. I. Title. II. Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 226.

QL1.S54 no. 226 [QL737.S62] 591'.08s [599'.55] '76-6966
Contents

Page

Introduction 1

Materials, Methods, and Terminology 1

Discussion of Skin Thickness 3

Myological Descriptions 3

Muscles of the Superficial Neck and Face Region 3

Muscles of the Jaws 7

Muscles of the Middle Ear 8

Tongue and Hyoid Muscles 8

Muscles of the Pharynx 9

Muscles of the Soft Palate 10

Muscles of the Larynx 10

Dorsal Muscles of the Trunk 10

Epaxial Spinal Musculature 11

Transversospinalis System 11

Longissimus System 12

Iliocostalis System 12

Deeper Muscles of the Neck 13

Muscles of the Thorax 15

Diaphragm 15

Muscles of the Abdomen 15

Muscles of the Tail 17

Muscles of the Shoulder 18

Muscles of the Forelimb 20

Muscles of the Pelvic and Genital Regions 25

Functional Anatomy 26

Facial Muscles 26

Jaw Muscles 27

Swimming Muscles 28

Forelimb Muscles 30

Hindlimb Muscles 31

Conclusion 31

Addendum 32

Literature Cited 33

List of Abbreviations 35

Figures 1-54 37

Index 55

Observations on the Myology

of Dugong dugon (Miiller)

Daryl P. Domning

Introduction

Very little of the considerable research done to

date on the anatomy of the living sirenians has

been devoted to their muscular systems. The principal, and almost the only, treatment of sirenian

myology is found in James Murie's treatises (1872,

1880) on the gross anatomy of the manatee. Bahrdt

(1933) redescribed some limb muscles of the manatee, Slijper (1946) commented upon some details of

the back muscles, and other authors contributed

observations on visceral or skeletal muscles in describing other organ systems; but, so far as I am

aware, the only attempt at describing the sirenian

muscular system as a whole is that of Murie.

In order to investigate the differences in functional myology between manatees and dugongs and

between sirenians and other marine vertebrates,

and to have some basis for understanding the functional adaptations of extinct dugongids, it is first

necessary to gain at least as much knowledge of

the myology of Dugong as Murie has given us for

Trichechus. This is the aim of the present study.

ACKNOWLEDGMENTS.—I am most grateful to Dr.

C. O. Handley, Jr., for making available to me the

dugong cadaver and to Dr. R. W. Thorington, Jr.,

for his help with many aspects of the dissection;

both of the Department of Vertebrate Zoology,

National Museum of Natural History, Smithsonian

Institution. Preeminent among those who assisted

was Mrs. J. P. Lufkin of the University of California Museum of Paleontology, whose skill and

perseverance in inking the drawings deserve much

Daryl P. Domning, Department of Paleontology, University of

California, Berkeley, California 94720.

of the credit for this paper. For discussions, criticisms, material aid, and other favors too numerous

to enumerate, I also thank N. Hotton III, C. Jones,

J. H. Miles, Jr., R. H. Pine, C. E. Ray, and F. C.

Whitmore, Jr., of the National Museum of Natural

History; H. E. Kaiser of the University of Maryland; B. Dalzell, J. T. Gregory, T. R. Olson, J. L.

Patton, J. A. Robinson, and D. E. Savage of the

University of California, Berkeley. Thanks are also

due to the California Academy of Sciences and the

Steinhart Aquarium, San Francisco, which provided

me with access to comparative material. Thanks

also to my parents, to Sr. M. Constance, to the

Pallottine Sisters of Laurel, Maryland, and to the

University of California Museum of Paleontology,

all of whom provided invaluable logistical support.

This work was supported by a visiting research

appointment at the Smithsonian Institution and a

National Defense Education Act Title IV Fellowship.

Materials, Methods, and Terminology

The dissection was performed on an immature

female dugong (Dugong dugon (Miiller) Palmer,

USNM 307611) captured in the Palau Islands in

June 1957 by the George Vanderbilt Foundation of

Stanford University. The specimen was preserved

in formalin and weighed about 300 pounds when

fresh. Its second molar was worn and the third

molar unerupted. Since this description is based

on only the left side of one individual, and hence

is subject to all the limitations which that implies,

this account should in no way be taken as definitive. I have cited all the significant statements in

the literature known to me bearing on each muscle
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

of either manatee or dugong. All comparisons with

the manatee are, unless otherwise stated, based on

Murie's (1872, 1880) accounts of three specimens ot

Trichechus manatus manatus Linnaeus. I have usually omitted comparisons with the manatee, however, where its anatomy agrees with that of the

dugong. Measurements taken at the time of dissection (June 1971) are given in Table 1.

Unfortunately, time did not permit investigation of muscle innervation, so the homologies I

suggest are based only on gross relations. Quotation

marks denote names I have coined or used in other

than the usual fashion. Question marks before

muscle names denote doubtful identification.

The illustrations are semidiagrammatic and with

a few exceptions all structures other than muscles

and bones are omitted. The directions of the muscle fibers are indicated by solid lines and tendinous

or aponeurotic fibers by dashed lines. Origins are

denoted by patterns of circles, insertions by patterns of vertical dashes. The abbreviations beginning with capital letters refer to muscles and

those beginning with lower-case letters refer to

other structures; all are explained in the "List of

Abbreviations."

TABLE 1.—Measurements (cm) of immature female Dugong dugon (USNM 307611) from Palau Islands

TRUNK

Total length, snout to caudal notch 185

Girth, neck just behind vertex of cranium 78

Girth, just in front of flippers 99

Girth, just behind flippers 103

Girth, about 85 cm behind snout (maximum girth) .... 121

Girth at anus 102

Minimum girth of peduncle 39

HEAD

Length, tip of snout to vertex of cranium 33

Girth, anterior end of snout and mandible 71

Girth at eye, behind chin 66

Girth at eye, including chin 73

Length, side of mouth 8

Length, lower lip, angle to angle around front

of mouth 24

Width, lower jaw, transversely between angles of

mouth 11

Height, lower jaw, anterior side of lip to ventral

tip of chin 12.5

Width, anterior end of muzzle 18

Height, anterior end of muzzle (not including

upper rostral pad) 12

Distance, dorsal tip of muzzle to nostrils 7

Width across both nostrils 5

Width of each nostril 2

Height of each nostril 1.5

Diameter of eye 1

Distance, tip of snout to eye 19

Distance, lateral side of nostril to eye 15

Distance, angle of mouth to eye 11

Distance between eyes (through head) 18.5

Distance between eyes (over top of head) 26

Distance, eye to ear 11

Distance between ears (through head) 21.5

Distance between ears (over top of head) 31

Distance, tip of snout to ear 30

Diameter of ear opening 0.3

FLIPPERS

Distance, tip of snout to anterior insertion of

flipper 40

Distance between tips of outstretched flippers 103

Distance between insertions of flippers (through

body) 27

Distance between insertions of flippers (over back) .... 59

Length, anterior insertion to tip* 32

Length, axilla to tip* 30

Maximum width* IS

Maximum thickness (at proximal end)* 5.5

Thickness at metacarpals* 3.3

Girth at insertion* 27

Girth at middle* 27

Girth l/j of length from tip* 28

TAIL

Length, anterior edge of fluke to caudal notch 28.5

Width across flukes, tip to tip 53

Distance, caudal notch to nearest point on anterior

edge of left fluke 22

Distance, tip to notch, along posterior edge of

left fluke 32.5

GENITAL ORGANS*•

Distance, anus to caudal notch

Distance, anus to vulva

Length, teat

60

6

1

•Left flipper.

*• Damage to specimen in ventral midline prevented location of umbilicus.
NUMBER 226

Discussion of Skin Thickness

Measurements of skin thickness (including both

epidermis and cutis) are given in Table 2 and Figure 1 for comparison with the data of Matthes

(1929) on sirenian skin thickness. The distribution

of thickness differs in several respects from that in

Matthes' young Trichechus senegalensis, in addition to the dugong's hide being in general proportionately thicker than the latter's. The dugong's

skin is thickest on the back rather than on the side;

on the chest at the level of the flipper it thins less

than in the manatee; and, in contrast to the manatee, there is a conspicuous thickening on the dorsal

side of the peduncle (less so on the ventral side).

The latter feature clearly parallels the similar development in the dorsoventrally expanded peduncles of whales. The epidermis is, as often described,

very thin in comparison to the cutis.

There was no development of blubber in the

animal under study; the cutis lay directly upon the

superficial muscles and aponeuroses. The animal

was in general very lean, the most conspicuous deposits of fat lying just forward of and behind the

shoulder joint beneath the dermal muscles, and

between the cutaneus trunci and the deeper muscles

on the side of the thorax.

TABLF 2.—Thickness of skin of immature female Dugong dugon (USNM 307611)

measured (in mm) at 10 cm intervals from head to tail

Area measured

Dorsal midline

Middle of left side

Ventral midline

head

0 10

9

5

20

9

8

13

30

18

12

9

40

20

7

12

50

20

9

12

flipper

60

21

11

10

70

24

14

14

80

23

14

12

90

22

12

10

100

21

12

10

110

19

12

10

120

17

12

10

130

16

12

7

r

anus

140

22

10

7

150

21

00 00

160

17

9

10

170

6

180

—

flukes

tail

185

—

Myological Descriptions

MUSCLES OF THE SUPERFICIAL NECK AND FACE REGION

M. SPHINCTER COLLI SUPERFICIALIS (SpC: Figures

2, 4-6, 18, 19, 22, 32, 33) [Murie, 1872:164, figs.

8, 9, 13, 30: "platysma myoides, P.c3"].—Coarse

and fat-veined as Murie described; thins dorsally

from a maximum thickness of 1.5 cm over the

chest.

Origin: Anteriorly, from midventral line with

fellow of opposite side; posteriorly line of origin

diverges laterally to a point ventral to axilla, the

fibers arising by small separate tendons from fasciae

over chest. On the muscle's deep side a few fibers

arise from surface of sphincter colli profundus pars

auris just medial to shoulder. In midventral line at

level of axilla, in V-shaped space formed by divergence of lines of origin of the muscle, there is a

small squarish sheet of coarse fibers; since this lies

in chest fasciae in same plane as sphincter colli

superficialis and its fibers run in same direction,

it may be regarded as a division of the latter.

Insertion: Passes dorsolaterally, radiating slightly,

covering throat and shoulder and overlapping

lower edge of pars jugularis of platysma; inserts

onto hide at side of neck and front of shoulder.

Overlies supraspinatus, not infraspinatus as stated

by Murie. I did not observe any slip passing onto

forelimb as in the manatee (Murie, 1872, fig. 13:

"P.c3#").

M. PLATYSMA.—I apply this term to the entire

thin sheet of muscle which covers the cheek, neck,

and anterior shoulder regions just beneath the skin.

It has 3 major divisions:

—"PARS JUGULARIS" (P1J: Figures 2-6, 11, 13, 18,

19, 32, 34).—Continuous sheet including parts
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

sometimes distinguished as platysma myoides, pars

buccalis, and pars mentalis. Coarse-fibered and

veined with fat.

Origin: Anteriorly, from fascia connected with

hide over after edge of levator nasolabialis; more

ventrally its fibers are mingled with those of orbicularis oris all around corner of mouth, and a few

arise from surface of mentalis. Passes back as most

superficial layer of cheek, though at throat its

ventral border is overlapped by sphincter colli

superficialis. Dorsally arises, together with frontalis

and sphincter colli profundus pars auris, by

aponeurosis from side of jugal posteroventral to

orbit.

Insertion: Passes back into superficial fascia over

forward part of shoulder, the more ventral fibers

reaching level of axilla; each bundle of fibers terminates in a small, separate tendon, which is lost in

fascia. Dorsal fibers sweep up and back to mingle

with those of pars temporalis, and some attach to

anteroventral side of auditory canal along with

those of auricularis profundus.

—"PARS TEMPORALIS" (PIT: Figures 2-4, 11,

18).—May correspond to platysma cervicale of other

mammals. Very thin, coarse, fat-veined sheet covering back of neck.

Origin: Superficial fascia over temporal fossa.

Insertion: Mingles ventrally with other parts of

platysma and passes back into superficial fascia over

anterodorsal part of scapula.

—"PARS SCAPULARIS" (PIS: Figures 2-4, 18-20, 43,

44).—Somewhat fusiform sheet, fibers less coarse

than in pars jugularis.

Origin: By small separate tendons from among

and mainly beneath dorsal fibers of pars jugularis

and ventral fibers of pars temporalis.

Insertion: By single tendon onto fibrous raphe

joining trapezius and deltoideus over infraspinatus,

attaching to raphe 2.5 cm forward of after edge of

deltoideus.

There are two smaller muscles related to the

platysma which may or may not be homologs of

normal mammalian postauricular muscles:

"M. AURICULARIS SUPERFICIALIS" (AuS: Figures 2,

4, 18).—Small but conspicuous muscle posterodorsal

to ear, about 2 cm long; fibers less coarse than in

pars jugularis.

Origin: Surface of pars temporalis near its ventral edge.

Insertion: Passes over insertion of frontalis and

around back of auditory canal to insert on latter's

posteroventral side.

"M. AURICULARIS PROFUNDUS" (AuP: Figure 11).—

Small fusiform bundle 4.5 cm long and 1 cm wide

lying on deep side of pars temporalis dorsal to

dorsal edge of pars jugularis and diverging from

latter posteriorly. Lies in same plane as pars jugularis and clearly derived from it. Also lies approximately parallel to auricularis superficialis. Passes

superficially to a bowling-pin-shaped bar of cartilage

1.5 cm long lying posteroventral to auditory canal,

pointing anteroventrally, and having no direct muscular or skeletal attachments.

Origin: Fasciae on deep side of pars temporalis,

2 cm behind rear end of zygomatic process.

Insertion: Partly tendinous, together with fibers

of pars jugularis, onto anteroventral side of auditory

canal.

The pars jugularis evidently corresponds, in the

manatee, to the anteriormost parts of Murie's "panniculus carnosus" (Murie, 1872, figs. 8-10, 12: "P.c1

"

and part of "P.c2"); the other divisions, including

the auriculares, seem to have no trichechid homologs. On the other hand, the portion of Murie's

(1872) "P.c2" that he shows coming from the underside of the jaw up to the angle of the mouth is

absent in the dugong.

M. SPHINCTER COLLI PROFUNDUS.

—?PARS AURIS (Au: Figures 5, 6, 13, 19, 22, 23,

32-35) [Murie, 1872:163-164, figs. 8, 9: "panniculus

carnosus, P.c2"; Murie, 1880: pi. 8, fig. 5]: Remarkably massive, up to 4 cm thick; covers ventrolateral

side of neck and anterior part of chest just beneath

sphincter colli superficialis.

Origin: Fleshy and tendinous from ventral side

of sternum, from origin of sternomastoideus (here

continuous with it) to posterior end of bone,

meeting its fellow along midline. Posteriorly mingles with and partly overlies cutaneus trunci,

arising from its surface by fasciae and small tendons; for the more lateral connections of the two

muscles, see description of cutaneus trunci.

Insertion: Passes beneath frontalis and pars

jugularis of platysma and superficial to masseter to

insert by very strong aponeurosis onto ventrolateral
NUMBER 226

side of zygomatic process of squamosal, lower part

of lateral side of jugal, and fasciae anteroventral to

jugal beneath palpebralis. (This aponeurosis is

really a deeper division of that from which frontalis

and jugularis arise.) Deep side of auris is tendinous

where it passes over masseter.

PARS INTERMEDIA.

?M. FRONTALIS (Fr: Figures 2, 4-6, 11, 18, 19,

32, 34).—Small triangular muscle just forward of

ear; fibers less coarse than in pars jugularis of

platysma and at most 6 cm long.

Origin: Aponeurotic from zygomatic process adjacent to pars jugularis of platysma; anteroventrally

overlaps latter. Fibers begin in aponeurosis 4 cm

forward of ear opening.

Insertion: Passes beneath auricularis superficialis

and dorsal to ear to mingle with fasciae between

partes jugularis and temporalis of platysma.

M. ORBICULARIS ocui.i (OOc: Figures 3, 4, 7)

[Murie, 1872:195, fig. 8: "orbicularis palpebrarum"],—Fibers completely continuous around

posterior angle of eyelids, though still divided into

dorsal and ventral portions anteriorly. Otherwise

normal. Putter (1902:180) stated that in one manatee the ventral part was better developed; I did not

observe this, nor did Putter (1902:185) attribute it

to his dugong.

I did not dissect the muscles of the eyeball.

Putter (1902:179-180, 185, 371) attributes to both

the manatee and dugong no features out of the

ordinary except that the musculi recti all take their

origins behind the optic foramen rather than

around it.

M. LEVATOR NASOLABIALIS (LeN: Figures 3-6,

12, 13) [Murie, 1872:149, figs. 8, 10, 12: "levator

labii superioris alaeque nasi"].—Most superficial of

snout muscles; fan-shaped, its fibers radiating forward and predominantly anteroventral in direction.

Origin: Tendinous from anterolateral edges of

jugal and lacrimal and dorsal side of supraorbital

process of frontal to as far back as level of latter's

posterolateral corner.

Insertion: Mingles with fibrous tissue, other muscle fibers, and hide dorsolateral to external nares

and down along front of snout to upper lip, where

it mingles with platysma and orbicularis oris. None

of these are separable at front of snout, but fuse

into a homogeneous mass of isolated fibers in a

matrix of fibrous tissue underlying hide and adherent to premaxillae. Near nares, however, levator

nasolabialis does not closely approach midline or

connect with fellow of opposite side as in the

manatee.

—PARS PALPEBRALIS (Pip: Figures 4-7).—Divided

into a larger anterior and a smaller posterior group

of very loosely connected bundles of coarse fibers.

Not found in the manatee.

Origin: From hide about 4 cm below eye.

Insertion: Passes beneath pars jugularis of platysma to tendon (in common with mandibularis,

p. 6) posteroventral to angle of mouth.

—PARS ORALIS.—

M. ORBICULARIS ORIS (OOr: Figures 4-7)

[Murie, 1872:150, figs. 10, 11].—Chief component

of lips. Discontinuous at angle of mouth, where

dorsal part overlaps ventral without continuity of

fibers. Less developed on lower lip. Mingles extensively with platysma, buccinatorius, and levator

nasolabialis; closely adherent to hide.

M. BUCCINATORIUS (Bu: Figures 5, 6, 9, 10, 13,

14, 16, 17, 24, 25) [Murie, 1872:150, figs. 10, 11].—

Prominent, thick muscle of cheek, immediately in

contact with inner side of mouth. Has two closely

adherent layers: Superficial layer (pars buccalis) is

posteroventral in direction and covers posterior

part of deep layer; a few isolated fibers pass anteroventrally across anterior part of deep layer.

Deep layer (pars molaris) is still more anteroventral

in direction, and mingles with fibers of orbicularis

oris on upper lip; not distinct or separable from it

on lower. Fleshy origin from entire lateral and

alveolar borders of premaxilla and maxilla from

near tip of rostrum back to end of tooth row (here

associated with retractor labiorum); and from

alveolar border of mandible, anteriorly by shiny

tendinous sheet passing anteromedially to 2 cm

ahead of tooth row, and posteriorly fleshy from

anteromedial side of base of ascending ramus.

M. MAXILLONASOLABIALIS (Mnl: Figures 5, 6,

13, 14) [Murie, 1872:148, figs. 8, 10, 11, 12: "levator

labii superioris proprius"].—According to Miller,

et al. (1964:135), this muscle actually homologous

to levator labii superioris alaeque nasi of primates.

Second layer of snout muscles, beneath levator

nasolabialis; likewise fan-shaped and radiating forward but more horizontal in direction than latter,

with some fibers even passing anterodorsally. Fibers

coarse, rather loosely connected; covered by thick

blanket of fasciae.

Origin: Tendinous from a strip of about 4 cm
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

along anterior side of jugal, medial to levator

nasolabialis.

Insertion: Mingles with other muscle fibers and

fibrous tissue at anterior end of snout.

M. LATERALIS NASI (LaN: Figures 5, 6, 12, 13)

[Murie, 1872:148-149, figs. 11, 12: "levator anguli

oris," "depressor labii superioris alaeque nasi,"

and/or "zygomaticus" (not equivalent to zygomaticus of other animals)].—Third and deepest layer

of snout, continuous dorsally with muscle mass

lying within mesorostral fossa between premaxilla

and nasal passage. May represent an anterior and

lateral expansion of what corresponds to pars ventralis m. lateralis nasi in, for example, the horse,

and its modification into a major unit of snout

system; or may be an expanded dilatator nasi.

Modified anterolateral part of muscle may be regarded separately as follows: Fibers pass anterodorsally; ventral part traversed by large bundle of

nerves and vessels issuing from infraorbital

foramen.

Origin: Fleshy from most of lateral surface of

premaxilla; maxilla exposed behind it.

Insertion: Like overlying layers, becomes lost in

muscle and tissue mass at front of snout. Dorsally,

fibers less distinct and mixed with much fibrous

tissue; muscle extends into mesorostral fossa to

occupy its normal position.

In the muscle mass occupying the mesorostral

fossa I recognized two parts, inseparable and distinguished only by different direction of fibers:

first, fibers scattered in fibrous tissue over narial

passages, mostly transverse and attached to hide

(perhaps representing M. transversus nasi (TrN:

Figure 3)); second, a thick muscle with origin on

dorsomedial side of frontal process of premaxilla

and insertion on ventrolateral side of nasal passage

(lateralis nasi). Latter extends from rear of mesorostral fossa to diminish and lose itself in tissue at

front of snout, and is continuous with sheet-like

portion on lateral side of premaxilla described

above. These two parts within mesorostral fossa

may correspond, respectively, to Murie's "compressor nasi" plus "dilatator naris", and "pyramidalis

nasi" (1872:148, figs. 10-12).

?M. MENTALIS (Mt: Figures 4-7, 16) [Murie:

1872:150, figs. 8, 9, 10, 11: "depressor labii inferioris"].—Covers side of mandibular symphysis

beneath platysma, which sends a few fibers onto its

surface near its rear edge. Mandibularis tendon

pierces it from beneath and emerges onto its surface

about 1.5 cm from its rear edge. Not connected to

fellow of opposite side as in manatee, but separated

from it by about 1 cm of thick fibrous tissue.

Origin: Fleshy from lateral side of symphysis

from dorsal border adjacent to second and third

incisor alveoli (and beneath orbicularis oris) down

to ventral extremity of symphysis; vessels from

mental foramen, however, pass beneath it.

Insertion: Onto hide at lower corner of symphysis.

Its attachments are the reverse of those of the

seemingly corresponding muscle in the manatee,

causing it to pull up on the hide at the chin rather

than down at the lip.

The muscle Murie (1872:149, fig. 9) termed

"levator labii inferioris" is absent in the dugong;

the front of the mandible is covered by a thick pad

of fasciae containing a very few transverse muscle

fibers, probably derived from the orbicularis oris.

"M. RETRACTOR LABIORUM" (ReL: Figures 6, 7, 9,

10, 14, 25).—Strap-like, 1 cm wide, lying directly on

lateral surface of mandible beneath palpebralis.

Without homolog in manatee. Does not seem to

correspond to a normal zygomaticus, and is perhaps

a derivative of buccinatorius.

Origin: Fleshy, nearly inseparable from buccinatorius, at posterodorsal edge of latter's origin on

maxilla at rear of tooth row.

Insertion: Tendinous into fibrous tissue and fibers

of orbicularis oris at angle of mouth.

M. MANDIBULARIS (Mn: Figures 5-7, 10, 17, 33)

[Murie, 1872:151, fig. 11].—Approximately as in

manatee; long, narrow, and straplike. Perhaps a

derivative of buccinatorius.

Origin: Tendinous from small area on anteromedial side of base of ascending ramus of mandible,

posterodorsal to coronoid canal (= large foramen

at rear of lower tooth row).

Insertion: By tendon passing ventrolaterally

through mentalis onto hide on anteroventral side

of mandibular symphysis. Palpebralis joins this

tendon just behind mentalis. Tendon does not join

fellow of opposite side.

M. DEPRESSOR ANGULI ORIS (DAO: Figures 4, 5)

[Murie, 1872:150, figs. 8-10].—This muscle, well

developed in Trichechus, may be represented vestigially in Dugong by, first, a few fibers embedded

in anterior tendon of mandibularis where it is

exposed on surface of mentalis; and, second, a

small thin tendon emerging from surface of men-
NUMBER 226

talis near its after edge just ahead of palpebralis

tendon, passing upward parallel to latter, and

becoming lost in fasciae and fibrous tissue near

angle of mouth. Incorporation of depressor anguli

oris fibers into the mandibularis-palpebralis tendon

results in the unusual situation of three muscles

pulling in divergent directions on a single tendon.

MUSCLES OF THE JAWS

M. MASSETER (M: Figures 5-8, 10, 13, 14, 16, 23,

34) [Murie, 1872:151, figs. 10, 30: "masseter,

Ma1"].—Covers side of posterior half of mandible

beneath sphincter colli profundus pars auris.

Crossed by numerous nerves and vessels and superficially sheathed in shining tendon towards origin.

On deep side near origin it is partly divided; deep

division smaller (about 4 cm wide) than other, with

more vertically oriented fibers, and fused with

superficial part anteriorly and ventrally. Both divisions contain parallel tendinous sheets which join

the superficial sheath.

Origin: Tendinous on superficial side and fleshy

deeper, from ventral and posteroventral edges of

jugal back to behind level of tip of squamosal, and

anteromedially on jugal as far as maxillary suture.

Insertion: Fleshy on whole posteroventral half of

posterior part of mandible, especially on latter's

posteroventral edge.

M. ZYGOMATICOMANDIBULARIS (Z: Figures 3, 6-14,

16) [Murie, 1872:151, fig. 11: "masseter, Ma2"].—

Deep to masseter (though exposed posterodorsal to

it) and separated from it by a large mass of blood

vessels passing forward from rear edge of mandible.

Its fibers pass nearly at right angles to those of

masseter, as in Trichechus. Covered by shining

fascia near insertion, and considerably larger than

temporalis.

Origin: Tendinous from strip about 2 cm long

on ventrolateral edge of zygomatic process of

squamosal adjacent to posterior end of jugal; fleshy

from medial side and ventral edge of latter, and

whole medial side of zygomatic process; fused posteriorly with temporalis.

Insertion: Fleshy on anterior half of ascending

ramus and coronoid process of mandible; fibers

coming from ventral edge of zygomatic arch insert

in hook-shaped pattern below main insertion.

M. TEMPORALIS (T: Figures 3, 5, 6, 8-10, 12, 13,

17, 19, 20-22) [Murie, 1872:151, figs. 8, 10].—Hidden by thick sheet of fascia covering whole temporal fossa. Relatively small, as in manatee, and

covered, especially at rear, by shining fascia. Fused

posterolaterally with zygomaticomandibularis. Contains a tendinous sheet continuous posteriorly with

the superficial sheath.

Origin: Fleshy from lateral side of cranium,

covering squamosal dorsal to root of zygomatic

process, part of parietal, dorsal wing of alisphenoid,

and posteriormost edge of frontal.

Insertion: Tendinous onto rim of coronoid process and fleshy onto its medial side down to a point

just posterior to coronoid canal. Only development

of a "superficial" division is a fold on anterior edge,

which just manages to cover a small part of lateral

side of temporalis tendon; there is no insertion on

lateral surface of bone.

M. PTERYGOIDEUS EXTERNUS (PtE: Figures 9, 13,

17, 24, 25) [Murie, 1872:180].—Short, thick; oval in

cross-section.

Origin: Fleshy from anteroventral part of lateral

surface of pterygoid process.

Insertion: Fleshy into pterygoid fossa anteroventral to condyle on medial side of ascending ramus

of mandible.

Turnbull (1970:349) alluded to "peculiarities" of

the temporalis and pterygoideus externus in sirenians. He has informed me that he was referring to

the apparent (from osteological materials) absence

of a superficial temporalis (probably represented at

least in part by the zygomaticomandibularis) and

large size of the pterygoideus externus (confirmed

by this dissection).

M. PTERYGOIDEUS INTERNUS (PtI: Figures 9, 10, 13,

14, 17, 24, 25) [Murie, 1872:180].—Wide and fanshaped; complexly pinnate.

Origin: Fleshy and tendinous from posterolateral

side of pterygoid process, adjacent and posteroventral to origin of pterygoideus externus.

Insertion: Fleshy and tendinous on whole posteroventral part of medial side of mandible.

M. DIGASTRICUS (Di: Figures 6, 8-10, 17, 23-25, 31,

34) [Murie, 1872:180, figs. 9, 10, 30; 1880, pi. 8: fig.

5].—As in manatee, consists of only one belly

(anterior).

Origin: Fleshy from lateral sides of stylohyoid

and epihyoid; no fibers attach to skull.

Insertion: Fleshy on medial edge of lower half of

posterior border of mandible down to its angle,

thence about 3 cm anterodorsally along ventro-
8 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

medial edge of mandible's ventral border. Does not,

nor does any other muscle, completely cover rearfacing flat surface of posterior border, which is

primarily produced by stresses of muscles inserting

on lateral and medial sides of mandible along its

after edge, stimulating bone deposition laterally

and medially along the edge.

MUSCLES OF THE MIDDLE EAR

These I did not dissect, but I have gleaned the

following information from the literature:

M . TENSOR TYMPANI.—

Origin: From posterior side of bridge connecting

tympanic to tegmen tympani (Robineau, 1969:26).

Insertion: Tendinous on processus muscularis on

medial side of malleus (Robineau, 1965, fig. 5; 1969,

fig. 6).

M . STAPEDIUS.

Origin: From fossa muscularis minor on underside of petrosal, posterolateral to fenestra ovale

(Robineau, 1969:10, figs. 5, 6). This was confirmed

by my observation of the remnant of a tendon attached at this point in a dried Dugong skull (USNM

197900).

Insertion: Tendinous on posterior side of neck

of stapes (Robineau, 1969, fig. 6). Doran (1878:467)

states that the site of insertion is usually indicated

by a slight depression.

TONGUE AND HYOID MUSCLES

M. STYLOCLOSSUS (Styg !_3: Figures 8, 23, 24, 25, 30,

31) [Murie, 1872:180, figs. 18, 37].—Has three divisions, as follows, proceeding ventrally:

—FIRST (Styg,, Figures 8, 23, 24, 25, 30).—Thickest

and strongest division.

Origin: Fleshy from anterolateral edges of stylohyoid and of proximal end of epihyoid.

Insertion: Partly tendinous into posterolateral

part of tongue.

—SECOND (Styg2; Figures 24, 25, 30).—

Origin: Fleshy from anterior side of epihyoid,

distal to first division.

Insertion: Into posterolateral part of tongue

ventral to first division.

—THIRD (Styg3; Figures 24, 25, 31).—

Origin: Tendinous from anterolateral edge of

epihyoid lateral to second division.

Insertion: Longest division, inserting (partly tendinously) into ventrolateral side of tongue, lateral

to genioglossus and hyoglossus.

M. HYOGLOSSUS (Hg: Figures 24, 25, 31).—Thin,

about 2.5 cm wide. Not observed by Murie in the

manatee.

Origin: From fibrous raphe in midline with its

fellow, and fleshy from ventral sides of basihyoid

(lateral to other muscle attachments) and (perhaps

by a few fibers) thyrohyoid.

Insertion: Passes anterodorsally into tongue,

medial to third division of styloglossus.

M. GENIOGLOSSUS (Gg: Figures 17, 24, 25, 30)

[Murie, 1872:180: ?"genio-hyo-glossus"].—Thin,

lying in parasagittal plane beneath tongue. Converges on and unites with fellow of opposite side

posteriorly, merging with fibrous tissue connecting

pharynx and rear of tongue.

Origin: Tendinous from fossa on posterodorsal

surface of mandibular symphysis.

Insertion: Passes posterodorsally, blending dorsally with fibers of tongue. Posteroventrally, a few

fibers insert on dorsal sides of keratohyoids and

basihyoid.

The intrinsic muscles of the tongue (Murie's

"lingualis", 1872:180) were not dissected. Gudernatsch comments briefly on the muscular structure

of the tongues of dugong (1908:601-604) and

manatee (1909:185-186).

The sternohyoideus is evidently absent. Murie

(1872:179, fig. 9) says "the sterno-hyoid and sternothyroid are interblended" in the manatee, and

Stannius (1845:7) says the same; but the absence

here of attachments to either the basihyoid or the

manubrium seems to leave little ground for asserting its existence at all in the dugong.

Murie (1872:179-180) found an "anterior remnant" of an omohyoideus, but I observed nothing

of this sort.

M. THYROHYOIDEUS (Thh: Figures 6, 23-28, 31,

34) [Owen, 1838:38: "thyreo-hyoideus"; Murie,

1872, fig. 9].—Roughly triangular; covers anterolateral side of thyroid cartilage and lies adjacent

and parallel to thyrohyoid on latter's posterior side.

Origin: Fleshy from lateral side of lamina of thyroid cartilage.

Insertion: Fleshy onto ventral side of basihyoid

between mylohyoideus attachments; no apparent

connection with thyrohyoid.
NUMBER 226

M. MYLOHYOIDEUS (My: Figures 9, 10, 17, 24, 25,

31, 34) [Murie, 1872:180, fig. 30].—Thick, about

4.5 cm wide; forms a sling under deeper intermandibular muscles.

Origin: Fleshy from medial side of mandible, between mandibular foramen and molars.

Insertion: Anterior half joins fellow in midline;

posteriorly has fleshy attachment to ventral side of

basihyoid, medial to origin of hyoglossus and lateral

to thyrohyoideus.

I did not observe a keratohyoideus, but Murie

(1872:179) says it is "feebly represented" in

Trichechus.

M. GENIOHYOIDEUS (Gh: Figures 17, 24, 25) [Murie,

1872:180].—Forms a thin pouch beneath tongue,

open dorsally, and containing a large mass of

fasciae and fibrous tissue, which itself seems partly

hollow anteriorly. Posteriorly the two sides converge to form rear of pouch, ending in a mass of

fibrous tissue.

Origin: Fleshy from crescentic area (concave up)

on posterior side of mandibular symphysis, ventral

to origin of genioglossus.

Insertion: Ends posteriorly in fibrous tissue connected with anterior edge of hyoglossus, and posteroventrally connected with mylohyoideus. It has

here no direct attachment to the basihyoid, though

it does in the manatee.

M. STYLOHYOIDEUS (Styh: figs. 24, 25, 31) [Murie,

1872:180, figs. 18, 30, 37].—Rather small and inconspicuous, lying along posterior side of epihyoid

and separated from it by several large vessels.

Origin: Fleshy from posterior sides of stylo- and

epihyoids at their juncture.

Insertion: Tendinous on posteroventral side of

basihyoid.

No distinct jugulohyoideus was observed, though

some fibers of the rectus capitis lateralis lie where

one would be expected; however, they did not seem

to be innervated by any branch of the facial nerve.

MUSCLES OF THE PHARYNX

M. HYOPHARYNGEUS (Hp: Figures 25, 30).—Rather

small; partly fused with stylopharyngeus and nearly

hidden beneath it. Posteriorly overlain by anterior

edge of thyropharyngeus.

Origin: Fleshy from protuberance on medial side

of epihyoid, in fusion with stylopharyngeus.

Insertion: With its fellow, on middorsal raphe of

pharynx.

M. THYROPHARYNGEUS (Thp: Figures 23, 25-28,

31) [Stannius, 1845:30: ?"thyreoideus transversus"].

—Triangular in outline.

Origin: Fleshy from side of thyroid cartilage

dorsal to origin of thyrohyoideus.

Insertion: With its fellow, on middorsal raphe of

pharynx, partly overlying posterior edge of hyopharyngeus.

M. CRICOPHARYNGEUS (Crp: Figures 23-31).—

Origin: Fleshy from side of cricoid cartilage and

adjacent caudal cornu of thyroid cartilage; on the

muscle's posterior edge a small slip arises tendinously from cricoid cartilage just lateral to cricoarytenoideus dorsalis, which passes beneath it.

Insertion: With its fellow, on middorsal raphe of

pharynx behind thyropharyngeus. Posterior fibers

blend with those of esophagus.

It is not clear to which of these Murie's "constrictores superior and medius" (1872:180, fig. 18)

correspond; judging by his figure, the "constrictor

medius" seems to be the cricoarytenoideus dorsalis

(p. 10), and the "constrictor superior" the combined

cricopharyngeus and thyropharyngeus.

M. STYLOPHARYNGEUS (Styp: Figures 25, 30, 31)

[Murie, 1872:180, figs. 18, 30].—Well developed,

partially divided longitudinally into anterior and

posterior halves. Proximal end lies against wall of

tympanic cavity. Adjacent and parallel to stylohyoideus; in the manatee, they are "closely adherent."

Origin: Fleshy from medial side of stylohyoid;

some connection also to protuberance on medial

side of epihyoid together with hyopharyngeus.

Insertion: Into side of pharynx just forward of

and partly fused with hyopharyngeus.

A distinct palatopharyngeus was not observed;

its fibers are apparently inseparably mingled with

those of the hyopharyngeus, stylopharyngeus, and

pterygopharyngeus. Murie (1872:180), however,

found it "fairly developed," and his palatoglossus

also was not observed.

M. PTERYGOPHARYNGEUS (Ptp: Figures 13, 14,

25).—Very short; not distinct posteriorly.

Origin: Fleshy from posterior side of ventral tip

of pterygoid process.

Insertion: Passes posteriorly to mingle with hyopharyngeus and stylopharyngeus on dorsal surface

of pharynx.
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

MUSCLES OF THE SOFT PALATE

M. TENSOR VELI PALATINI (TeV: Figures 14, 24,

25) [Murie, 1872:180: "tensor palati"].—Quite robust; lies against anterior wall of tympanic cavity

and fills fossa on posterior side of pterygoid process.

Origin: Tendinous from anteromedial edge of

tympanic. Sheathed in shining fascia near origin.

Insertion: Into soft palate immediately ventromedial to pterygoid process, by tendon passing anteromedially around trochlear surface of process.

I failed to find a leva tor veli palatini; Murie's

(1872:180) "levator palati" was not very well developed either. The m. palatinus was not dissected.

MUSCLES OF THE LARYNX

M. CRICOTHYROIDEUS (Crt: Figures 23-29, 31)

[Owen, 1838:38; Murie, 1872, fig. 30].—Anteroventral and closely adherent to cricopharyngeus.

Origin: Fleshy from ventrolateral side of cricoid

cartilage.

Insertion: Fleshy on posterolateral side of thyroid

cartilage.

M. CRICOARYTENOIDEUS DORSALIS (CrD: Figures

24-30) [Murie, 1872:180, fig. 18: ?"constrictor

medius"].—Covers dorsal side of cricoid cartilage.

Origin: Fleshy from posterior half of dorsolateral

surface of cricoid cartilage.

Insertion: Runs anterolaterally around esophagus

and beneath cricopharyngeus to fleshy insertion on

muscular process of arytenoid cartilage.

M. CRICOARYTENOIDEUS LATERALIS (CrL: Figures

27, 29) [Owen, 1838:38: "crico-arytenoideus"].—

Fused with and posterior to thyroarytenoideus.

Origin: Fleshy from anterior edge of cricoid

cartilage.

Insertion: Runs nearly vertically to fleshy attachment on underside of muscular process and posterolateral edge of arytenoid cartilage.

M. THYROARYTENOIDEUS (Tha: Figures 26-30)

[Owen, 1838:38: "thyreo-arytenoideus"].—Covered

by lateral portion of thyroid cartilage.

Origin: Tendinous from near dorsal (internal)

midline of transverse part of thyroid cartilage.

Insertion: Fleshy on anteroventral side of muscular process and lateral side of arytenoid cartilage.

M. ARYTENOIDEUS TRANSVERSUS (ArT: Figures

26-30) [Owen, 1838:38: "arytenoideus obliquus and

transversus"].—Lies immediately dorsal to thyroarytenoideus and anterior to cricoarytenoideus dorsalis.

Origin: Fleshy from anterodorsal side of muscular

process of arytenoid cartilage.

Insertion: Runs anteromedially to join its fellow

between arytenoid cartilage and esophagus. Owen

(1838:38) found them attached to "a small round

cartilage in the posterior interspace of the

arytenoids."

Concerning the above muscles, Murie (1872:179)

says only that "each and all of the laryngeal muscles are relatively well developed. The extrinsic

laryngeal muscles maintain a fair size, with attachments of the ordinary kind."

?M. HYOEPIGLOTTICUS (He: Figure 26) [Owen,

1838:38: "hyo-epiglottideus"; Stannius, 1845:30;

Murie, 1872:179: "hyoepiglottideus"].—This was

absent in Murie's manatee, though Stannius found

it weakly developed, and Owen identified it in his

dugong. I did not observe it in the USNM specimen,

but it was present in the larynx of a young male

Palauan dugong (California Academy of Sciences

11038) as a thick bundle of fibers, medially situated

and apparently undivided, passing steeply posterodorsally to insert into the substance of the epiglottis.

It passed close to the front of the thyroid cartilage

but did not seem to attach to it; the origin had

evidently been on some part of the hyoid apparatus,

but this had been cut away and was not preserved.

I have included this muscle in the illustration of

the National Museum specimen's larynx (Figure 26)

to show its position.

M. ARYEPIGLOTTICUS (Ae: Figure 27) [Murie,

1872:179: "aryteno-epiglottideus"].—Possibly represented by a few fibers on outer dorsal surface of

pharynx forward of arytenoideus transversus, passing anteroventrally. Not differentiated into superior

and inferior parts as in the manatee. (This is also

termed "arytenoideus obliquus"; see "M. arytenoideus transversus.")

A thyroepiglotticus was not observed, though a

few such fibers were found in Murie's (1872:179)

manatee ("thyro-epiglottideus"). The vocalis and

ventricularis are evidently absent in both dugong

and manatee.

DORSAL MUSCLES OF THE TRUNK

M. SPLENIUS (Spl: figures 5, 6, 13, 15, 19-24)
NUMBER 226 11

[Murie, 1872:145, fig. 8].—Triangular, covering dorsolateral side of neck just beneath cervical trapezius.

Thin forward, but up to 3 cm thick aft.

Origin: Aponeurosis from dorsal midline of neck

(beneath aponeuroses of trapezius and (posteriorly)

rhomboideus, though the three aponeuroses are not

very well separable) along whole cervical and anterior thoracic region. In the manatee, however, its

fibers arise from the surface of the underlying

longissimus and semispinalis capitis, to judge by

Murie's account.

Insertion: Tendinous onto posterior side of sigmoid ridge of squamosal, posteromedial to cranial

origin of trapezius. I think Murie (1872:145) was

mistaken in saying it attached to the "exoccipital

ridge."

EPAXIAL SPINAL MUSCULATURE

The epaxial muscles of the Sirenia are characterized by extensive fusion, obscuring most of the

divisions that are easily observed in land mammals.

The extreme shortening of the neck has reduced

and simplified the musculature of this region, and

the loss of hind limbs has removed the division

between trunk and tail muscles, so that there is

a single continuous epaxial muscle mass from the

occiput to the tip of the tail. This is composed of

the transversospinalis and longissimus systems,

which are virtually inseparable; the iliocostalis

remains distinct.

Transversospinalis System

Apart from the semispinalis capitis, this appears

to be composed entirely of multifidus and shorter

fascicles, though Slijper (1946:77, 112, table 3) indicates some semispinalis fascicles may also be present; he (1946:78, tables 3, 6) also describes a

"spinalis" arising from the skull to the fifth thoracic

vertebra and inserting from the seventh to the

twelfth, which I failed to find. His specimen, however, was much younger than mine (only 110 cm

long), and perhaps the spinalis had become fused

with the other epaxial muscles in the older animal.

As for the manatee (T. inunguis), Slijper indicates

the absence of the spinalis and the presence of

semispinalis fibers, as well as a stronger develop

ment of the transversospinalis relative to the longissimus than in the dugong (Slijper, 1946, tables 3, 6).

Murie (1872:144, fig. 39) likewise identified semispinales in the manatee, and also a "spinalis dorsi"

(including "levator caudae internus"), but does not

seem to indicate by the latter term a spinalis in

the precise sense used by Slijper (1946); rather

merely the outer parts of the transversospinalis

complex.

The transversospinalis mass in the dugong lies

medial to the longissimus and dorsal to the metapophyses of the vertebrae; from about the middle

of the thoracic region back it is enclosed between

the spinous and metapophysial tendinous sheets of

the longissimus (q.v.). It only becomes separable

from the longissimus just forward of the base of the

flukes, and it extends to the end of the tail. It

consists throughout of undifferentiated short muscle

fascicles and tendons, none of which appear to

span more than four vertebrae (i.e., appear to be

semispinalis fibers).

M. SEMISPINALIS CAPITIS (SeC: Figures 3, 12-15,

20-24, 36-39) [Murie, 1872:145, fig. 8: "complexus"].—Thick, encasing back and side of neck

just beneath splenius. A short, shallow longitudinal cleft on surface of muscle at about level of

atlas and axis is only vestige of a possible division

into biventer cervicis and complexus portions.

Origin: Posteriorly continuous with undifferentiated epaxial mass. Along its ventral edge it has

fleshy attachments to dorsal side of tip of transverse process of atlas between attachments of rectus

capitis lateralis and obliquus capitis caudalis, and

to side of postzygapophysis of axis; also arises by

tendons from lateral tips of prezygapophyses of

cervicals 3-7, and from dorsal sides of transverse

processes of thoracics 1-7. (Murie, 1872:145, traced

it back to "above the head of the sixth rib.")

Insertion: Fibers pass anteriorly and anterodorsally to insert pinnately on both sides of tendinous

sheet, thickened dorsally, which begins about level

of third thoracic. Tendon inserts on and covers

lateral border of supraoccipital, and is exposed

there; ventrally it is covered by fibers of the muscle

having fleshy insertion on most of dorsolateral

border of exoccipital and on latter's posterior side

lateral to condyle, nearly down to top of rectus

capitis lateralis insertion. Finally, a fleshy insertion

into large nuchal fossa of supraoccipital; this part

of muscle overlaps exposed tendon with a fold over

latter's posterodorsal side.
12

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Longissimns System

The principal epaxial muscle mass, readily

separable into two parts, hardly of comparable

importance.

M. LONGISSIMUS CAPITIS (LnC: Figures 6, 13, 15,

20,22-24) [Murie, 1872:144: "trachelo-mastoid"].—

Rather small, straplike; about 3 cm wide, lying

ventral and parallel to splenius, and like it overlain posteriorly by shoulder girdle.

Origin: By thin aponeurosis on side of semispinalis capitis, adjacent to and in same plane as a

triangular bundle of fibers rooted at rear of cleft

between semispinalis capitis and longissimus dorsi.

The fibers of the bundle pass anteriorly and become tendinous, but have no apparent direct connection with longissimus capitis.

Insertion: Passes forward across semispinalis capitis, thickening somewhat, to fleshy insertion on

posterolateral side of posttympanic process of

squamosal. I suspect Murie (1872:144-145) was

wrong in saying it inserted on the exoccipital.

M. LONGISSIMUS DORSI (LnD: Figures 3, 22-24,

36-39, 41, 42, 49, 50, 51, 52) [Murie, 1872:144, figs.

8, 39: "transversalis colli" + "longissimus dorsi,"

including "levator caudae externus"; Slijper, 1946:

47, 74, 75, 76, 112, table 3].—A continuous unit

extending from atlas to end of tail. Anteriorly lies

ventrolateral to semispinalis capitis, separated from

it by cleft extending back as far as third thoracic.

This anterior part is so completely continuous with

rest of mass that I see no reason to distinguish a

separate longissimus cervicis.

Origin: Fleshy and tendinous on after side of

transverse process of atlas (dorsal and medial to

scalenus and apparently continuous with semispinalis capitis origin), side of centrum of axis, and

ends of transverse processes of cervicals 3-7. At its

attachment on C7 and along its ventral edge as far

back as sixth rib it is fused with iliocostalis. Also

has fleshy origins from dorsal sides of transverse

processes from first thoracic back into flukes, dorsolateral sides of neural arches from T9 back into

flukes, and dorsal sides of all ribs inside their

angles.

Insertion: Fibers pass posteromedially to insert

on strong aponeurosis from level of fourth thoracic

back. Aponeurosis at first lies on medial side of

muscle, but a little way aft it starts to pick up

fibers passing posterolaterally from vertebrae to

insert on its medial side, and so comes to lie in

midst of muscle about halfway between neural

arches and tips of transverse processes. Ventral edge

of aponeurosis does not touch vertebrae. Anteriorly

it is buried within back muscles, but from ninth

thoracic back is exposed as broad shining sheet just

beneath most superficial aponeurosis of trunk, adjacent to midline, and continuing posteromedial

direction of longissimus fibers to insert on summits

of neural spines of tenth thoracic and following

vertebrae. From its medial side, beginning about

level of eighth thoracic, this aponeurosis sends off

another, perpendicular to itself, passing ventromedially to insert as separate tendons on metapophyses of posterior thoracics and succeeding

vertebrae. (These tendons, however, are nearly

inseparable from those of transversospinalis fascicles

lying dorsal to them and medial to spinous aponeurosis. Transversospinalis fibers, passing aft from

neural spines, insert on dorsal side of metapophysial

sheet and possibly even on medial side of spinous

sheet. It appears that all fibers lying above

metapophysial sheet are transversospinalis, but it

must be borne in mind that the latter mass is

inseparable from longissimus throughout nearly its

whole length, and it is difficult to draw precise

boundaries between them.) Some fibers even arise

from underside of metapophysial sheet and pass

posterolaterally to insert on medial side of main

longissimus sheet. Just forward of base of flukes,

spinous sheet's ventral edge diverges from fleshy

part of muscle, the aponeurosis continuing posteromedially to end of tail. Metapophysial sheet, now

separated from other and still buried in muscle,

divides into separate round tendons to aftermost

caudals.

Slijper (1946, table 3) found the spinous insertions beginning on the 13th thoracic rather than

the 10th, and the metapophysial on the 16th, which

I was not able to precisely determine, perhaps due

to the greater age of my specimen. In his manatee,

both insertions began on the sixth thoracic. (Murie

does not describe the back muscles in detail.)

Iliocostalis System

Least developed of the epaxial systems; consists

of a single unit and has no attachment to pelvis.

M. ILIOCOSTALIS THORACIS (I1T: Figures 3, 22-24,

41, 42, 49) [Murie, 1872:144, fig. 8: "cervicalis ascen-
NUMBER 226 13

dens" + "sacro-lumbalis"].—Forms long, narrow

band, widest (5.5 cm) at level of ninth rib, and less

than 1 cm thick; lateral to longissimus and covering ribs just distal to their angles. Consists of series

of bundles of fibers pinnate on small tendons,

oriented generally anteroventrally. Extends from

seventh cervical to last rib, where its after end

abuts against forward end of intertransversarius

coccygeus. Dorsal edge fused with longissimus from

anterior end back to sixth rib. Behind this, aponeurotic sheet covering trunk is connected to rib

cage along line separating iliocostalis and longissimus. Slijper (1946:47, 74, table 3) speaks of an

"ilio-costalis lumborum," fused with longissimus in

the dugong but free in the manatee; neither I nor

Murie (1872) observed such a structure. Slijper

(1946:74) adds that (in Trichechus but evidently

not Dugong) this muscle is also separate from "intertransversarius caudae dorsalis" (my intertransversarius coccygeus), seemingly precluding identity

of the latter with his "ilio-costalis lumborum,"

though in Dugong intertransversarius is indeed

tightly adherent to a continuation of abovementioned aponeurosis between longissimus and

laterally adjacent muscles. Finally, he (Slijper,

1946:74) states that an "ilio-costalis cervicis" even

continues iliocostalis as far as atlas; Murie (1872:

144) found an attachment to the axis, but I saw

no insertion forward of seventh cervical.

Origin: Tendinous and fleshy from lateral sides

of ribs just distal to angles.

Insertion: Tendons with their pinnate fibers pass

anteroventrally, each overlapping ones ahead of it.

Tendons narrow as they approach surface of muscle

and insert, along with some fibers, on protuberances

just distal to muscle's areas of origin on posterolateral sides of ribs, four or five ribs forward of tendons' points of origin. Only a few fibers attach to

first rib, just lateral to tuberculum. A tendon inserts on transverse process of seventh cervical, in

fusion with longissimus.

DEEPER MUSCLES OF THE NECK

M. RECTUS CAPITIS DORSALIS PMAJOR (RCMa: Figures 12, 15, 21, 40) [Murie, 1872:145; "rectus capitis

posticus major," in part?].—Small, fusiform; 1 cm

wide; lies ventral to dorsomedial edge of semispinalis capitis.

Origin: Fleshy from after end of neural spine of

axis. In my specimen it was somewhat asymmetrical, the muscle on left side arising posterior to its

fellow, from connective tissue slightly behind spine

of axis.

Insertion: Tendinous onto top of supraoccipital,

just below nuchal line and adjacent to midline.

M. RECTUS CAPITIS DORSALIS PlNTERMEDIUS (RCI:

Figures 12, 15, 21, 38, 40) [Murie, 1872:145: "rectus

capitis posticus major," in part?].—Robust; medial

to semispinalis capitis just ventral to rectus major.

Origin: Fleshy from apex of axis, anterolateral

to rectus major.

Insertion: Fleshy and tendinous onto supraoccipital ventral to rectus major, from midline out to

semispinalis capitis, and from near nuchal line

down onto exoccipital along posterior border of

semispinalis capitis insertion.

M. RECTUS CAPITIS DORSALIS MINOR (RCMi: Figures 12, 15, 21, 36, 37, 39) [Murie, 1872:145: "rectus capitis posticus minor"].—Fused with rectus

intermedius, as in manatee.

Origin: Fleshy from apex of atlas, adjacent to

midline.

Insertion: Fleshy onto supraoccipital in fusion

with rectus intermedius.

M. RECTUS CAPITIS LATERALIS (RL: Figures 6, 13-

15, 20, 22-25, 30, 31, 35-37) [Murie, 1872:145, fig.

29: "rectus lateralis"; Murie, 1880:34, pi. 8: fig.

5].—About 4.5 cm long, 1.5 cm wide.

Origin: Fleshy from tip of transverse process of

atlas and for about 3 cm anteroventrally along the

process.

Insertion: Fleshy on posterolateral side of paroccipital process, with an extension of about 1 cm

anteroventrally onto, apparently, proximal end of

stylohyoid (as in manatee; perhaps homologous to

jugulohyoideus?); also very slight tendinous attachment to most posteroventral edge of squamosal.

Though well developed in the manatee, a rectus

capitis ventralis (Murie's "rectus (capitis) anticus

minor," 1872:147, fig. 29; 1880:34, pi. 8: fig. 5)

was, surprisingly, totally absent in my specimen,

which had no muscular connection between the

ventral arch of the atlas and the base of the skull.

There is a partly separable deep division of the

longus capitis arising from cervicals 5 and 6, but

this hardly seems a likely homolog.

M. OBLIQUUS CAPITIS CAUDALIS (OCa: Figure 21,

36-40) [Murie, 1872:145: "obliquus inferior"].—

Well developed, about 3 cm wide.
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Origin: Fleshy from side of neural arch of axis,

from edge of apex down to postzygapophysis.

Insertion: Runs steeply anteroventrally and laterally to fleshy insertion on posterolateral side of

neural arch of atlas, from within about 2 cm of

midline out nearly to tip of transverse process.

M. OBLIQUUS CAPITIS CRANIALIS (OCr: Figures 14,

15, 24, 25, 35, 37) [Murie, 1872:145: "obliquus superior"; Murie, 1880:34, pi. 8: fig. 5].—Very small

bundle of fibers ventromedial to rectus capitis lateralis.

Origin: Fleshy from anteroventral side of transverse process of atlas, adjacent to anterior articular

surface.

Insertion: Fleshy on posterior side of exoccipital,

between condyle and insertion of brachiocephalicus.

In manatee attachment seems to be slightly farther

outboard and nearer stylohyoid.

M. STERNOMASTOIDEUS (Stm: Figures 6, 13, 14, 22,

23, 34, 35) [Murie, 1872:152, figs. 9, 29, 30; Murie,

1880; pi. 8: fig. 5].—Very long, narrow, fusiform;

passes deep to parotid gland together with brachiocephalicus, separated from latter by external jugular vein. Stannius (1845:34), in asserting connection

of this muscle with the deltoideus, mistook the

cephalohumeralis for the sternomastoideus.

Origin: Fleshy from ventral side of manubrium

adjacent to midline; inseparable from sphincter

colli profundus pars auris adjoining it behind, and

medial to pectoralis major (not anterior as in manatee).

Insertion: By long, narrow tendon onto anteroventrolateral side of posttympanic process of squamosal. Imperfectly divided into two or more

bundles, but all insert ultimately on this same

tendon; no aponeurosis or other part branching oft

inner side as in manatee.

M. STERNOTHYROIDEUS (Stt: Figures 5, 23-28, 31,

34, 35, 41) [Owen, 1838:38; Murie, 1872:179, fig.

9].—Broad, thin sheet covering ventral side of

trachea, formed by muscles from each side converging dorsal to manubrium and running forward

touching in midline. Not divided by any fibrous

bands.

Origin: Tendinous from anterior edge of first

costal cartilage and anterodistal edge of first rib;

covered by sternocostalis.

Insertion: Fleshy on posteroventral side of thyroid

cartilage, behind thyrohyoideus.

M. SCALENUS (Sc: Figures 6, 22-25, 35-37, 41, 42)

[Stannius, 1849:36: "scalenus posticus"; Murie,

1872:152, fig. 29; Murie, 1880:35, pi. 8: fig. 5].—

Prominent, about 5 cm wide, immediately beneath

subscapularis. Serratus magnus arises from dorsal

edge. Not in separate bundles as shown by Murie

(1880:35), but partly divisible into superficial and

deep portions as in manatee.

Origin: Fleshy from first two ribs distal to their

angles; in vicinity of third rib becomes indistinguishable from serratus. (Murie [1872, 1880] recorded its attachment to first three ribs.)

Insertion: Fleshy and tendinous on lateral extremities of transverse processes of cervicals 2-4,

ventral to longissimus attachments, and on posteroventral side of transverse process of atlas ventral to

longissimus and dorsal to longus colli. Murie did

not find an atlas insertion in his first manatee

(1872), but did in the second (1880) ; however, I

saw no superficial accessory tendon as in the latter

instance. Anteriorly muscle is partly covered by

shining tendinous sheet, as in manatee.

M. LONGUS CAPITIS (LoCa: Figures 13, 14, 24, 25,

35, 41) [Murie, 1872:147, fig. 29: "rectus (capitis)

anticus major"; Murie, 1880:34, pi. 8: fig. 5].—Very

prominent and powerfully developed; lies anteromedial and parallel to scalenus and is similar to it

in appearance, though slightly smaller.

Origin: Tendinous from anteromedial side of

ventral process and ventral side of neck of first rib,

and by thin tendinous slip (penetrating longus colli

between divisions 1 and 2) from ventral tips of

transverse processes of cervicals 5 and 6. Some fibers

pass lateral to ventral process of rib and seem to be

lost in mass of fasciae and blood vessels in this

region. In Murie's (1872) first manatee it arose from

undersides of third thoracic vertebra and head of

second rib; in his second (1880) it attached to transverse processes of cervicals 5 and 6, centrum of first

thoracic, and head of first rib.

Insertion: Fleshy and tendinous on occipitosphenoidal eminence of skull.

M. LONGUS COLLI (LoCo^: Figures 25, 35-37, 41)

[Murie, 1872:147, fig. 29; Murie, 1880:34, pi. 8: fig.

5].—Imperfectly divided into three parts, as follows,

proceeding medially:

—FIRST (LoCox: Figure 35).—

Origin: Tendinous from ventrolateral processes

of cervicals 5 and 6, lateral to longus capitis origins.

Insertion: Fleshy and tendinous onto ventral side

of atlas medial to scalenus.
NUMBER 226 15

—SECOND (LoCo2: Figure 35).—

Origin: Tendinous from anterovental side of

neck of first rib, anteromedial to longus capitis

origin.

Insertion: Runs anteromedially to join with third

division on ventral side of atlas, medial to first

division.

—THIRD (LoCo3: Figure 35).—

Origin: Broadly tendinous from ventral sides of

first and second or third thoracics, and partly from

first rib together with second division.

Insertion: Tapers anteriorly and fuses with second division; together they form a single mass,

larger than first division, with fleshy and tendinous

insertion on atlas between first division and midline. Small tendons of longus colli also insert on

ventrolateral sides of cervicals 2-6, just inboard of

longus capitis origins.

This arrangement differs in detail from both of

those described by Murie (1872, 1880), though the

overall pattern is similar. The details of this muscle's attachments are doubtless quite variable, and

the same is probably true of many of the muscles

in this region, due to the shortness of the neck.

MUSCLES OF THE THORAX

MM. INTERCOSTALES EXTERNI (IntE: Figures 3, 23,

24, 34, 42, 49, 52) [Murie, 1872:151, fig. 9].—Quite

strongly developed; run posteroventrally between

all ribs, along whole length of each (except caudal

edges of distal ends of the most anterior ribs), and

covering their anterolateral sides.

I did not observe any distinct levatores costarum,

though Murie did (1872:144); the fibers are evidently blended with either the external intercostals

or the transversospinalis fascicles.

MM. INTERCOSTALES INTERNI (IntI: Figures 24, 41,

42, 50) [Murie, 1872:151, fig. 44; Murie, 1880, pi. 8:

fig. 2].—Considerably' thinner than external; run

posterodorsally (nearly vertically) between ribs. Do

not attach to cartilages.

M. STERNOCOSTALIS (Stc: Figures 22, 23, 24, 35, 41)

[Murie, 1880, pi. 8: fig. 2].—Thin, largely tendinous

sheet; divided into two slips, the anterior smaller

and more tendinous. Murie's (1880) plate also shows

a slight division. Seemingly a derivative of the intercostales.

Origin: Tendinous from almost entire lateral

edge of manubrium, anterior to attachment of first

rib cartilage.

Insertion: Larger posterior part has fleshy and

tendinous insertion on anterolateral sides of distal

end of first rib and proximal end of its cartilage;

anterior slip diverges to insert farther up shaft of

rib.

DIAPHRAGM

The nearly horizontal diaphragm is mostly tendinous, as in Trichechus. Its muscular fibers are

confined to a narrow band along each side, with

fleshy origins from ribs 3-17 near their distal ends

and from a transverse line across the rib cartilages

and the posterior border of the sternum. The fibers

are at most 6-8 cm long and arch dorsomedially and

anteriorly. In the manatee the diaphragm extends

"from the first to the last rib" (Murie, 1872:154,

figs. 44, 49, 50). The high myoglobin content of the

diaphragm (Blessing, 1972) suggests its extensive use

in hydrostatic adjustments during diving, as well as

in respiration.

MUSCLES OF THE ABDOMEN

M. CUTANEUS TRUNCi (CuT: Figures 2, 3, 18, 19, 22,

23, 32, 33, 49, 50-52) [Murie, 1872:163, figs. 8-10,

30, 46, 49, 50: "panniculus carnosus, P.c1," in part,

including "P.c**" and "P.c***"].—Very extensive,

mostly thin sheet of loosely connected coarse fibers,

extensively veined with fat. Covers underside of

body and tail from axilla to base of fluxes, and ventrolateral side of thorax; continuous with its fellow

in ventral midline.

Origin: In two parts. Medial part (Murie's

"P.c**") arises by fasciae and small tendons from

posterolateral edge of sphincter colli profundus

pars auris, and is overlapped by latter posteriorly

and medially, as described above for that muscle.

Between these connections the two muscles are

separable along their adjacent borders for about

6 cm. Lateral part arises from fasciae above and behind axilla, widens, and overlaps posterodorsal edge

of latissimus. Two parts merge about 12 cm abaft

axilla; in fork between them they fuse with diminutive latissimus, ventral to which a few cutaneus fibers pass parallel to it out of axillary

fasciae. In this region, bounded by latissimus, cu-
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

taneus trunci, and (ventrally) pectoralis minor, lies

mammary gland (undeveloped in my immature

specimen).

Insertion: Lateral fibers sweep back and up onto

sides, inserting at dorsal midline by superficial

aponeurosis covering back and sides from middle of

thorax back to flukes. Anteriorly, fibers end about

as high on side as shoulder joint; farther aft, line

along which fibers end descends till, at level of anus,

muscle is completely on underside of body. More

medial fibers run aft in parallel down length of

belly and tail nearly to flukes, muscle not decreasing in width behind anus until almost to flukes,

where it quickly tapers to a point. This sheet surrounds genital opening and anus, and some fibers

attach to hide on side of genital fold just forward

of anus. Fibers lateral enough to run aft clear of

anus continue parallel for a while, then sweep out

and upward to insertion; those near midline behind anus pass posterodorsally in pinnate fashion.

Both insert on aponeurosis on muscle's deep side

(continuous with aforementioned superficial aponeurosis of back and sides) which attaches to tips

of third to about eighth chevron bones in addition

to sheathing tail. Lateral border of caudal part of

cutaneus, in forward half of tail, forms a fold over

this aponeurosis. Thickness of muscle varies greatly

as in manatee; from thin (0.5 cm) dorsal and anterior edges it thickens gradually to 2 cm ventrally

just ahead of anus, but at level of anus swells very

abruptly to about 3.5 cm and then thins again as

it runs aft.

This arrangement differs in several respects from

that in the manatee. The sheet shown by Murie

(1872, fig. 8) passing over the whole shoulder region is here absent, though perhaps represented

in part by the upper portion of the cutaneus

trunci and by the jugularis and scapularis parts of

the platysma. The slip to the humerus (Murie,

1872:163, fig. 9: "P.c#"; Stannius, 1845:35) is also

absent. In these respects the dugong is more modified from the primitive ungulate condition than is

the manatee. In Trichechus the caudal portion is

not so well developed as in Dugong; it ends at the

sixth chevron bone. Finally, I observed no distinct

slip opposite the genital region, as occurred in

Murie's female manatee. (Elsewhere, he (1872:162)

homologized this with a levator ani.)

M. OBLIQUUS ABDOMINIS EXTERNUS (OAE: Figures

23, 33-35, 49) [Murie, 1872:155, figs. 8, 9, 30, 44,

50].—Covers approximately the distal thirds of ribs,

just beneath cutaneus trunci; between its upper

edge and lower edge of iliocostalis are exposed ribs

and intercostales externi. Composed of separate

pinnate segments attached to each rib and directed

posteroventrally, parallel to ribs; segments are 9-15

cm long measured in this direction.

Origin: Pinnately from tendons arising along distal thirds of outer sides of ribs 3-19 (and with

weaker tendinous sheet to second rib), thus having

a serrate dorsal outline; also fleshy from aponeurosis

between rib 19 and lumbar and sacral vertebrae, adjacent to intertransversarius coccygeus.

Insertion: By strong shining aponeurosis to ventral midline, forming part of outer rectus abdominis

sheath. Muscular portion of obliquus overlapped

by that of cutaneus trunci. Posteriorly it tapers to

a point ending opposite ischium, a strong aponeurotic sheet still attaching to muscle's deep side.

Thus, apart from the attachment to the second

rib, it does not differ from the arrangement in the

manatee.

M. OBLIQUUS ABDOMINIS INTERNUS (OAI: Figures

34, 50, 52) [Murie, 1872:155, fig. 9].—Small, thin,

and inconspicuous; fibers about 8 cm long, leading

anteroventrally and covering transversus abdominis

between ends of ribs and rectus abdominis.

Origin: Fleshy from distal ends of ribs 6-19;

Murie found it beginning at third rib.

Insertion: By aponeurosis to ventral midline, fibers not quite reaching edge of rectus abdominis.

Aponeurosis divides as usual to form parts of both

inner and outer rectus sheaths.

M. TRANSVERSUS ABDOMINIS (TrA: Figures 50-54)

[Murie, 1872:154, fig. 9: "transversalis"].—Strong

layer about 1.5 cm thick and about 7 cm wide.

Origin: Fleshy from medial sides of ribs 3-19

near distal ends; continued somewhat forward of

this by aponeurotic attachment, and posteriorly

connected to whole anteroventral side of ilium and

part of ischium via aponeurosis between last rib

and pelvis, from deep side of which aponeurosis it

arises. Muscular portion extends back to pelvis;

Murie does not mention such a posterior extension.

Insertion: Fibers pass ventromedially to insert on

strong aponeurosis lying against wall of abdominal

cavity and forming part of inner rectus sheath.

Rectus overlaps ventral edge of transversus by about

2.5 cm.

M. RECTUS ABDOMINIS (RA: Figures 23, 24, 33-35,
NUMBER 226 17

41, 49, 50, 52, 53) [Murie, 1872:155, figs. 9, 37, 46,

50].—Strong, about 8 cm wide and 2 cm thick.

Pectorales arise from surface of its forward end.

Composition of its aponeurotic sheath same as in

terrestrial mammals, except that aponeuroses of

obliquus internus are absent abaft rib cage, since

obliquus does not extend there; and its outer

aponeurosis is of course lacking in the sheath forward, where rectus overlies rib cartilages. Cutaneus

trunci very tightly adherent to surface of sheath

throughout its length. Rectus extends laterally

nearly to free ends of ribs.

Origin: Fleshy from posterolateral edge of sternum and after edge of last (in my specimen the

fourth) sternal rib cartilage; laterally sends slips

forward to third cartilage and, by a tendinous sheet,

first and second cartilages and end of first rib (these

forward extensions lying superficial to cartilages).

Insertion: Tapers rather abruptly at pelvis to

fleshy insertion on middle of anterolateral side of

ischium.

MUSCLES OF THE TAIL

The mm. sacrococcygei dorsales lateralis et medialis (Murie's "levatores caudae externus et internus," 1872:144, figs. 8, 39) are continuations of,

and inseparable from, respectively, the longissimus

and transversospinalis systems, and have already

been described with the epaxial spinal muscles.

" M . INTERTRANSVERSARIUS COCCYGEUS" (Intr : Fig -

ures 3, 49, 50, 52, 53) [Murie, 1872:146-147, figs.

8, 39, 44, 50: "lumbo-caudalis"].—Conspicuous,

very long, narrow, and fusiform, lying along ends

of transverse processes from second lumbar to end

of tail, and covered only by cutaneus aponeurosis.

Forward end abuts against after end of iliocostalis

thoracis, though the two are clearly separate and

distinguished by different directions of fibers. Murie

(1872, fig. 8), however, shows it below and overlapping iliocostalis. Attachment of cutaneus aponeurosis along dorsal edge of iliocostalis continues

along intertransversarius. Latter is, on its deep side,

separated by its aponeurosis from short fibers (Intrd,

Figures 50, 52), divided into dorsal and ventral

bundles, lying between transverse processes. The

long, fusiform intertransversarius probably developed by fusion of short bundles of this type lying

outboard of tips of transverse processes.

Origin: Fleshy from after edge of last rib at

about its middle, from crest on lateral side of

proximal end of ilium, and from aponeurosis on

its deep side which passes from last rib to lumbar

vertebrae and attaches to tips of transverse processes from second lumbar to posterior caudals. Begins in manatee at sacral or first caudal.

Insertion: Aponeurosis from deep side extends

laterally onto ventral side of muscle and turns

dorsally again, passing into muscle through about

the forward two-thirds of its length, and forming

an internal tendon of pinnate insertion for fibers

passing posteroventrally from lateral surface of

deep part of aponeurosis. Farther aft (about middle

of tail) this tendon emerges onto ventrolateral side

of muscle, and continues back to insert on transverse processes of aftermost caudals. Murie, however, found it only along first 8 or 9 caudals,

ending by a tendon on surface of sacrococcygeus

ventralis lateralis. Stannius (1845:35-36; 1849:22)

describes a system of "Musculi transversarii," with

inferior and superior parts, seemingly answering to

my intertransversarius at least in part, but evidently passing forward across all the ribs, outboard

of the iliocostalis, attaching to each of them!

M . SACROCOCCYGEUS VENTRALIS LATERALIS (SVL:

Figures 49-52) [Murie, 1872:145-146, figs. 8, 9, 37,

39, 44, 50: "sacro-coccygeus"].—Broad but rather

thin (1.5 cm or less, decreasing posteriorly and ventrally); for most of length triangular in cross-section,

intertransversarius lying on its dorsolateral side.

Anteriorly on deep side, fuses with sacrococcygeus

ventralis medialis. Covered by cutaneus aponeurosis.

Origin: Fleshy from undersides of tips of caudal

transverse processes and aponeurosis between them,

and anteriorly from medial sides of ribs 17-19 and

ventral sides of 16th thoracic and following vertebrae, in fusion with medialis. A long, narrow, fusiform part even extends forward, ventral to

diaphragm, to tendinous attachment on sides of

keels of thoracics 12 and 13, adjacent to midline,

and with possibly some tendinous strands going

even beyond. This part, entirely continuous with

sacrococcygeus mass, evidently corresponds to the

separate quadratus lumborum slips found by Murie

(1872:146, fig. 44); these, however, only went as far

forward as last two thoracics and last rib. His

sacrococcygeus proper also extends only as far as last

rib. Stannius (1845:35) found hypaxial muscles

extending only about to last lumbar vertebra.

Insertion: Aponeurotic onto tips of second and
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

following chevron bones and undersides of aftermost caudals, covering medialis. Muscular part extends back about to middle of flukes. Insertion in

manatee begins at third chevron bone.

M. SACROCOCCYGEUS VENTRALIS MEDIALIS (SVM:

Figure 51) [Murie, 1872:146, figs. 9, 37, 39, 44:

"infracoccygeus"].—Lies beneath lateralis; fused

with it in sacral and anterior caudal region. Fibers

more posteriorly oblique than those of lateralis.

Origin: Fleshy from lateral sides of all chevron

bones, fasciae between them, and ventrolateral

sides of caudal centra; and from ribs and thoracic

and lumbar vertebrae in fusion with lateralis, as

described above.

Insertion: By thick aponeurosis (together with

lateralis) on tips of second and following chevrons

and undersides of aftermost caudals. Aponeurosis

not as divided into separate tendons as seems to

be the case in the manatee. Covers most of muscle's

lateral surface.

"M. FLEXOR HAEMALIS" (FH: Figure 51).—Not

found in Murie's manatee; slender, cylindrical,

lying along tips of chevron bones, increasing

somewhat in size posteriorly, and encased by the

rather closely adherent sacrococcygeus ventralis

aponeurosis.

Origin: Fleshy and tendinous from tips of

seventh and following chevrons.

Insertion: Fibers pass posterodorsally onto externally enveloping tendinous sheet, which continues in this direction and sweeps inward to tips

of eighth and following chevrons and ventral sides

of aftermost caudals.

MUSCLES OF THE SHOULDER

M. TRAPEZIUS (Trp: Figures 3, 5, 12, 13, 15, 18-

20, 22, 43, 44) [Murie, 1872:156, fig. 8].—Rather

thin sheet covering nearly entire blade of scapula,

superficial to supraspinatus and infraspinatus, and

partly covered by panes temporalis and scapularis

of platysma.

Origin: By aponeurosis from dorsal midline,

anteriorly just reaching skull near lateral end of

nuchal line, and extending back to level of caudal

angle of scapular cartilage. Aftermost fibers not as

posteriorly directed as in manatee, and do not arise

as far back on midline. Anteriorly a separate slip

1.5 cm wide arises by a tendon from anterolateral

side of sigmoid ridge of squamosal, dorsal to

cephalohumeralis origin; this tendon may be traced

up as far as nuchal line, adherent to bone.

Insertion: Tendinous on entire length of scapular

spine and along a line diverging thence and crossing

infraspinatus at about a 50° angle towards caudal

angle of scapular cartilage. This line forms juncture

between trapezius above and deltoideus and teres

major below, and on it inserts pars scapularis of

platysma. Above dorsal end of scapular spine is a

tendinous embayment in trapezius, about 4.5 cm

long, nearly dividing it into cervical and thoracic

portions. Dorsal half of this tendinous band not

attached to bone beneath. In Trichechus, trapezius

evidently attaches only to scapular spine and not

to surface of infraspinatus.

M. RHOMBOIDEUS (Rh: Figures 20, 22, 46, 47)

[Murie, 1872:156, figs. 8, 13].—Small and narrow

as a whole, though individual loosely connected

bundles of fibers are long.

Origin: Aponeurosis in dorsal midline of anterior

thoracic region, just beneath trapezius aponeurosis.

Fibers begin about 3 cm from midline, just over

after corner of splenius.

Insertion: Fleshy on nearly whole vertebral

border of scapular cartilage, on its medial side, to

within 2 cm of caudal angle. Ventrally it is in

contact with serratus and overlaps it by about 1 cm.

M. SERRATUS MAGNUS (SeM: Figures 3, 18-20, 22,

23, 33, 34, 41-43, 46, 47) [Murie, 1872:153, figs. 13,

29].—Divided into anterior (SeMa) and posterior

(SeMp) parts, latter overlapping and fusing with

former near insertion. On medial side change in

direction of fibers appears about 6 cm farther aft

than on lateral side. The two parts are fully

separable only near muscle's attachment to scalenus.

Origin: Anterior part, from dorsomedial edge of

scalenus and tendinously from angle of first rib.

Posterior part, tendinous and fleshy from second

rib about 4 cm distal to its angle and from progressively more distal parts of ribs 3-9; merges

ventrally with scalenus and posteriorly with

obliquus abdominis externus and intercostales

externi. On its inner side its fibers are seen to

attach pinnately to tendinous bands from ribs.

Insertion: Fleshy and tendinous onto whole

medial side of scapular cartilage and strip about

3 cm wide along vertebral border of scapula.

Fibers of anterior part insert on nearly all of this
NUMBER 226 19

area; those of posterior part, lying lateral to former,

occupy aftermost edge of this area and extend forward thence, ventral to and diverging from main

area of insertion, ending about halfway to forward

edge of scapula. Insertion of posterior part extends

down after edge of scapula to teres major protuberance. Superficial fibers of posterior part insert pinnately on superficial tendinous sheet.

In the manatee, Murie (1872:153) traced the

serratus only as far back as the sixth rib, and

distinguished a part of it extending to the atlas. I

did not observe this, nor the "twist" he described in

"the nuchal portion of the muscle". He did not

find separate anterior and posterior parts.

M. CEPHALOHUMERALIS (Ch: Figures 5, 13, 19, 22,

23, 33, 34, 46, 47) [Murie, 1872:156, figs. 13, 29:

"cephalo-humeral"].—Slender and strap-like, descending steeply across side of neck and covering

forward side of shoulder.

Origin: Tendinous from anterolateral side of

lower end of sigmoid ridge of squamosal, immediately behind auditory meatus. Murie may be wrong

in saying it arose from "outer occipital."

Insertion: Passes ventrally and posteriorly around

upper end of humerus, crossing and covering deltoid crest, its inner edge fusing somewhat with

brachiocephalicus just medial to deltoid crest.

Passes down nearly whole length of front side of

humerus, and ends by fiat, thin tendon in fascia

beneath sphincter colli superficialis and in close

association with front edge of pectoralis major,

near latter's insertion. Also a partial tendinous

insertion onto humerus at upper end of pectoralis

major insertion.

M. BRACHIOCEPHALICUS (Brc: Figures 6, 14, 15,

22, 23, 33-35, 46) [Murie, 1872:157, fig. 13: "levator

claviculae(P)"].—Slender and strap-like, similar to

cephalohumeralis and nearly parallel with and

posteromedial to it; passes deep to portion of

parotid gland, parallel to sternomastoideus.

Origin: Tendinous from posteroventral edge of

paroccipital process of exoccipital, between rectus

capitis lateralis and obliquus capitis cranialis.

Insertion: Tendinous into fascia on medial side

of deltoid crest of humerus, in fusion with cephalohumeralis.

M. LATISSIMUS DORSI (LaD: Figures 22, 32, 33, 46,

47) [Stannius, 1849:14, 16; Murie, 1872:153, figs. 8,

9, 13; Bahrdt, 1933:237, fig. 22].—Relatively small,

partly fused posteriorly with cutaneus trunci. Passes

dorsal to mammary gland. Lies superficial to ribs

and intercostales between serratus and obliquus

abdominis externus; has no direct connection to

ribs, as it evidently does in the manatee.

Origin: Anterior edge and medial side of cutaneus

trunci between latter's lateral and medial portions.

Insertion: Pinnate onto flat tendon attached to

humerus in fusion with tendon of pectoralis minor

(q.v.); not connected to insertion of teres major,

in contrast to Trichechus and many other mammals.

M. PECTORALIS MAJOR (PMa: Figures 22, 23, 33-

35, 46-48) [Murie, 1872:157, figs. 9, 13, 30; Bahrdt,

1933:238, fig. 22].—Wide and strong; 2 cm thick

anteriorly.

Origin: Fleshy and tendinous from ventral side

of sternum (between sphincter colli profundus pars

auris and sternocostalis) from its forward end to

within about 2 cm of its after end; and from surface

of rectus abdominis for about 3 cm posterolaterad

from sternum, out to medial sides of fourth rib

cartilage and pectoralis minor insertion. A small

fleshy slip also arises from forward edge of distal

end of fourth rib cartilage.

Insertion: By strong tendon onto anteromedial

side of humerus at lower end of deltoid crest. On

dorsal side of muscle a very thin, anteriorly partly

separable sheet, more anterior in direction, joins to

tendon of latissimus and pectoralis minor. From

muscle's distal (posterior) edge a smaller but strong

tendon is sent off, nearly perpendicular to rest of

muscle, to pass across elbow joint and insert on

joint capsule, on proximal end of radius beneath

biceps tendon and adherent to brachialis, and

possibly on adjacent tip of ulna. (The radial insertion was observed by Murie but not Bahrdt.) Ventrally, a tendinous sheet comes off pectoralis major

and crosses brachialis to joint superficial fascia on

anterior side of forelimb.

M. PECTORALIS MINOR (PMi: Figures 22, 23, 33-35,

46, 47) [Murie, 1872:157, figs. 9, 13, 30].—Much

smaller than pectoralis major, which overlaps and

fuses with its forward edge. After part covered

only by medial part of cutaneus trunci. Passes

medial to mammary gland.

Origin: From surface of rectus abdominis to

within 1 cm of latter's lateral border and approaching to within about 3 cm of midline. Anterolaterally adjoins posterior edge of fourth rib

cartilage. The trend of its fibers is continued

posteromedially by glistening fascia on surface of
20

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

rectus abdominis, parallel to obliquus abdominis

externus fascia farther aft, and crossing over fascia

of obliquus abdominis internus.

Insertion: Pinnate onto flat tendon joining that

of latissimus dorsi and attaching to humerus on a

line from after side of pectoralis major insertion

up ridge (actually medial side of deltoid crest)

forming lateral side of bicipital groove. In manatee, inserted onto head of humerus.

In using the terms "pectoralis major" and "pectoralis minor," I am merely following Murie's

denotation of the muscles' relative sizes and not

taking a position on their homologies with the

pectoral muscles of other mammals. The anteriorly

directed deep division of the pectoralis major, however, is significant in this connection and seems to

be a vestige of a "posterior deep pectoral" sheet.

MUSCLES OF THE FORELIMB

Attention should be called here to the illustrations of the manatee's forelimb provided by Bahrdt

(1933, fig. 24), especially the schematic cross-sections.

M. DELTOIDEUS (D: figs. 3, 5, 18-20, 34, 43, 44)

[Murie, 1872:158, fig. 8; Bahrdt, 1933:237, fig. 22].—

Prominent, up to 1.5 cm thick.

Origin: Fleshy from tip of acromion process and

after side of scapular spine, and along tendinous

band (in common with trapezius, q.v.) crossing

surface of infraspinatus to rear edge of scapula.

This band attaches to surface of infraspinatus by

a thin tendinous sheet. In manatee, muscle is evidently attached only to scapular spine.

Insertion: Fleshy on deltoid crest of humerus;

not divided as in Trichechus, nor is there an extension toward elbow. (This extension was evidently

not found by Bahrdt in his manatee.) Near insertion, after half of medial side of muscle is covered

by shining tendinous sheet on which most of posterior fibers insert pinnately.

M. SUPRASPINATUS (Sup: Figures 5, 19, 20, 34, 43,

44, 46, 47) [Murie, 1872:156, fig. 13].—Quite massive; extends about 3 cm in front of scapula and

adheres closely to subscapularis. Upper part

crossed by a number of small tendinous bands generally parallel to fibers, but muscle is not complexly pinnate.

Origin: Fleshy from whole supraspinous fossa of

scapula.

Insertion: Anterior fibers insert on tendon within

muscle which does not extend much above lower

end of scapular spine; this, along with most of

fleshy part of muscle, attaches to summit and posterolateral side, and somewhat to medial side, of

greater tuberosity of humerus. A partly separable

and entirely fleshy division of muscle arises chiefly

from lower edge of scapular spine and fuses posteriorly with infraspinatus; its insertion is continuous with that of latter rather than with rest of

supraspinatus.

M. INFRASPINATUS (Inf: Figures 20, 43, 44) [Murie,

1872:156, fig. 8].—Considerably smaller than supraspinatus; entirely covered by deltoideus and trapezius. Extends about 3 cm behind scapula. Near

insertion, anterior fibers mingle with those of

supraspinatus.

Origin: Fleshy from infraspinous fossa of scapula

and base of scapular spine, as far down as ventral

end of spine.

Insertion: Pinnate on strong tendon (visible on

middle of lower part of lateral side) attaching to

lateral edge of greater tuberosity of humerus, between head and deltoideus insertion, in fusion with

after part of supraspinatus.

M. SUBSCAPULARIS (Su: Figures 43, 46, 47) [Murie,

1872:156, figs. 9, 13].—Covers nearly whole medial

side of scapula, extending about 3 cm forward of

and abaft scapula (measured just above neck);

closely adherent to supraspinatus anteriorly.

Origin: Fleshy from medial side of scapula below

serratus insertion, down to 1 cm above border of

glenoid cavity. For about 1 cm abaft neck of

scapula it arises from aponeurosis between rear

edge of scapula and front edge of teres major.

Insertion: Narrows and passes between scapula

and coracobrachialis to strong tendinous and fleshy

insertion on posteromedial side of lesser tuberosity

of humerus. A tendinous sheet covers large part of

medial side of muscle; forward of this another tendinous band, about 1 cm wide, thickened posteriorly and buried in muscle anteriorly, is visible;

both pass down into humeral insertion, and have

fibers inserted pinnately on them.

M. TERES MAJOR (Ter: Figures 3, 18-20, 43, 44,

46, 47) [Stannius, 1849:14; Murie, 1872:156, figs. 8,

13; Bahrdt, 1933:237, fig. 22].—Prominent and well

developed.

Origin: Fleshy from posterior edge and lateral

side of scapula and its cartilage, from and including tip of teres major process to halfway along

edge of cartilage.
NUMBER 226 21

Insertion: Pinnate onto strong superficial tendinous sheet attached to posteromedial edge of shaft

of humerus. An aponeurosis connects muscle's front

edge to rear edge of scapula.

A teres minor is lacking in both dugong and

manatee.

M. CORACOBRACHIALIS (Cob: Figures 46, 47) [Barkow, 1851:119; Murie, 1872:159-160, fig. 13: "biceps, B1

"; Murie, 1880:32; Bahrdt, 1933:237, figs.

22, 24: "biceps," in part].—Fusiform; consists of

several distinct bundles; complexly pinnate. Lies

posterior to lesser tuberosity of humerus and

crosses subscapularis and teres major insertions.

Origin: Fleshy from medial side of coracoid process of scapula.

Insertion: Tendinous on proximal side of medial

epicondyle of humerus.

M. BICEPS BRACHII (B: Figures 44, 46-48) [Barkow, 1851:119; Murie, 1872:159-160, fig. 13: "biceps, B2

"; Murie, 1880:32, pi. 8: fig. 3; Bahrdt,

1933:237, figs. 22, 24: "biceps," in part].—Fusiform;

single-headed. Smaller than coracobrachialis. Fills

bicipital groove of humerus and crosses latissimus

and pectoralis insertions. Bahrdt thought it more

strongly developed in Dugong than in Trichechus.

Origin: Fleshy from anterolateral rim of glenoid

cavity.

Insertion: Pinnate on strong externally sheathing

tendon to coronoid process of ulna and adjacent

medial side of neck of radius, covering distal insertion of pectoralis major just behind proximal insertion of brachialis.

M. TRICEPS BRACHII [Murie, 1872:158, fig. 13:

"triceps"; Murie, 1880, pi. 8: fig. 3; Bahrdt,

1933:236, figs. 22, 24: "triceps"].—Very massive,

with three divisions.

—LONG HEAD (TrLo: Figures 43, 44, 46-48)

[Bahrdt, 1933:236: "third" head].—Largest division;

thick and fleshy.

Origin: Fleshy, and pinnate from superficial tendon, from after edge of neck of scapula, for 3 cm

dorsally from glenoid cavity.

Insertion: Pinnate on deep tendon onto tip and

medial side of olecranon process.

—LATERAL HEAD (TrLa: Figures 43, 44, 47),

[Bahrdt, 1933:236: "second" head].—Rather flat;

fused distally with medial head and anteriorly (less

intimately) with brachialis. Partly overlies medial

head. Pinnate similarly to long head.

Origin: Tendinous and fleshy from after side of

neck of humerus.

Insertion: On olecranon process, lateral and partially deep to insertion of long head, by a shining

tendinous sheet covering lateral side of olecranon

and continuous with antebrachial fascia. Also has

fleshy attachment to olecranon by way of fusion

with medial head.

—MEDIAL HEAD (TrM: Figures 44, 46, 47):

[Bahrdt, 1933:236: "first" head].—Slightly larger

than lateral head; thin laterally where latter overlies it, but much thicker medially, where it contains a tendon.

Origin: Fleshy from posterior side of humerus,

from neck down onto after side of medial epicondyle.

Insertion: Fleshy, and pinnately on tendon, onto

olecranon process, lateral, anterior, and medial

sides.

As in the manatee, no separate anconeus was

observed; it may have become fused with the

triceps.

M. BRACHIALIS (Br: Figures 43, 44, 46-48) [Barkow, ,1851:119: "brachialis internus"; Murie,

1872:160, figs. 8, 13: "brachialis anticus"; Murie,

1880:32, pi. 8: fig. 3; Bahrdt, 1933:237, figs. 22,

24].—Very strongly developed. Posterior border

fused with and overlapped by lateral head of triceps. Distally has two divisions, and is fused with

brachioradialis at latter's origin. Passing down radius, it is partly covered by shining fascia.

Origin: Fleshy from whole lateral side of humerus, from neck down to lateral epicondyle. Some

fibers from superficial shining fascia.

Insertion: First, fleshy and tendinous of radial

tuberosity; second, tendinous along line crossing

anterior side of radius mediodistally, finally ending

tendinously on anteromedial side of distal end of

radius, adjacent to brachioradialis. Part of its tendon passes into wrist fasciae beneath abductor

pollicis longus and flexor carpi radialis. Fibers

pinnate on the various tendons.

Barkow does not mention a separate proximal

insertion, nor does Bahrdt; Murie (1872:160) found

the insertion on "the upper half of the radius."

Bahrdt's distal insertion was "fleshy," and he did

not find an extension beyond the radius (though

I found this of almost negligible extent).

M. BRACHIORADIALIS (Brr: "Figures 43-47) [Murie,

1872:158, fig. 8: "supinator longus"; Bahrdt,
22 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

1933:238, figs. 22, 23, 24].—Forms anterior edge of

forearm.

Origin: Fleshy and by single strong tendon from

anterior side of lateral epicondyle of humerus, continuous with origins of brachialis and extensor

carpi radialis. Some superficial fibers arise from

underside of a shining fascia covering brachialis

and brachioradialis near elbow joint.

Insertion: Pinnate on central tendon which becomes exposed at distal end of radius and covers

latter's anterior side; inserts on lateral sides of

anteriormost carpals, with its anterior edge prolonged down to forward side of proximal end of

metacarpal i.

Neither Bahrdt nor Murie noted a fusion with

the brachialis or an extension to the metacarpal,

but the relations of the muscle are such that these

are to be expected.

M. EXTENSOR CARPI RADIALIS (ECR: Figures 43-

45) [Murie, 1872:158, fig. 8; Bahrdt, 1933:238-239,

figs. 22, 23, 24].— Not subdivided. Quite wide (1.7

cm) proximally.

Origin: Fleshy and tendinous from anterolateral

side of lateral epicondyle of humerus, between origins of brachioradialis and extensor digitorum communis.

Insertion: Complexly pinnate onto tendon passing beneath abductor pollicis longus and extensor

pollicis brevis et longus, and through anterior

groove in distal end of radius, to proximal end of

metacarpal n. No connection to metacarpal m as

in Bahrdt's and Murie's specimens. Murie found

its tendon of insertion crossed by those of "primi

internodii pollicis" (part of my extensor pollicis)

and "long supinator" (my brachioradialis); but

since latter inserted on anterior carpal, just as in

dugong, it would seem unable to cross extensor

carpi radialis; so his statement is evidently in error.

Indeed, Murie's (1872) figure 8 shows the two muscles lying parallel. He probably meant that extensor pollicis crosses brachioradialis and extensor

carpi radialis.

M. EXTENSOR DIGITORUM COMMUNIS (EDC: Figures

43-45) [Murie, 1872:159, fig. 8; Bahrdt, 1933:239,

figs. 22, 24].—Very narrow proximally and much

less prominent than adjacent muscles; widens distally.

Origin: Tendinous from lateral epicondyle of

humerus behind extensor carpi radialis, and from

elbow joint capsule; fleshy and tendinous from lateral side of proximal end of radius.

Insertion: Complexly pinnate. Passing through

anterior groove on ulna, adjacent to extensor pollicis, its tendon divides over distal carpals into

three parts, passing respectively to second phalanges

of digits II and in and to proximal phalanx of

iv; no branch to v as in Murie's and Bahrdt's animals. Tendon to iv comes off higher than others.

M. EXTENSOR DIGITI QUINTI (EDQ: Figures 43-45)

[Murie, 1872:159, fig. 8: "extensor minimi digiti";

Bahrdt, 1933:239, figs. 22, 24].—Closely adherent

deeply to extensor digitorum communis.

Origin: Tendinous from lateral epicondyle of

humerus behind extensor digitorum communis,

from joint capsule, posterolateral corner of proximal

end of radius, and lateral corner of semilunar notch

of ulna.

Insertion: Pinnate on both sides of tendon passing through posterior groove in ulna and diverging

from that of extensor digitorum communis; inserts

on proximal end of metacarpal v and also continues

down to insert on proximal phalanx. Tendon's division lies over proximal end of metacarpal; branch

to metacarpal is so short that it hardly constitutes

a separate tendon.

M. EXTENSOR CARPI ULNARIS (ECU: Figures 43, 44)

[Murie, 1872:159, fig. 8; Bahrdt, 1933:239, figs. 22,

24].—Flat and smaller than extensor digiti quinti.

Proximally overlies extensor pollicis; distally, the

bare ulna. Pinnate between deep proximal and

superficial distal tendinous sheets.

Origin: By very broad tendon from lateral epicondyle of humerus behind forward half of extensor

digiti quinti tendon, and crossing and covering

latter's after half. Also, from smaller tendinous attachment on lateral side of olecranon process, beneath triceps tendon and superficial to extensor

digiti quinti. Bahrdt describes a bifurcate tendon,

but fails to state whether after branch connects to

ulna.

Insertion: Becomes tendinous and passes into

thick tendinous covering at rear of wrist along with

flexor carpi ulnaris. Inserts on posterior sides of

aftermost carpal (corresponding to pisiforme) and

of proximal end of metacarpal v. Murie found it

inserting on unciforme (hamate), os magnum (capitate) and metacarpal. In stating that "its fibers . . .

mingle with those of the carpi radialis," Murie
NUMBER 226 23

(1872:159) perhaps meant instead the flexor carpi

ulnaris.

M. EXTENSOR POLLICIS BREVIS ET LONGUS (EP: Figures 43-45) [Murie, 1872:159, fig. 8: "extensores

primi and secundi internodii pollicis"; Bahrdt

1933:240, fig. 23].—Thin and flat; anterior edge

overlaps abductor pollicis longus. Almost entirely

covered by other extensors. Murie found it partly

divisible.

Origin: Fleshy from anterolateral side of shaft of

ulna and lateral side of olecranon process.

Insertion: Fibers insert pinnately on tendinous

sheet, covering muscle superficially, which passes

into tendon, adjacent and subparallel to that of abductor pollicis longus, and emerging from beneath

extensor digitorum communis at wrist joint. This

tendon passes through posterior groove on radius

and inserts on anterolateral side of proximal end

of metacarpal i.

?M. ABDUCTOR POLLICIS LONGUS (AbP: Figures 43-

47).—My identifications of this and the previous

muscle are somewhat uncertain, since their homologs in other animals vary a good deal in attachments and even in presence or absence, and since

no other author seems to have described this muscle in a sirenian. I found it well developed, filling

the interosseous space laterally.

Origin: Fleshy from posterolateral side of radius

and anterolateral side of ulna.

Insertion: Emerges from beneath extensor digitorum communis just proximal to extensor pollicis, and becomes tendinous on deep side where it

crosses extensor carpi radialis (which also becomes

superficially tendinous at this point); passes

obliquely medially across front edge of wrist and

onto palm, where it becomes continuous with superficial aponeurosis crossing palm to base of metacarpal v; but chief insertion is onto palmar side of

proximal end of metacarpal i.

M. PRONATOR TERES (PrT: Figures 46, 47) [Murie,

1872:160, fig. 13: "pronator radii teres"; Murie,

1880:32, pi. 8: fig. 3; Bahrdt, 1933:240, figs. 22,

24].—Vestigial; represented only by a very thin

tendon with few or no fibers of its own, and adherent to antebrachial aponeurosis.

Origin: Anterior side of medial epicondyle of

humerus, in fusion with flexor carpi radialis.

Insertion: Medial side of radius, about two-thirds

of way down. Quite separable from flexor carpi

radialis except at origin, but adherent to brachialis

near insertion.

Bahrdt apparently found it better developed,

and it was still more so in Murie's (1872) first manatee, where it had a distinct belly; but in his later

dissection it was inseparable from the flexor carpi

radialis.

M. FLEXOR CARPI RADIALIS (FCR: Figures 46-48)

[Murie, 1872:160, fig. 13; Murie, 1880:32, pi. 8:

fig. 3; Bahrdt, 1933:240, figs. 22, 24].—Slightly overlaps and fused posteriorly with flexor digitorum

superficial at origin. Covered by tendinous sheath

except near origin; complexly pinnate.

Origin: Fleshy from anterodistal side of medial

epicondyle of humerus with pronator teres and

flexor digitorum superficialis; fleshy from medial

side of middle quarter of shaft of radius.

Insertion: By very wide, strong tendon onto

medial side of distal carpal at bases of metacarpals

i and ii. Murie (1872, 1880) found it attached to

bases of metacarpals i and n.

M. FLEXOR DIGITORUM SUPERFICIALIS (FDS: Figures 46, 47) [Murie, 1872:160, fig. 13: "flexor sublimis"; Murie, 1880:32-33, pi. 8: figs. 3, 4; Bahrdt,

1933, figs. 22, 24].—Tendon traceable on surface

nearly to origin; on deep side it begins about middle of forearm, and fibers extend nearly to wrist.

Origin: Fleshy from distal side of medial epicondyle of humerus in fusion with flexor carpi

radialis and flexor carpi ulnaris; along its after edge

it arises from anterior edge of flexor carpi ulnaris,

and a few fibers also arise from middle of after side

of radius.

Insertion: Pinnate on strong tendon which divides over bases of metacarpals, small posterior

part going to join tendon of flexor digitorum profundus to digit HI, while larger part inserts on

phalanges of digit H. Between these, a very delicate

tendon goes to distal part of metacarpal in.

Murie (1872, 1880) found this muscle only

partly distinct from flexores profundus and longus

pollicis, and inserting on digits ii-rv.

M. FLEXOR DIGITORUM PROFUNDUS (FDP: Figures

43-48) [Murie, 1872:160, fig. 13: "flexor profundus";

Murie, 1880:32-33, pi. 8: figs. 3, 4; Bahrdt, 1933,

figs. 22, 24].—Much larger than flexor superficialis.

Antebrachial fascia passes between it and flexor

carpi ulnaris to insert on posterior edge of ulna.

Belly nearly covered by flexores superficialis and

carpi ulnaris.
24

Origin: Fleshy from posterior edge of olecranon

process and nearly whole medial side of ulna, encircling part of insertion of long head of triceps.

Insertion: Pinnate on strong tendon which

divides below wrist, small posterior part going to

phalanges of digit iv, larger, joined by branch of

flexor superficialis tendon, to those of digit ill.

No flexor pollicis longus is present, which is to

be expected from the reduction of the pollex. Murie

suggested (1880:33) it might be represented by the

tendon from the flexor digitorum mass to the

second digit.

M. FLFXOR CARPI ULNARIS (FCU, Figures 43, 45-

47) [Murie, 1872:160, figs. 13, 14; Murie, 1880:32-

33, pi. 8: fig. 3; Leboucq, 1889:608; Bahrdt,

1933:240, figs. 22, 24].—Evidently fused with

palmaris longus.

Origin: Fleshy and tendinous from posterodistal

side of medial epicortdyle of humerus. Partly divisible; more anterior and superficial part consists of

a round, thick tendon, at first barely exposed on

surface but spreading out distally into a sheet,

thicker forward where covered by posterior edge of

flexor digitorum superficialis. Fibers arise from deep

side of this sheet. After, more thick and fleshy part

passes somewhat anteriorly beneath first, separated

from it by ulnar nerves.

Insertion: Deeper part merges with flexor digitorum superficialis, its fibers inserting on latter's

internal tendon. Superficial part, though also

fused proximally with flexor superficialis, diverges

from it, becomes thicker, broad, and flat, widening

wrist; and finally attaches tendinously on posteromedial side of proximal end of metacarpal v.

Leboucq stated that in a dugong fetus the "muscle

cubital interne" inserted tendinously on a tubercle

representing the pisiforme.

M. PALMARIS LONGUS (PaL: Figures 43, 45-47)

[Murie, 1872:160, figs. 13, 14; Murie, 1880:32-33,

pi. 8: fig. 3; Bahrdt, 1933:240, figs. 22, 24].—

Inseparable from flexor carpi ulnaris (q.v.), or perhaps absent entirely. In his first dissection Murie

(1872, fig. 13) found it parallel to flexor carpi

ulnaris, with essentially the same attachments, and

apparently with two divisions. He (1872:160) said

it "enwraps the [flexor carpi] ulnaris, and is in

continuity with the tough superficial fascia of the

forearm." In his second dissection (1880) he found

a muscle passing from the distal ulna to metacarpal

v, which he thought either a palmaris longus or a

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

"flexor brevis minimi digiti"; and if the latter,

palmaris was fused with flexor carpi ulnaris. Bahrdt

took both to be represented by a single mass.

Freund (1904:390-391) surmised that they should

insert farther down on the metacarpal in the

dugong than in the manatee, but with only Murie's

figures for comparison I can see no difference.

?M. ABDUCTOR DIGITI QUINTI (AbD: Figures 43, 46,

47) [Murie: 1872:161, figs. 13, 14: "abductor minimi

digiti"; Murie, 1880:34, pi. 8: figs. 3, 4].—Small

bundle, hardly separable from flexor digiti quinti

brevis, on posterior and slightly palmar side of

metacarpal v.

Origin: Tendinous from antebrachial fascia and

palmar side of ulnar carpal.

Insertion: Fleshy and tendinous on posteromedial

edge of distal end of metacarpal v.

?M. FLEXOR DIGITI QUINTI BREVIS (FDQ: Figures

46, 47) [Murie; 1872:161, figs. 13, 14: "flexor brevis

minimi digiti"; Murie, 1880:33, 34, pi. 8: fig. 3].—

Broad, flat mass of fibers without any clear division,

though posterior fibers have more posterior direction than others.

Origin: Forms posterodistal continuation of palmar aponeurosis, and thereby has some tendinous

attachment to palmar side of ulnar carpal.

Insertion: Fleshy on palmar side of distal end of

metacarpal v.

I have arbitrarily followed Murie's 1872 figures

in assigning the above two names (his text has their

order reversed), though the homologies are hardly

certain. Part of the second may correspond to the

"opponens minimi digiti" of his second animal

(1880:34, pi. 8: figs. 3, 4). It somewhat resembles a

palmaris brevis, except for its insertion onto the

bone.

The muscles of the palm differed considerably

from those Murie described:

MM. LUMBRICALES (Lu ni-v: Figures 43, 44, 46-

48).—Murie distinguished but a single lumbrical

muscle in one animal (1880:33, pi. 8: fig. 4), but it

is possible that some of his "superficial interossei"

represent the lumbricales of my interpretation. I

found three well-developed and distinct muscles,

pinnate between superficial proximal and deep

distal tendons, attaching to the three posterior

digits:

—in (Lu in: Figures 46-48).—The smallest, a flat

band.
NUMBER 226 25

Origin: Fleshy from fascia over insertion of

flexor carpi radialis tendon.

Insertion: Narrows quickly to tendon inserting

on anterior edge of metacarpal Hi distal to its

midsection.

—iv (Lu iv: Figures 47, 48).—Robust and triangular in distal cross-section, extending deeply

between metacarpals m and iv.

Origin: Tendinous from wrist fascia beneath

tendon of flexor carpi radialis.

Insertion: Tendinous on anterior edge of distal

end of metacarpal iv.

—v (Lu v: Figures 43, 44, 46-48).—Robust but

flattened.

Origin: Tendinous from wrist fascia behind and

adjacent to iv.

Insertion: Fleshy on whole anterior edge of

metacarpal v except promixal end.

MM. INTEROSSEI (Into II-IV: Figures 43, 46, 47,

48) [Murie, 1872:161, figs. 13, 14, 15; Murie,

1880:33, pi. 8: figs. 3, 4].—I did not find these in

two distinct layers as did Murie, unless his "superficial interossei" are my lumbricales. However, both

dorsal and palmar interossei may be represented in

the single layer observed, the dorsals having migrated palmad. All seem to be pinnate. I list them

by the digits on which they insert:

—II (Into II : Figures 47, 48).—Three hardly

separable bundles lie on palmar side of metacarpal.

Anterior has fleshy origin from whole after edge

of metacarpal i and tendinous insertion on anteromedial side of distal end of metacarpal n. Other

two arise tendinously from base and fleshily from

palmar side of metacarpal II and insert tendinously

at metacarpal-phalangeal joint. Former two may

correspond to first interossei dorsales, and latter to

first palmar.

—in (Into in: Figures 47, 48).—Imperfectly divisible into forward and after parts, with forward

again subdivided. Arises like foregoing from base

and palmar side of metacarpal and inserts at

metacarpal-phalangeal joint. May represent fused

second and third dorsales.

—iv (Into iv: Figures 43, 47, 48).—Partly divisible, after part wider and more noticeably pinnate

on surface. Forward part tendinous distally where

obliquely crossed by flexor profundus tendon.

Origin, as before, tendinous from base and fleshy

from side of metacarpal iv, and tendinous insertion

on metacarpal-phalangeal joint. Forward part may

be second palmar, after and larger section, fourth

dorsales.

The third palmar of human anatomy, attached

to digit v, is absent or fused with lumbricalis v,

though Murie (1872, 1880) seems to have distinguished it in the manatee. For the interossei as a

whole, he described a much more complex arrangement than I encountered, so that it would be

pointless to attempt a detailed comparison.

In one manatee Murie (1880:34, pi. 8: figs. 3, 4)

found a thumb muscle ("flexor brevis pollicis

or .. . adductor pollicis"), but this was absent in

my dugong.

MUSCLES OF THE PELVIC AND GENITAL REGIONS

There is no coccygeus muscle, but the strong

aponeurosis extending between the whole length of

the innominate and the transverse processes of the

anterior caudal vertebrae, and continuing aft

between the intertransversarius and sacrococcygeus

ventralis lateralis, may in part represent the

coccygeus.

M. RETRACTOR iscHH (Rel: Figures 52-54)

[Stannius, 1845:9; Stannius, 1849:35: "retractor

ischi" or "ischio-caudalis"; Murie, 1872:161-162,

figs. 46, 50: ?"ischio- or ilio-coccygeus," in part].—

Murie quotes Rapp (1837) by mistake instead of

Stannius (1849), concerning this muscle.

I found this muscle fairly thick, though it was

thin and weak in Stannius' (1849) specimen; Riha

(1911:415) failed to find it at all in his dugong

material.

Origin: Fleshy from ventromedial edge of ischium

and distal end of ilium.

Insertion: Runs medially and posteroventrally

parallel to pelvis to tendinous insertion on side of

tip of third chevron bone. In Stannius' (1849)

manatee it attached to the first two chevron bones.

I did not observe anything resembling Murie's

(1872:162, fig. 50) "levator ani" or "transversus

perinaei."

M. iscHiococcYGEUs (Isc: Figures 49, 52, 53)

[Murie, 1872:161-162, figs. 46, 50: "ischio- or iliococcygeus"].—I found this much more completely

fused with cutaneus than did Murie, being inseparable from it except at origin. A small slip medial

to ischium connects ischiococcygeus with retractor

ischii.
26 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Origin: Fleshy from after side of distal end of

ischium.

Insertion: Passes aft and fuses immediately with

overlying cutaneus. Medial side sheathed by aponeurosis attached to tips of third and following

chevron bones, as described with cutaneus; anteriorly aponeurosis also reaches retractor ischii.

M. SPHINCTER ANI (SpA: Figures 49, 50, 52)

[Stannius, 1849:41; Murie, 1872:162, figs. 37, 50;

Riha, 1911, fig. 14; Freund, 1930:439, figs. 6-8].—

Only a single layer of striated fibers, about 3 cm

wide, could be discerned external to longitudinal

smooth fibers of rectum. Posterodorsal edge in

contact with anteroventral end of third chevron

bone. Overlain posterolaterally and laterally by

cutaneus. Murie is vague as to whether sphincter

was distinctly divided into inner and outer parts

in the manatee, but it seems not to have been. Riha

and Freund indicate an undifferentiated sphincter

ani. Stannius found the sphincter ani double.

M. CONSTRICTOR VULVAE (CoVu: Figures 49, 50,

52) [Murie, 1872:162, fig. 50: "sphincter vaginae";

Freund, 1930:438, figs. 6-8].—Band of fibers about

2 cm wide, with both middorsal and midventral

fibrous raphes, former attaching to constrictor vestibuli (q.v.). Posterodorsal edge in contact with

sphincter ani. Arrangement similar in manatee, as

described by Freund.

M. URETHRALis (U: Figures 52, 53) [Freund, 1930:

438-439, figs. 7, 8].—Thin band about 2 cm wide.

Origin: Tendinous from anterior side of ischium,

medial and anteroventral to rectus abdominis

attachment.

Insertion: Passes around front of vagina and

urethra to join its fellow ventral to peritoneum.

This was not noted by Murie, unless it corresponds to part of his "erector clitoridis," which I

doubt. Freund found it in his manatee, where it

seemed to have essentially the same relations as in

the dugong.

M. CONSTRICTOR VESTiBuu (CoVe: Figures 49, 50,

52-54) [Murie, 1872:162-163, fig. 50: "erector clitoridis"; Freund, 1930:438, figs. 6, 7, 8].— Freund

regards the true erector clitoridis, or ischiocavernosus, as absent in the manatee; I provisionally

follow his interpretation.

Consists in dugong of two fusiform slips, nearly

equal in diameter, tightly united in tendinous

wrapper; medial slip much the shorter, its fibers

not reaching pelvis.

Origin: Lateral slip, fleshy from medial, and

partly lateral, side of distal end of ischium.

Insertion: Becomes encased in thick fibrous covering and inserts into fibrous tissue on dorsal side

of vagina, directly above clitoris, anterior to constrictor vulvae and united to latter's middorsal

fibrous raphe.

This arrangement seems to correspond more to

Murie's specimen than to Freund's, where the two

slips of the muscle seem larger and better developed; they are not encased in a tendinous wrapper,

and both attach to the pelvis.

The genital muscles of the male dugong have

been best described by Riha (1911:413-415), and

those of both dugong and manatee by Petit (1925:

251-269); a brief description of the male manatee

is given by Murie (1872:163, fig. 37).

Functional Anatomy

I have deliberately refrained from including with

the muscle descriptions, in the usual fashion, comments on their "action," for two reasons: first, the

"actions" of most of them are obvious from their

forms and attachments, though their real functions

in the living animal may be very difficult to determine; and second, those on whose functions I wish

to comment seem more effectively dealt with as

systems than as isolated units. However, a thorough

analysis of functional myology is beyond the scope

of this paper, which I intend primarily as a descriptive foundation for future analytical work;

hence the following comments are only my superficial impressions of the workings of some parts of

the animal.

FACIAL MUSCLES

The well-developed platysma complex has two

noteworthy features: the curious pars scapularis and

the pair of auriculares. For the former I can see no

clear purpose, but for the latter several possibilities

occurred to me. They may, by pulling the auditory

canal against the small auricular cartilage, close

it against water pressure during dives; dugongs are

said to dive as deep as 10 or 12 fathoms (Annandale, 1905:242). Pinnipeds are able to close the ear

canal voluntarily with auricular muscles (M0hl,

1968:175-176), or the muscles may alter the direc-
NUMBER 226 27

tion of the outer part of the canal to improve directionality of hearing; manatees are known to be very

efficient at localizing noises (Hartman, 1971:219).

Or they may merely be vestigial structures. Yet another explanation is furnished by Fraser and Purves

(1960:131-132) in their study of hearing in cetaceans, where they conclude that auricular muscles

provide directional hearing by constricting the

canals to equalize sound intensities at the cochleae,

and may also protect the ears against high sound

intensities.

Anyone observing a living sea cow will be impressed by the virtuosity of its facial equipment in

feeding (all the more noticeable because this is

likely to be the only part of the animal in motion).

While I cannot venture here to analyze the dynamics of the dugong's complex lip movements, attention should be called to some of the underlying

structural equipment.

As is well known, the sides of the upper lip are

controlled separately; their corners are equipped

with large stiff bristles and they act together rather

like forceps to pull food into the mouth. The substance of the snout is a mass of muscle fibers scattered through dense fibrous tissue, to which are

connected three pairs of muscles which act in concert to raise, lower, and pull laterally the corners of

the lip. These are arranged in layers on the side of

the rostrum: the most superficial (levator nasolabialis) is anteroventral in fiber direction; the middle

(maxillonasolabialis), horizontal; and the deepest

(lateralis nasi), anterodorsal. The mentalis appears

to assist in pulling food into the mouth by raising

the side of the lower lip (also armed with bristles).

The modification of the lateralis nasi as a snout and

lip muscle is noteworthy.

I am at a loss to understand the purpose of the

queer triradiate arrangement of the mandibularis,

depressor anguli oris, and sphincter colli profundus

pars palpebralis; perhaps their lack of attachment

to the corner of the mouth is exceptional in this

individual, but that would hardly speak for the

functional importance of such a connection where

it did occur. The mandibularis, combined with the

vestigial and mostly tendinous depressor anguli oris,

may pull the front of the lower lip transversely, but

the function of the palpebralis is not obvious.

The other mouth muscles (orbicularis oris, buccinatorius, retractor labiorum) show nothing unusual functionally, though the homology of the

latter is unclear.

Without personally verifying Murie's (1872) description of the manatee's facial muscles, I would

not venture a functional comparison with the dugong; but the two are basically similar in structure.

They also share the remarkable development of

blood-vessel bundles issuing from the infraorbital

and mental foramina to supply the lip muscles, as

well as the general wealth of retia mirabilia

throughout the body. These no doubt serve a

variety of functions, but the facial plexuses likely

provide oxygen reservoirs for the vigorous activity

of the lips while submerged. The chewing muscles

of the manatee also have a relatively high myoglobin content (Blessing, 1972).

The sphincter colli profundus pars auris is discussed under "Swimming Muscles."

JAW MUSCLES

Without quantitative data, such as muscle

weights, on the relative forces exerted by the jaw

muscles, a vector analysis of jaw mechanics cannot

be given. A qualitative examination of the structures, however, indicates that the dugong has quite a

normal sort of "ungulate-grinding" jaw apparatus

(to use Turnbull's (1970) term), emphasizing horizontal rather than orthal motion. (That chewing in

Dugong is mainly lateral is confirmed by the transverse striations visible on the teeth of many specimens.)

Herring (1972) has given an enlightening account

of jaw mechanics in pigs and peccaries that reveals

a number of striking similarities between the former and sea cows. The two groups have in common

a relatively unrestricted craniomandibular joint

lying well above the tooth row, a posteriorly thickened joint capsule, a fairly well-developed coronoid

process, a single-bellied digastricus with a lowered

origin (on a paroccipital process or the hyoid arch),

a massive pterygoid process, highly pinnate adductor musculature, and, of course, lateral chewing;

all in contrast to peccaries. The thickened pad behind the mandibular condyle, at least in Dugong,

fills the space between the condyle and the postglenoid process, bracing the condyle when it serves

as a fulcrum in lateral chewing. The pad may

function analogously in pigs, although these lack a
28

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

postglenoid process entirely. The elevation of the

joint above the occlusal plane is common to many

mammals which use the masseter-pterygoid complex extensively for grinding. In both sirenians and

pigs, the lowering of the digastricus increases its

mechanical advantage for jaw-opening and improves its position for retracting the mandible, but

its shortening permits only a small gape. The heavy

pterygoid processes probably reflect use of the pterygoidei externi as protractors of the mandible, in

sirenians, for use of the rostrum in feeding. Herring

(1972:504) suggests that Sus also protracts the mandible for incision. In the adductor muscles, there is

a strong resemblance between the patterns of internal tendons of the masseteres in Dugong (Figure

7) and Sus (Herring, 1972, fig. 5D). These morphological and functional similarities suggest that detailed investigation of suoid jaw mechanics should

shed light on feeding adaptations in sirenians.

In the light of Herring's discussion, I propose the

following as a hypothetical description of the dugong's jaw movements: To use the rostral pads, the

jaw is brought forward by the pterygoidei externi

and masseteres, and depressed by the digastrici and

possibly the geniohyoidei; then closed by the masseteres (superficial division?) and pterygoidei interni, pressure being maintained between the rostral

pads. To switch to chewing with the molars, the

digastrici retract the mandible and the temporales

and zygomaticomandibulares, together with the

masseteres (deep division?) and pterygoidei interni,

provide the orthal force needed. Most mastication is

accomplished by a combination of this orthal force

with lateral grinding. The grinding takes place on

one side of the mouth at a time, the condyle on

that side remaining relatively fixed as the center of

rotation of the mandible, while the masseter and

pterygoideus internus on that side and the temporalis and zygomaticomandibularis on the other close

and draw the jaw medially, grinding the food between the lingual sides of the upper teeth and the

labial sides of the lowers, as the latter move dorsomedially. The recovery stroke is made by the pterygoideus externus opposite the fixed condyle.

The jaw apparatus of the manatee differs from

that of the dugong chiefly in having the coronoid

process extended horizontally quite far forward,

providing a better lever arm for the temporalis and

zygomaticomandibularis. This increase in orthal

strength is evidently correlated with the longer

dental series and greater surface area for chewing.

SWIMMING MUSCLES

The sirenian vertebral column does not show any

distinct anticliny, nor are distinct diaphragmatic

vertebrae present. As in cetaceans, the main point

of flexion of the column in swimming is near the

level of the anus (Hartman, 1971:118). The undesirability of a flexible thorax in a cetacean or

sirenian evidently led to loss of the ancestral transversospinalis structure (prediaphragmatic origin and

postdiaphragmatic insertion of spinalis and semispinalis fascicles), and loss of the hind limbs allowed

fusion of the transversospinalis with the sacrococcygeus dorsalis medialis, in effect extending the latter

up to the anterior thorax. This unit then fused

with the larger longissimus system to form a single

epaxial extensor mass which, since the thorax was

relatively inflexible, bent the spine at the base of

the tail and farther aft rather than in the trunk

region.

In sirenians, the metapophyses are relatively low

on the neural arches and the spines have a slight

caudal inclination. Slijper (1946:112-114) notes that

in this regard the dugong resembles some, generally

more primitive, whales; in other (generally more

advanced) whales, the spines of the lumbar and

caudal vertebrae incline forward and the metapophyses shift upward. He (1946:112) attributes the

latter facts to an increase in importance of the

longissimus at the expense of the transversospinalis,

"in consequence of the appearance of a more localised mobility." The manatee, on the contrary, has

shorter neural spines, larger metapophyses, and

longer centra than the dugong, and in these respects

tends to resemble the archaeocete whale Basilosaurus. Indeed, Slijper (1946, tables 3, 6) affirms

that the transversospinalis is better developed relative to the longissimus in the manatee than in the

dugong.

That sirenians are considerably less specialized

for swimming than modern cetaceans is additionally

clear from such features as lesser streamlining,

lower aspect ratio of flukes, very slight development

of longissimus and sacrococcygeus ventralis tendons, and absence of a separate system of "fluke elevator" tendons. The latter deficiency implies the
NUMBER 226 29

absence in sirenians of a "double lever" action of

the flukes (Parry, 1949), and this is confirmed, at

least for manatees, by Hartman's (1971, fig. 17a)

observations showing that there is little or no

rearward force exerted by the caudal fin during the

latter half of a power stroke. Hartman (1971:118)

does, however, mention a slight passive lag of the

tail behind thrusts of its base.

There are other indications besides the difference

in structure of vertebrae and back muscles that

manatees are less efficient swimmers than dugongs:

the aspect ratio of the caudal fin is still lower, a

whale-like peduncle is not developed, the hypaxial

muscles do not arise as far forward, the intertransversarius coccygeus does not extend so far forward

or back (implying less transverse flexibility and

hence agility), and the skeleton is much heavier.

Such a difference in swimming ability is consistent

with the dugong's open-coast habitat, supposedly

more migratory habits, and greater exposure to

sharks and killer whales (in contrast to the manatee's more protected-water habitat), and with observations on captive dugongs (Kenny, 1967; Oke,

1967; Aung, 1967) indicating that they spend most

of their time actively swimming, unlike the more

sluggish manatees.

There are few reliable data on the swimming

speeds of sirenians. Hartman (1971:128-131, 260-

261) estimated the cruising speeds of wild Florida

manatees at from 4 to 10 km/hr, with sprints up to

25 km/hr usually confined to 20-30 m and never

sustained over 100 m. Stroke rates per minute

varied from 20 when idling to 30-40 when cruising

and 50 in full flight, stroke amplitude varying directly with rate. (A "stroke" is one complete undulation of the tail.)

The manatee data are not detailed enough to

permit analyses like those done by Bainbridge

(1958, 1961); however, they do confirm his observation (1958) that amplitude varies with frequency

at frequencies below 3 to 5 beats per second, making the graph of speed against frequency describe a

concave-upwards curve in this frequency range.

There are no data of comparable accuracy on

dugong swimming speeds. Macmillan (1955:18)

stated that traveling dugongs surface to breathe

"about every hundred yards or so at about oneminute intervals or less," which indicates a cruising

speed in the neighborhood of 6 km/hr. He (1955:

19) adds that "when towing a dinghy, a large

dugong attains a speed of ten knots or more in its

initial burst, and when towing a wood float it can

go a great deal faster and fight longer." Similarly

Jonklaas (1961:3) states: "It was not possible to

estimate the maximum speed of a dugong, but

judging from the two captives in a state of excitement, it would be safe to estimate a speed of at

least 10 knots for short distances." Hence dugongs

can easily exceed 18 km/hr. In the absence of evidence that their cruising or flight speeds are significantly different from those of manatees, we must

conclude that the payoff from their more efficient

body design is in the form of greater endurance—

not surprising if they normally live in more open

waters (though they do prefer protected waters

when these are available (Heinsohn, 1972:207)) and

range over greater distances (though this is not

proven).

Sirenians can, apparently by contraction of diagonally opposite sacrococcygeus ventralis lateralis

and longissimus muscles, oscillate their tail fins

about the long axes of their bodies. Hartman (1971:

118, fig. 18) describes this action in manatees as

used for steering, or counteracting roll or yaw when

at rest. I have frequently observed a captive Trichechus inunguis at Steinhart Aquarium, San Francisco, continually and gently oscillating his tail in

this manner, with an amplitude of several inches,

while stationary and feeding; this may buffer against

movements of the head, jaws, and flippers.

The large epaxial and hypaxial locomotor muscles are supplemented in the dugong by an unusual

development of part of the subcutaneous muscles

(cutaneus trunci). This consists of a thick mass on

the underside of the tail, extending back to the

level of the flukes, connected to the ischium (by a

separate "ischiococcygeus"), continuous with the

abdominal sheet that helps support the viscera, and

inserting pinnately on a deep aponeurosis (attached

to the tips of the chevron bones), which emerges to

sheath superficially the sides of the tail. Its action

is clearly to flex the tail, though whether it is important in normal swimming may be questioned.

It is noteworthy that in the manatee the caudal extension of the cutaneus is much less developed.

Nonetheless, manatees can flex their tails to an impressive degree (Murie, 1880, pis. 5, 7). Forward

motion in manatees is initiated by an upstroke
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

(Hartman, 1971:118); when frightened, dugongs

can accelerate quickly from a standstill by a reverselobster-like backstroke of the sharply flexed tail

(observed in the Ceylonese dugong; Mr. Ranil Senanayake, pers. comm.). This is in accord with the

much greater size and strength of the epaxial versus the hypaxial muscles and the greater ventral

than dorsal flexibility of the body. The small hypaxial muscle, which I have termed "flexor haemalis" (not noted in the manatee), may help to cock

the flukes in this extreme flexed position and, perhaps, even produce a rudimentary "double lever"

action on the upstroke. Although cetaceans are able,

at least under passive manipulation, to attain this

degree of flexion (Slijper, 1936:251), they do not

seem to assume such a position nearly as habitually

as do sirenians.

In normal swimming, as opposed to flexion of

the body when at rest, the tail is, of course, not

as strongly flexed, and the dorsal and ventral excursions are about equal in Trichechus (Hartman,

1971, fig. 17a) and doubtless also in Dugong.

The powerfully developed sphincter colli profundus pars auris also acts to flex the body, both

by depressing the head and by pulling in opposition

to the cutaneus trunci and rectus abdominis

(through direct connection with the former, and via

the sternum with the latter). Thus, there are two

parallel and anastomosing linkages of ventral

flexors running from the zygomatic arch of the skull

to the underside of the flukes: (1) auris-cutaneus

trunci, and (2) auris—sternum-rectus abdominisischium-ischiococcygeus-cutaneus trunci. How these

function in the living animal is unknown.

In summary, sirenians closely parallel cetaceans

in the design and development of their swimming

apparatus; the arrangement of bones and muscles

is fundamentally the same in the two orders and

the same mechanical principles apply to both. The

essential difference is that sirenians possess fewer

of the refinements possible with this design, such as

long tail tendons and special fluke elevator equipment, and are in general less advanced in this type

of locomotor adaptation than any living cetacean.

Their consequent lesser speed and endurance (also

reflected in other features, such as low myoglobin

content of muscles; Blessing, 1972) is not a handicap as they are not active predators. Trichechids are

in turn less well designed for swimming than the

more active dugongids, and may approximate a

structural stage through which the earliest dugongids passed.

FORELIMB MUSCLES

A survey of the literature reveals no evident

differences in use of flippers between manatees

and dugongs. In both animals they are used primarily as steering and balancing organs, and as a

secondary means of locomotion (paddling for short

distances forward, back, sideways, or upward; or

"walking" along the bottom). They are not used

as hydrofoils, as are cetacean flippers, but are held

against the sides when swimming (except when in

use for steering). They are probably not, as sometimes stated, used to uproot vegetation, but do at

times serve to maneuver loose plant material to

the mouth. They also perform a variety of actions

such as scratching, mouth cleaning, supporting the

body when resting on the bottom, and embracing

other animals. (Representative references on this

topic are Dexler and Freund, 1906; Jones, 1959;

Jonklaas, 1961; Silas, 1961; and Hartman, 1971.)

The extensive use of the flippers is reflected in the

relatively high myoglobin content of the pectoral

and forelimb muscles (Blessing, 1972).

The flipper is highly flexible and maneuverable;

the wrist can be bent somewhat, and the digits to

a lesser extent. When used in locomotion the flipper is always feathered (Hartman, 1971:123-127,

figs. 20, 21), though, since the forearm bones cannot rotate (not even, it seems, in Dugong, where

they are not fused), this is done with the shoulder

joint. The elbow is free of the body, in contrast to

the cetacean flipper, and on the whole the sirenian

forelimb retains far more dexterity and is far less

specialized than the cetacean.

The clearest differences between dugong and

manatee forelimb anatomy are in the shoulder

region. Skeletally, we may observe in the manatee

scapula the striking forward prolongation of the

acromion process and the backward-projecting

tuber spinae; and in the humerus, the large lesser

and small greater tuberosities, virtual absence of
NUMBER 226 31

a deltoid crest, and absence of a bicipital groove—

all in contrast to the conditions in dugongids. The

manubrium is proportionately wider in manatees

than in Dugong.

With regard to the muscles, the serratus magnus

is not divided into separate anterior and posterior

parts in the manatee, though they are distinct in

the dugong. The manatee's thoracic trapezius is

quite different from the dugong's, passing directly

and strongly backwards from the tuber spinae

rather than almost transversely from the surface of

the infraspinatus and the scapular cartilage. The

deltoideus likewise arises only from the scapular

spine. Both trapezius and deltoideus attach to the

whole of the long acromion process; it is almost

as if their scapular attachments are about the same

length as in the dugong, but have shifted anteroventrally along the extended spine. The latissimus

shares the insertion tendon of the teres major, not

that of the pectoralis minor as in the dugong; the

latter muscle in the manatee inserts more proximally. In the absence of a bicipital groove, the

manatee biceps lies parallel and adjacent to the

coracobrachialis; Murie (1872, 1880) in fact considered them a single muscle. The antebrachial

muscles are not significantly different in the two

animals, but the palmar muscles seem to be less

developed and differentiated in the dugong, perhaps indicating less mobility of the digits.

Since the movements of the distal joints are

similarly restricted in the two animals and flipper

movements seem to involve mainly the shoulder

joint, it is not surprising that whatever anatomical

differences there are should be found, for the most

part, proximally. But if we are ignorant of any

difference in function between manatee and dugong

flippers, how are we to explain these striking differences in form? I could not pretend to answer

this question without much further study, but here

is a first try at a solution: The divided serratus

magnus of the dugong suggests greater specialization for moving the scapula in a parasagittal plane.

On the other hand, the manatee's long acromion

process suggests greater ability to abduct the forelimb. The height of the lesser tuberosity may indicate the same, as Howell suggested (1930:228). The

more medial supraspinatus insertion would seem to

rotate the palmar side of the manatee's forelimb

forward (swinging the limb outward) during extension of the limb. The manatee's wider manubrium

may indicate a more robust pectoralis major for

adductive movements. So it could well be that the

dugong's forelimb is used less in ways involving

abduction and adduction than the manatee's. This

may reflect the manatee's greater need to use the

flippers in maneuvering in restricted bodies of

water (cf. Hartman, 1971:123-124). Observations

on the actions of wild dugongs should be made

with this possible difference in mind.

HINDLIMB MUSCLES

No vestiges of hindlimb muscles have ever been

identified in a sirenian. Dugongs are not known to

ever possess remnants of limb bones attached to

the pelvis, but vestigial femora are occasionally

found in manatees, and these individuals may well

have traces of leg muscles. These, however, would

likely be impossible to homologize with those of

normal quadrupeds; even in those mysticete whales

where vestigial hind limbs are well developed, the

muscles are too variable to be identified confidently

(Struthers, 1893).

The pelvis in living sirenians, as in cetaceans,

serves as an anchorage for several trunk, tail, and

urogenital muscles, so it is unlikely that it would

tend to be further reduced in the course of

evolution.

Conclusion

The greatest desideratum in the study of sirenian

functional anatomy (apart from redescription of

the manatee's myology) is sound natural history

data showing what the animals actually do in life—

how they eat, how far and fast they swim, how and

why they move all parts of their bodies. Without

this firm connection to reality, our attempts at

deciphering muscle "functions" cannot claim to be

more than idle speculation. Our ability to analyze

vertebrate myology is still rudimentary; we cannot

yet confidently solve equations of muscle function

in which one of the unknowns is the function

itself. Without the guidance of the natural historian, the functional anatomist is only building

castles in the air.
32 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Addendum

After this paper had gone to press, Dr. Roger Saban graciously sent me a copy of his recent

paper on "La musculature peauciere de la tete chez un jeune Lamantin du Senegal (Trichechus

senegalensis Link 1795; Mammifere, Sirenien)" (Zentralblatt fur Veterindr Medizin, Reihe C:

Anatomia Histologia Embryologia, 4(3):232-248, 1975). This paper sheds welcome light on

differences in facial musculature between the African manatee, the West Indian manatee (described by Murie), and the dugong; of special interest in regard to the latter are the following

points. Saban found two divisions of the sphincter colli profundus pars intermedia which are

absent in the dugong: a ventral part posterior to the pars palpebralis and a dorsal part

(zygomatico-labialis) fused with and anteriorly continuing the platysma beneath the palpebralis.

He also found a "buccinator pars mentalis" which he homologized with Murie's mandibularis;

however, as it arises in common with the buccinator pars longitudinalis from the pterygoid

process rather than from the mandible (Saban, in litt., 26 May 1976), I prefer to identify it

with my retractor labiorum. Saban observed the same attachments of the M. mentalis as I did

in the dugong, which suggests that Murie's observation was in error. T. senegalensis contrasts

with T. manatus in possessing the sphincter colli profundus partes intermedia ventralis et

palpebralis and in several other points. Remarkably, the well-developed sphincter colli profundus ?pars auris found in both the dugong and the West Indian manatee does not appear

in T. senegalensis; Saban (in litt., 26 May 1976) suggests that its homolog in the latter is the

pars intermedia ventralis.

There remains a need for restudy of T. manatus to clarify the many doubtful points of

Murie's description, and I hope to undertake a dissection of T. inunguis in the near future.

Possible functional differences between the species of Trichechus are a wholly unexplored topic.
Literature Cited

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1905. Notes on the Species, External Characters and

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Aung, S. H.

1967. A Brief Note on Dugongs (Dugong dugon) at Rangoon Zoo. International Zoo Yearbook, 7:221.

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1933. Beitrage zur Entwicklungsgeschichte der Sirenenflosse. Jenaische Zeitschrift fur Naturwissenschaft,

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Bainbridge, R.

1958. The Speed of Swimming of Fish as Related to Size

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1960. Hearing in Cetaceans. Bulletin of the British Museum (Natural History), Zoology, 7(1): 1-140, 53

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Freund, L.

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Gudernatsch, J. F.

1908. Zur Anatomie und Histologie des Verdauungstraktes

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plate, 3 figures.

Hartman, D. S.

1971. Behavior and Ecology of the Florida Manatee,

Trichechus manatus latirostris (Harlan), at Crystal

River, Citrus County. Ph.D. dissertation, Cornell

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Heinsohn, G. E.

1972. A Study of Dugongs (Dugong dugong) in Northern

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1972. The Role of Canine Morphology in the Evolutionary Divergence of Pigs and Peccaries. Journal of

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Howell, A. B.

1930. Aquatic Mammals: Their Adaptations to Life in the

Water, xii + 338 pages. Springfield, 111.: C. C.

Thomas.

Jones, S.

1959. On a Pair of Captive Dugongs (Dugong dugong

(Erxleben)). Journal of the Marine Biological Association of India, 1(2): 198-202.

Jonklaas, R.

1961. Some Observations on Dugongs (Dugong dugong -

Erxleben). Loris. 9:1-8, 4 figures.

Kenny, R.

1967. The Breathing Pattern of the Dugong. Australian

Journal of Science, 29(10):372-373. 2 figures.

Leboticq, H.

1889. Recherches sur la morphologie de la main chez les

mammiferes marins: Pinnipc-des, Sir6niens, Cetacces.

Archives de Biologie, 9:571-648, plates 36-41.

Macmillan, L.

1955. The Dugong. Walkabout, 21 (2): 17-20, 2 figures.

Matthes, E.

1929. Die Dickenverhaltnisse der Haut bei den Mammalia

im allgemeinen, den Sirenia im besonderen. Zeitschrift fiir wissenschaftliche Zoologie, 134(2/3):345-

357, 1 figure.

Miller, M. E., G. C. Christensen, and H. E. Evans

1964. Anatomy of the Dog. xii + 941 pages. Philadelphia

and London: \V. B. Saunders.

M0hl, B.

1968. Hearing in Seals. Pages 172-195 in R. J. Harrison

et al., editors, The Behavior and Physiology of Pin33
34 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

nipeds. 8 figures. New York: Appleton-CenturyCrofts.

Murie, J.

1872. On the Form and Structure of the Manatee (Manatus americanus). Transactions of the Zoological

Society of London, 8(3):127-202, figures 1-50 [contained on plates 17-26].

1880. Further Observations on the Manatee. Transactions

of the Zoological Society of London, ll(2):19-48,

plates 5-9.

Oke, V. R.

1967. A Brief Note on the Dugong (Dugong dugon) at

Cairns Oceanarium. International Zoo Yearbook,

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Owen, R.

1838. [On the Anatomy of the Dugong.] Proceedings of

the Zoological Society of London, 6:28-45.

Parry, D. A.

1949. The Anatomical Basis of Swimming in Whales.

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Petit, G.

1925. Recherches anatomiques sur l'appareil genitourinaire male des Sir^niens. Archives de Morphologie, 23, iv + 326 pages, 74 figures.

Putter, A.

1902. Die Augen der Wassersaugetiere. Zoologische Jahrbiicher, Abteilung fur Anatomie, 17(1/2):99-402,

plates 2-4, 41 figures.

Rapp, W. L. v.

1837. Die Cetaceen zoologisch-anatomisch dargestellt. vi 4

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Cotta.

Riha, A.

1911. Das maim lithe Urogenitalsystem von Halicore

dugong Erxl. Zeitschrift fur Morphologie und Anthropologie, 13:395-422, 15 figures.

Robineau, D.

1965. Les osselets de l'ouie de la Rhytine. Mammalia,

29(3):412-425, 5 figures.

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chez les Sireniens. Me'moires du Museum National

d'Histoire Naturelle, series A (Zoology), series 2,

60(1): 1-32, 17 figures.

Silas, E. G.

1961. [Comments on S. B. Mani's] "Occurrence of the

Sea Cow, Halicore dugong (Erxl.), off the Saurashtra

Coast." Journal of the Bombay Natural History

Society, 58(l):263-266.

Slijper, E. J.

1936. Die Cetaceen: vergleichend-anatomisch und systematisch. . . . Capita Zoologica, 7: vii + 590 pages, 256

figures.

1946. Comparative Biologic-anatomical Investigations on

the Vertebral Column and Spinal Musculature of

Mammals. Verhandelingen der Koninklijke Nederlandsche Akademie van Wetenschappen, Afd. Natuurkunde, series 2, 42(5):1-128, 125 figures.

Stannius, F. H.

1845. Beitrage zur Kenntniss der amerikanischen Manati's.

37 pages, 2 plates. Rostock: Adler's Erben.

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Struthers, J.

1893. On the Rudimentary Hind-limb of a Great FinWhale (Balaenoptera musculus) in Comparison with

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Right-Whale. Journal of Anatomy and Physiology,

new series 7, 27:291-335, plates 17-20.

Turnbull.W. D.

1970. Mammalian Masticatory Apparatus. Fieldiana

(Geology), 18(2): 147-356, 48 figures.
List of Abbreviations

MUSCLES

Abbreviations in parentheses on illustrations denote grooves

on bones for tendons of muscles indicated; question marks

denote doubtful identification

AbD

AbP

Ae

ArT

Au

AuP

AuS

B

Br

Brc

BIT

Bu

Ch

Cob

CoVe

CoVu

CrD

CrL

Crp

Crt

CuT

D

DAO

Di

ECR

ECU

EDC

EDQ

EP

FCR

FCU

FDP

FDQ

FDS

FH

Fr

Gg

Gh

He

Hg

Hp

PAbductor digiti quinti

PAbductor pollicis longus

Aryepiglotticus

Arytenoideus transversus

Sphincter colli profundus

?pars auris

A in it ulat is profundus

Auricularis superficialis

Biceps brachii

Brachialis

Brachiocephalicus

Brachioradialis

Buccinatorius

Cephalohumcralis

Coracobrachialis

Constrictor vestibuli

Constrictor vulvae

Cricoarytenoideus dorsalis

Cricoarytenoideus lateral is

Cricopharyngeus

Cricothyroideus

Cutaneus trunci

Deltoideus

Depressor anguli oris

Digastricus

Extensor carpi radialis

Extensor carpi ulnaris

Extensor digitorum communis

Extensor digiti quinti

Extensor pollicis brevis et longus

Flexor carpi radialis

Flexor carpi ulnaris

Flexor digitorum profundus

PFlexor digiti quinti brevis

Flexor digitorum superficialis

Flexor haemalis

PFrontalis

Genioglossus

Geniohyoideus

PHyoepiglotticus

Hyoglossus

Hyopharyngeus

IIT

Inf

IntE

IntI

Into II-IV

Intr

Isc

LaD

LaN

LeN

LnC

LnD

LoCa

LoCo, ,

Lu III-V

M

Mn

Mnl

Mt

My

OAE

OAI

OCa

OCr

OOc

OOr

PaL

PIJ

PIP

PIS

PIT

PMa

PMi

P rT

PtE

PtI

Ptp

RA

RCI

RCMa

RCMi

Rel

ReL

Rh

RL

Sc

llioi ostalis thoracic

Infraspicatus

Intercostales externi

Intercostales interni

Interossei

Intertransversarius coccygeus

Ischiococcygeus

Latissimus dorsi

Lateralis nasi

Levator nasolabialis

Longissimus capitis

Longissimus dorsi

Longus capitis

Longus colli

Lumbricales

Masseter

Mandibularis

Maxillonasolabialis

PMentalis

Mylohyoideus

Obliquus abdominis externus

Obliquus abdominis internus

Obliquus capitis caudalis

Obliquus capitis cranialis

Orbicularis oculi

Orbicularis oris

Palmaris longus

Platysma pars jugularis

Sphincter colli profundus pars palpebralis

Platysma pars scapularis

Platysma pars temporal is

Pectoralis major

Pectoralis minor

Pronator teres

Pterygoideus externus

Pterygoideus internus

Pterygopharyngeus

Rectus abdominis

Rectus capitis dorsalis

Pintermedius

Rectus capitis dorsalis

Pmajor

Rectus capitis dorsalis minor

Retractor ischii

Retractor labiorum

Rhomboideus

Rectus capitis lateralis

Scalenus
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SeC

SeM

SpA

SpC

Spl

Stc

Stm

Stt

Styg,3

Styh

Styp

Su

Sup

SVL

SVM

T

Ter

TeV

Tha

T hh

T h p

TrA

TrLa

TrLo

T rM

TrN

T r p

U

Semispinalis capitis

Serratus magnus

Sphincter ani

Sphincter colli superficialis

Splenius

Sternocostalis

Sternomastoideus

Sternothyroideus

Styloglossus

Stylohyoideus

Stylopharyngeus

Subscapularis

Supraspinatus

Sacrococcygeus ventralis lateralis

Sacrococcygeus ventralis medialis

Temporalis

Teres major

Tensor veli palatini

Thyroarytenoideus

Thvrohyoideus

Thyropharyngeus

Transversus abdominis

Triceps brachii, lateral head

Triceps brachii, long head

Triceps brachii, medial head

PTransversus nasi

Trapezius

Urethralis

Zygomaticomandibularis

OTHER STRUCTURES

ac

af

ap

ar

b

(bg)

bo

1>S

bv

bv(if)

bv(mf)

bv &n

bv & n(mdf)

c

ca

ch

or

(1

e

earn

CK

ejv

en

auricular cartilage

antebrachial fascia

aponeurosis, superficial

arytenoid cartilage

basihyoid

bicipital groove

basioccipital

basisphenoid

blood vessels

blood vessels from infraorbital foramen

blood vessels from mental foramen

blood vessels and nerves

blood vessels and nerves from mandihular

foramen

cervical vertebra

caudal vertebra

chevron bone

cricoid cartilage

diaphragm

epihyoid

external auditory meatus

epiglottis

external jugular vein

external nares

eo

ep

es

et

f

tm

g

gt

h

il

is

j

k

1

lac

Ig

ll

m

ma

mdf

mf

ml

nix

inn

nph

occ

p

pa

pal

pas

Pg

ph

pm

ps

ptp

r

•Vi*

rc

s

sac

sc

sec

sli

so

sq

st

t

tc

th

to

litre

ty

u

urp

V

vo

z

exoccipital

epithelium of mouth cavity

esophagus or esophageal fibers

ethmoturbinal

frontal

foramen magnum

glenoid facet (temporal condyle)

greater tuberosity of humerus

humerus

ilium

ischium

jugal

joint capsule

keratohyoid

lumbar vertebra, transverse process

lacrimal

deep cervical lymph glands

lesser tuberosity of humerus

mandible

position of mammary gland

mandibular foramen

mental foramen

malleus

maxilla

nictitating membrane

nasal pharynx

occipital condyle

petrosal

parietal

palatine

right posterior articulating surface of atlas

parotid gland

pharynx

premaxilla

presphenoid

pterygoid process

radius

ribs

rib cartilage

symphysis

sacral vertebra, transverse process

scapula

scapular cartilage

stylohyoid

supraoccipital

squamosal

sternum

thyrohyoid

wall of tympanic cavity

thyroid cartilage

tongue

trachea

tracheal cartilages

tympanic

ulna

upper rostral pad

vulva

vomer

zygomaticomandibularis insertion
10 30 50 70 90 110 130 150 170 185 cm

20

10

X X

flipper flukes

anus

FIGURE 1.—Graph of skin thickness given in Table 2 (D = thickness in dorsal midline;

L = thickness along side; V = thickness along ventral midline).

AuS PJT PIS

PU SpC

FIGURE 2.—Lateral view, dermal muscles and superficial aponeuroses; fascia over shoulder

region removed behind pars jugularis of platysma. (For identification of other structures, see

Figures 4 and 18.)

TrN

LeN 00c

sq !

SeC

IntE

FIGURE 3.—Dorsal view, superficial muscles shown on right side of animal, deeper layer (with

splenius, longissimus capitis, shoulder muscles, and forelimb removed) on left; superficial layer

shown on both sides oi snout.
38 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

PIP

SpC

FIGURES 4-6.—Lateral view of head: 4, superficial layer with facial bristles; 5, deeper layer (t = vestigial tendon of DAO); 6, deeper layer with shoulder girdle removed (note vessels and nerves crossing

masseter).
NUMBER 226 39

00c

FIGURE 7.—Lateral view of jaw, masseter folded back to expose its insertion; position of external auditory meatus

(earn) shown schematically; mandible (m) outlined.

FIGURE 8.—Lateral view of jaw, zygomatic arch cut through

jugal and root of zygomatic process, and arch removed to

show temporalis, which is cut away from zygomaticomandibularis ventrally (M = masseter insertion, Z = zygomaticomandibularis insertion).
40

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURES 9-10.—Mandible (cut just behind symphysis) and

attached structures: 9, medial view; 10, dorsal view.

PtI

Di

PIJ

FIGURE 11.—Medial view, left zygomatic process (cut off at

root) and attached dermal muscles (sphincter colli profundus

pars auris omitted) (sq = zygomatic process of squamosal).

earn
NUMBER 226 41

FIGURES 12-14.—Skull, showing muscle attachments: 12, dorsal view; 13, lateral view;

14, ventral view.
42

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

RCI+RCMi

RCMa

SeC

RCI

FIGURE 15.—Posterior view of skull, showing muscle

attachments.

PtI

FIGURES 16-17.—Mandible, showing muscle attachments:

16, lateral view; 17, medial view.
NUMBER 226 43

FIGURE 18.—Lateral view of shoulder region, showing superficial muscles; fascia removed behind

pars jugularis of platysma (sq = outline of zygomatic process of squamosal).

Au

SpC

Ch Sup

FIGURE 19.—Lateral view of shoulder region, most of superficial dermal muscles removed.
44 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

S e C ll&r )

SeM

FIGURE 20.—Dorsolateral view of neck and shoulder region; platysma, cephalohumeralis, and

anterior trapezius removed, splenius-rhomboideus aponeurosis cut and folded back to show

left and right semispinalis capitis.

SeC(r) RCMa(l)

RCI(r)

RCMa(r)

bv

Spl RCMa(l) SeC(l) RCI +

RCMi (I)

OCa(l) RCMa(l)

FIGURK 21.—Dorsolateral and somewhat posterior view of deep

dorsal neck muscles, left semispinalis capitis and rectus capitis

dorsalis major cut (latter in two places) and pulled away. Note

asymmetrical arrangement of left and right rectus muscles.
NUMBER 226 45

RL SeC

Spl

Sc

LnD

S p C

e J v bv&n St c

FIGURE 22.—Lateral view of neck and shoulder region, shoulder girdle and limb removed;

position of mammary gland (ma) indicated.

Ch

Spl Di R L

C r t St t Stm

FIGURE 23.—Lateral view of neck and shoulder region, deeper dissection than in Figure 22;

latissimus dorsi and most of cutaneus muscles and parotid gland removed; deep attachment of

superficial aponeurosis (ap) cut; part of parotid gland (pg) shown.
46

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

IntI

RA

FIGURE 24.—Lateral view, deep dissection of tongue, throat, and neck region; sternomastoideus,

pectorales, glands, and most of scalenus and mandible removed. Deep fibers of scalenus (split

longitudinally) shown attaching to rib; keratohyoid (k) outlined; anterior end of mandible (m)

outlined (c, = atlas).

LoCa

FICUKE 25.—Lateral view, deep throat muscles; hyoid arch cut through stylohyoid and folded

down. Deep fibers of scalenus shown attaching to rib; cervical vertebrae exposed; mandible

(m) cut (t, = first thoracic vertebra).
NUMBER 226 47

CrD

Tha

th

FIGURE 26.—Parasagittal section of larynx (cut just forward

of epiglottis and just behind bifurcation of trachea), slightly

to right of midline; anterior end to right. Parts of right

cricothyroideus and thyroarytenoideus (cut obliquely) shown;

right arytenoid cartilage (ar), nasal pharynx (nph) with longitudinal folds of lining, and trachea (tr) with longitudinal

striations of lining shown.

FIGURE 28.—Diagrammatic left lateral view of laryngeal cartilages, showing muscle attachments. The epiglottis is not

cartilaginous in sirenians (es = attachment of esophageal

fibers).

FIGURE 27.—Left lateral view of larynx, thyroid cartilage cut

near midline, and left ala, with attached muscles, turned

back; pharynx (ph) enclosing epiglottis.

Crt Crp

FIGURE 29.—Diagrammatic left lateral view of laryngeal cartilages, showing muscle attachments, with thyroid cartilage

removed.
Styg

Styg

Thh

Styg.

ArT

FIGURES 30-31.—Diagrammatic views of laryngeal cartilages and left half of hyoid apparatus,

showing muscle attachments: 30, dorsal view (es = attachment of esophageal fibers); 31, ventral

view.

My

IntE

FIGURES 32-34.—Ventral view of left throat and chest region: 32, superficial layer; 33,

deeper layer than Figure 32 (note fibers of sphincter colli superficialis arising from

sphincter colli profundus pars auris, and part of external rectus sheath folded back to

expose rectus abdominis); 34, deeper layer than Figure 33.
NUMBER 226 49

LoCa RCMi

LoCo

LoCa

OCa

LnDiSeC

Sc

LoCo

FICURF. 36.—Posterior view of atlas, showing muscle

attachments.

RCMi

OCa

LoCo

FIGURE 37.—Posterolateral view of atlas,

showing muscle attachments.

FIGURE 35.—Diagrammatic ventral view of neck and chest,

showing muscle attachments (except pectorales, cutaneus

capitis, and sternomastoideus) on animal's right side and

deep neck and chest muscles on left. Centra of thoracic vertebrae and origin of longus colli thereon shown by dashed

outlines. Deep fibers of scalenus shown attaching to rib.

Longus colli divisions are not very distinct. Note origins of

pectorales from surface of rectus abdominis. In most dugongs

only three ribs attach to sternum; this specimen had four

(sh = stylohyoid cut; t, = third thoracic vertebra).

FIGURE 38.—Lateral view of axis,

showing muscle attachments.
50

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SeOLnO RCMi

FIGURE 39.—Dorsal view of atlas, showing muscle

attachments.

39

40

FIGURE 40.—Dorsal view of axis, showing muscle

attachments.

LoCo

Sc

FIGURE 41.—Anterior view of

left first rib, showing muscle

attachments.

LnO

41

FIGURE 42.—Anterior view of left

second rib, showing muscle

attachments. 42

Trp + D+PIS

Trp

Sup

lnt

FIGURE 43.—Lateral view of forelimb; trapezius and deltoideus removed, but attachments

shown. Extensor digiti quinti tendon pulled back to show its proximal insertion; cut edge of

antebrachial fascia (af) removed. (Note: In Figures 43, 44, 46, 47, the limb is shown in the

position it had assumed in the fixed specimen; whether it could have been this strongly flexed

in the living animal is not certain.)
NUMBER 226 51

Sup bif

AbP r~A B % >/> « ECR

(ECR)(EP) Brr EP

FIGURE 44.—Lateral view of limb bones, showing muscle attachments.

FDP

FIGURE 45.—Lateral view, deep antebrachial muscles. Retracted distal part

of abductor pollicis longus shows the muscle's deep side. Abbreviations in

parentheses denote grooves on ulna for tendons of muscles indicated; extensor digitorum communis groove faintly divided for the tendon's three

incipient divisions to digits u-rv.
52

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Rh

Su

Into

LaD

FIGURE 46.—Medial view of forelimb; brachial plexus of vessels removed proximally. Deep sides

of latissimus dorsi and pectorales visible.

FD5

Into

FIGURE 47.—Medial view of limb bones, showing muscle attachments. Insertions of anterior

(SeM.) and posterior (SeMp) serratus magnus distinguished.
NUMBER 226

TrLo

FIGURE 48.—Medial view, deep antebrachial and palmar muscles. (FDP =

grooves on joint capsules for flexor digitorum profundus tendons to digits

in and iv).

IntE

LnD aP Intr

OAE

|Isc\ C h 4 CuT

SpA a

FIGURE 49.—Lateral view of posterior trunk and tail, most of cutaneus trunci and

outer rectus abdominis sheath removed. Dashed line crossing obliquus abdominis externus shows outline of muscular part of cutaneus trunci; behind anus, cutaneus is

shown cut in sagittal plane; and farther aft it is shown intact except for removal of

dorsal part of its aponeurosis; deep attachment of superficial aponeurosis (ap) cut; some

dugongs have only 18 ribs; this specimen had 19.

OAI

LnD

Intrd

CoVu CoVe

FIGURE 50.—Lateral view of posterior trunk and tail, second layer removed from ventral

side. Deep bundles (Intr,,) and origin on pelvis of intertransversarius coccygeus shown.

Caudal part of cutaneus trunci cut in sagittal plane, and its aponeurosis removed

posteriorly to expose sacrococcygeus ventralis lateralis. Latter is triangular in crosssection, the apex of the triangle forming the ridge shown as a longitudinal line aligned

with the cut edge of an aponeurosis (ap); this marks the ventral extent of the intertransversarius, which arises from aponeurosis on surface of sacrococcygeus ventralis

lateralis.
54 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

SVUSVM

LnD

CuT

FIGURE 51.—Lateral view of deep ventral muscles of posterior trunk and tail. Structure of

longissimus dorsi shown schematically; both origins and insertions continue forward and back

in addition to the few attachments shown. Position of pelvis shown by dashed outline. Genital

and anal muscles omitted; see Figure 52. Posterior part of sacrococcygeus ventralis lateralis cut

away from sacrococcygeus ventralis medialis and removed; aponeuroses of both cut and turned

down to expose chevrons and flexor haemalis; diaphragm (d) cut and removed dorsally to

expose sacrococcygeus.

CoVe

LnD Intr,

SVL

[ntE

CuT

FIGURE 52.—Lateral view of pelvic and genital region; structures attached to pelvis cut and

pelvis pulled back and upward. Deep bundles (Intrd) and origin on pelvis of intertransversarius

coccygeus shown. Most of rectus abdominis and more superficial muscles removed, inner rectus

sheath exposed. Cutaneus trunci cut in sagittal plane ahead of fifth chevron bone, but shown

intact farther aft except for removal of dorsal part of its aponeurosis. Note part of transversus

abdominis still attached to pelvis (r = longitudinal muscle fibers of rectum).

FIGURES 55-54.—Left pelvis, showing muscle attachments:

53, lateral view; 54, medial view.
Index

Valid names and page of primary description in italics

iAbductor digiti quinti, 24

Abductor minimi digiti, 24

7 Abduct or pollicis longus, 21, 22, 23

Adductor pollicis, 25

Anconeus, 21

Aryepiglotticus, 10

Aryteno-epiglottideus, 10

Arytenoidei obliquus and trans versus, 10

Arytenoideus transversus, 10

Auricularis profutidus, 4, 26-27

Auricularis superficialis, 4, 5, 26-27

Auris. See Sphincter colli profundus ?pars auris

Biceps brachii, 19, 21, 31

Biventer cervicis, 11

Brachialis, 19, 21, 22, 23

Brachialis anticus, 21

Brachialis internus, 21

Brachiocephalicus, 14,19

Brachioradialis, 21-22

Buccalis. See Buccinatorius pars buccalis; Platysma pars buccalis

Buccinatorius, 5, 6, 27, 32

Buccinatorius pars buccalis, 5

Buccinatorius pars molaris, 5

Cephalo-humeral, 19

Cephalohumeralis, 14, 18,19

Cervical is ascendens, 12

Coccygeus, 25

Complex us, 11

Compressor nasi, 6

Constrictor veslibuli, 26

Constrictor vulvae, 26

Constrictores superior and medius, 9. 10

Coracobrachialis, 20, 21, 31

Crico-arytenoideus, 10

Cricoarytenoideus dorsalis, 9,10

Cricoarytenoideus lateralis, 10

Cricopharyngeus, 9, 10

Cricothyroideus, 10

Cubital interne, 24

Cutaneus truci, 4,15-16, 17, 19, 25, 26, 29-30

Deltoideus, 4, 14, 18, 20, 31

Depressor anguli oris, 6-7, 27

Depressor labii inferioris, 6

Depressor labii superioris alaeque nasi, 6

Diaphragm, 15,17

Digastricus, 7-8, 27-28

Dilatator naris, 6

Dilatator nasi, 6

Erector ditoridis, 26

Extensor carpi radialis, 22, 23

Extensor carpi ulnaris, 22-23

Extensor digiti quinti, 22

Extensor digitorum communis, 22, 23

Extensor minimi digiti, 22

Extensor pollicis brevis et longus, 22, 23

Extensores primi and secundi internodii pollicis, 22, 23

Eyeball, muscles of, 5

Flexor brevis minimi digiti, 24

Flexor brevis pollicis, 25

Flexor carpi radialis, 21, 23, 25

Flexor carpi ulnaris, 22, 23, 24

}Flexor digiti quinti brevis, 24

Flexor digitorum profundus, 23-24

Flexor digitorum superficialis, 23, 24

Flexor haemalis, 18, 30

Flexor pollicis longus, 23, 24

Flexor profundus, 23

Flexor sublimis, 23

IFrontalis, 4, 5

Genioglossus, 8, 9

Genio-hyo-glossus, 8

Geniohyoideus, 9, 28

tHyoepiglotticus, 10

Hyoepiglottideus, 10

Hyoglossus, 8, 9

Hyopharyngeus, 9

Ilio-coccygeus, 25

Ilio-costalis cervicis, 13

Ilio-costalis lumborum, 13

Iliocostalis thoracis, 11,12-13, 16, 17

Infracoccygeus, 18

Infraspinatus, 3, 4, 18, 20, 31

Intercostales externi, 15, 16, 18, 19

Intercostales interni, 15

Intermediate. See Sphincter colli profundus pars intermedia

Interossei, 24, 25

Intertransversarius caudae dorsalis, 13

Intertransversarius coccygeus, 13, 16, 17, 25, 29

Ischio-caudalis, 25

Ischiocavernosus, 26

Ischiococcygeus, 25-26, 29, 30

Jugularis. See Platysma pars jugularis

Jugulohyoideus, 9, IS

Keratohyoideus, 9

Lateralis nasi, 6, 27

Latissimus dorsi, 15,19, 20, 21, 31

Levator anguli oris, 6

Levator ani, 16, 25

Levator caudae externus, 12, 17

Levator caudae internus, 11,17

Levator claviculae, 19

55
56 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Levator labii inferioris, 6

Levator labii superioris alaeque nasi, 5

Levator labii superioris proprius, 5

Levator nasolabialis, 4, 5, 6, 27

Levator palati, 10

Levator veli palatini, 10

Levatores costarum, 15

Lingualis, 8

Longissimus capitis, 12

Longissimus cervicis, 12

Longissimus dorsi, 11, 12, 13, 14, 17, 28, 29

Longus capitis, 13, 14, 15

Longus colli, 14-15

Lumbo-caudalis, 17

Lumbricales, 24-25

Mandibularis, 5, 6, 7, 27

Masseter, 4, 5, 7, 28

Maxillonasolabialis, 5-6, 27

}Mentalis, 4, 6, 27, 32

Mentalis. See Platysma pars mentalis

Molaris. See Buccinatorius pars molaris

Multifidus, 11

Mylohyoideus, 8, 9

Obliquus abdominis externus, 16, 18, 19, 20

Obliquus abdominis interims, 16, 17, 20

Obliquus capitis caudalis, 11, 13-14

Obliquus capitis cranialis, 14, 19

Obliquus inferior, 13

Obliquus superior, 14

Omohyoideus, 8

Opponens minimi digiti, 24

Oralis. See Sphincter colli profundus pars oralis

Orbicularis oculi, 5

Orbicularis oris, 4, 5, 6, 27

Orbicularis palpebrarum, 5

Palatinus, 10

Palatoglossus, 9

Palatopharyngeus, 9

Palmaris brevis, 24

Palmaris longus, 24

Palpebralis. See Sphincter colli profundus pars palpebralis

Panniculus carnosus, 4, 15

Pectoralis major, 14, 17,19, 20, 21, 31

Pectoralis minor, 16, 17,19-20, 21, 31

Platysma pars buccalis, 4

Platysma pars jugularis, 3, 4, 5. 6, 16

Platysma pars mentalis, 4

Platysma pars scapularis, 4, 16, 18, 26

Platysma pars temporalis, 4, 5, 18

Platysma cervicale, 4

Platysma myoides. 3, 4

Pronator radii teres, 23

Pronalor teres, 23

Pterygoideus externus, 7, 28

Pterygoideus internus, 7, 28

Pterygopharyngeus, 9

PyTamidalis nasi, 6

Quadrat us lumborum, 17

Recti oculi, 5

Rectus abdominis, 16-17, 19, 26, 30

Rectus capitis anticus major, 14

Rectus capitis anticus minor, 13

Rectus capitis dorsalis ?intermedius, 13

Rectus capitis dorsalis ?major, 13

Rectus capitis dorsalis minor, 13

Rectus capitis lateralis, 9, 11,13, 14, 19

Rectus capitis posticus major, 13

Rectus capitis posticus minor, 13

Rectus capitis ventralis, 13

Rectus lateralis, 13

Retractor ischii, 25, 26

Retractor labiorum, 5, 6, 27, 32

Rhomboideus, 11,7*

Sacrococcygei dorsales lateralis et medial is, 17, 28

Sacro-coccygeus, 17

Sacrococcygeus ventralis lateralis, 17-18, 25, 28, 29

Sacrococcygeus ventralis medialis, 17, IS, 28

Sacro-lumbalis, 13

Scalenus, 12,14, 18

Scalenus posticus, 14

Scapularis. See Platysma pars scapularis

Semispinalis, 11

Semispinalis capitis, 11, 12, 13

Serratus magnus, 14, 18-19, 20, 31

Sphincter ani, 26

Sphincter colli profundus }pars auris, 3, 4-5, 7, 14, 15, 19, 27,

30,32

Sphincter colli profundus pars intermedia, 5, 32

Sphincter colli profundus pars oralis, 5

Sphincter colli profundus pars palpebralis, 5, 6, 7, 27, 32

Sphincter colli superficialis, 3. 4. 19

Sphincter vaginae, 26

Spinalis, 11

Spinal is dorsi, 11

Splenius, 10-11, 12, 18

Stapedius, 8

Sternocostalis, 14,15, 19

Sternohyoideus, 8

Sternomastoideus, 4,14, 19

Slernothyroideus, 8, 14

Styloglossus, 8

Stylohyoideus, 9

Stylopharyngeus, 9

Sub scapularis, 14, 20, 21

Supinator longus, 21, 22

Supraspinatus, 3, 18, 20, 31

Temporalis, 7, 28

Temporalis. See Platysma pars temporalis

Tensor palati, 10

Tensor tympani, 8

Tensor veli palatini, 10

Teres major, 18, 19, 20-21, 31

Teres minor, 21

Thyreo-arytenoideus, 10

Thyreo-hyoideus, 8

Thyreoideus transversus. 9

Thyroarytenoideus, 10

Thyroepiglotticus, 10

Thyroepiglottideus, 10

Thyrohyoideus, 8,9, 14
NUMBE

R 226

57

Thyropharyngeus, 9

Trachelo-mastoid, 12

Transversalis, 16

Transversalis colli, 12

Transversarii, 17

Transversospinalis, 11, 12, 15, 17, 28

Transversus abdominis, 16

?Transversus nasi,6

Transversus perinaei, 25

Trapezius,4, 11, 7*, 20, 31

Triceps brachii, lateral head, 21, 22

Triceps brachii, long head, 21

Triceps brachii, medial head, 21

Urethralis, 26

Ventricularis, 10

Vocalis, 10

Zygomatico-labialis, 32

Zygomaticomandibularis, 7, 28

Zygomaticus, 6



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