December 2001

U. S. Department of Commerce

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Southeast Fisheries Science Center, 75 Virginia Beach Drive, Miami, FL 33149

The Anatomy of Sea Turtles The Anatomy of Sea Turtles

Jeanette Wyneken, Ph.D.

Illustrated by Dawn Witherington

NOAA Technical Memorandum NMFS-SEFSC-470
NOAA Technical Memorandum NMFS-SEFSC-470

THE ANATOMY OF SEA TURTLES

by

Jeanette Wyneken, Ph.D.

U. S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

Conrad C. Lautenbacher, Jr., Administrator

NATIONAL MARINE FISHERIES SERVICE

William T. Hogarth, Assistant Administrator for Fisheries

December 2001

Unpublished reports are used for documentation and timely communication of preliminary results,

interim reports, or special-purpose information, and have not received complete formal review, editorial

control, or detailed editing.
The National Marine Fisheries Service (NMFS) does not approve, recommend or endorse any proprietary

product or material mentioned in this publication. No reference shall be made to NMFS, or to this

publication furnished by NMFS, in any advertising or sales promotion which would indicate or imply

that NMFS approves, recommends or endorses any proprietary product or proprietary material herein or

which has as its purpose any intent to cause directly or indirectly the advertised product to be used or

purchased because of NMFS publication.

Correct citation of this report is:

Wyneken, J. 2001. The Anatomy of Sea Turtles. U.S. Department of Commerce NOAA Technical

Memorandum NMFS-SEFSC-470, 1-172 pp.

The scientific contents of the The Anatomy of Sea Turtles

© 2001 Jeanette Wyneken.

Copyright claimed on pages iii-172 exclusive of page 4

Copies of this report can be obtained from:

National Marine Fisheries Service

Southeast Fisheries Science Center

75 Virginia Beach Drive

Miami, FL 33149

or

National Technical Information Service

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(503) 605-6000

(800) 553-6847 (rush orders)

ii

NOTICE
The Anatomy of Sea Turtles The Anatomy of Sea Turtles

Jeanette Wyneken, Ph.D.

Illustrated by Dawn Witherington
iv
The need for an up-to-date guide to the anatomy of

sea turtles became clear toward the end of the

1900s. Increasing numbers of individuals developed the interest, talents, and techniques to study

the biology of sea turtles, contend with their illnesses and injuries, and address the nature of sea

turtle mortalities. This manual was written in

response to these needs and was designed to be

accessible to a variety of users. It provides a fundamental background, reference photos of normal

anatomy, and diagrams to guide novice or professional biologists, stranding personnel, and veterinarians. Species identification, standard dissection

techniques, standard measurements, and basic

anatomy are covered with a diverse audience in

mind. While this manual does not serve as a

necropsy guide, it may serve as a reference when

conducting necropsies. It is designed particularly

with the understanding that many users will be

working with it in the field or under less-than-ideal

conditions. The Anatomy of Sea Turtles is organized so that it can be used either as a guide to dissection or as an anatomical reference to species

identification, standard methods, and dissection

(pp. 1-42) or as an anatomical reference to sea turtle structures or systems.

Most of the photos in this guide are by the author.

However, several individuals contributed pictures

that enhanced the quality of the manual. These

include Larisa Avens, George Balazs, Peter

Bennett, Beth Chittick, Larry Crowder, Bill

Dailey, Sheryan Epperly, Craig Harms, Eve

Haverfield, Bruce Homer, Chris Johnson, Ursula

Keuper-Bennett, Joanne Braun McNeill, Anne

Meylan, David Owens, Denise Parker, Donna

Shaver, Tom Smoyer, J. Vasconcelos, and Wendy

Teas. Access to specimens, dissection assistance,

and/or comments on drafts of the manual were

provided by George Balazs, Ruth Boettcher, Mike

Bresette, Brian Cousin, Lisa Csuzdi, Nancy

DiMarco, Sheryan Epperly, Kristin Fick, Allen

Foley, Jerris Foote, T.H. Frazzetta, Ellis Greiner,

Craig Harms, Kristin Hart, Hector Horta, Elliott

Jacobson, Chris Johnson, Ken Kardong, Jennifer

Keller, Kate Kelso, Greg Lewbart, Peter Lutz,

Charles Manire, Carol Hardy McFadden, Joanne

Braun McNeill, Nancy Mette, Jeff Miller, Debra

Moore, Steve Morreale, David Owens, Joe

Parsons, Robert Prescott, Peter C. H. Pritchard,

Tony Redlow, Anders Rhodin, Kurt Rusenko,

Cheryl Ryder, Michael Salmon, Karrie Singel,

Melissa Snover, Trish Sposato, Fred Steinberg,

Kelly Stewart, Wendy Teas, Mike Walsh, James

Weege, Pat Wells, Donna Weyrich, Dale Wilke,

Blair Witherington, Wayne Witzell, and Larry

Wood. The Cayman Turtle Farm, Chelonian

Research Institute, Florida Fish and Wildlife

Conservation Commission, Gumbo Limbo

Environmental Center, Harbor Branch

Oceanographic Institution, The Marinelife Center

of Juno Beach, Mote Marine Laboratory,

Philadelphia Academy of Sciences, National Marine

Fisheries Service-Beaufort Laboratory, National

Marine Fisheries Service-Miami Laboratory, North

Carolina Wildlife Commission, University MRI,

Inc., and the U.S. Fish and Wildlife Service provided access to specimens and logistical help.

Many individuals provided thoughtful discussions

during the preparation of this manual and The

Anatomy of Sea Turtles video. The quality and

coverage of The Anatomy of Sea Turtles was greatly improved by their attention and suggestions.

This manual’s illustrations and layout are by

Dawn Witherington.

v

PREFACE
The following people contributed photos that enhanced the quality of this manual. Where known, turtle

tag numbers or their identifications are also provided.

Ursula Keuper-Bennett and Peter Bennett: Figs. 11, Tutu; Fig. 20, Ake

Beth Chittick: Fig. 145

Larry Crowder: Fig. 141

Bill Dailey: Fig. 21

Craig Harms: Figs. 81, 161, 187

Bruce Homer: Fig. 176 

Chris Johnson: Figs. 9, 17

Heather Kalb and David Owens: Fig. 234

Joanne Braun McNeill: Fig. 15

Anne Meylan: Fig. 77

Peter C. H. Pritchard: Fig. 189

Tom Smoyer (Harbor Branch Oceanographic Institution): Figs. 10, 12, 13, 14, 19, 31, 45, 58, 70, 71, 90, 106, 229

J. Vasconcelos: Fig. 24

vi

PHOTOGRAPHIC CREDITS
Basic Terminology and Characters for Species Identification............................................................... 1

Species Identification ............................................................................................................................. 4

Skull Anatomy ....................................................................................................................................... 8

Species Identification from Skulls ......................................................................................................... 13

Rhamphotheca Structure ........................................................................................................................ 26

Standard Measurements ......................................................................................................................... 28

Methods of Dissection ........................................................................................................................... 33

Skeletal Anatomy ................................................................................................................................... 43

Muscle Anatomy .................................................................................................................................... 59

Circulatory Anatomy.............................................................................................................................. 74

Lung and Airway Anatomy ...................................................................................................................105

Gastrointestinal Anatomy ......................................................................................................................108

Glands .................................................................................................................................................... 115

Nervous System......................................................................................................................................125

Sense Organs ..........................................................................................................................................146

Urogenital System ..................................................................................................................................153

Selected Bibliography.............................................................................................................................166

Index ......................................................................................................................................................169

vii

TABLE OF CONTENTS
BASIC TERMINOLOGY AND CHARACTERS

The Anatomy of Sea Turtles 1

Anatomical Terminology

There are several terms used here that describe the

spatial relationships of structures. Below, these are

defined specifically for sea turtles (Figs. 1-2). 

Dorsal is toward the top of the shell (the carapace). 

Ventral is toward the plastron. 

Anterior is toward the head. 

Posterior is toward the tail. 

Medial is toward the midline.

Lateral is away from the midline, toward the sides. 

Proximal is close to the body or the start of a structure.

Distal is away from the body or main structure.

Deep to is underneath a structure

Characters for Species Identification

Sea turtle identification, from external characters, is

based upon the scales on the head, form of the jaws,

the number of claws on the feet, and the numbers and

arrangement of the plates or scutes on the shell. The

scutes of the carapace (the top shell) are numbered

from front to back (Fig. 3). The primary scutes (Fig.

4) used as key characteristics are the marginals,

laterals (costal), vertebrals, and nuchal, as well as

the inframarginal or bridge scutes. 

The bottom shell is the plastron. It also has distinct scute patterns, but these are used more often

as landmarks for internal structures than for

species identification (Fig. 5). From anterior to

posterior, the intergular scute is closest to the

neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.

Some individuals have a single unpaired interanal

scute that is found between or posterior to the anal

scutes. 

ventral

anterior posterior

dorsal

distal proximal

medial

lateral

2

3

4

5

1

Fig. 2. Relative anatomical position.

Fig. 1. Anatomical terminology.

Fig. 3. Numbering the carapace scutes.
Scutes of the carapace and plastron. The lateral

scutes are also known as costals or pleurals. The last

marginal scutes on each side are termed

supracaudals or postcentrals (Fig. 4). The scutes

between the plastron and the carapace are the

inframarginals (Fig. 5). While the number of

inframarginals is somewhat variable, the most

common count is often listed as a key characteristic.

Cheloniidae (hard-shelled sea turtles) are

characterized by the scales on the head, carapace,

and inframarginal scute patterns and numbers, as

well as the numbers of claws on the flippers

(Figs. 6-7). Most species have 2 claws. Claw I is

usually larger than claw II and becomes strongly

curved in adult males. The number of claws on

the front and hind limbs is the same. 

claw I

CHARACTERS FOR SPECIES IDENTIFICATION

2 The Anatomy of Sea Turtles

intergular

gular

humeral

inframarginal

pectoral

abdominal

femoral anal supracaudal

1st marginal nuchal

1st costal vertebral

Fig. 4. Scutes of the carapace. Fig. 5. Scutes of the plastron and bridge.

Fig. 6. Position and numbering of claws. Fig. 7. The single claw occurs on the first digit.

No claw forms on the second digit.
CHARACTERS FOR SPECIES IDENTIFICATION

The Anatomy of Sea Turtles 3

Leatherbacks lack both distinctive head scales as

adults and have minimal keratin covering on the

jaws. The hard-shelled sea turtles have keratinous

scales on the dorsal and lateral head that are used in

identification of species (Fig. 8). The prefrontal

scales occur in pairs. One or more supernumerary

scales may occur along the midline and separate the

pairs. Other head scales (supraocular, postocular,

frontal, frontoparietal, parietal, interparietal,

temporal, and tympanic scales) may vary slightly

in form but not in position relative to one another.

In some cases, individual variations in the head

scales can be used to identify individual turtles.

Several internal bony and jaw (rhamphotheca)

characters also may be used for species

identification. These are described later (Species

Identification from Skulls, pp. 13-25; Rhampotheca

Structure, pp. 26-27; Skeletal Anatomy, pp. 50-51).

prefrontal

scales

supernumery

scale

supraocular

scales

frontal scale

frontoparietal

scale

parietal

scales

postocular

scales

temporal

scales

tympanic

scales

interparietal

scale

Fig. 8. Head scales of cheloniid turtles. The major sets of scales used in species

identification are the prefrontals. There are often supernumerary scales (multiple extra

scales) between the prefrontals. These lack pattern and are usually small. The other

labeled scales serve as landmarks.

A key to the species is found on the next page.

It summarizes species identification using

external characteristics.
SPECIES IDENTIFICATION

4 The Anatomy of Sea Turtles

4 inframarginal

scutes

without

pores

4 inframarginal

scutes

without

pores

4 inframarginal

scutes

with

pores

4 inframarginal

scutes

with

pores

scutes

imbricated

(overlapping)

head carapace plastron

4 lateral

scutes

4 lateral

scutes

Green turtle - Chelonia mydas

Hawksbill - Eretmochelys imbricata

Kemp’s ridley - Lepidochelys kempii

Olive ridley - Lepidochelys olivacea

Leatherback - Dermochelys coriacea

5 lateral

scutes

6 or more

lateral

scutes

5 lateral

scutes

ridges no scutes

6 or

more

vertebral

scutes

1 pair of

prefrontal

scales

2 pairs of

prefrontal

scales

more than 1 pair

of prefrontal

scales

more than 1 pair

of prefrontal

scales

more than 1 pair

of prefrontal

scales

no scales

Loggerhead - Caretta caretta

3 inframarginal

scutes

without

pores
SPECIES IDENTIFICATION

The Anatomy of Sea Turtles 5

Species Identification

Sea turtles can be separated into the hard-shelled

(cheloniid) and the leathery-shelled (dermochelyid)

species. There is just one dermochelyid species, the

leatherback, Dermochelys coriacea (Figs. 9-10). It is

black with white speckling. Five dorsal ridges run the

length of the carapace, two ridges form the margins,

and few ridges occur ventrally. A notch occurs in each

side of the upper jaw and the limbs lack claws. 

The cheloniids can be distinguished from one

another by the scales on top of the snout, called the

prefrontals and by the scutes on the carapace. The

green turtle, Chelonia mydas (Figs. 11-13), has one

pair of prefrontal scales (Fig. 12). The carapace is

smooth with 4 pairs of lateral scutes. Carapace color

changes with age. It is black in hatchlings, then

turns brown and tan in juveniles, and in adults, it is

olive or gray-green, sometimes with speckles of

yellow and brown. The plastron is white in

hatchlings. It turns creamy yellow, sometimes 

temporarily pink or gray depending on the population. 

Adults have a creamy yellow plastron except in the

more melanistic green turtles (referred to as black

turtles) found in some Pacific waters. The green turtle

has one claw on each limb. There are 4

inframarginal scutes on each side and two Rathke’s

pores, one each in the axillary and inguinal scales

(see Glands, pp. 122-123).

Fig. 9. Dermochelys coriacea, adult. Fig. 11. Chelonia mydas, adult.

Fig. 12. Chelonia mydas, juvenile.

Fig. 10. Dermochelys coriacea, hatchling.

Fig. 13. Chelonia mydas, hatchling.
SPECIES IDENTIFICATION

6 The Anatomy of Sea Turtles

The remaining species have 2 pairs of prefrontal

scales (Fig. 8) and, as young, they have keels (ridges)

on their shells. The loggerhead, Caretta caretta (Figs.

14-17), has a large head and brown carapace with 5,

or sometimes 4, lateral scutes. The nuchal scute (the

marginal just dorsal to the neck) is in contact with the

first lateral scute. In hatchlings, the carapace is

brown with various shades of grey (Fig. 14). The

plastron of hatchlings is creamy to brown. In juveniles to adults it is creamy and tan. The carapaces of

juveniles (Fig. 16) develop streaks of yellow and tan.

Sometimes the scutes of juveniles slightly overlap

one another at their margins. In adults, there is no

overlap of scutes. The carapace is primarily brown

with occasional individuals retaining some tans or

even black (Fig. 17). The shells of loggerheads often

host large epibiont communities. Loggerheads have

two claws on each limb.

The hawksbill, Eretmochelys imbricata, as a hatchling,

is dark mahogany brown on both the carapace and the

plastron (Fig. 18). As the turtle grows, the head

elongates and the carapace develops a distinctive

pattern of yellow, black, tan and brown radiating

through the scutes (Fig. 19). This color persists

though adulthood. The nuchal scute does not touch

the first lateral scute in hawksbills. This distinguishes the hawksbill carapace from the loggerhead pattern. The head of the hawksbill is nearly twice as long

as it is wide and has a long narrow beak or rhamphotheca (Fig. 20). Hawksbills have two claws on

Fig. 16. Caretta caretta, immature. Immature loggerheads often have sharp keels on their vertebral

scutes and posterior marginal. These recede with larger size and age so that loggerheads found in coastal

waters often bear little of or no signs of the keels.

Fig. 17. Caretta caretta, adult. The jaws have

thick, robust rhampotheca (beak-like structures)

for crushing food.

Fig. 15. Caretta caretta, plastron. Loggerheads often

have 3 inframarginals however, this characteristic

is variable. 

Fig. 14. Caretta caretta, hatchling.
SPECIES IDENTIFICATION

The Anatomy of Sea Turtles 7

The last two species that occur in U.S. waters are the

ridleys (Figs. 21-24). These turtles are mostly gray in

color. The Kemp's ridley, Lepidochelys kempii, occurs

in east coast waters. The olive ridley, Lepidochelys

olivacea occurs in Pacific and South Atlantic waters

(but occasionally strays into tropical North Atlantic

regions). The hatchlings of both species are gray-brown.

The carapace assumes a nearly round appearance as

the turtle grows and the marginal scutes become wide

(Fig. 21). There are 4 (sometimes 3) inframarginal

scutes. Characteristic pores are found within each

inframarginal scute (Fig. 22) in both ridley species.

Ridley turtles have two claws on each limb.

Fig. 18. Eretmochelys imbricata hatchling (left)

and Caretta caretta hatchling (right). Note that

the nuchal scute touches the first lateral in

loggerheads but not in hawksbills.

Fig. 19. Eretmochelys imbricata, immature. The

narrow head and imbricate (overlapping) scutes

of the hawksbill are clear.

Fig. 21. Lepidochelys kempii, adult

Fig. 20. Eretmochelys imbricata, adult.
Kemp's ridley turtles are dark grey to grey-green in

color. They have 5 lateral scutes (4-6 is common). 

Olive ridleys turtles are dark grey. They typically

have more than 6 normally aligned lateral scutes,

6 or more normally aligned vertebral scutes (Fig.

23) and many supraoccular scales (Fig. 24).

Skull Anatomy

The skull is organized into an inner braincase, the

neurocranium, which houses the brain and an outer

bony superstructure, the splanchnocranium. The

anterior splanchnocranium along with the mandibles

form the jaws. The splanchnocranium also houses

the sense organs and provides the muscle attachment

sites for jaw, throat and neck muscles. The braincase

is found along the midline, internal to the skull roof,

snout, and jaw bones of the splanchnocranium. The

external bones of the splanchnocranium (Fig. 25) are

the same in all species, however their specific form

and some articulations differ. Skull shape and the

patterns of bones of the palate (roof of mouth; Figs.

26-27) are diagnostic for species identification.

Lateral bones (Fig. 28) are important landmarks for

locating internal structures. The jaws (Fig. 26) and

the neurocranium (Fig. 29), also are composites of

several bones.

SPECIES IDENTIFICATION/SKULL ANATOMY

8 The Anatomy of Sea Turtles

Fig. 22. Lepidochelys inframarginals with

Rathke’s pores. Fig. 24. Lepidochelys olivacea, adult

Fig. 23. Lepidochelys hatchlings. L. kempii

(right) has just 5 lateral and vertebral scutes

while L. olivacea (left) has 6 or more lateral and

vertebral scutes. 
SKULL ANATOMY

The Anatomy of Sea Turtles 9

Figs. 26a and 26b. Ventral

bones of the skull (with the

hyoid skeleton of the throat

removed) are shown with

the lower jaw and anterior

neck vertebrae articulated.

Both the upper and lower

jaws are composed of

multiple bones. The

posterior braincase, part

of the neurocranium,

articulates with the

cervical vertebrae. The

vertebrae are composed of

several parts: a vertebral

body or centrum located

ventrally and dorsal

arch elements. C1 - C4:

Cervical vertebrae.

Figs. 25a and 25b.

The dorsal and lateral

bones are identified

here. With the exception

of the supraoccipital,

these are bones of the

splanchnocranium.

postorbital

jugal

frontal

maxilla

prefrontal

external

nares premaxilla

parietal

squamosal

supraoccipital

palatine

atlas C1

basisphenoid

splenial

angular

maxillary

dentary

auditory

canal

axis C2

C3

C4

pterygoid

a b

a b
SKULL ANATOMY

10 The Anatomy of Sea Turtles

vomer

maxilla

paletine internal

nares

premaxilla

NOTE: Maxillae

do not touch

NOTE: Pterygoid

processes.

Compare with

L. olivacea

a

b

Figs. 27a and 27b. The specific articulations and forms of the bones are characteristic of

each species. The bones that make up the palate are frequently used as key characteristics.

For example, in this ridley skull, the vomer prevents the maxillae from touching. In the

loggerhead, a grossly similar skull, the vomer does not reach the premaxillae, so the

maxillaries articulate. The pterygoid process shape and position are also key characteristics.
SKULL ANATOMY

The Anatomy of Sea Turtles 11

Figs. 28a and 28b. The

lateral bones, identified on

this cheloniid skull, vary in

form with species. The eye

would be housed in the

orbit and the auditory

canal (ear) would occupy

the notch posterior to the

quadratojugal.

Fig. 29. The lower jaw is a composite of the

dentary, angular, surangular, prearticular,

splenial (not shown) and articular bones.

The cartilaginous portion is Meckel’s

cartilage; it is found in the Meckelian

groove in life.

postorbital

orbit parietal

squamosal

bone

auditory canal

jugal quadrate quadratojugal

bone

maxilla

premaxilla

dentary

Meckelian 

groove

prearticular

angular

surangular

articular

a

b
SKULL ANATOMY

12 The Anatomy of Sea Turtles

prootic opisthotic parietal postorbital

squamosal

stapes rostrum basisphenoidale pterygoid

Figs. 30a and 30b. The neurocranium is partially exposed by the removal of the jugal,

quadratojugal, and quadrate of a hawksbill skull. The braincase is small and housed

internal to the skull roof. Anterior bones (rostrum basisphenoidale and pterygoid) and

lateral bones (prootic and opisthotic) form walls of the braincase.

a

b
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 13

Species Identification from Skulls

The following descriptions are based upon bony

characteristics alone and do not include other

diagnostic features of the scales or the form of

the rhampotheca (keratinaceous beak, see

Rhamphotheca Structure, pp. 26-27).

Chelonia mydas (Figs. 31 - 33). The skull is

rounded with a short snout and shallow parietal 

notches (Fig. 31). The upper jaw is described by a

smooth U-shaped outline; the palate between the

margins of the upper jaw and the internal nares

(the alveolar surface) has a pair of ridges that run

parallel to the outer edge of the jaw (Fig. 32). The

lower jaw, has a ridge running parallel to the inner

surface (Fig. 33) and a midline cusp.

Figs. 31a and 31b. Chelonia

mydas, lateral view. a

b
SPECIES IDENTIFICATION FROM SKULLS

14 The Anatomy of Sea Turtles

Figs. 32a and 32b. Chelonia mydas, dorsal and ventral skull. Note ridges on

palate at arrows.

b

a
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 15

Figs. 33a and 33b. Chelonia mydas, ventral skull and lower jaw. Midline cusp of

lower jaw at arrow.

U-shaped palate

a

b
SPECIES IDENTIFICATION FROM SKULLS

16 The Anatomy of Sea Turtles

Caretta caretta (Figs. 34 and 35). The head of the

loggerhead is relatively large, wide posteriorly, and the

snout tapers anterior to the orbits. The parietal notches

(wide U-shape emarginations formed by the posterior

borders of the squamosal, parietal and supraoccipital

bones) are large (Fig. 34). The jaws are robust and

shaped like a wide V. Loggerheads have a relatively

long secondary palate. (The secondary palate is the

shelf of bone that separates or partially separates

food and air passages.) The palate lacks alveolar

ridges and the two maxillary bones contact one

another posterior to the premaxillary bones (Fig. 35).

Figs. 34a and 34b. Caretta

caretta, dorsal skull and

lower jaw. Parietal notches

are at arrows.

a

b

parietal notch
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 17

Figs. 35a and 35b. Caretta caretta, ventral skull and lower jaw. Note that the two

maxillary bones touch at the middle of the palate.

a

b

secondary

palate
SPECIES IDENTIFICATION FROM SKULLS

18 The Anatomy of Sea Turtles

Lepidochelys kempii (Fig. 36). The skull is similar

in overall shape to that of the loggerhead but can be

distinguished from the loggerhead by the features

of the palate. The Kemp’s ridley skull is roughly

triangular in shape. The parietal notches are well

developed (Fig. 36). The snout tapers anterior to

the orbits. The jaws are shaped like a wide curved

V and there is a relatively long secondary palate.

The palate has longitudinal alveolar ridges and the

two maxillary bones are separated by the vomer

which extends anteriorly to articulate with the

premaxillary bones (Figs. 27 and 36). The orbits

are relatively small when compared with other

species and each has a ridge of bone along its

dorsal margin that extends laterally from the

anterior portion of the postorbital bone.

Figs. 36a and 36b. Lepidochelys

kempii, dorsal and ventral skull. a

b

alveolar

ridges
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 19

Lepidochelys olivacea (Figs. 37-39). The olive

ridley skull is similar in shape to skulls of the

loggerhead and Kemp’s ridley. It is roughly

triangular in shape, wide posteriorly, and has deep

parietal notches. The jaws are shaped like a wide

V. The palate lacks alveolar ridges. The two

maxillary bones are separated by the vomer which

articulates with the premaxillary bones. The orbits

are larger than in L. kempii (Figs. 39-40) and the

pterygoid bones are broad at their narrowest point

when compared with other species.

Figs. 37a and 37b. Lepidochelys olivacea, dorsal skull

Figs. 38a and 38b. Lepidochelys olivacea, ventral skull. The pterygoid bone of

the olive ridley is proportionately wider and the pterygoid processes are more

pronounced than in the Kemp’s ridley.

pterygoid 

bone

pterygoid 

process

palatine

bone

a b

a b
SPECIES IDENTIFICATION FROM SKULLS

20 The Anatomy of Sea Turtles

Figs. 39a and 39b. Lepidochelys olivacea,

lateral skull. When measured across its

longest axis, the orbits of L. olivacea are

proportionately larger than those of L. kempii.

Figs. 40a and 40b. Lepidochelys kempii,

lateral skull. Note the proportionally smaller

orbit and slightly more hooked snout.

a

b

a

b
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 21

Eretmochelys imbricata (Figs. 41-42). The

hawksbill skull is long and narrow in all but the

youngest turtles (hatchlings). The length is

approximately equal to twice the width (measured

at the skull's widest part; Fig. 42). Hawksbill skulls

have deep parietal notches and the snout tapers to a

point. The jaws are V-shaped and narrow (Fig. 41).

The secondary palate is well developed and the

internal nares are situated in the anterior third of

the mouth. The two maxillary bones are separated

by the vomer which extends anteriorly to articulate

with the premaxillary bones (Fig. 42).

Figs. 41a and 41b.

Eretmochelys imbricata, dorsal

skull and lower jaw with

rhampotheca. The jaws are very

narrow and V-shaped.

parietal notch is deep

“V”- shape

a

b
SPECIES IDENTIFICATION FROM SKULLS

22 The Anatomy of Sea Turtles

Figs. 42a and 42b. Eretmochelys imbricata, ventral skull and lower jaw. The

skull is longer and narrower than that of any other species. The secondary palate

is long so that the internal nares (arrow) are relatively far back. 

W

L

~ 2X W=L

a

b
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 23

Dermochelys coriacea (Figs. 43 - 44). Leatherback

skulls are unlikely to be mistaken for those of any

other species. The skull is wide and rounded

anteriorly with large orbits; there are no parietal

notches (Fig. 43). The bones articulate loosely;

there is little or no secondary palate (Fig. 44). The

margins of the jaws are sharp and possess notches.

There are pointed cusps on the anterior maxillary

bones. The lower jaw comes to a dorsally directed

point at the mandibular symphysis (where the two

halves of the lower jaw join). The lower jaw has a

cartilaginous portion medial to the dentary.

Figs. 43a and 43b.

Dermochelys coriacea, dorsal

skull and lower jaw. The

bones fit together more

loosely than in other

species. The leatherback

skull and skeleton has been

described as neotenic (having

embryonic characteristics)

in form because of the lack

of bony fusions. a

b
SPECIES IDENTIFICATION FROM SKULLS

24 The Anatomy of Sea Turtles

Figs. 44a and 44b. 

Dermochelys coriacea,

ventral skull and lower jaw.

Note the lack of a secondary

palate and the loose

articulations of the bones.

notch

a

b
SPECIES IDENTIFICATION FROM SKULLS

The Anatomy of Sea Turtles 25

Fig. 45. Skulls of all the species found in US waters.

Clockwise from top right: Dermochelys coriacea (a),

Eretmochelys imbricata (b), Chelonia mydas (c),

Lepidochelys olivacea (d), Lepidochelys kempii (e),

Caretta caretta (f). The hawksbill, green turtle and

Kemp's ridley skulls are from immature animals,

others are from adults. 

a

b

c

d

f

e
26 The Anatomy of Sea Turtles

RHAMPHOTHECA STRUCTURE 

Chelonia mydas

Rhamphotheci Upper Rhamphotheca Lower Rhamphotheca

• Snout rounded, outer keratin smooth and 

delicately built.

• Edges are outlined by serrations and spike-like cusps.

• Upper rhamphotheca serrated, short, pointed cusps.

• Inner surface with vertically aligned ridges. 

• Lower rhamphotheca is serrated with vertical 

spike-like processes. 

• Parallel inner ridge with row of smaller cusps. 

• Midventral ridge without spikes connects the two.

• Alveolar surface has two depressions to either 

side of the midline ridge. 

Rhamphotheca (beak)

The rhamphotheci are the keratinous beaks of the

upper and lower jaws in cheloniids. They cover the

maxillary, premaxillary, and vomer bones of the

upper jaw, and the dentary of the lower jaw. They

differ with diet and can be used to identify species. 

Several terms are used to describe the positions of

parts of the mouth or rhamphotheci. Alveolar 

refers to the surfaces and edges of the 

jaws where teeth would be found in nonchelonian

reptiles. Palatal refers to the horizontal surface

forming the roof of the mouth. Buccal refers to the

portion of the lower plate next to the tongue.

Below, species-specific characteristics of the

rhamphotheci (Fig. 46), useful in species

identification, are illustrated and described.

Rhamphotheci Upper Rhamphotheca Lower Rhamphotheca

Eretmochelys imbricata

• Rhamphotheca moderately built.

• Snout narrow and pointed with sharp alveolar 

edges. 

• Upper rhamphotheca’s palatal portion is mostly

smooth. 

• Slight ridge, parallel to the maxillae; ridge may

wear in older turtles.

• Lower rhamphotheca is narrow and smooth. 

• Triangular process extends anteriorly from the 

buccal (posterior) margin.

Fig. 46. Rhamphotheca characteristics by species.
The Anatomy of Sea Turtles 27

RHAMPHOTHECA STRUCTURE

Rhamphotheci Upper Rhamphotheca Lower Rhamphotheca

Caretta caretta

• Rhamphotheci robustly constructed with sharp 

alveolar edges. 

• In young, upper and lower jaw come to a point.

• Upper rhamphotheca: palatal portion is wide 

and forms crushing surface inside mouth. 

• Two V-shaped palatal ridges are found in young

turtles; worn smooth in older animals.

• Lower rhamphotheca is trough-like with a thick

crushing surface.

• U-shaped cutting surface is found along the 

posterior margin. 

Rhamphotheci Upper Rhamphotheca Lower Rhamphotheca

Rhamphotheci Upper Rhamphotheca Lower Rhamphotheca

• The rhamphotheci are heavily constructed with 

thick alveolar surfaces.

• Both upper and lower jaws come to anterior 

hook-like points.

• Upper rhamphotheca: forms wide crushing surface

with sharp-edged alveolar margins. 

• The palatal portion has large cusps bilaterally. 

• Lower rhamphotheca is trough-like with two 

depressions that receive the palatal cusps. 

• Sharp U-shaped ridge marks the posterior border. 

Lepidochelys kempii

• Rhamphotheci are heavily constructed with thick

alveolar surfaces.

• Both the upper and lower rhamphotheci are 

pointed at the anterior midline. 

• Upper rhamphotheca forms a wide plate with a 

sharp-edged alveolar surface.

• Palatal portion has a ridge bilaterally extending

just anterior to the internal choanae. 

• Lower rhamphotheca has a sharp, wide, V-shaped

ridge running posteriorly along the buccal 

margin.

Lepidochelys olivacea
STANDARD MEASUREMENTS

28 The Anatomy of Sea Turtles

Standard Measurements

Several different lengths are measured when

describing turtle size (Fig. 47). Each measurement

is taken in order to ensure that comparative data are

available to share with other programs world-wide.

Over-the-curve measurements are taken with a

non-stretching tape measure while straightline

measurements are taken with calipers. The following

are the standard measurements and their landmarks. 

Standard Length (SCL and CCL) are measured

from the mid-point of the nuchal scute to the

posterior-most tip of the carapace in cheloniids

(Figs. 48-49). Standard carapace length is a

straightline measurement from the anterior-most 

point on the midline of the nuchal scute to the

posterior-most tip of the last marginal (supracaudal

or postcentral) scute. Curved carapace length uses

the same landmarks but is taken over the curve of

the carapace with a tape measure. If the tape

crosses epibionts, notation should be made

describing this aberration in the measurement. In

leatherbacks, SCL is measured from the middle of

the nuchal notch to the posterior-most tip of the

caudal peduncle. To measure the CCL of a

leatherback, pull the tape tight between the middle

of the nuchal notch and the terminal tip of the caudal

peduncle, without forcing the tape along the ridge.

Fig. 47. Landmarks for standard measurements.

Each is described in detail in the text.

Fig. 48. Straightline Standard Length: SCL.

Fig. 49. Over-the-Curve Standard Length: CCL. 
STANDARD MEASUREMENTS

The Anatomy of Sea Turtles 29

Maximum Carapace Length (SCLmax and

CCLmax), also sometimes called greatest length,

is from the anterior-most part of the carapace to

the posterior-most tip of the carapace on the same

side (Figs. 52-53). 

Fig. 52. Maximum Straightline Carapace Length:

SCLmax.

Fig. 53. Maximum Over-the-Curve Carapace

Length: CCLmax.

Fig. 50. Minimum Straightline Carapace Length

(Notch-to-Notch): SCLmin.

Fig. 51. Minimum Carapace Length Over-theCurve (Notch-to-Notch): CCLmin.

Minimum Carapace Length (SCLmin and

CCLmin), also known as notch-to-notch length,

is measured from the mid-point of the nuchal scute

to the notch where the two most posterior

marginal scutes meet (Figs. 50-51). 
STANDARD MEASUREMENTS

30 The Anatomy of Sea Turtles

Carapace Width (SCW and CCW) is measured at

the widest part of the carapace (not at specific

scutes). In leatherbacks, carapace width is at

measured the widest points, typically on the most

lateral ridges. Care should be taken to ensure that

the calipers and/or tape measure are perpendicular

to the animal's long axis. The maximum width taken

using a tape measure will not always fall on the same

location as that measured with calipers (Figs. 54-55).

Fig. 54. Straightline Width: SCW.

Fig. 55. Over-the-Curve Width: CCW. 

Maximum Head Width (HW) is measured using

calipers at the widest part of the head (Fig. 56). 

Fig. 56. Maximum Head Width (HW) is measured

at the widest part with the calipers perpendicular

to the long axis of the skull. This position varies

with species so that, in some, it is near the jaw

joint and in others, it is found more posteriorly.

Maximum Head Length (HL) is measured along

the midline from the anterior-most part of the

upper jaw to the posterior-most bone of the skull -

the supraoccipital crest (Fig. 57). This bone is

identified by feeling for the landmark (palpating). 

Fig. 57. Maximum Head Length (HL) is measured

from the posterior tip of the supraocciptal crest

(found by palpating) to the anterior-most part of the

head, often the rhamphotheca (beak) of the upper jaw.
STANDARD MEASUREMENTS

The Anatomy of Sea Turtles 31

Body Depth (BD) is recorded with the animal

propped on its side or by digging a trench for the

caliper jaws under an adult animal on land. This

measurement is taken with calipers at the point of

maximum carapace height when the bottom jaw of

the calipers is held parallel to the plastron (Fig. 58).

Fig. 58. Body Depth (BD) measurements are taken

at the body’s maximum height. On a live turtle, an

average of at least 3 measurements should be

taken between breaths because the depth changes

during breathing. 

Fig. 61. Plastron Length (CPL) is measured with

an aligned tape measure. This method gives a

slightly longer measurement than one obtained

with calipers.

Plastron Length (SPL), straightline or curved

(CPL), is defined by the posterior-most part of

the plastron hard structure to its anterior-most

hard structure. These points may extend beyond

the intergular or gular scute at the ventral base of

the neck and the anal or interanal scute of the

plastron (Figs. 60-61). 

Fig. 60. Plastron Length (SPL) is measured with

calipers extended from the anterior-most end of

the plastron to the posterior-most end. These

landmarks may occur beyond the scutes.

Fig. 59. Tag tear-out scar on a leatherback.

When measuring the animal, be sure to look for

tags or tag scars on the front and hind flippers and,

in the leatherback, near the tail (Fig. 59).
STANDARD MEASUREMENTS

32 The Anatomy of Sea Turtles

Total Tail Length (TTL) is measured from the

posterior-most point of the plastron to the tail tip.

The Plastron-to-Vent Length (PVTL), a separate

measurement, is from the middle of the cloaca, or

vent, to the posterior-most tip of the plastron. The

Vent-to-Tip (VTTL) measure is taken from the

middle of the vent to the tip of the tail or it can be

calculated by subtraction (Figs. 62-63). 

Fig. 63. The Vent-to-Tip measurement (VTTL),

shown here, is taken from the middle of the cloaca

(vent) to the tip of the tail.

Fig. 62. Tail Length (TTL) is typically measured

with a tape measure extending from the posteriormost part of the plastron to the tip of the tail. The

tape measure is allowed to follow the curl in the

tail. Caliper measures tend to be slightly shorter. 

Fig. 65. Circumference also can be taken with the

turtle on its plastron. For very large animals, it

may be necessary to dig under the turtle in order

to get the tape aligned properly. When the tape is

stretched over epibionts, such as barnacles, this

should be noted.

Fig. 64. Circumference (CIRCUM) is taken with

a tape measure. It can be measured with the turtle

lying on its carapace.

Circumference (CIRCUM) is the greatest

circumference taken perpendicular to the turtle's

long axis (excluding the flippers; Figs. 64-65).
Methods of Dissection

Tools and Preparation. Before beginning your

dissection, make sure you have all necessary tools,

data sheets, pens, and pencils. Tools should

include large and small calipers, a tape measure

(Fig. 66), a camera, one or more saws, snips (metal

or bone shears), one or more sharp knives, scalpel

blades and handles, a sharpening stone or steel,

and hemostats or pliers (Fig. 67). Other useful

tools are blunt probes, forceps with and without

teeth, scissors, pipettes and/or syringes for

removing fluid. Bowls, plastic bags or jars and

string or rubber bands are also useful. Protective

gear should minimally include gloves; boots, 

coveralls or aprons are recommended. Access to

towels will be important. Be sure to start with

sharp instruments and be prepared to sharpen them

frequently. Turtle skin can be tough and dulls

knives and scalpel blades quickly. For clean up,

herbal and anti-bacterial soaps are good for

neutralizing odors and disinfecting, respectively.

A 10% chlorine bleach (sodium hypochlorite)

solution will help disinfect floors, bowls, or trays.

Mix 1 part liquid chlorine bleach with 9 parts

water. Check stock solution concentrations; some

brands are stronger than others. Bleach solution is

too harsh for use on most good tools.

METHODS OF DISSECTION

The Anatomy of Sea Turtles 33

Fig. 67. Examples of tools used for

the dissection (left to right): Metal

snips, blunt scissors, pointed

scissors, hemostatic forceps, forceps

without teeth, blunt probes, and

scalpels. A syringe and knife (at the

top) are particularly useful.

Fig. 66. Tools used to measure the

animal: a nonstretching tape

measure and large sliding calipers

(tree calipers). 
METHODS FOR DISSECTION

34 The Anatomy of Sea Turtles

External examination. A complete description of

the carcass should start with an external

examination. Species, size, and sex, (if mature)

should be noted. Foreign materials, anomalies, and

healed or fresh wounds should be described

including their locations. Tumors are common in

some species, especially green turtles, and should

also be described by size, color, texture and location.

Starting the dissection. Start by removing the

plastron. Make a cut through the skin of the neck

then extend it laterally (Fig. 69). Cut around the

axillary regions near the plastron and along the seam

made by the marginal and inframarginal scutes (Fig.

70). Bony processes from the plastron bones extend

into the peripheral bones near the anterior and

posterior inframarginal scutes. Hence, the cut cannot

follow the seam completely. The skin and muscle

near the hind limbs are thin, so care should be taken

here to avoid cutting into the body cavity. The cut

should follow along the plastron’s posterior margin.

When positioning the carcass for dissection, pay

attention to proximity to buildings, drainage and

tides. Before beginning a dissection, consider the

time of day as dissections may take hours. In some

cases, packing the animal or some parts of the animal

in ice is a good strategy to minimize decomposition.

Fig. 69. An outline is shown to trace the path of the

initial cut needed to successfully remove the plastron.

Instructions for use of this guide. 

Dissections typically proceed by body region while

investigators tend to look-up structures by system.

Hence, the dissection will be briefly described by

region. The more complete description of each

structure, should it be needed, will be found in

sections dedicated to the details of organ systems.

The following are instructions for the most common

dissections. Individuals differ in the order in which

they proceed. There is no one correct way, however,

all dissections should start with a thorough external

examination and verification of the species.

Photographs are helpful for verifying species,

documenting anomalies, and addressing questions.

In most cases, it is easiest to work with a carcass

that is placed on its back (Fig. 68). Working with

very large animals may require the assistance of

heavy equipment to move the carcass.

Fig. 68. Carcasses should be placed on their backs for

access to most viscera.
METHODS FOR DISSECTION

The Anatomy of Sea Turtles 35

Fig. 70. The cut may be made with a knife or

scalpel blade. When using a knife, be sure the point

is kept very near to the plastron so that it does not

cut the viscera.

The anterior part of the plastron is attached to the

pectoral apparatus (the shoulder bones) via thick

connective tissue. (In cheloniids, this is near the

midline at the margins where the humeral and

gular scutes meet). This connection must be cut

close to the plastron (Fig. 71) in both hard-shelled

and leatherback sea turtles to avoid damaging the

heart, great vessels, or thyroid gland (Figs. 72-73).

Once this attachment is free, lift the plastron while

separating muscle and blood vessels from the shell

by blunt dissection and careful cutting. Blunt

dissection, the use of the hands or blunt

instruments to separate structures, will often free

the shoulder muscles from the plastron and from

the peritoneum (the translucent connective tissue

covering the organs). 

Before removing the plastron completely from

both sides, locate the greenish gray Rathke's

glands in green turtles and ridley turtles. They

are located deep to the Rathke's pores (Fig. 22)

and embedded in fat. The gland feels denser than

the fat when palpated. If a sample is needed,

section the gland, and like most organs, if

dropped in water, it will sink whereas fat will

float, making it possible to distinguish the two.

Fig. 71. To free the plastron, the attachment from

the acromion processes to the plastron (at arrow)

must be cut.

Internal Landmarks. Once the plastron is

removed, you will see that the ventral surface of the

body is mostly covered by muscles (Figs. 72-73).

There are 3 major groups of muscles that must be

cut or dissected away to expose the viscera. These

are the longitudinal muscles along the neck, the

large pinnate (feather-shaped) “chest” muscles used

for swimming, and the fan-shaped pelvic muscles

that were attached to the plastron (Fig. 73).

Good landmarks that you can use to find organs are

the acromion processes (Fig. 73) and the long

triangular coracoid processes (procoracoids; see

Skeletal Anatomy, p. 51; Muscle Anatomy, p. 61) on

each side of the body. The two acromion processes

cross the anterior body just posterior to the neck and

extend to the shoulder joint. They attach medially, via

ligaments, to the plastron. The coracoid processes

extend posteriorly from the shoulder joint toward the

abdomen. These two parts of the shoulder girdles

serve as attachments for many of the large muscles

that move the flippers (Fig. 73; see Skeletal Anatomy

Figs. 112-115). The space defined within the borders

of the right and left acromion and coracoid process

serves as a landmark for the heart, great vessels, and

thyroid gland. The major blood vessels will also act as

guideposts for locating the thyroid and thymus glands. 
METHODS FOR DISSECTION

36 The Anatomy of Sea Turtles

Fig. 72. The massive pectoral and pelvic

musculature can be seen in this leatherback. The

two white patches on the anterior body are the cut

ligaments of acromion processes. The head is

toward the bottom of the picture.

Fig. 73. The ventral pectoral and pelvic

musculature covers most of the peritoneum and

organs. These must be removed to expose the

peritoneal cavity. The paired acromion processes

are visible adjacent to the midline but the fanshaped coracoids are covered by the pectoral

muscles. Anterior is toward the top of the picture.

acromion

process pectoral

muscles

pelvic

muscles acromion

ligaments
METHODS FOR DISSECTION

The Anatomy of Sea Turtles 37

Fig. 74. The peritoneum has been removed to

expose the layout of the organs. The heart is

centrally located, posterior to the trachea. The

liver is to each side of the heart. The pectoral

girdle was removed from the animal's right side

(left in photo) and reflected laterally on the

animal's left side. 

Rotating the acromion and coracoid anteriorly will

help separate the muscles from the peritoneum

(encasing the viscera). The heart, liver, and major

blood vessels (Fig. 74) usually can be seen

through this layer. To expose the viscera, remove

the flippers and shoulder girdles by breaking the

attachments of the scapula to the carapace. Free

the shoulder muscles attached to the shell and neck

(cut or break them). Twist the acromion and

coracoid until the scapula, which extends from the

shoulder joint to the anterior carapace, is free. Use

blunt dissection to remove the remaining

attachments then lift the shoulder girdle and

flipper out of the body.

Cardiovascular anatomy. Open the pericardium

(Fig. 75) to reveal the heart. The pericardial cavity

will often contain fluid, particularly in specimens

that have been frozen and thawed.

Fig. 75. The pericardium contains the heart and

pericardial fluid. The great vessels (aortas and

pulmonary arteries) are seen posterior to the

thyroid, at the fingertip, and the horizontal

arteries. The heart is attached posteriorly via the

gubernaculum, a cord of tissue at the base of the

pericardium. The peritoneum, a translucent

fibrous membrane surrounding the organs, is seen

to either side of the pericardium. 

gubernaculum

pericardium

liver

peritoneum
METHODS FOR DISSECTION

38 The Anatomy of Sea Turtles

Upon opening the pericardium, 3 of the chambers of

the heart are visible: the single ventricle, left

atrium and right atrium (Fig. 76). The ventricle is

attached to the pericardium via a fibrous connective

tissue cord called the gubernaculum cordis (Fig.

75). After the gubernaculum is cut, the heart can be

rotated anteriorly to reveal the fourth chamber, the

sinus venosus. The sinus venosus is thin-walled; it

collects venous blood from the head, ventricle, lungs

and body (see Circulatory Anatomy, Fig. 129).

The great vessels (pulmonary artery, left aorta, and

right aorta) arise from the anterior and ventral part of

the heart. The right aorta gives off a branch almost

immediately, the brachiocephalic trunk (Fig. 76)

which then branches to the left and right. Small

thyroid arteries arise from the brachiocephalic trunk

and drain the single thyroid gland. The thyroid gland

feels like a round gelatinous mass. Careful trimming

of fat and connective tissue will reveal the red to

brown thyroid (Fig. 75). The brachiocephalic trunk

then forms subclavian arteries laterally, which

become axillary arteries as they pass toward the

flippers. The right and left thymus glands can be

found by following the brachiocephalic trunk to the

subclavian and axillary arteries. Feel for the thymus

glands along the subclavian and axillary arteries

before trying to locate them visually. After you have

identified the thymus and thyroid glands, you can

remove the heart for detailed examination by cutting

through all the vessels and the sinus venosus. You

may tie off the vessels before cutting if you want to

minimize blood draining into the body cavity.

Gastrointestinal Tract and Related Structures.

Next examine the gastrointestinal (GI) tract. Expose

the esophagus leading to the stomach and the

trachea to the lungs with a midventral cut in the

neck skin. Open the neck skin and muscle as deep as

the hyoid (the skeletal structures that support the

tongue and some neck muscles). Cut along the inner

surface of the lower jaw to free the tongue, glottis,

trachea, and esophagus. The trachea and esophagus

will exit posterior to the hyoid apparatus. The

esophagus is deep and slightly to the (turtle's) right

of the trachea. Cartilaginous rings characterize the

trachea. The esophagus is a collapsed muscular tube.

If you have difficulty finding the esophagus, you can

run a blunt instrument or tube down the throat and

locate the structure by moving your probe. 

In the body cavity, the esophagus makes a sharp

curve to the left to join to the stomach. The

stomach leads to the small intestine with its

digestive glands (liver and pancreas). The large

intestine joins the distal small intestine and the GI

tract ends with the rectum (Fig. 77).

Fig. 76. The heart has 4 chambers: the sinus venosus,

right atrium, left atrium, and ventricle. The two

aortas and pulmonary trunk emerge from the anterior

aspect of the ventricle and are seen between the two

atria. The brachiocephalic trunk is a landmark for

locating the thyroid and thymus glands. The heart

is pushed laterally to show the sinus venosus.

right

atrium left

atrium

brachiocephalic

trunk

sinus

venosus

ventricle
METHODS FOR DISSECTION

The Anatomy of Sea Turtles 39

Figs. 77a and 77b. The gut of a hawksbill after it

has been removed and cut free from the liver,

spleen, mesenteries, and cloaca. The GI tract

includes the esophagus, stomach, small intestine,

and large intestine, which are easily distinguished

from one another.

Once you have located the esophagus, tie it off near

the mouth with string or rubber bands that will not

slip. You can then cut it away from the mouth and

start removing the gut for examination. Separate

the esophagus and stomach from the trachea and

liver by blunt dissection. The stomach is attached

to the liver's left lobe ventrally and to the left lung

dorsally. These attachments must be cut or broken

carefully in order to free the stomach and leave the

liver and left lung intact. 

Continue to remove the gut by tearing or breaking

the mesenteries (flat tissues that suspend and

support the organs) and blood vessels. Be careful

not to cut the stomach or intestines. The stomach

joins the small intestine at the pyloric sphincter, a

thick muscular sphincter or valve. Just past the

pyloric sphincter, the pancreas can be seen running

distally along the duodenum (Fig. 77) past the

common bile duct (a short attachment to the

gallbladder which is found in the liver's right lobe).

The pancreas is usually smooth, shiny (pink to

peach colored), except in turtles that have

decomposed. The common bile duct from the

gallbladder can be identified by the green bile stain.

The spleen can be found near the distal end of the

pancreas. It is nearly round to oblong in shape, dark

red, and highly vascular (see Circulatory Anatomy,

Fig. 158 and Gastrointestinal Anatomy Fig. 164). 

The intestine is long and must be cut away from its

highly vascular, fan-shaped mesentery. The posterior

part of the intestine is the colon (large intestine),

which ends in a muscular rectum (Fig. 77). The

a b

rectum

caecum

ileum and jejunum

large

intestine

duodenum

and pancreas

stomach

esophagus
METHODS FOR DISSECTION

40 The Anatomy of Sea Turtles

Figs. 78a and 78b. The lungs are in contact with

the carapace. By tracing the trachea posteriorly to

the 2 bronchi, the lungs can be found. They extend

for most of the length of the carapace. The gonads

are found at the base of each lung. In this animal,

the testes are shown.

left aorta trachea

primary 

bronchi right aorta

right

lung

colon

cut

kidney

testis

left

lung

rectum is often pigmented. It enters the cloaca, a

chamber that receives urine, eggs or sperm. Before

cutting through the rectum, tie it off with string or

rubber bands.

The urinary bladder (discussed shortly) is

anatomically ventral to the rectum and is

suspended on the midline of the pelvis. It too,

connects to the cloaca.

Before opening the gut to examine the contents and

the lining, it helps to tie it off in 3 or more sections

so that there are landmarks available when

describing the parts. By using pairs of ties, the gut

can be cut without spilling the contents. The gross

appearance of the lining of the intestines does not

always allow one to describe the location of a

structure, tissue, or contents, so preset landmarks

are useful. When opening the intestine, it helps to

have trays or bowls ready to receive contents.

If you have not removed the liver with the gut, do so

now by carefully freeing it from its attachments to the

lungs and the peritoneum. The dense liver is composed

of two lobes, with a connection of varying size between

the two (Fig. 73). The right lobe is usually larger and,

on its posterior surface, houses the round gallbladder.

The gallbladder is usually dark green and may be full

and convex or collapsed and concave (when empty). 

Once the gut is removed, it is easy to see the lungs

and the gonads (Fig. 77) at their posterior margin. 

a b
METHODS FOR DISSECTION

The Anatomy of Sea Turtles 41

Gonads. The gonads are attached to the peritoneal

wall, posterior to the lung and anatomically ventral

to the kidneys. The ovaries of mature and maturing

turtles have a number of round yellow follicles that

appear as small (~2 mm - 2 cm) diameter spheres

embedded throughout the length of the long narrow

organ. Immature ovaries are more compact, flat,

often elongate, and fusiform in outline. They are

often pink and granular in appearance. Ovaries

tend to be attached along their length by one edge.

The oviduct transports the follicles, then eggs, to

the cloaca when mature. The oviduct is located

lateral to the ovary and is not attached to it. Each

oviduct extends anteriorly from the cloaca for

about 2/3 the length of the body. In mature turtles,

it has an "accordion" appearance. In immature

turtles, it is a simple flat tube that is very narrow in

the youngest and increasingly wide in older turtles

(see Urogenital Anatomy, Figs. 220-221).

The testis is often yellow or tan, and smooth. It is

fusiform in outline and is attached to the body wall

by its flat dorsal surface. The vas deferens is a

coiled tube that is found lateral to the testis

transports sperm to the cloaca. In breeding males,

both the testis and the vas deferens become enlarged.

When in doubt about the sex of the turtle, the coiled

vas deferens, even in young turtles, is an important

clue (see Urogenital Anatomy, Figs. 221-222).

Lungs. The lungs are located dorsally and are

attached to the carapace and vertebral column

(Fig. 78). In some species (e.g., Lepidochelys

kempii and Caretta caretta) the lungs are more

closely attached to the vertebral column than in

other species. The lungs can either be examined in

the body, or by removing them. To remove the

lungs, free their lateral borders, being careful not

to cut into the lung tissue. The medial border of the

lung will be firmly attached to each side of the

vertebral column. Sometimes it helps to free the

trachea from the associated connective tissue prior

to breaking the fibrous connections between the

lung and the vertebrae. 

The trachea bifurcates into two bronchi. A

bronchus enters each lung and continues with

multiple internal openings into the lung. Each

bronchus extends almost to the posterior end. The

lungs are spongy and highly elastic.

Urinary bladder and kidneys. The urinary bladder

is suspended from the midline on the dorsal surface

of the pelvis (Fig. 79). It is located between the

rectum and the anterior pelvis (pubis). The bladder

opens into the cloaca and is not connected to the

kidneys. Urine flows from the kidneys, through the

ureters, to the cloaca. Urine enters the bladder from

the cloaca (see Urogenital Anatomy, Fig. 219).

The kidneys are located posterior to the lungs. They

are "retroperitoneal" which means that they lie

beneath the peritoneal lining next to the carapace. 

Fig. 79. A kidney in this young leatherback, is

exposed and its circulation injected to separate

arteries from veins. The urinary bladder is seen on

the midline, as is the collapsed large intestine to

one side. The dorsal aorta is along the vertebral

column and gives off many branches. 

dorsal

aorta

large

intestine

kidney

urinary

bladder
METHODS FOR DISSECTION

42 The Anatomy of Sea Turtles

They are deep relative to the gonads and slightly

medial from the posterior-most border of the

lungs. By making a cut in the peritoneum and

teasing it away, the lobular red kidneys (Fig. 79)

and their extensive systems of arteries and veins

can be exposed. The ureters, often difficult to find,

extend from each kidney to the cloaca.

At the anterior end of each kidney, and very near the

vertebral column, there is a small elongate adrenal

gland. The adrenal glands are often yellow or

orange. They are frequently easier to locate by

palpation than by sight (see Glands, Fig. 186). 

Brain. To examine the brain, cut off the head near

the base of the skull. Secure it with a vice or hold

it carefully on a no-skid surface. In Dermochelys

coriacea the brain and its tracts make a series of

dorsoventral turns as it proceeds from anterior to

posterior. A single cut will not expose this well

protected structure. In the cheloniids, one of the

easiest ways to expose the brain, in the absence of

special saws, is to make a straight cut from the top

of the snout, proceed along the inside of the top of

the orbits, then continue to the posterior end of the

head (Fig. 80). Once the skull cap is removed, the

small brain can be seen (Fig. 81) with its (anterior

to posterior) olfactory tracts to the nose, optic

lobes, cerebral hemispheres and cerebellum (see

Nervous System, Figs. 187 and 189). Sometimes

the fibrous covering, the dura mater, remains

covering the brain. This can be cut away. 

Fig. 80. The brain can be exposed by a cut parallel

to the skull’s long axis, running from the snout,

through the tops of the orbits and posteriorly

toward the middle of the supraocciptal crest.

Fig. 81. The brain, along the midline, is elongate

and white. Grossly, one can see the olfactory

tracts. The olfactory bulbs, cerebral hemispheres,

and optic lobes are covered by the dura mater; the

cerebellum is the single round structure at the end

of the exposed brain. If the brain is removed, then

lateral and ventral cranial nerves and the

pituitary can be seen. The two round, lobed

structures dorsal and posterior to the eyes are the

salt glands. The remaining dark tissue is muscle.

brain

salt

gland
SKELETAL ANATOMY

The Anatomy of Sea Turtles 43

Skeletal Anatomy

The skeleton is composed of bones and cartilages.

Typically, it is divided into 3 main parts: the skull,

axial skeleton and appendicular skeleton (Figs. 82-

84). In sea turtles, each of these bony groups is a

composite of several structures. The skull

includes the braincase, jaws, and hyoid

apparatus (Figs. 85-86). The axial skeleton is 

composed of the carapace, vertebrae, and ribs and

the derivatives of the ribs. The plastron (Fig. 83) is

a composite including derivatives of the axial and

appendicular skeleton (ventral ribs plus shoulder

elements). The appendicular skeleton includes the

flippers, hind limbs, and their supporting

structures (the pectoral and pelvic girdles). 

Fig. 82. This CT (computed tomography) scan of an

immature ridley turtle shows the three parts of the

skeleton: the skull, axial, and appendicular skeletons and

the spatial relationships of the bones. Cartilage (at the ends

of many bones) is not detected by this imaging technique

so bones appear loosely articulated. The arrangement of

the forelimbs is such that the shoulder joint is inside the shell.

The elbow flexes so the forearm moves from an anterolateral

position to a medial position. Lines crossing the posterior

skull and carapace are image processing artifacts.

Fig. 84. In this lateral view of an immature loggerhead,

the hyoid process can be seen clearly as it passes

posterior and ventral to the skull. Note that the orbits

contain a ring of bones (scleral ossicles) that support the

eyes. The right hind limb is directed laterally so it cannot

be seen clearly.

Fig. 83. Individual plastron bones are not fused in

immature turtles. The processes from the lateral plastron

do not yet articulate with the peripheral bones. The hyoid

apparatus (the body of the hyoid and both bony hyoid

processes), which is usually lost in skeletal preparations,

can be seen in the throat region. The distal phalanges of

the flippers were outside of the field of view in this CT

scan so the ends of the flippers are omitted.
SKELETAL ANATOMY

44 The Anatomy of Sea Turtles

Figs. 85a and 85b. Loggerhead skull (ventral)

showing parts of the ceratohyal or the body of the

hyoid, and paired hyoid processes of the hyoid

apparatus. Two cartilaginous hyoid processes are

lost in skull preparation. Hyoid bones are loose in

the prepared skull but are suspended between and

behind the lower jaws in life. The hyoid apparatus

supports the tongue and glottis and serves as

muscle attachment sites for some of the throat

muscles. Part of the atlas (ventral cervical

vertebra 1) is resting on the occipital part of the

skull, posterior to the hyoid apparatus.

Fig. 86. Hyoid apparatus. The hyoid body supports

the glottis in its concavity. Muscles attach to the

hyoid processes (ceratobranchial bones) that move

the throat. Cartilaginous processes are missing.

ceratohyal

bone

ceratobranchial

bone

a b

dentary 

bone

ventral cervical

vertebra 1
SKELETAL ANATOMY

The Anatomy of Sea Turtles 45

Figs. 87a and 87b. Lateral view of the cervical vertebrae from an

adult green turtle. Each vertebra is composed of a ventral body and

a dorsal arch. The ventral part of the atlas is missing from this series.

The atlas articulates with the occipital condyle at the back of the

skull. C7 articulates with the cervical vertebra fused to the carapace.

Fig. 88. The atlas (C1) and axis

(C2) complex and C3 - C4, in

lateral view. Dorsal is to the

right. The vertebral arches of the

successive cervical vertebrae

articulate via sliding joints

(arrows) that allow some dorsalventral bending of the neck, but

little twisting. Each vertebra is

composed of separate dorsal and

ventral elements.

atlas axis

C4

C5

C6

C7

C3

C2

C3

C4

b

a

Like all turtles, sea turtles have 7 mobile cervical

vertebrae (an 8th is fused to the carapace; Figs. 87-

88) and 10 thoracic vertebrae. There are 2-3 sacral

vertebrae and 12 or more caudal vertebrae (Figs.

89-90). The caudal vertebrae of females are short

and decrease in size distally; those of mature

males are large with robust lateral and dorsal

processes (Fig. 89). Each thoracic vertebra

articulates with a pair of ribs, bilaterally arranged.

Each rib head is aligned with the junction of two

vertebral bodies (Fig. 91). Fusions of vertebrae

and ribs with dermal bone result in unique

carapacial bones. Neural bones are associated

with the vertebral column, pleurals are formed by

the ribs and their dermal expansions, and

peripheral bones form the margin of the carapace

(Figs. 92-93). The anterior-most bone is the

nuchal and the posterior-most is the pygal.

Between the last neural bone and the pygal is the

suprapygal, which lacks any vertebral fusion

(Figs. 92-93). The lateral processes of the sacral

vertebrae are not fused to the carapace (Fig. 89). 

vertebral body

of atlas
46 The Anatomy of Sea Turtles

SKELETAL ANATOMY

S1

S2

S3

caudal

vertebrae

Figs. 89a and 89b. The sacral and caudal vertebrae of

an adult male green turtle. The large dorsal and lateral

processes are the sites of attachments for the muscles

that move the prehensile tail of mature males. S: sacral

The lateral extensions of the sacral vertebrae are formed

by rib-like processes that articulate with the ilium.

Fig. 90. Cleared and stained hatchling loggerheads.

(Left) Dorsal view with carapace removed showing

vertebral regions and the level of ossification at the

time of hatching. (Right) Dorsal view showing ribs,

vertebrae and initial dermal bone hypertrophy

along the ribs as the carapace develops. The

plastron was removed in this specimen. 

a b

In hatchlings and Dermochelys, the carapace is

composed of ribs and vertebrae. In cheloniids, as

they mature, the shell becomes increasingly

ossified. Dermal bone hypertrophies between the

ribs and grows outward to form the carapace (Figs.

90 and 92-93). The ribs grow laterally to meet the

peripheral bones (lying beneath the marginal

scutes) in Caretta caretta, Eretmochelys imbricata

and Chelonia mydas. In Lepidochelys kempii, the

peripheral bones also widen with age and

increasing size. The spaces between the ribs and the

carapace, fontanelles, are closed by a membrane

underlying the scutes. The fontanelles are closed

completely by bone in some adult ridleys and

loggerheads, but are retained posterolaterally in

green turtles and hawksbills (Fig. 93). 
SKELETAL ANATOMY

collapsed

spinal cord

rib

head

vertebral

body rib

Figs. 91a and 91b. Ventral view of the carapace showing the arrangement of the

ribs and vertebral bodies. The vertebral arch is incorporated into the vertebral

(neural) bones of the carapace and hence, is not seen in this view. The spinal cord

travels in the space formed between the neural bones and the vertebral bodies.

b

a

The Anatomy of Sea Turtles 47
Figs. 93a and 93b. Ventral view of this hawksbill

carapace shows the vertebral bodies (dorsal

elements), ribs, and fontanelles. The ribs have

fused with the peripheral bones anteriorly. D:

dorsal elements.

a

Figs. 92a and 92b. The bones of the carapace

dorsal view are identified in this Kemp’s ridley. The

bony arrangement of the shell is such that in some

species supernumerary neural bones are common. 

nuchal neural bones

pleural

bones

peripheral

bones

a b pygal suprapygal

attachment

to cervical

vertebra 8

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

ribs

fontanelles

b

SKELETAL ANATOMY

48 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 49

SKELETAL ANATOMY

The carapace is composed of bone covered by

keratinous scutes (cheloniids, Fig. 94) or blubber

and skin in Dermochelys (Fig. 95). The margins of 

cheloniid scutes and the bones' sutures do not align

with one another (Fig. 96). In the leatherback, the

blubber overlies ribs and vertebrae and itself is

covered dorsally with waxy skin and embedded

dermal ossicles (Fig. 95).

nuchal marginal

scutes

lateral

(costal

scutes) supracaudal

scutes

vertebral

scutes

Figs. 94a and 94b. The scutes are keratinous

epidermal structures that grow above the carapace

bones. Scutes grow two ways. They increase in size

(area) at their margins. The entire scute can

increase in thickness.

Fig 95. Dermal ossicles are bony plates

that reside deep to the skin in the

leatherback carapace.

a b
SKELETAL ANATOMY

50 The Anatomy of Sea Turtles

The plastron is composed of 4 pairs of bones in sea

turtles (from anterior to posterior: epiplastron,

hyoplastron, hypoplastron and xiphiplastron) and

1 unpaired bone (entoplastron; Fig. 97). The shape

of the entoplastron bone is sometimes used as a key

characteristic (Fig. 98) for species identification. 

Fig. 96. Immature loggerhead skeleton showing outgrowth of

dermal bone to form the shell. The spaces between the ribs and

the peripheral bones are the fontanelles. The pattern of the

scutes is barely visible but hints at the lack of alignment with

bony sutures. The distal parts of the flippers are cut off by the

field of view in this CT image. 

Figs. 97a and 97b. The plastron is composed of 9

bones that are separate in hatchlings but become

fused in older turtles. Anterior is toward the top of

the picture.

epiplastron

entoplastron

hyoplastron

hypoplastron

xiphiplastron

a b
SKELETAL ANATOMY

The Anatomy of Sea Turtles 51

Eretmochelys

imbricata

Chelonia

mydas

Lepidochelys

kempii

Caretta

caretta

Fig. 98. The distinct shape of the entoplastron bones

may serve as a key characteristic to distinguish some

cheloniid species. In E. imbricata and C. mydas the

elongated shaft is narrow. The bone is roughly Tshaped in hawksbills and the shaft narrows abruptly.

It is arrow-shaped in green turtles; wide anteriorly

with a shaft that narrows gradually. In L. kempii

and C. caretta, the shaft is wide. The overall shape

is almost dagger-like in the Kemp's ridley as the shaft

narrows gradually. The bone is cruciform in

loggerheads; the lateral processes are distinct and

the shaft tapers along its posterior half. The

entoplastron has not been described diagnostically

for the olive ridley. Entoplastron bones change

shape during ontogeny, hence it is recommended

that this characteristic be used only in adults.

In Dermochelys, there is no hypertrophy of bone between

the ribs of the carapace. The bony carapace remains

composed solely of an expanded nuchal, ribs, and

vertebrae. Ventrally, the plastron is composed of a ring

of reduced plastron bones. No entoplastron is present.

The anterior appendicular skeleton includes the

flippers and pectoral girdles. The pectoral girdles are

composed of two bones, the scapula, with its

acromion process, and the coracoid (= procoracoid);

these form a triradiate structure (Fig. 99).

Fig. 99. The pectoral girdle, (left to right) in ventral, posterior, and anterior views, is

composed of two bones and 3 parts that serve as a major site for attachment of the

swimming musculature. The acromion process extends medially from the ventral part

of the scapula. The coracoid a ventral bone, is flat and wide distally. The shoulder joint

(glenoid fossa), is formed by the coracoid and the scapula. (After Wyneken, 1988). 

glenoid

fossa

coracoid

acromion

process

acromion

process

scapula

glenoid fossa

coracoid
SKELETAL ANATOMY

52 The Anatomy of Sea Turtles

Fig. 100. Skeletons of

flippers (left and right)

shown in dorsal view.

Note the flat wide

wrist and the elongated

digits that form the

flipper blade. 

claw

radiale intermedium

radius

pisiform centrale

phalanges metacarpal

distal carpals

ulna

ulnare

I

II

III

IV

V

The scapula is aligned dorsoventrally and attaches to

the carapace near the first thoracic vertebra.

Ventrolaterally it forms part of the shoulder joint, the

glenoid fossa (Fig. 99). The acromion processes

extend medially from each scapula to articulate with

the entoplastron via ligaments. The coracoids form

the remainder of the glenoid fossa and then extend

posterior medially. Each terminates in a crescentshaped coracoid cartilage. The acromialcoracoid

ligament extends from the acromion to the coracoid.

The majority of the flipper retractor and abductor

muscles attach to the coracoid processes and the

acromialcoracoid ligaments.

The forelimb is composed of the humerus, radius

and ulna, carpals, metacarpals, and 5 phalanges

(Figs. 100-103). The flipper blade is formed by

widening and flattening of the wrist bones and

elongation of the digits (Fig. 100). The humerus,

which articulates with the shoulder at the glenoid

fossa, is flattened with its head offset by ~20° from

the bone's shaft (Fig. 101). There is a large bony

medial process extending beyond the humeral

head to which flipper abductor and extensor

muscles attach (Fig. 101). Distal to the head and

almost diagonally opposite is the lateral process

or deltoid crest to which attach flipper protractor

muscles (Figs. 101-103). In Dermochelys, the

humerus is extremely flattened. It is composed

primarily of cancellous bone, relatively little

cortical lamellar bone, and with thick vascular

cartilage on its articular surfaces (Figs. 104-105).

In prepared skeletons, the cartilage is often lost.

The extensive vascular channels in the cartilage

are indicative of chondro-osseus bone formation

(Fig. 104). This is unlike the cheloniid bone,

which is formed by deposition of relatively thick

layers (lamellae) of cortical bone around a cellular

bony core (cancellous bone; Fig. 105).

The flipper (Fig. 100) is composed of wrist

elements (radiale, ulnare, centrale, pisiform,

distal carpals) and elongated metacarpals and

phalanges (Figs. 100, 102-103). The radius and

ulna are short in sea turtles and, in adults,

functionally fused by fibrous connective tissue. 
SKELETAL ANATOMY

The Anatomy of Sea Turtles 53

intermedium

centrale

humerus

lateral

process

distal

carpals

radius

ulna

pisiform medial

ulnare

metacarpal

I

V

IV

II

III

Figs. 102a and 102b. Dorsal view of a leatherback flipper. 

a b

Fig. 101. The cheloniid humerus is

distinctive in its form with a slightly offset head and enlarged medial

process. Almost opposite the medial process and just distal to the

head is a U-shaped lateral process

(deltoid crest) to which attaches the

major ventral swimming muscles.

(After Wyneken, 1988). 

head

deltoid

crest

ulnar

condyle radial condyle

medial process
SKELETAL ANATOMY

54 The Anatomy of Sea Turtles

intermedium

humerus

medial

process

centrale

radius

ulna

pisiform

distal carpals

ulnare

metacarpal

I

V

IV

II

III

Figs. 103a and 103b. Ventral view of the leatherback flipper. The articulated forelimbs of

this leatherback shows some of the extensive cartilages at the bone ends and the extreme elongation of the digits. The large humerus has an almost primitive form with its flattened profile and extended medial process. The head and distal articulations to the radius and ulna

are largely cartilaginous. 

a b

The pelvis is composed of 3 pairs of bones; pubis,

ischium, and ilium. The pubic bones and the ischia

form the ventrally positioned part of the pelvis

(Fig. 106). The two ilia are oriented dorsoventrally,

articulate with the sacral vertebrae, and attach the

pelvis to the carapace via ligaments. All 3 bones

form the acetabulum (hip socket) on each side.

They are separate bones joined by cartilage in

hatchlings but quickly ossify and fuse to form a

single structure in older turtles. The pelvic bones of

the leatherback, however, remain connected by cartilage throughout life (Fig. 107) and become separate elements when skeletons are prepared.
SKELETAL ANATOMY

The Anatomy of Sea Turtles 55

Figs. 106a and 106b. This loggerhead pelvis, dorsal view, shows the 3 bones fused (pubis, ischium,

and ilium) that form each side. The epipubic cartilages that would form the anterior edge of the

pelvis in life are missing from this preparation.

The ilia articulate with the sacral vertebrae and

carapace. Anterior is toward the bottom of the picture.

Fig. 104. Chondro-osseus bone formation.

Vascular channels are seen in this cut end of a

leatherback humerus.

Fig. 105. Longitudinal sections through humerii.

The loggerhead humerus (top) has relatively more

lamellar bone (light color) than in the

leatherback humerus (bottom). The lamellar bone

is deposited in layers in some cheloniid species

and populations; in others, layers are not distinct.

a

ischium

lateral

pubic

process

pubis

thyroid

fenestra

pelvic

symphysis

ilium

acetabulum

b
SKELETAL ANATOMY

56 The Anatomy of Sea Turtles

The hind limb articulates with the pelvis via the

head of the femur which fits in the acetabulum. The

femur has a relatively straight shaft with a strongly

offset head. There are major and minor trochanters

distal to the head (Fig. 108); these are attachments

for most of the thigh retractors and adductors,

respectively. The distal femur articulates with the

tibia and fibula. The short ankle consists of the

calcaneum, astragalus, and distal tarsals. There are

five digits. The 1st and 5th metatarsals are wide and

flat and the phalanges are extended adding breadth

to the distal hind limb area (Figs. 109 - 110).

femoral

head

minor

trochanter

minor

trochanter

major

trochanter

major

trochanter

tibial

condyle

tibial

condyle

tibial

condyle

fibular

condyle

fibular

condyle fibular

condyle

Fig. 108. Left and right

femurs anterior view

(left) immature turtle,

posterior view (right)

mature turtle. The femur,

an hour glass-shaped

bone, has an offset head.

The trochanters become

more pronounced as the

turtles age.

Figs. 107a and 107b. The pelvis of the leatherback

is composed of both bone and cartilage throughout

life. Hence, skeletal preparations of the pelvis

usually result in 3 pairs of bones which do not

retain their spatial relationships. Anterior is

toward the top of the picture.

pubis

ischium ilium

a b
SKELETAL ANATOMY

The Anatomy of Sea Turtles 57

Figs. 109a and 109b. Dorsal view of a leatherback hind limb. The articulated hind limb

shows the extensive cartilages between bones that are typical of the leatherback skeleton.

The hind foot is wide and the digits somewhat elongated. Digits are designated by

numbers, with I being the digit on the tibial side and V on the fibular side.

a

calcaneum

fibula

tibia

astragalus

tarsals

metatarsal

femur

I

V

IV

II

b III
SKELETAL ANATOMY

58 The Anatomy of Sea Turtles

Figs. 110a and 110b. Ventral view of the leatherback hind limb. The femur is the

bony element of the thigh, the tibia and fibula are the bony elements of the shank.

The ends of these bones are cartilaginous. The ankle is somewhat flattened and

laterally expanded, resulting in wide placement of the digits. This architecture

contributes to the rudder-shape of the hind limb.

a

femur

calcaneum

fibula

tibia

astragalus

tarsal

metatarsal

V I

IV

II

III

b
MUSCLE ANATOMY

The Anatomy of Sea Turtles 59

Muscle Anatomy

The muscles are responsible for moving

structures, modifying the function of other

muscles, and stabilizing joints. Muscles originate

and insert via tendons. The origin of a muscle is its

fixed point while the insertion is typically the

point that it moves. Muscles can attach via their

tendons to bones, muscles, skin or eyes. Where

known, the innervations of the muscles are

reported. For reading ease, the designation of M.,

prior to muscles names, has been omitted. Names

and key concepts are given in bold the first time

the muscle is discussed.

Muscle functions are described with each figure.

As they apply to sea turtles, these functions are as

follows. Flexion bends one part relative to another

at a joint; extension straightens those parts.

Protraction moves one part (usually a limb) out

and forward; retraction moves that part in and

back. Abduction moves a part away from the

ventral surface; adduction brings the part toward

the body's ventral surface. Rotation turns a

structure. Depressor muscles open (a special form

of abduction) a structure, jaws in this case, while

levators close jaws (a kind of adduction).

Muscle groups. The muscles described here are the

major or large muscles (detailed discussion of most

muscles can be found in the primary literature). For

convenience, muscles are grouped by region; axial

muscles, include the head muscles; ventral

muscles include both proximal pectoral and pelvic

muscles that are associated with the plastron;

forelimb and respiratory muscles are those found

on the flippers, carapace, and scapula involved in

flipper movements and breathing. Posterior

muscles are the large muscles of the hip, thigh, and

lower leg. Muscles of the flipper blade and hind

foot are not discussed or illustrated in detail here

because they are obscured by extensive connective

tissue and are difficult for most to identify, even

with special dissection equipment and techniques.

Ventral Muscles. The massive ventral musculature

is found after removing the plastron (Fig. 111). This

musculature is dominated by a superficial muscle, the

pectoralis major, which originates on the plastron

and inserts on the lateral process and shaft of the

humerus. Anterior to the pectoralis and ventral to the

acromion processes are two muscles: the deltoideus

(ventral part), which originates on the ventral

scapula, acromion, and anterior plastron bones and the

supracoracoideus, which has several subdivisions.

Its anterior part originates on the acromion (Figs.

112-114). Both the deltoideus and the anterior part

of the supracoracoideus insert on the lateral process

of the humerus. These 3 ventral muscles function in

swimming and respiration (by movement of the

shoulders and plastron). Their innervations are via

the supracoracoid nerve from the ventral portion of the

brachial plexus (see Nervous System, Figs. 204-206). 

After removing the pectoralis major, deep locomotor

muscles are found associated with the pectoral girdle

(Figs. 112-114). The biceps brachii has several

subdivisions, or heads, in sea turtles. The superficial

head (Figs. 112-114) originates on the coracoid and

extends via a long tendon to insert on the radius and

ulna; the profundus head inserts on the humerus and

radius. Innervation is via the inferior brachial flexor

and median nerves. The coracobrachialis magnus

originates on the dorsal side of coracoid process and

inserts on the medial process of the humerus. The

posterior part of the supracoracoideus (Fig. 112)

originates on the coracoid and its cartilage and inserts

in the lateral process of the humerus. These muscles

are innervated by the supracoracoid nerve. There is an

extensive series of arteries and veins running within

and between these very active muscles (Fig. 114).

A pair of superficial posterior muscles, the left and

right rectus abdominis (Fig. 111) are found ventrally.

Each originates on the lateral pubis and inserts on

the plastron. They stabilize the pelvis and may

function in compressing the plastron during breathing.
60 The Anatomy of Sea Turtles

MUSCLE ANATOMY

supracoracoideus deltoideus pectoralis

major

rectus

abdominus

a b

Figs. 111a and 111b. Superficial ventral muscles of

the pectoral and pelvic girdles. The large pectoralis

major is a forelimb retractor and adductor. Both

the deltoideus and the supracoracoideus protract

and abduct the humerus. The rectus abdominus is

a pelvic stabilizer. Anterior is toward the top of

the picture.
MUSCLE ANATOMY

a

Figs. 112a and 112b. The deep pectoral muscles are exposed after removal of the pectoralis major. These forelimb retractors, separated on the animal's left (right in picture),

are the biceps brachii superficialis and coracobrachialis magnus. The posterior part of

the supracoracoideus both adducts and retracts the flipper.

deltoideus head

acromion

process

coracobrachialis magnus

coracoid

process

supra

coracoideus

(posterior

part)

pectoralis

major

(cut away

medially)

biceps brachii

superficialis

acromial

coracoid

ligament

supra

coracoideus

(anterior part)

b

The Anatomy of Sea Turtles 61
MUSCLE ANATOMY

62 The Anatomy of Sea Turtles

Fig. 113. Diagrams of cheloniid right shoulder

muscles including locomotor and respiratory

muscles. Superficial ventral muscles (top left),

deep ventral muscles (bottom left), posterior

muscles (bottom right), and lateral muscles (top

right). The extensor digitorum, extensor radialis

intermedius, tractor radii, and flexor carpi all

control the extension and flexion of the flipper

blade. Ext.= extensor, h.= head, Inf.= inferior,

Interm.= intermedialis. (After Wyneken, 1988)

brachialis

inf.

tractor

radii

triceps

scapular h.

deltoideus

ventral part

acromion

pectoralis major

ext. radialis

interm.

triceps

humeral h. ext. digitorum

acromialcoracoid

ligament

supracoracoideus

anterior part

triceps

humeral h.

carapace

testoscapularis

(cut)

testocoracoideus

subscapularis

latissimus

dorsi

teres

major

triceps

scapular h.

flexor carpi

ulnaris

biceps superficialis

biceps

profundus

tractor radii extensor

digitorum

ext.

radialis

interm.

biceps

profundus

biceps

superficialis

acromialcoracoid

ligament

brachialis inf.

triceps

humeral h.

triceps

scapular h.

coracoid

cartilage

deltoideus

supracoracoideus

anterior part

supracoracoideus

posterior part

testoscapularis

(cut)

subscapularis

latissimus

dorsi

teres major

triceps

humeral h.

extensor

radialis

interm.

extensor

digitorum

brevis

coracobrachialis

biceps

profundus

biceps

superficialis

triceps

scapular h.

flexor

carpi

ulnaris

testocoracoideus

coracobrachialis
MUSCLE ANATOMY

The Anatomy of Sea Turtles 63

a

Figs. 114a and 114b. The deep pectoral muscles of the animal's right side are shown in detail. The

supracoracoideus has two parts: posterior, which protracts and anterior, which retracts the forelimb. 

pericardium

coracoid

process

b

cut acromial

coracoid

ligament

pectoral arteries

and veins

biceps

superficialis

supracoracoideus

(anterior part)

supracoracoideus

(posterior part)

acromion

process
MUSCLE ANATOMY

64 The Anatomy of Sea Turtles

Forelimb and Respiratory Muscles. The

latissimus dorsi/teres major complex, the

scapular head of the deltoideus, and the

subscapularis originate on the carapace and/or

shoulder girdle and insert on the proximal

humerus (Fig. 113). The latissimus dorsi and teres

major together originate on the scapula and the

carapace from the attachment point of the scapula,

along the first pleural bone to the anterior

peripheral bones. They insert via a common

tendon just distal to the head of the humerus. The

scapular head of the deltoideus arises from the

anterior scapula and inserts on the lateral process

and shaft of the humerus. The subscapularis

muscle is very large, originates on the medial and

posterior scapula, and inserts on the large medial

process and the shaft of the humerus. These

muscles are innervated by the deltoid nerve (a

branch of the brachial plexus). 

There are two sheet-like respiratory muscles located

dorsally, which are often destroyed when removing

the pectoral girdles (Figs. 113 and 115). These are

the testocoracoideus (origin: carapace near the

anterior inframarginals; insertion: dorsal coracoid)

and testoscapularis (origin: carapace posterior to

the latissimus dorsi; insertion: dorsal scapula and the

scapular attachment to the carapace). They are

innervated by cervical spinal nerves. 

The remaining dorsal shoulder muscle, the

triceps brachii (= triceps superficialis) has two

heads in cheloniid sea turtles (Figs. 113-116). The

humeral head arises from the humerus, and the

scapular head arises from the scapula. Both

converge to form a common tendon inserting on

the proximal ulna. This muscle may have only a

humeral head in Dermochelys. The triceps is

innervated by the superficial radial nerve (a branch

from the superior brachial nerve of the brachial

plexus).

Fig. 115. Ventral pectoral muscles with arteries

and veins. The pectoral artery is found running

along the deep muscles of the shoulder. The

testoscapularis, a respiratory muscle, is deep to the

pectoralis. Other pectoral muscles originating on

the coracoid are reflected medially (to the right) in

this picture.

testoscapularis 

muscle
MUSCLE ANATOMY

The Anatomy of Sea Turtles 65

Fig. 116. Superficial dorsal forelimb

muscles (right). The two heads of the

triceps brachii, (triceps scapular head and

triceps humeral head) are forelimb

adductors, which twist the flipper. The

more medial biceps and flexor carpi

ulnaris muscles flex the flipper blade. The

extensor digitorum muscle becomes

diffuse in adults as fibrous connective

tissue stiffens the flipper blade. Young

turtles can extend the digits, somewhat

mature turtles cannot.

Fig. 117. Ventral forelimb muscles (right). Most of

the ventral muscles flex the flipper blade relative to

the upper arm. The extensor radialis extends the

flipper. The scapular head of the triceps may twist the

flipper blade along its axis, or abduct the forearm.

Fig. 118. Dorsal forelimb muscles of an immature

hawksbill. In young animals, the muscle divisions of the

forearm and the flipper, particularly, are more obvious

than in older animals. Less connective tissue is present

and the digits can flex and extend to a limited extent.

triceps

scapular

head

extensor

digitorum

extensor radialis

intermedias

brachialis

inferior

tractor

radii tendon

triceps

scapular

head

triceps

numeral

head

flexor

carpi

ulnaris

triceps

humeral

head

biceps

superficialis

and profundus

biceps

profundus

triceps

scapular head extensor

carpi

ulnus

flexor carpi

ulnaris

I

II

III

IV

V

IV

triceps

humeral

head

extensor

digitorum

brevis

& longus

biceps

superficialis
MUSCLE ANATOMY

latissimus

dorsi

scapula

cervical

vertebra

(cut)

head

triceps

brachii

scapular

head

triceps

brachii

humeral

head

teres

major

muscle

subscapularis

muscle

coracobrachialis

magnus muscle

latissimus

dorsi

(cut)

Figs. 119a and 119b. Dorsal view of the pectoral musculature. The carapace, skin

and fat have been removed (from left). The head, cut cervical vertebra, and

scapular ends provide landmarks for orientation. The latissimus dorsi, a large

sheet-like muscle, is shown intact (animal's right) and cut (animal's left). It, plus

the teres major and deltoideus (scapular head, not shown), abduct and sometimes

protract the flipper. The large subscapularis is a strong flipper protractor. The

coracobrachialis, a ventral muscle, is seen extending from the shoulder

posteriorly, toward its origin, the coracoid.

a

b

66 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 67

MUSCLE ANATOMY

The biceps muscle may have one or two parts

(Figs. 112 and 114). When two heads are present,

the biceps superficialis arises from the coracoid

and inserts on the pisiform of the wrist. The muscle

has two bellies in series, with a short tendon in the

middle. The second and most prominent head, the

biceps profundus, also originates on the posterior

coracoid, but ventral to the biceps superficialis and

inserts via a tendon with the brachialis on the ulna

(Fig. 114). In Dermochelys and Lepidochelys, often

there is just a single head inserting on the radius

and ulna. 

left

flipper

carpal

extensors

coracobrachialis

muscle

biceps biceps profundus superficialis

(cut)

distal

humerus

teres

major

subscapularis

latissimus

dorsi

(cut)

triceps

brachii

(cut)

scapula

Figs. 120a and 120b. The

pectoral muscles of the left

shoulder, arm and flipper.

The large subscapularis

covers most of the scapula.

The large coracobrachialis

is seen ventrally, covering

much of the coracoid. The

biceps muscle has one or

two heads (varying among

species and among

individuals). The biceps

superficialis extends from

the shoulder (mostly the

coracoid) to the pisiform

bone of the wrist, and

probably helps control the

twist or rotation of the

flipper blade. The biceps

profundus (seen only as a

partial separation here) acts

as a flipper retractor and a

flexor of the flipper blade at

the elbow.

a

b
MUSCLE ANATOMY

Axial Muscles. Most axial muscles are associated

with the neck and tail of sea turtles. The majority

of the neck muscles are illustrated with the neck

circulation (Figs. 131, 141, 143-153). These

include the transverse cervical muscles, and the

biventer cervical muscle. Here, the superficial

muscles of the throat and the jaw muscles are

described. The tail musculature is not discussed

because it has not been studied in any detail.

The major deep muscles of the neck are the longus

colli and retrahens colli. The longus colli muscles

are short, segmentally arranged, and travel

obliquely between successive cervical vertebrae;

they serve to extend the neck. The retrahens colli

originate on the cervical vertebrae and extend

posteriorly to insert on the dorsal vertebral

elements of the carapace. They are neck flexors

and retractors, to the extent that marine turtles

extend and retract the neck.

Head Muscles. Just beneath the skin of the throat

is a thin layer of muscle, the intermandibularis,

which has fibers running between the two dentary

bones. It inserts on a flat midline tendon (raphe)

that runs the length of the throat (Fig. 121). The

intermandibularis becomes the constrictor colli

posterior to the jaw joint (Fig. 121), originating on

a dorsolateral cervical tendon. Just deep to the

intermandibularis are muscles running obliquely

between the jaws and inserting on the hyoid, the

geniohyoideus. Posterior to the geniohyoideus is a

pair of strap-like muscles, the coracohyoideus

that extend to the hyoid apparatus from the

coracoid (Figs. 122-123). These muscles assist in

depressing the jaw, swallowing, and pumping the

throat (gular flutter). They are innervated by the

facial nerve. Muscles of the tongue, innervated by

the hypoglossal nerve, and the glossopharyngeal

nerve are not described here.

The jaw muscles of turtles are mostly located

inside the skull. Because of these deep positions,

most are described but not illustrated. Unlike

mammals, turtles lack a mandibularis muscle;

instead they have an adductor mandibulae with

several heads. The heads originate on the parietal,

supraoccipital, quadrate, prootic, and opisthotic

bones (Fig. 31) and converge on a tendon that

inserts primarily on the lower jaw (dentary, with

small insertions on the squamosal bone posterior

to the jaw joint). Medial to the adductor

mandibulae complex is a pair of connected

muscles. The intermandibularis muscle runs from

the lower jaw to the tendon of the

pseudotemporalis muscle which itself continues

to the parietal bone. These jaw closing muscles are

all innervated by the trigeminal nerve. The jaws

Fig. 121. Ventral and superficial neck muscles.

The constrictor colli muscle of the ventral neck is

exposed lateral to and overlying the trachea.

Connective tissue that loosely attached the muscle

to the skin is still present on the turtle’s anterior

neck. The midline raphe (tendon) is visible along

the anterior half of the muscle.

raphe

intermandibularis

muscle

depressor

mandibulae

muscle

constrictor

colli

muscle

68 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 69

MUSCLE ANATOMY

constrictor

colli muscle

trachea

esophagus

hyoid

body

process

lateralis

posterior

branchiohyoideus

muscle cut

and reflected

anteriorly

carotid

artery coracohyoideus

muscle

Figs. 122a and 122b. Dissection of the ventral neck muscles, showing the deep muscles

(right in picture) and superficial muscles (left). The parallel fibers of the intermandibularis

arise from the lower jaw, and terminate in the cut raphe (found overlying the hyoid

body and anterior trachea). The branchiohyoideus is cut between the hyoid body and

the hyoid process (process lateralis posterior) on the turtle’s left. The coracohyoideus

travels along the trachea to the hyoid. The carotid artery lies deep to these muscles.

a b

are opened by the depressor mandibulae muscle,

which has several parts. The depressor mandibulae

arises from the quadrate, quadratojugal, and

squamosal bones and inserts on the articular of the

lower jaw; in Dermochelys a portion also inserts on

the auditory tube. These parts are innervated by the

facial nerve.
MUSCLE ANATOMY

Figs. 123a and 123b. This oblique axial section

through the neck of a hawksbill, is just posterior to

the jaw joint ventrally and supraoccipital crest

dorsally. The muscles, major blood vessels, trachea,

and esophagus can be identified. Their relative

positions and extent are seen in this dissection.

supraficial

adductor

mandibulae

hyoid

element

trachea

carotid artery esophagus

(collapsed)

coracohyoideus

muscle constrictor colli

geniohyoideus

muscle

depressor

mandibulae

articular

process

transverse

cervical

muscle

pterygoideus 

muscle

(ventral part)

adductor

mandibulae

spinal

canal

basiocciptal

exoccipital

otic cavity

quadrate

longus

colli

muscle

splenius

capitus

muscle

a b

external

jugular

vein

70 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 71

MUSCLE ANATOMY

Posterior Muscles. The major posterior muscles can

be identified after removing the rectus abdominus and

the skin covering the hind legs and tail. Ventrally, these

are the puboischiofemoralis externus and internus,

the pubotibialis, the flexor tibialis complex and the

ambiens (Figs. 125-126; see also Nervous System).

These ventral hip muscles are innervated by the

obturator and tibial nerves of the sacral (=lumbosacral)

plexus. The puboischiofemoralis externus, a thigh

adductor, covers much of the ventral pelvis, and arises

from the ventral pubis, ischium, and membrane

covering the thyroid fenestrae (Fig. 106); it inserts

on the femur’s minor trochantor. Different parts of

this muscle can either protract or retract the leg.

The puboishiofemoralis internus is large in

cheloniids and has both superficial and deep

components. It may be absent in Dermochelys and

replaced in function and position by the

iliofemoralis. When present, it originates on the

dorsolateral pubis, ilium, and the sacral vertebrae. It

inserts on the femur's major trochanter. 

The pubotibialis, part of the flexor tibialis complex,

is found in cheloniids but is absent in Dermochelys.

This muscle originates on the pubic symphysis and

lateral pubis; it inserts on the tibia with the flexor

tibialis internus. The flexor tibialis internus, a Yshaped muscle, originates on the sacral and postsacral

vertebrae dorsally, and ventrally on the pelvic

symphysis and lateral pubis. It passes distally and

wraps around the gastrocnemius muscle to insert on

the tibia. The flexor tibialis externus has two heads

(Figs. 125-126) and is somewhat medial to the

internus. The dorsal head arises from the ilium and the

ventral head from the posterior ischium. Both

converge to insert, via a single tendon, on the tibia and

the gastrocnemius muscle of the shank; some fibers

insert on the skin and connective tissues of the shank.

The adductor femoris (Fig. 126) originates on the

lateral ischium and inserts on the posterior femoral

shaft. The ischiotrochantericus (not shown), a leg

retractor, originates on the anterior pubis and pubic

symphysis. It inserts on the major trochanter of the

femur. The dorsal hip and thigh muscles (illustrated

in Circulatory Anatomy; Figs. 156-157 and Nervous

System; Fig. 207), include the hip abductors:

iliotibialis, femorotibialis, and ambiens. The

ventrally positioned ambiens (Fig. 125) originates

on the pubioischiadic ligament, and inserts on the

"patellar" tendon across the knee to the anterior tibia.

The iliotibialis originates on the dorsal ilium and

inserts with the ambiens on the patellar tendon. Deep

to these two muscles, the femorotibialis (see

Nervous System, Fig. 207), arises from the dorsal

and anteroventral surfaces of the femur, and inserts

with the iliotibialis and ambiens. The peroneal and

femoral nerves of the sacral plexus innervate most

of these dorsal hip muscles.

The hind foot extensors (Fig. 124) are large sheet-like

muscles originating on the dorsal and lateral femur

and inserting on the dorsal and anterior fibula and

digits. They flex the lower leg or extend the digits.

Fig. 124. Anterior and dorsal foot extensors of a

loggerhead right hind limb. The leg is abducted and

flexed at the knee. The foot extensors flex the lower

leg or extend and spread the digits.

knee

foot

left thigh

(medial) extensor

digitorum
MUSCLE ANATOMY

puboischiotibialis

ambiens

abdominal vein

flexor tibialis tail

puboischiofemoralis externus

(cut)

puboischiofemoralis 

internus

Figs. 125a and 125b. The superficial ventral hip muscles. The puboischiofemoralis

externus is an adductor of the leg. The puboishiofemoralis internus (the anterior

ventral portion is seen here) is a protractor and abductor of the leg. The flexor tibialis

complex, including the pubotibialis, flexes and retracts the leg and controls the shape

of the trailing edge of the foot, perhaps during steering. More anteriorly, the ambiens

is a weak adductor and protractor of the hind leg and can extend the shank. 

a

b

72 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 73

MUSCLE ANATOMY

a

pubotibialis

(cut)

adductor

femoris

ischial

tuberosity

sciatic

nerve and

peroneal 

nerves

flexor tibialis

(cut)

flexor tibialis

(cut)

tail

puboischiofemoralis

internus

Figs. 126a and 126b. The deeper ventral hip muscles are shown after removing

the superficial limb retractors. The adductor femoris and puboishiofemoralis

internus are antagonistic muscles, with the former adducting the thigh and the

later abducting it. 

b
CIRCULATORY ANATOMY

Circulatory Anatomy

The circulatory anatomy includes the heart, arteries,

veins, and lymphatic vessels. The heart is

multichambered and serves as the main pump.

Arteries have thick walls of muscles and elastic fibers;

they carry blood away from the heart.Veins carry

blood to the heart; they have thinner layers of muscle

and elastic tissues and tend to collapse in dead animals.

Most veins contain valves. The lymphatic vessels

transport tissue fluid from outside the circulatory

system back to the blood. The lymphatic vessels are

very thin walled and difficult to photograph. They

surround the arteries and veins like sheaths.

Heart. The heart is located within the pericardium

and bordered ventrally by the acromion and coracoid 

processes (Figs. 127-129). Dorsally it is bordered by

the lungs and laterally by the lobes of the liver.

Within the pericardial sac, the heart is bathed with

clear, colorless to slightly yellow pericardial fluid.

All turtle hearts have four parts or chambers (Fig.

127): a sinus venosus, two large atria and a

ventricle. The ventricle is thick-walled and

internally subdivided into three compartments, the

cavum venosum, cavum arteriosum and cavum

pulmonae (not shown). These three ventricular

compartments are separated only partially from

one another.

The posterior part of the pericardium and ventricle

apex are attached to the peritoneum by the

gubernaculum cordis (Fig. 129). This structure

anchors the heart during ventricular contraction.

brachiocephalic

trunk

pericardial

fluid

ventricle

pulmonary

artery

left

atrium

left aorta

right atrium

pericardium

right aorta

abdominal

veins

Figs. 127a and 127b. Ventral heart. The heart is

exposed after removing the pericardium. The more

dorsal sinus venosus is not visible. Both aortas

turn dorsally and are obscured partially by the

brachiocephalic trunk. The pulmonary arteries

arise from a common base, the pulmonary trunk.

The abdominal veins from the posterior muscles

are exposed posterior to the heart.

a b

74 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 75

CIRCULATORY ANATOMY

vent

pubis

right aorta

left

aorta

pulmonary

artery

left atrium

ventricle

right

atrium

acromion

processes

epipubic

cartilage

abdominal

vein

Figs. 128a, 128b, and 128c. Landmarks for

location of the heart after removal of the plastron.

The two acromion processes and acromialcoracoid ligaments frame the pericardium

ventrally. When the plastron is removed carefully,

the paired abdominal veins are preserved. They

drain the ventral pelvic muscles; blood flows

anteriorly returning toward the two lobes of the

liver. View c shows a close-up of the heart after

removal of the ventral pericardium.

a b

c
CIRCULATORY ANATOMY

Arteries. Arising from the anterior and ventral part

of the heart are the great vessels: two aortas and a

pulmonary trunk (Fig. 129). The right aorta

supplies blood to the head, limbs, and lower body,

the left aorta to the viscera. The pulmonary trunk

divides into the right and left pulmonary arteries

taking the blood to the right and left lungs,

respectively.

The branches of the major vessels are good

landmarks for locating organs and hence can serve

like a map to locate specific structures. The right

aorta gives off a branch right away called the

brachiocephalic trunk and then continues

posteriorly to the lower body where it joins the left

aorta. The brachiocephalic trunk bifurcates; each

branch produces a small thyroid artery to the

thyroid gland anteromedially (Fig. 130). The

branches of the brachiocephalic continue laterally

as subclavian arteries (Figs. 129-130). The

brachiocephalic trunk acts as a landmark for

locating the thyroid and thymus glands (Glands;

Figs. 159-160). 

pectoral

muscle

sinus

venosus gubernaculum

cordis pericardium

ventricle

pulmonary

trunk

brachiocephalic

trunk

carotid

artery

left atrium

left

systemic

aorta

right

systemic

aorta

precaval

veins

esophagus

trachea

acromion

process

right

atrium

Figs. 129a and 129b. The four chambers of the

heart can be identified in this ventral view. The

ventral pericardium has been trimmed away to

show both the heart and its great vessels. The apex

of the ventricle is anchored to the pericardium and

peritoneum posteriorly. The venous drainage from

the anterior body to the precaval veins can just be

seen lateral and anterior to the left atrium.

a b

76 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 77

CIRCULATORY ANATOMY

thyroid gland

esophageal

arteries

carotid

artery

ventral

cervical

artery thyroid

artery

thyroid

artery

pulmonary

trunk

left

atrium

ventricle

right

atrium

brachiocephalic

trunk

right

aorta

subclavian

artery

Figs. 130a and 130b. Anterodorsal view of the

heart and its major arteries. The great vessels

emerge as three large vessels. The right aorta

gives rise to the brachiocephalic trunk before it

bends posteriorly. The thyroid arteries arise from

the brachiocephalic trunk shortly after it

bifurcates, (or, in this case, from the carotid

arteries). It then gives rise to the left and right

subclavian arteries. The right carotid is not

dissected free of its connective tissue.

The carotid arteries (Figs. 129-130), then the

ventral cervical arteries, arise from either the

brachiocephalic trunk or the subclavian arteries

lateral to the thyroid arteries (Fig. 130). The

carotids (often termed common carotids) supply

blood to the head. They bifurcate near the skull to

form the external and internal carotid arteries.

The ventral cervical arteries travel anteriorly then

bifurcate to supply branches to the esophagus. The

subclavian arteries continue laterally towards the

flippers; near the junction of the scapula and

coracoid they become the axillary arteries. There,

branches to the scapular musculature arise

(anterior subscapular artery). The axillary artery

gives off both a branch to the carapace just prior to

entering the forelimb, the marginocostal artery

which travels posteriorly along the lateral aspect of

the shell, and a branch to the ventral pectoral

muscles, the pectoral artery (Fig. 131). As the

axillary artery crosses the humerus, it becomes the

brachial artery supplying radial, ulnar, then

distally the digital arteries of the flipper.

a b
CIRCULATORY ANATOMY

internal

carotid artery

esophageal artery

common

carotid

artery

thyroid artery

subclavian artery

brachial artery

left

pulmonary

artery

radial artery

ulnar artery

digital

arteries

pulmonary trunk

marginocostal

left aorta

gastric artery

posterior gastric artery

pancreaticoduodenal

artery

common iliac

artery

coeliac artery

femoral artery

sciatic artery vertebral

artery

epigastric artery

gonadal artery

adrenal artery

dorsal aorta

inferior mesenteric artery

superior mesenteric artery

right aorta

brachiocephalic trunk

costal artery

external

iliac artery

internal

iliac

artery

renal

arteries

external carotid artery

}

Fig. 131. Major arteries, ventral view. The major

arteries are shown diagrammatically. Some

subdivisions are not labeled for diagram clarity.

These include the ventral cervical, axillary, anterior

scapular, pectoral, anterior pancreaticoduodenal,

and haemorrhoidal arteries.

The major arterial and venous paths are

summarized diagrammatically in Figs. 131-132.

These diagrams show the most common routes

taken by vessels. However, the circulatory system

is among the most variable of all organ systems

and hence, sometimes vessels branch in unique

and unexpected manners.

78 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 79

CIRCULATORY ANATOMY

internal jugular vein external

jugular

vein

axillary vein

scapular vein

subclavian vein

dorsal brachial vein

antebrachial

vein

internal

brachial vein

pulmonary vein

left atrium

transverse abdominal vein

splenic vein

intercostal veins

marginocostal vein

hepatic portal vein

duodenal vein

external iliac vein

epigastric vein

abdominal vein

dorsal vertebral vein

sinus venosus

precava

postcava

thyroscapular vein

efferent renal & gonadal veins

ischiatic vein

renal

portal vein

cloacal vein

popliteal vein

crural vein

caudal vein

femoral vein

}

Fig. 132. Major veins, ventral view. Note that all

branches are not shown or labeled to minimize

diagram complexity. These include the azygos,

transverse and central vertebral, eosophageal,

hepatic, pectoral, pericardial, vesicular, pelvic,

lipoidal, hypogastric, gastric, anterior and

posterior pancreatic, mesenteric, common

mesenteric, and inferior mesenteric. 
CIRCULATORY ANATOMY

Fig. 133. This lateral view

of a green turtle has all

superficial neck muscles cut

and reflected dorsally. The

arteries and veins were

injected with latex to provide

contrast. The carotid artery

(at arrow) is deep and lies

adjacent to the longus colli

muscles of the cervical

vertebrae. 

The left aorta, the middle of the three great vessels,

turns dorsolaterally and passes the level of the

stomach before producing three branches: the

gastric artery, the coeliac artery and the superior

mesenteric artery. The gastric artery bifurcates

quickly and sends branches to the greater (lateral

aspect) and lesser (medial aspect) curvatures of the

stomach (Figs. 135-136). The coeliac artery

branches shortly after leaving the left aorta and

forms the anterior pancreaticoduodenal artery

to the pancreas, duodenum and stomach and the

posterior pancreaticoduodenal artery to the

distal pancreas, duodenum, liver, and gallbladder

(Fig. 136). The superior (or anterior) mesenteric

artery gives off many branches that fan out through

the intestinal mesenteries and supply the small

intestines. After giving off the superior mesenteric

artery, the left aorta continues posteriorly where it

joins the right aorta (typically) to form a single dorsal

aorta. The position where the two join is variable,

but generally is within the middle third of the body.

trachea

dorsal

aorta

left aorta

right

aorta

gastric artery

coeliac artery

superior

mesentric

artery

Fig. 134. The ventral view of the left aorta and its

major branches in a loggerhead after removal of the

heart and viscera. Anterior is

toward the top of the picture.

The right aorta joins the left

aorta very early in this

loggerhead, just posterior to

the origin of the superior

mesenteric artery.

80 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 81

CIRCULATORY ANATOMY

liver

right lobe

liver 

left lobe

stomach gastric

artery

acromio-coracoid

ligament

left

coracoid

process

pyloric

artery

Figs. 135a and 135b. Circulation of the stomach. The ventral gastric artery drains

to the lesser curvature of the stomach. It becomes the pyloric artery at the level of

the pyloric sphincter. 

a

b
CIRCULATORY ANATOMY

deep

pectoral

muscle

(right)

duodenum

reflected

anteriorly

& ventrally

pancreas

stomach

spleen

pyloric artery

and coronary

ventricular

vein

dorsal

gastric artery

posterior

pancreaticoduodenal artery coeliac artery

anterior

pancreaticoduodenal artery

Figs. 136a and 136b. Arteries and veins of the stomach, pancreas, and duodenum.

The dorsal gastric artery drains to the greater curvature of the stomach. The coeliac

artery, the second artery arising from the left aorta, supplies these branches to the

duodenum, the stomach near the pyloris, and to the pancreas.

a

b

82 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 83

CIRCULATORY ANATOMY

The dorsal aorta (Figs. 134, 137-138) continues

posteriorly and gives off paired branches, the

costal arteries of the carapace, gonadal arteries

to the ovaries or testes (there may be more than

one per gonad), a pair of adrenal arteries, and

three or more renal arteries to each kidney (Figs.

137-138). A pair of epigastric arteries branches

off the dorsal aorta at the level of the kidneys;

they travel laterally to join the marginocostal

artery of the carapace.

Right external

jugular vein with

vertebral branches

scapula

esophagus

caudal artery

renal arteries

right kidney

left kidney

adrenals

dorsal aorta

costal artery

left

lung

right

lung

right aorta

left

aorta

Figs. 137a and 137b. The carapace has been

removed from this green turtle and the arteries

injected with latex. The right and left aortas join

along the middle third of the body. Costal

(intercostal) branches extend anteriorly and across

the body. Branches to the gonads, adrenals,

kidneys, and hind limbs arise, then the caudal

artery continues posteriorly along the midline to

the tail and cloaca. This animal was missing its

right hind limb.

a b
CIRCULATORY ANATOMY

vertebral

arteries

lung

dorsal

aorta

adrenal

glands

adrenal

artery

gonadal

artery

right

kidney

left kidney

renal

arteries

common

iliac artery

external

vertebral artery iliac artery

Figs. 138a and 138b. The carapace has been

removed from this green turtle. The arteries are

injected with latex to show the arterial branches to

the gonads, adrenal glands, and kidneys.

Variability is common in the circulatory system

and is shown here. In this animal, the right

gonadal artery is long and crosses dorsal and to

the right adrenal gland, rather than extending

lateral or anterior to it. There are 3 asymmetric

(rather than symmetric) pairs of renal arteries

supplying the kidneys. The epigastric arteries do

not arise in the typical manner from the dorsal

aorta, but instead from the left common iliac. The

common iliacs continue as the external iliacs then

divide to form the femoral and sciatic arteries. The

internal iliacs arise directly from the dorsal aorta,

in this case, turn ventrally, and supply blood to the

bladder and large intestine. The caudal (vertebral)

artery continues posteriorly along the midline.

a b

84 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 85

CIRCULATORY ANATOMY

The arteries to the pelvic limbs, the external and

internal iliac arteries, may leave the dorsal aorta

on each side via paired trunks (common iliacs), or

they may branch off separately (Figs. 138-139).

The external iliac supplies the femoral and sciatic

arteries to the hind leg (Fig. 130). The internal iliac

provides branches to the bladder and gonadal ducts,

and the haemorrhoidal artery to the large

intestine. The dorsal aorta then extends to the tail as

the vertebral (caudal) artery (Figs. 131, 138-139).

Pulmonary Trunk. The pulmonary trunk divides

shortly after leaving the heart and supplies the

right and left pulmonary arteries to the lungs (Figs.

129-130). The pulmonary arteries enter the lungs

along the dorsal side of the bronchus, and travel

posteriorly with the bronchi giving off multiple

branches throughout the lung. The pulmonary

artery walls are thickened as a muscular sphincter

near the lungs. The lumen of each of the great

vessels near the heart should be roughly uniform

in thickness, except for the pulmonary arteries as

they approach the lungs. 

Pulmonary Veins. Capillaries, venules (small

veins), and veins within the lung coalesce into

branches that drain into the pulmonary veins (not

shown). The pulmonary veins travel along the

ventral surface of each bronchus, then exit the lung

anteriorly and arch medially. They enter the left

atrium dorsolaterally.

Systemic Veins. The venous circulation is

described by tracing the veins away from the heart.

However, it should be remembered that venous

blood typically flows toward the heart. (It is

noteworthy that flow direction can reverse in some

veins.) Multiple terms are used to describe the

major veins. The synonyms are given to clarify

terminology. Venous blood from the body drains

into the sinus venosus from 4 major veins: the left

precava (= left common cardinal, = left superior

vena cava), the right precava (= right common

cardinal, = right superior vena cava), the left

hepatic vein, and the postcava (= posterior vena

cava, = right hepatic vein; Fig. 132). The left and

right precaval veins each drain the anterior body.

Each precava receives branches from the

subclavian and azygos veins and anteriorly from

the internal and external jugular veins. The azygos

vein is narrow and supplies the deep pectoral

muscles (Fig. 140). The subclavian vein extends

laterally. It receives the thyroscapular vein with

thyroid branches from the thyroid gland and the

scapular musculature, the scapular, transverse

scapular, and subscapular veins. The transverse

scapular vein supplies drainage for the cephalic

vein from the dorsal arm and the posterior and

ventral flipper (Fig. 132). After receiving the

thyroscapular branch, the subclavian vein extends

laterally and forms the axillary vein in the axilla

(armpit). Many branches arise in the axillary as the

venous component of the rete system. The axillary

components rejoin as the brachial vein in the upper

arm, and then bifurcate as the internal brachial

vein to the posterior flipper and the dorsal brachial

vein to the anterodorsal flipper. As in the arterial

system, a vascular circumflex forms near or just

distal to the wrist, and receives drainage from the

interdigital veins found medial to each digit.

Because of the extensive connective tissue layers in

the forearm and flipper blade, these vessels were

traced by destructive dissection and so are

illustrated diagrammatically (Fig. 132).
CIRCULATORY ANATOMY

The external jugular vein is located relatively

dorsal and superficial in the neck. The biventer

cervical (= splenius capitus) and transverse

cervical muscles are good dorsal landmarks for

the external jugular. These muscles are obvious

from the exterior and are to either side of the

vessels; the external jugular is located deep and

between them (Figs. 141-142), and medial to the

transverse cervical muscle.

Fig. 140. The azygos artery and veins and branches

of the pectoral vein supply the deep pectoral

musculature. Here the pectoralis major has been

reflected anteriorly to expose the azygos vessels (at

arrows) supplying the coracobrachialis-anterior

and -posterior parts, as well as branches to the

biceps profundus. 

Fig. 139. Dorsal arteries to the posterior musculature and kidneys of a loggerhead.

kidney

renal arteries

dorsal aorta

common

iliac arteries

caudal

artery

ilium

left

hind foot

epigastric

arteries

86 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 87

CIRCULATORY ANATOMY

dorsal shoulder

muscles

left

forelimb

biventer

cervical muscle

external jugular vein

transverse cervical muscle

head

right

forelimb

Figs. 141a and 141b. Green turtle cervical circulation. The external jugular vein

was dissected free on the turtle's right and injected to provide contrast. It shows

the transverse cervical branch extending medially into the muscle. 

a

b
88 The Anatomy of Sea Turtles

CIRCULATORY ANATOMY

scapula

cervical

vertebra

(cut)

external

jugular vein

internal

jugular vein

precava

head

vertebral vein

and branches

transverse

cervical vein

Figs. 142a and 142b. Dorsal view of the neck of a green turtle with the carapace

removed. The precava (superior vena cava) receives blood from the subclavian

veins. The relatively small external jugular vein of green turtles receives relatively

few branches when compared with the anatomy in other cheloniids.

a

b
CIRCULATORY ANATOMY

vertebral

branches

of external

jugular vein

transverse

cervical

muscle

retracted

external

jugular vein

1st left

marginal

1st right

marginal

supraoccipital

crest

external

jugular

vein

biventer

cervical

muscle

nuchal scute

Figs. 143a and 143b. Dorsal view of the external

jugular veins and the vertebral vein. In this turtle

the transverse veins are not obvious. There is an

anterior bifurcation of the vertebral vein at the

level of the neck rather than at the skull in this

individual. The external jugular vein of this

hawksbill receives dorsal and ventral vertebral

branches from the cervical musculature

proximally and distally. However, there are no

branches along most of the intervening length.

a b

The Anatomy of Sea Turtles 89
90 The Anatomy of Sea Turtles

CIRCULATORY ANATOMY

biventer

cervical

muscle

external

jugular vein

transverse

cervical

muscle

1st left

marginal

scute

nuchal scute

Figs. 144a and 144b. The external jugular vein

and its network of vertebral branches are obvious

in this Kemp’s ridley. Multiple vertebral branches

are common in this species between the prominent

dorsal neck muscles. 

a b
CIRCULATORY ANATOMY

biventer

cervical

muscle

carapace

transverse

cervical

muscle

external

jugular vein

with vertebral

branches

skull

Figs. 145a and 145b. Dorsal view close-up of a Kemp’s ridley external jugular

vein, and its transverse branch arises medially (toward the left in this picture). 

a

b

The Anatomy of Sea Turtles 91
CIRCULATORY ANATOMY

biventer

cervical

muscle

external

jugular

vein

cervical

branch of

external

jugular

transverse

cervical

muscle

1st right

marginal scute

nuchal scute

Figs. 146a and 146b. The external jugular vein is

large and is associated with many anastomoses

(networks of interconnected blood vessels) as well

as cervical (vertebral) branches to the neck

muscles of loggerheads.

a b

92 The Anatomy of Sea Turtles
The Anatomy of Sea Turtles 93

CIRCULATORY ANATOMY

transverse

cervical

biventer

cervical

external

jugular

vein

Figs. 147a and 147b. Dorsal neck circulation in a

leatherback. The external jugular vein is large and

is associated with many small cervical (vertebral)

branches to the neck muscles. The vessel is located

deep between the transverse cervical and biventer

cervical muscles.

a b
CIRCULATORY ANATOMY

vertebral

vein

transverse

cervical

branches

external

jugular

vein

transverse

cervical

muscle

esophagus

(cut)

Figs. 148a and 148b.

Lateral view of the external

jugular vein and both right

and left transverse cervical

branches in a green turtle.

The vertebral vein is visible

for part of its length, and is

medial and deep to the cut

skin of the dorsal neck.

a

b

The external jugular vein (often termed the dorsal

cervical sinus) is a commonly used venipuncture

(blood collection) site in sea turtles. The external

jugulars are large and extend from the base of the

neck into the head where they drain the structures

of the head. Each gives off at least one transverse

branch that joins the other medially (Figs. 141-

147). Often a small central vertebral vein extends

along the midline from the junction of the

transverse cervical veins and provides drainage to

the dorsal cervical muscles, cervical vertebrae, and

the spinal meninges. In Chelonia mydas and

Eretmochelys imbricata, the external jugular is

smaller in diameter and branches little (Figs. 141-

143, 148-149). This vessel branches frequently in

the dorsal cervical region of Caretta caretta and

Lepidochelys kempii (Figs. 144-146). In

Dermochelys, it branches near the head (Fig. 147).

All species have vertebral branches from the

external jugular draining the cervical structures. 

94 The Anatomy of Sea Turtles
CIRCULATORY ANATOMY

biventer

cervical muscle

cervical

branch

vein

1st left

marginal scute 2nd left

marginal scute

hyoid

process

transverse

cervical muscle

lateral

vertebral

arteries

external

jugular

vein

nuchal scute Figs. 150a and 150b. The

external jugular, injected with

latex to provide contrast, is very

large in this Kemp's ridley. After

removing the connective tissue,

the external jugular dropped to a

more ventral position than would

be found in life. Lateral vertebral

arteries from the carotid are seen

in this deep dissection.

Fig. 149. Lateral view of

hawksbill cervical circulation.

The external jugular vein in

hawksbills has few branches

along most of its length. The

vessel branches proximally to

receive vertebral branches (near

the nuchal scute) and ventrally,

draining the ventrolateral neck

muscles. Ventral cervical arteries

are exposed adjacent to the

trachea near the plastron. 

a

b

The Anatomy of Sea Turtles 95

biventer

cervical muscle

transverse 

cervical

branches

trachea

external

jugular vein
CIRCULATORY ANATOMY

vertebral

branches

trachea

left

flipper

right flipper

cut

muscles

head

external

jugular vein

Figs. 151a and 151b. This lateral view of a Kemp’s ridley shows the many vertebral

branches off the external jugular going to the deep cervical musculature.

a

b

96 The Anatomy of Sea Turtles
CIRCULATORY ANATOMY

biventer

cervical muscle

transverse

cervical muscle

external

jugular

vein

1st left

marginal scute

nuchal scute

Figs. 152a and 152b. This lateral dissection of a loggerhead's external jugular shows

the extensive branching that is typical of this species. The transverse cervical muscle

has been split along its length to expose the vein. Both the muscles and veins are

displaced ventrally because their supporting connective tissues have been removed.

a

b

The Anatomy of Sea Turtles 97
CIRCULATORY ANATOMY

The internal jugular vein is smaller in diameter

than the external jugular and is found more deeply

adjacent to the longus colli muscles. It receives

multiple branches from the esophagus

(esophageal veins) before it drains into the precava (Fig. 153).

Fig. 153. The internal and external jugular veins from the precava are exposed in this

dissection of a green turtle. The external jugular vein (downward pointing arrow) is

mostly covered by the cut neck musculature which has been reflected dorsally. The

internal jugular (upward pointing arrow) is partially injected with latex. The internal

jugular vein is usually accompanied by the vagus nerve, however it is not distinct in

this photo.

98 The Anatomy of Sea Turtles
CIRCULATORY ANATOMY

left

flipper

cephalic vein

scapula

thoracodorsal

artery

precava

transverse

scapular vein

subscapular vein

and artery

scapular vein

Figs. 154a and 154b. Venous and arterial branches of the posterior aspect of the flipper.

The cephalic vein from the flipper drains into the transverse scapular vein along the

scapular musculature, then to the scapular vein, which then joins the precava. The

thoracodorsal artery is a branch from the subclavian or the brachial in most turtles.

a

b

The Anatomy of Sea Turtles 99
100 The Anatomy of Sea Turtles

Venous return from the posterior body is by both

direct routes (to the postcava and the left hepatic

vein) and indirect routes (via the renal portal and

hepatic portal systems). Portal systems are those

that start and end in capillaries. The renal portal

system consists of veins draining into the

postcava, abdominal, renal portal, and external

iliac veins. The hepatic portal system includes the

veins draining into the hepatic portal, common

mesenteric, mesenteric, and duodenal veins.

These will be discussed separately.

The postcava runs anteriorly from the capillaries

of kidneys through the right lobe of the liver (Fig.

132). It emerges from the right lobe of the liver

and enters the right side of the sinus venosus.

Posteriorly, the postcava receives multiple pairs of 

renal veins from the ventral surface of the

kidneys. Gonadal veins also pass from gonads,

through the kidneys, and to the postcava. Branches

from the iliac veins drain the pelvic musculature,

and the costal veins from the carapace

occasionally drain into the postcava. Anteriorly it

receives multiple hepatic veins from throughout

the liver. The postcava is part of the renal portal

system. The left hepatic vein drains blood

through the liver and from the paired abdominal

veins, (Fig. 132) which are located just anterior to

the pelvis and in the peritoneum. There is usually

a transverse abdominal vein connecting the

abdominal veins. Blood can flow in either

direction through this vein. The abdominal veins

receive pectoral veins (Fig. 127) descending

from the pectoral muscles. Pericardial veins

usually enter the abdominals near the pectoral

veins and posterior to these, a pair of vesicular

veins enters from the bladder. The abdominals

extend along the dorsal pelvic musculature and

receive pelvic veins from the left and right sides.

In the hind limb, crural veins extend from the

medial to the posterior thigh and shank. Crural

branches from the shank, the tibial and popletial

veins, plus the femoral veins (from the

dorsolateral thigh and shank; Figs. 132 and 156)

drain to enter the abdominals, usually just

posterior to the pelvic veins. Paired lipoidal veins

from the left and right inguinal fat pads, enter the

abdominal veins from near the crural veins.

External iliac veins drain into the abdominals at

or near the junction of the femoral and crural veins

with the abdominal veins. The epigastric vein

(Fig. 157) extends from the marginocostal vein on

each side and travels with the epigastric artery

along the posterolateral margin of the carapace. It

runs along the upper thigh, and drains into the

external iliac vein.

CIRCULATORY ANATOMY

coracoid liver

testis

post cava

coracoid

kidney

Fig. 155. Ventral view of the

postcava. The postcava emerges

from the liver and passes to the

kidneys. Blood is drained from

the kidneys and posterior body

to the liver. 
CIRCULATORY ANATOMY

flexor tibialis

externus

pubotibialis

crural vein femoral

artery

popletial

vein

gastronemius

muscle

ventral

flexor tendon

foot

pelvis

Figs. 156a and 156b. The right hind limb of this loggerhead shows

the positions of the femoral artery, crural, and popletial veins. These

arteries and veins travel with the sciatic nerve.

a

b

The Anatomy of Sea Turtles 101
102 The Anatomy of Sea Turtles

CIRCULATORY ANATOMY

peritonium

with fat

rectus

abdominus

epigastric

vein

iliotibialis

flexor tibialis

caudal

vein

tail

left hind limb

Fig. 157. Lateral and posterior

view. The epigastric vein travels

dorsally to the dorsal hind leg

extensors (iliotibialis) and

flexors (flexor tibialis). This

vein is medial to the marginal

scutes and just ventral to the

dorsal fat layer. It receives

drainage from into the caudal

veins just dorsal to the tail.

The paired renal portal veins receive the ischiadic

veins from the posterior hip muscles. The caudal

veins (Fig. 157) extend along the lateral tail and

receive the cloacal veins, medially from the cloaca

and rectum. The caudal veins drain into the ischiadic

veins, as well as the epigastric vein in sea turtles.

The renal portal vein also receives drainage from the

narrow vertebral veins, which are found lateral to

the vertebral column and enter the kidneys anteriorly

and dorsally. The vertebrals receive costal veins

from the shell, which are connected laterally with

the marginocostal vein (Fig. 132). From the cloaca,

bladder, rectum, and in males, the penis, blood

drains to the hypogastric vein, which enters the

kidneys posteriorly and ventrally. The renal portal

veins drain from the dorsal kidney capillaries into

the external iliacs at the level of the epigastric veins,

or into the posterior extent of the abdominal veins. 

The hepatic portal vein receives drainage from the

abdominal veins. It passes dorsally between the right

and left lobes of the liver. Anteriorly, it receives

several branches from the stomach, the gastric

veins, with several branches forming the anterior

a

b
pancreatic veins (along the left half of the

pancreas), the posterior pancreatic veins (from the

right half of the pancreas), and the long duodenal

vein (Figs. 134 and 136). The spleen, found near the

posterior end of the pancreas, is highly vascular and

is drained by several splenic veins to the hepatic

portal vein (Fig. 158). 

More posteriorly, multiple mesenteric veins travel

with the mesenteric arteries radiating from the small

intestines and through the fan-shaped mesentery

(Fig. 158). The mesenteric veins converge on the

common mesenteric vein, which drains into the

hepatic portal vein. The inferior mesenteric vein

drains branches from the large intestine up to the

iliocaecal junction (where the large intestine meets

the ileum), then itself enters the common mesenteric

vein leading to the hepatic portal vein. 

CIRCULATORY ANATOMY

ventricle

stomach

spleen

large

intestine

mesentery

mesenteric veins }

Figs. 158a and 158b. The

spleen is exposed to the left

of the stomach and distal to

the pancreas (covered by

mesentery). Several splenic

veins cover the spleen's

surface. Mesenteric veins,

in the fat-rich mesentery,

drain blood returning from

the small intestines.

a

b

The Anatomy of Sea Turtles 103
NOTE: Cavum arteriosum

doesn’t lead to arterial arches.

Circulation through a turtle heart during ventilation.

Circulation through a turtle heart during apnea

(inferred from Shelton and Burggren, 1976)

CIRCULATORY ANATOMY

Circulation Through the Heart. The route blood

takes though the heart differs depending upon

whether blood is shunted toward the lungs and the

body, or primarily toward the body. Unlike

mammalian cardiopulmonary systems, the pulmonary

and systemic blood flows are not always separate.

The extent of separation between the pulmonary and

systemic circuits of flow differs somewhat between

Dermochelys and the cheloniids. There is a nearly

complete separation of systemic (body) and pulmonary

(lung) circulation in the leatherback heart, but the

intra-cardiac flow is less well separated into pulmonary

and systemic outflows in the cheloniid species.

Studies of turtles generally show that whether

blood is shunted to or away from the lungs is a

function of arterial blood gas levels. Venous blood

returning from the head, limbs, and body enters

the sinus venosus, then flows to the right atrium.

From the right atrium, blood enters the ventricle

where it flows along at least two possible routes.

The diagram below (Fig. 159) summarizes the

route blood takes through the heart. Blood from

the kidneys returns to the left atrium via the

pulmonary veins. It then flows from the left atrium

to the ventricle and usually out through the aortas

to the body. 

Fig. 159. Circulation through a turtle heart during breathing and during breath-holding (apnea).

104 The Anatomy of Sea Turtles
LUNG and AIRWAY ANATOMY

The Anatomy of Sea Turtles 105

Lungs and Airways

The pulmonary system is composed of the

glottis, trachea, a bronchus to each lung, and the

left and right lungs. The airways begin at the

glottis, which is located in the middle to posterior

portion of the tongue (Fig 160). The glottis and its

muscles are supported ventrally by the hyoid

apparatus. The glottis opens during air passage

and is closed during breath-holding. The glottis

leads directly into the trachea, which is supported

by complete cartilaginous rings that are usually

white, except in decomposing animals or some 

turtles with pulmonary disease. The trachea is long

and bifurcates into two bronchi dorsal and anterior

to the heart. These then enter the anterior part of the

lungs next to the pulmonary arteries. The bifurcation

begins internally, anterior to the external division to

form the bronchi. The bronchi extend for virtually the

length of the lungs and have many openings into the

complex internal lobes of the lungs (Fig. 161). Unlike

the bronchi of mammalian lungs, these openings

lead to chambers that are not supported by cartilage.

There are no secondary bronchi in sea turtles.

Fig. 160. Parasagittal section of a hawksbill showing the airway. The hyoid apparatus,

including both bony and cartilaginous portions, supports the glottis ventrally. The glottis,

located between the hyoid and the surface of the tongue, is closed in this dissection.The

large tracheal diameter is maintained by cartilaginous rings. The trachea is lined by

smooth epithelium.

brain

olfactory

sac

mouth

tongue

hyoid

glottis

trachea

{
106 The Anatomy of Sea Turtles

LUNG and AIRWAY ANATOMY

The lungs are located dorsally and are attached

dorsally to the carapace and vertebral column. In

some species, (e.g., L. kempii and C. caretta) the

lungs are more closely attached to the vertebral

column than in other species. Ventrally, the left

lung is attached to the stomach via the

gastropulmonary ligament. The right lung is

attached to the right lobe of the liver by the

hepatopulmonary ligament. Posteriorly, the

lungs attach to the peritoneum that overlies the

kidneys and adrenal glands and are adjacent to the

gonads. The medial border of each lung is firmly

attached (Fig. 162) via fibrous connections to

dorsolateral surfaces of the vertebral column. 

Fig. 161. Longitudinal section through a loggerhead bronchus. The lungs of

cheloniids are spongy in construction and red in color. They also have a large

surface area but are not as densely constructed as the lungs of leatherbacks.

The large-bore trachea has many openings to the chambers of the lung along

its length. These openings are not supported by cartilage once they leave the

bronchus. The unsupported airways extend to the air exchange surfaces called

faveoli and ascini. The trachea and bronchus are supported by cartilage, which

resists collapse during ventilation and diving.
All sea turtles have multichambered lungs (there

are multiple lobes contained within the body of the

lung). The lobes are not obvious externally. The

lung tissue is spongy and highly elastic (Figs. 161

and 163) in sea turtles. 

Ventilation of the lungs occurs without the

assistance of a diaphragm. Marine turtles ventilate

by movements of ventral muscles of the pelvic and

pectoral girdles that attach to the plastron,

compression of the inguinal region, and rocking of

the shoulder muscle masses to change the pressure

within the pleuroperitoneal cavity. Sea turtles

have a large tidal volume. Under normal

circumstances, they breath-hold until blood

oxygen levels drop to low levels. 

LUNG and AIRWAY ANATOMY

Fig. 162. CT scan showing the lungs in a Kemp's

ridley. This CT shows the position, form, and the

extent of the lungs and airways in a living Kemp's

ridley turtle. The medial surfaces of the lungs are

attached tightly to the vertebral column.

Fig. 163. Longitudinal section

through a leatherback lung. The

lungs of leatherbacks are

characterized by more dense

construction. The high surface

area, dense parenchyma, high

levels of connective tissue, and

extensive blood supply make

leatherback lungs particularly

spongy and deep red in color. 

The Anatomy of Sea Turtles 107
108 The Anatomy of Sea Turtles

GASTROINTESTINAL ANATOMY

Figs. 164a and 164b. The gastrointestinal tract

with digestive glands and the spleen. The GI tract

from the esophagus to the rectum from a Kemp’s

ridley turtle shows the different regions as well as

the associated digestive glands, the liver and

pancreas. The gall bladder stores bile, produced

by the liver, and releases it through the common

bile duct when food enters the duodenum. The

spleen, located at the distal end of the pancreas, is

not a digestive gland; rather it is a lymphoid organ

in turtles involved in immunological activity. 

Gastrointestinal Tract

The gastrointestinal tract (GI tract or gut)

extends from the mouth to the cloaca (Fig. 164). It

is demarked by structural and functional divisions.

The mouth captures and processes food. The

esophagus conveys food to the stomach and

expels excess water. It also works with the tongue

in swallowing. The stomach starts the chemical

and physical process of digestion. In the small

intestines, digestive enzymes are added to food to 

break down proteins and complex carbohydrates.

The small intestines are regionally specialized to

absorb amino acids, carbohydrates, sugars, water,

fatty acids, and minerals (particularly calcium and

phosphorus). The large intestine (colon) typically

reclaims water. The length of the gut is somewhat

related to diet. It is proportionally longer in green

and leatherback turtles than in loggerheads,

ridleys, and hawksbills. 

ileum

colon

jejunum

pancreas

duodenum

liver

right lobe

liver

left lobe

stomach

pylorus

spleen

gall

bladder

esophagus

a b
GASTROINTESTINAL ANATOMY

The mouth includes several GI, respiratory, and ear

structures: the mandibles and the pharynx

includes the palate, esophagus, glottis,

Eustachian tubes, and internal choanae (Fig.

165). For convenience, these structures will be

described together here. The glottis and internal

choanae are part of the respiratory system and the

Eustation tube connects the pharynx with the

middle ear cavity. The tongue is fixed to the floor

of the mouth and is not protrusible. The glottis is

located on the middle part of the tongue (see Sense

Organs, Fig. 209), just posterior and ventral to the

internal choanae (internal nares); it acts as a valve

to open and close the airway. The esophagus starts

at the back of the tongue; it is a muscular tube that

leads to the stomach. It passes slightly dorsal and to

the right of the trachea. The Eustachian tubes (one

on each side), are found in the posterolateral

aspects of the mouth, medial to the jaw joint; they

function in maintaining normal pressure in the

middle ear (Fig. 165). 

internal

choanae

palate

Eustachian

tubes

esophagus

(cut)

Figs. 165a and 165b. Ventral view of the palate with the tongue and hyoid

apparatus cut away. The roof of the mouth has internal choanae (internal nares)

that open above the glottis (removed in this picture). In the posterior lateral parts

of the palate, near the jaw joint, are the openings to the Eustachian tubes, which

lead to the middle ear cavity. 

a b

The Anatomy of Sea Turtles 109
110 The Anatomy of Sea Turtles

GASTROINTESTINAL ANATOMY

The esophagus (Fig. 166) is lined with papillae

that are sharp and keratinized; they point inward

towards the stomach. The papillae end where the

esophagus joins the stomach (Fig. 166). The

papillae are presumed to trap food while excess

water is expelled prior to swallowing. In Atlantic

green turtles, the esophagus enters the stomach in

a smooth transition. However, in Pacific green

turtles, there is a muscular specialization at the

base of the esophagus called a crop. Its function

is unclear. In cheloniids, the esophagus descends

to a position just inside the plastron and bends to

the left in an S-shaped curve to join the stomach.

In Dermochelys, the esophagus is exceptionally

long and extends almost half the length of the

body before looping to the left, and returning

anteriorly almost to the level of the axilla. There,

the esophagus bends left again and joins the

stomach (Fig. 167).

esophagus

transitional

papillae

gastroesophageal

sphincter

stomach

rugae

}

Figs. 166a and 166b. The esophagus and anterior

stomach lining. The papillae that line the

esophagus are keratinized for most of the length of

the esophagus. They end abruptly; several flat,

transitional papillae, lacking keratin line the

esophageal wall at the level of the

gastroesophageal sphincter. Posterior to this

sphincter, the stomach lining is very smooth and

has no papillae.

a b
GASTROINTESTINAL ANATOMY

Figs. 167a and 167b. Ventral view of a

leatherback hatchling's viscera and heart. This

dissection of a leatherback posthatchling shows

the extremely long esophagus, large stomach, and

small intestines. On the animal's right is the

remaining yolk sac. The yolk sac can persist well

after the time that the animal has begun feeding.

In this animal, the coracoid processes were cut

away and the acromion processes reflected

anteriorly to provide a clear view of the heart and

liver. The ventricle is pushed anteriorly exposing

the sinus venosus, which was injected with latex

to provide contrast.

right

acromion

process

gall

bladder

cut

pectoral

muscle

liver

right

lobe

right

atrium

pubis

small

intestine

yolk

sac

colon

trachea

liver

left lobe

left

atrium

sinus

venosus

ventricle

reflected

anteriorly

esophagus

stomach

duodenum

esophagus

pubic

cartilage

a b

The stomach is on the animals left side and

curves around the more medially located liver and

pericardium. It is attached to the liver's left lobe

by a gastrohepatic ligament and the left lung by

a gastropulmonary ligament. The stomach is

smooth-walled along its length. It ends in a short

muscular region, the pylorus (= pyloric

sphincter or valve). The pylorus is usually

constricted and the intestinal lining on the

duodenal side of the sphincter differs from that of

the stomach (Fig. 169).

The pancreas runs distally along the duodenum

from the pylorus to just past the common bile

duct (Fig. 170). Both the pancreas and the

common bile duct (from the gall bladder) deliver

digestive enzymes to the duodenum. The common

bile duct enters the duodenum via a small papilla,

the ampulla of Vater, on the duodenum’s internal

surface. Its location can be identified from the

green bile stain (Figs. 170-171). The pancreatic

duct (not shown) is difficult to locate in all but the

largest turtles; it enters the duodenum near or in

The Anatomy of Sea Turtles 111
common with the common bile duct. The

duodenum's lining is textured and, in some

species, it is "honey-combed" in appearance (Fig.

171). This textured lining is associated with

increased surface area and is well-developed in

green turtles and leatherbacks. It is not as

pronounced in the carnivorous/omnivorous species

(e.g., loggerheads, ridleys, and hawksbills). 

The transitions from one type of small intestine to

the next (duodenum to jejunum to ileum) are

often difficult to identify. Gross differences are

often not obvious and are best confirmed by

histological examination for the functional

characteristics of the tissues. The transition from

ileum to colon is clear. The ileum ends in a

muscular sphincter, the iliocaecal valve. The

proximal end of the colon is a caecum (pouch) that

bulges somewhat more than the remaining large

intestine (Fig. 77). It is more prominent in green

turtles than other species. The colon narrows

somewhat past the caecum; it is constricted weakly

by segmentally arranged bands of muscle. Distally,

the colon tapers to form a muscular rectum, which

is often pigmented; its muscular walls are

thickened and folded (Fig. 172). 

GASTROINTESTINAL ANATOMY

stomach

pyloric

sphincter

duodenum

Figs. 169a and 169b. Linings of the stomach and

duodenum. The stomach and duodenum are

separated by a short muscular sphincter, the

pylorus. While stomach lining is generally smooth,

that of the duodenum is often textured. In the

leatherback and green turtle, there are the

overlapping crypts containing mucus found along

the length of the duodenum and into the jejunum. 

a b

112 The Anatomy of Sea Turtles
GASTROINTESTINAL ANATOMY

Fig. 171. Longitudinal section through the liver

and gallbladder. The walls of the gallbladder are

removed dorsally to expose the common bile duct

to the duodenum.

Fig. 170. Longitudinal section of the duodenum.

The common bile duct opens into the duodenum at

a papilla (termed the Ampulla of Vater). The

common bile duct extends from the gallbladder to

the duodenum.

liver

liver

gallbladder

gallbladder

bile duct

ampulla

of Vater

(bile duct papilla)

duodenum

pylorus

duodenum

The Anatomy of Sea Turtles 113
114 The Anatomy of Sea Turtles

GASTROINTESTINAL ANATOMY

Figs. 172a and 172b. Ventral

view of the posterior viscera.

The rectum (collapsed here)

narrows as it joins the cloaca.

The urinary bladder, seen

just above the rectum, enters

the cloaca ventrally. The

dorsally-located kidneys

produce urine that travels

though the ureters to enter

the dorsal cloaca. Several

renal veins are exposed

medial to the kidney. The

testis of this immature male

is still attached to the

peritoneum (and is located

anatomically ventral to the

kidneys).

urinary

bladder

kidney rectum

renal veins

cloaca

ureter

colon

kidney

testis

dorsal pelvic

girdle

reflected

posteriorly right coracoid

cartilage

and deep

pectoral

muscle

left coracoid

cartilage

liver

left lobe

a

b

The rectum empties into the cloaca (Fig. 171), a

chamber that also receives the urine from the

kidneys, eggs or sperm, and connects ventrally into

the urinary bladder. The cloaca empties to the

outside via the cloacal opening or vent. Each

function of the cloaca is associated with a region into

which the products empty. The coprodeum received

feces from the rectum. The urodeum is associated

with the urinary papillae and the opening of the

urinary bladder. The proctodeum is the most distal

region and is associated functionally with copulation

and structurally with proximity to the genital ducts.
GLANDS

Glands

Glands are often lobular and may have ducts or are

ductless. They are involved the in production of

peptides and steroids, which can form skin coatings

(waxes), enzymes, or hormones. Glands are either

formed in the skin and its related structures

(ectodermal in origin) or from deeper within the

body (mesodermal in origin). Glands are discussed

below by region and function, when known.

The salt (lacrimal) gland (Figs. 81 and 172) is the 

largest gland in the head and is found dorsal and 

medial to the eye. These glands are large in all sea

turtles, but are especially hypertrophied in

Dermochelys (Fig. 172). The salt gland is

responsible for removal of excess salt from the body.

Anterior to the eye, there is a small Harderian

gland, associated with lubricating the eye.

Sea turtles, like most aquatic lower vertebrates,

appear to lack oral glands.

dorsal nares cartilaginous

septum

salt gland

sella tursica

neurocranium

salt gland

Figs. 172a and 172b. Dorsal view of the salt gland and braincase of a

leatherback. The extremely large salt glands dominate the skull space lateral to

the braincase and dorsal, medial, and posterior to the eye. The brain has been

removed leaving the braincase with the sella tursica retaining the pituitary gland. 

a b

The Anatomy of Sea Turtles 115
116 The Anatomy of Sea Turtles

GLANDS

The ductless pineal gland (epiphysis) is a dorsal

extension of the brain; it connects indirectly to the

dorsal surface of the braincase, it is located deep to

the frontoparietal scale in cheloniids and the "pink

spot" in Dermochelys (illustrated in the Nervous

System, Figs. 193-194, 196, 198-201). It is

responsible for modulating biological rhythms. 

The pituitary gland (hypophysis) is found in a

cavity, the sella tursica in the floor of the braincase

(Nervous System, Fig. 190). The pituitary is composed

of two parts, the neurohypophysis (infundibulum)

and the adenohypophysis. The neurohypophysis

produces releasing hormones (e.g. oxytocin) and

release-inhibiting hormones (e.g. antidiuretic

hormone), while the adenohypophysis produces

growth hormone, prolactin, thyroid-stimulating

hormone, gonadotropins, adrenocortacoids, and

melanophore-stimulating hormone.

More posteriorly are several glands derived from

pharyngeal pouches of the embryo. These ductless

glands are the thyroid, thymus, parathyroid, and

ultimobranchial bodies. All are located in the

ventral neck and upper body. The thyroid gland can

be located medially to the the acromion processes

(Figs. 75 and 173) by tracing along the

brachiocephalic trunk where it gives rise to thyroid

arteries (soon after its bifurcation to form the

subclavian arteries). The thyroid arteries “frame” the

single thyroid gland that is encased in connective

tissue (Fig. 173). The thyroid is round and is often

coated with a thin layer of fat. In fresh specimens, it

is bright red. However, in turtles that have been

frozen, then thawed, or that have started

decomposing, it may become brown. It is gelatinous

in texture in fresh and fresh-frozen animals. In

decomposing carcasses, it liquifies. The thyroid is

involved with increasing oxygen consumption when

reptiles exceed their preferred body temperatures,

and it functions in gonadal maturation.

The thymus glands can be located by tracing along

the subclavian arteries and palpating for a dense,

laterally elongated structure (Figs. 174-175). There

is a gray to pink thymus gland on each side of the

body that is composed of small lobes. It is usually

associated with fat. The thymus glands are more

dense and compact than the fat. They are often

easiest to find by palpating. The thymus glands

play a role in immune responses. In chronically ill

animals this gland is frequently thin and diffuse.

Fig. 173. Thyroid gland in

ventral view, medial to the

acromion processes. The

thyroid is the dark, round

structure at the tip of the

pointer. The heart has not

been exposed yet. Anterior is toward the top of the

figure. The two acromio-coracoid ligaments

extend posteriorly from the acromion process.
GLANDS

The parathyroid and ultimobranchial bodies are

difficult to identify and can only be distinguished

from one another histologically (Fig. 176). They

are very small and located along the carotid and

ventral cervical arteries. Generally, the parathyroid

glands are the more anterior glands and the

ultimobranchial bodies are more posterior. They

are brown or dark pink in color. They are best

located by feeling for the round, dense glands,

then using careful dissection. The two kinds of

glands have antagonistic functions. The

parathyroid gland releases parathormone, which

stimulates the mobilization of calcium and

phosphorus from storage (usually bones). The

ultimobranchial body releases calcitonin, which

lowers blood levels of calcium and phosphorus. 

Fig. 175. Ventral view of the two thymus glands,

just below the fingertips, are located adjacent to

the subclavian arteries. They are anterior to the

heart and lateral to the thyroid gland (seen as the

smooth oval tissue anterior to the great vessels).

Fig. 174. Ventrolateral view of the neck structures.

Positions of the trachea (with cartilaginous rings)

and esophagus to the animal's right provide

landmarks. The head is removed; anterior is

toward the top of the picture. The lobular right

thymus gland is at the bottom of the picture. 

The Anatomy of Sea Turtles 117

esophagus

trachea

thymus

thyroid

heart

subclavian

arteries

thymus
118 The Anatomy of Sea Turtles

GLANDS

subscapular

artery

subclavian

artery

carotid

artery

internal

jugular

vein

thymus

gland

right aorta

left aorta

pulmonary

artery

ultimobranchial

body

right 

atrium

(reflected

medially)

left atrium

(distended)

ventricle

Figs. 176a and 176b. Ventral view of an ultimobranchial body (or parathyroid)

and thymus gland. The carotid and ventral cervical arteries are the best

landmarks for locating the parathyroid and ultimobranchial glands. The glands

tend to be associated with the connective tissue on the dorsal surfaces of the

arteries. Typically, 2-4 glands are present on each side. The large thymus gland,

deep to the subclavian artery, is seen near the top of the picture.

a b
GLANDS

The liver is the largest visceral organ and is located

ventrally, but deep to the pectoral skeleton and

peritoneum (Fig. 177). It is dark brown to reddish

brown and composed of two lobes joined by one or

more connecting strips of hepatic tissues. The right

lobe houses the gallbladder on its ventral surface

and is typically larger than the left lobe (Fig. 177).

The liver is highly vascular; it receives blood from

the hepatic portal vein and the hepatic artery.

Blood from the body drains from the liver via the

hepatic veins to the sinus venosus.

The liver contains many bile ductules and

hepatocyte cords. The hepatocytes manufacture

bile which drains via bile ductules into the

gallbladder.

The gallbladder stores bile which is then

transported via the common bile duct to the

duodenum in response to the presence of fats. Bile

contains the enzymes involved with fatty acid

breakdown. 

The liver plays a major role in carbohydrate and

protein metabolism as well as in removal of toxins

from the blood. Blood from the stomach and

intestines percolates through hepatic tissues where

carbohydrates, amino acids, and peptides are

broken down. Other liver cells make serum

albumin and a number of clotting factors. 

Fig. 177. The liver is exposed in a green turtle.

The left and right lobes are located lateral and

slightly dorsal to the heart. Both lobes receive

blood from the hepatic portal system. 

Fig. 178. Dorsal view of

the duodenum (at top) with

the pancreas, spleen (at

arrow), and a portion of

the liver's right lobe. 

liver

left lobe

liver

right lobe

The Anatomy of Sea Turtles 119
120 The Anatomy of Sea Turtles

GLANDS

Pancreas. The pancreas is located along the

duodenum just past the stomach (Fig. 178-179). It

is a smooth and thick tissue that extends as an

irregular strip past the common bile duct and often

ends at or just past the spleen. It is pink to yellow

orange in color. The pancreas is a digestive gland

as well as an endocrine gland and produces

pancreatic polypeptides which stimulate flow of

gastric juices in the stomach. Other pancreatic

cells produce insulin which assists in the

metabolism of glucose. Some pancreatic cells

produce glucagon which stimulates the breakdown

of glycogen to increase blood glucose levels.

Rathke's glands are located deep to the

inframarginal scutes in Lepidochelys (Figs. 180-

181) and in the posterior axilla and anterior-most

inguinal regions in Eretmochelys and Chelonia

(Figs. 182-183). Rathke’s glands have not been

identified in Caretta and Dermochelys. While

prominent, they show no change with reproductive

condition or season. Their function is unknown.

The secretions of the glands have been

hypothesized to play various roles including

intraspecific communication, anti-fouling, and/or

anti-microbial function. 

Fig. 177. The long narrow pancreas is seen just

below the duodenum (at arrow) in this loggerhead

dissection. It is encased in the mesentery. A large

artery in the mesentery is seen supplying branches

to the proximal and distal pancreas. The dark,

oval spleen is seen below the pancreas, above the

loops of small intestines.
GLANDS

inframarginal

scutes

inframarginal

pores

Figs. 180a and 180b. Inframarginal Pores. Ridley turtles have pronounced inframarginal

or Rathke's pores associated with each inframarginal scute. The pores lead to the Rathke's

gland. In mature turtles, with fully developed plastron bones, the ducts from these pores are

surrounded by bone. They leave foramina (holes) in the hyoplastron and hypoplastron bones.

Figs. 181a and 181b.

When the plastron is

removed, the gray-green

Rathke's gland and its

ducts are exposed.

Each duct leads to an

inframarginal (Rathke's)

pore. The gland is

typically embedded in

fat. It extends the length

of the inframarginal

scutes from the axilla

to the anterior extent of

the inguinal region.

ducts from

inframarginal

pores to

Rathke’s

gland

Rathke’s

gland

marginal

scute

fat

a b

a b

The Anatomy of Sea Turtles 121
122 The Anatomy of Sea Turtles

GLANDS

Figs. 182a and 182b.

Rathke's pores in a

hawksbill. The posterior

Rathke's pore in this

hawksbill is found in the

anterior-most inguinal

scale.

Figs. 183a and 183b.

Anterior Rathke's pore

in a green turtle. The

anterior Rathke's pore

in this green turtle is

found in the most

posterior and lateral

axillary scale.

Rathke's pores and Rathke's glands are also found

in Chelonia mydas and Eretmochelys imbricata.

They are restricted to the posterior axilla and the

anterior-most inguinal scales. The pores typically

do not extend to the inframarginal scutes (Figs.

182-185).

Rathke’s

pore

Rathke’s

pore

a b

a b
Figs. 184a and 184b. Rathke's gland and pore in

a green turtle. As the plastron is removed, the gray

Rathke's gland can be found embedded in fat just

deep to the Rathke's pore.

Figs. 185a and 185b. Posterior Rathke's pore in a

green turtle. The posterior Rathke's pore in this

green turtle is found in the most anterior and

lateral inguinal scale.

GLANDS

Rathke’s pit

Rathke’s

gland

Rathke’s 

pore

a b

a b

The Anatomy of Sea Turtles 123
124 The Anatomy of Sea Turtles

GLANDS

dorsal aorta

adrenals

kidneys

Figs. 186a and 186b.

Adrenal glands. This dorsal

view of the adrenal glands

shows their elongate shape

and their position just

anterior and medial to the

kidneys. The adrenal arteries

are not clear in this

dissection. The left adrenal

is crossed by a costal artery. a b

The adrenal glands (Fig. 186) are paired, tan to

pink in color and are located lateral to the dorsal

aorta, usually anterior to the renal arteries. They are

usually medial to, and just anterior to, the kidneys.

The adrenal glands develop from the anterior

(cranial) poles of the embryonic kidneys. The

paired adrenals are elongated along the anteriorposterior axis and oval in cross section. They are

composed of two intermingling tissue types:

interrenal bodies, that produce steroids

(corticosterone) and chromaffin bodies that produce

catecholamines such as adrenaline (epinephrine and

norepinepherine). Unlike mammals, these tissues

are not organized into a distinct cortex and medulla. 
NERVOUS SYSTEM

Nervous System

The brain or central nervous system (CNS) of

sea turtles is longitudinally arranged along the midline of the skull (Fig. 187). The brain is housed in

a tubular braincase, composed anteriorly of the following bones: ethmoid, epiotic, prootic, opisthotic,

basisphenoid, laterosphenoid, and otic (Figs. 26

and 30). Posteriorly it is completed by the basioccipital, exoccipital, and supraoccipital. It is roofed

by the parietal and frontal bones (Fig. 25).

Two tissue layers, the meninges, cover the brain. 

The outer menix (singular) is the tough dura

mater. A more delicate leptomenix (sometimes

termed the pia mater) lies directly on the brain's

surface (Fig. 187). There are both subdural

(beneath the dura mater) and epidural (above the

dura mater) spaces within the brain case.

Epimeningeal veins occupy some of the epidural

space. The brain is bathed in clear cerebral spinal

fluid produced by the tela choroidea, a vascular

region of the brain (Fig. 187).

Figs. 187a and 187b. Exposed brain and cut

meninges. The anterior and posterior extent of the

dura mater and a vascular portion of the leptomenix (= pia mater) are seen in this exposed loggerhead brain. In life, both meninges would envelop the brain. 

a b

leptomenix

salt

gland

salt

gland

}

The Anatomy of Sea Turtles 125
126 The Anatomy of Sea Turtles

NERVOUS SYSTEM

Traditionally, the brain (Fig 189) is described by

three regions that are initially demarked during

development: the forebrain, midbrain, and

hindbrain. The following combinations of

external and internal landmarks roughly identify

these divisions. The forebrain extends from the

nose to the posterior cerebrum. The midbrain

extends from the eye to the posterior aspect of the

optic lobes. The hindbrain extends from the ear to

the posterior cerebellum. These regions, in turn, are

subdivided topographically and/or histochemically

into principal divisions: telencephalon and

diencephalon of the forebrain, mesencephalon of

the midbrain, metencephalon and myelencephalon

of the hindbrain (Fig. 189). 

Fig. 188. Parasagittal section of the brain and airways. The section though this green

turtle head shows the tight epidural space and the more voluminous subdural space

surrounding the brain. Because this cut is to the right of the midline, the cerebral

ventricles and part of the cerebellar ventricle can be seen. The nasopharyngeal duct,

part of the respiratory system, can be seen passing from the olfactory sacs to the

internal choane.

epidural space

nasopharyngeal

duct

tele choroidea

ventricle IV

cerebral

aqueduct

cerebral

spinal fluid
NERVOUS SYSTEM

olfactory nerve olfactory bulb cerebrum

optic nerve

optic lobe

cerebellum

ANTERIOR POSTERIOR

spinal cord

medulla

telencephalon

mesencephalon

oculomotor

nerve

FOREBRAIN MIDBRAIN HINDBRAIN diencephalon metencephalon myelencephalon

Figs. 189a and 189b. Leatherback brain showing major regions and landmark structures.

The brain is demarcated into its major regions and principal divisions.

The divisions of the brain and their major

components are as follows.

Telencephalon: cranial nerve I, (olfactory nerve),

olfactory bulbs, cerebral hemispheres, lateral

ventricles.

Diencephalon: hypothalamus, thalamus,

infundibulum and pituitary, pineal, optic chiasma,

cranial nerves II-III (optic and oculomotor nerves).

Mesencephalon: optic lobes, third ventricle,

cerebral aqueduct, cranial nerve IV (trochlear nerve).

Metencephalon: cerebellum, anterior part of

medulla, fourth ventricle, cranial nerves V-X

(trigeminal, abducens, facial, statoaccoustic,

glossopharyngeal, and vagus, respectively).

Myelencephalon: most of medulla, cranial nerves

XI-XII (spinal accessory and hypoglossal).

a

b

The Anatomy of Sea Turtles 127
128 The Anatomy of Sea Turtles

NERVOUS SYSTEM

The brain forms as a tube during sea turtle

development. It then undergoes considerable

regional specialization, torsion, and expansion to

form the structures found in adult turtles. Remnants

of the nerve tube cavity persist as the lateral

ventricles of the cerebral hemispheres, the third

ventricle and cerebral aqueduct, and the fourth

ventricle of the cerebellum and medulla (Fig. 188). 

Most of the cranial nerves arise ventrally and

laterally, and are easiest to observe when the brain

is removed (Figs. 189-191). 

XI spinal

accessory nerve

XII hypoglossal

nerve

VI abducens

nerve

IX glossopharyngeal nerve

V trigeminal

nerve

III oculomotor

nerve

II optic nerve

infundibulum

brain case

VII facial & VIII

statoacoustic

root

} X vagus nerve

}

Figs. 190a and 190b. Ventral surface of a ridley

brain. This brain is viewed from the posterior

aspect of the skull and is reflected anteriorly and

dorsally. Only the optic and olfactory nerves are

still attached to the head. The cut pituitary can be

seen in the sella tursica in the floor of the brain

case, while the infundibulum is removed with the

rest of the brain.

sella

tursica

a b
NERVOUS SYSTEM

spinal cord

cerebrum

olfactory

bulb

optic

nerves

optic

lobe trigeminal

nerve

cerebellum

facial and 

statoaccoustic roots

oculomotor 

nerve

spinal

accessory

nerves

medulla

Figs. 191a and 191b. Ventrolateral view of a loggerhead brain without the olfactory nerves.

The size of the brain of mature and maturing turtles is remarkably small for the body size.

This brain from a 72 cm SCL loggerhead is just less than 10 cm long.

Specific landmarks identifying the parts of the

brain differ slightly across cheloniids and, even

more when compared with Dermochelys (Figs.

192-202). Among the cheloniids, the brain is

closest to the skull roof in Lepidochelys kempii.

It is furthest from the skull roof in adult Caretta

caretta and Eretmochelys imbricata. 

Scalation patterns on the lateral head and the position of the ear provide species-specific landmarks

for some structures (Fig. 192). The brain of the

leatherback is housed deeply, except for the pineal,

which extends dorsally in a cartilaginous cone-like

chamber adjacent to the pink spot on the middorsal

surface of the head (Figs. 201-202).

a

b

The Anatomy of Sea Turtles 129
130 The Anatomy of Sea Turtles

NERVOUS SYSTEM

Fig. 192. Brain landmarks for marine turtles.

Overlays of brain positions are shown for 5 species.

The position of the head scales, the eye, and the ear

provide some reference points for identifying the

position of the brain, which varies in dorsal-ventral

position with species. The brain position of the

leatherback, in this drawing, is based more upon

the shape of the braincase because of the poor

condition of all leatherback brains examined. The

landmarks shown are accurate for large turtles,

however the brains of hatchlings and juveniles are

disproportionately larger.

Caretta caretta

Eretmochelys imbricata

Chelonia mydas

Lepidochelys kempi

Dermochelys coriacea

a
NERVOUS SYSTEM

supraoccipital

process

cerebellum

optic lobe

pineal

parietal

cerebrum

olfactory bulb

olfactory nerve

medulla

tela choroidea

frontal

nasal

olfactory

sac

interorbital

septum

optic nerve

premaxilla

rhamphotheca

palatine

dentary

infundibulum

& pituitary

body of hyoid pterygoid trachea

sphenoid

esophagus

tongue

a

b

The Anatomy of Sea Turtles 131

Figs. 193a and 193b. Parasagittal view of a loggerhead head. The brain, airways, oral

cavity, and esophagus are exposed. The interorbital septum is intact and the optic nerve

is seen passing through its foramen. There is a large subdural space, above the cerebrum

and olfactory nerve, in loggerheads.
132 The Anatomy of Sea Turtles

NERVOUS SYSTEM

cerebellum

optic

lobe

pineal cerebrum

olfactory bulb

olfactory

nerve medulla

tela choroidea

olfactory

sac

infundibulum

& pituitary

dura mater

dentary

optic

nerve

cerebellar

ventricle

ventricle

IV

ventricle optic

chiasma

spinal

cord

Figs. 194a and 194b. Parasagittal cut through the head of a subadult

loggerhead, close up. The positions of the brain, its parts, and the large

subdural space containing cerebral spinal fluid relative to the dorsal skull are

clear. The lateral ventricles are not exposed by this cut; the third ventricle and

cerebral aqueduct are seen ventral to the optic lobe. The cerebellar ventricle is

part of the 4th ventricle. Ventrally, the infundibulum leads to the pituitary

(dorsal to the palate). The pituitary is housed in a bony socket, the sella tursica. 

a

b
NERVOUS SYSTEM

tongue

external

nares

nasopharyngeal

duct

olfactory

sac

interorbital

septum

olfactory

bulb

cerebrum

optic lobe

optic

nerve

optic

peduncle

cerebellum

trachea

rhamphotheca

a

b

The Anatomy of Sea Turtles 133

Figs. 195a and 195b. Parasagittal cut through an immature green turtle head. This view

shows the spatial relationships of the CNS to other head structures. The brain is located close

to the dorsal skull. The cut removed part of the interorbital septum so that the eye muscles

are exposed dorsal to the palate and posterior to the olfactory sac. The intact olfactory

nerve can be seen extending to the olfactory sac.
134 The Anatomy of Sea Turtles

NERVOUS SYSTEM

Figs. 196a and 196b. Parasagittal cut through a subadult green turtle head (close up).

The brain is located very close to the dorsal skull in green turtles. The lateral ventricles are

just exposed by the parasagittal cut; part of the cerebral aqueduct is seen within and

ventral to the optic lobe. The cerebellar ventricle, part of the fourth ventricle, is exposed. 

glottis

optic nerve

mandible

interorbital

septum

olfactory

sac

olfactory

bulb

cerebellum

supraoccipital

process

IV

ventricle

tele

choroidea

cerebrum

pineal

optic

lobe

lateral

ventricle

spinal

meninges

a

b
NERVOUS SYSTEM

medulla

cerebellum

optic lobe pineal

optic nerve

olfactory bulb cerebral

hemisphere

olfactory nerve

olfactory sac

interorbital

septum

maxilla

premaxilla

dentary

esophagus trachea glottis tongue

a

b

The Anatomy of Sea Turtles 135

Figs. 197a and 197b. Parasagittal cut through the head of an immature Kemp’s ridley.

The anterior half of the brain is flexed slightly dorsally in this species.
136 The Anatomy of Sea Turtles

NERVOUS SYSTEM

Figs. 198a and 198b. Parasagittal cut near the midline of a juvenile Kemp's ridley turtle

(close up). The cerebral hemispheres are closer to the skull roof bones in ridleys than in

the other cheloniid species. The cut was positioned so that the optic chiasma (at the

posterior end of the optic nerve) was bifurcated. The pituitary is not seen in this section.

medulla

tela choroidea

cerebellum

optic lobe pineal

optic nerve

pterygoid

carotid canal

ventricle

cerebellar

ventricle

basioccipital

occipital

condyle

atlas

ventricle

IV

olfactory bulb

cerebrum

olfactory nerve

olfactory

sac

interorbital

septum

maxilla

glottis

tongue

a

b
NERVOUS SYSTEM

supraoccipital crest

pineal

optic lobe medulla

cerebellum

cerebrum

olfactory bulb

olfactory

nerve

nasal

sac trachea

glottis

esophagus

optic nerve

spinal

meninges

a

b

The Anatomy of Sea Turtles 137

Figs. 199a and 199b. Parasagittal section through a hawksbill head. The brain

is not as closely positioned to the skull roof in hawksbills as in other cheloniids.

The pineal gland is clearly exposed in this dissection. Other parts of the brain are

partially decomposed so their structure is slightly collapsed. The partial collapse

makes the spinal meninges more distinct. The trachea and oral cavities are

clearly exposed. The esophagus is collapsed in this specimen.
138 The Anatomy of Sea Turtles

NERVOUS SYSTEM

esophagus tongue glottis

trachea

hyoid

pineal cerebellum

cerebrum

olfactory bulb

olfactory nerve

nasal

sac

optic nerve

spinal

cord

medulla

fourth

ventricle

Figs. 200a and 200b. Parasagittal cut near the midline of a subadult hawksbill

turtle (close up). The subdural space is relatively large in the hawksbills. In this

dissection, the medulla was sliced so a portion is displaced ventrally to an abnormal

position. Structures from other systems are clearly exposed in this dissection. The

tongue, glottis, and trachea are shown with the supporting hyoid skeletal structure.

a

b
NERVOUS SYSTEM

interorbital

septum

salt gland

nasal sac

cerebellum

glottis

palate

premaxilla

supraoccipital

crest

spinal cord

covered with

spinal

meninges

atlas

trachea

tongue

axis

cervical

vertebra 3

oral papillae

esophagus

esophageal

papillae

body of hyoid

olfactory

nerve

olfactory bulb

cerebrum

pineal

optic lobe

cartilaginous part of

brain case

a

b

The Anatomy of Sea Turtles 139

Figs. 201a and 201b. Midsagittal section of an adult leatherback head. The braincase is largely cartilaginous around the dorsal and anterior aspects of the forebrain and midbrain. The parietal and frontal skull bones cover this cartilaginous

portion of the braincase. The brain is partially decomposed and has collapsed. The

extremely hypertrophied salt gland is visible where a portion extends medial to the eye.
140 The Anatomy of Sea Turtles

NERVOUS SYSTEM

medulla

spinal

meninges

esophagus

with

papillae

cerebellum

optic lobe

cartilage

cerebrum

pineal

olfactory bulb

olfactory nerve

nasal sac

optic nerve

interorbital

septum oral papillae

tongue

infundibulum

(pituitary) salt gland

Figs. 202a and 202b. A midsagittal cut of an adult leatherback head (close up). The

brain is partially decomposed, however the pineal is still attached to the skull roof

dorsally and the infundibulum remains attached to the pituitary ventrally. The

largely cartilaginous positions of the braincase are typical of leatherbacks.

a

b
NERVOUS SYSTEM

The relative sizes of parts of the brain vary through

ontogeny. The brain is proportionately larger in

hatchlings and juveniles than in subadults and

adults (Fig. 203). The olfactory nerves become

proportionately longer and the cerebral

hemispheres, optic lobes, and cerebellum are

proportionately smaller in subadult and adult turtles.

Peripheral Nerves -- The spinal nerves form the

peripheral nervous system. They leave the spinal

cord as paired dorsal and ventral nerve roots and exit

the vertebrae via intervertebral foramina. The dorsal

nerves are composed of somatic and visceral sensory

nerve fibers and may contain motor fibers as well; the

ventral roots are generally composed of both somatic

and visceral motor nerve fibers. These nerves function

as the autonomic nervous system. The autonomic

nervous system of turtles has both sympathetic and

parasympathetic components. However, these are

not anatomically segregated as "thoracolumbar"

sympathetic and "craniosacral" parasympathetic

regions as in mammals. Hence, nerves arising

along the length of the spinal cord may have both

sympathetic and parasympathetic components.

Two networks of interconnected spinal nerves, the

brachial plexus and sacral (= lumbosacral) plexus,

are associated with control of the limbs. They are

poorly described in the literature on sea turtles. In

cheloniids they are formed by ventral nerve roots and

their branches. The brachial plexus (Figs. 204-206)

arises at the level of cervical vertebrae VI-VIII in sea

turtles. These cervical nerves form a complex network

innervating the pectoral, arm (humerus), and flipper

muscles (Table 1) as well as sending branches to the

respiratory muscles. Most muscles receive innervation

from more than one branch of the plexus. A ventral

branch of nerve VI makes a large contribution to the

median nerve. Nerves VII & VIII give rise to the

inferior brachial nerve, which immediately divides

to form the superficial radial nerve and the deep

radial nerve to the anterior shoulder and dorsal flipper.

Next, the supracoracoideus, subscapular, and

ulnar nerves arise and travel to those pectoral muscles

and the ventral side of the flipper. The deltoideus

nerve arises primarily from nerves (VI and VII). 

There are no descriptions available for the brachial

and sacral plexuses of Dermochelys.

Fig. 203. Dorsal views of the brains of hatchling and juvenile turtles shows the negative allometric

growth of the brain relative to the size of the head. Hatchlings have disproportionately large brains.

The Anatomy of Sea Turtles 141
Fig. 204. The brachial plexus of a hawksbill. The brachial plexus arises from the most

posterior cervical vertebrae. Its nerves innervate the pectoral muscles and flippers. The

carapace and connective tissues have been removed to provide this posterodorsal view

of the brachial plexus. Its 3 rami arise from the intervertebral foramina and immediately

undergo a series of divisions and interconnections to form the nerves of the brachial plexus.

NERVOUS SYSTEM

142 The Anatomy of Sea Turtles

deep radial

nerve

supracoracoideus

nerve

subscapular

nerve

VIII

VII

VI

inferior

brachialis

nerve subscapularis

muscle

coracobrachialis

nerve

ventral

nerve VII

deltoideus nerve

triceps

humeral head

tractor ulnar nerve

radii muscle

pectoralis

major muscle

inferior

brachial nerve

deltoideus

muscle

Fig. 205. Branch of the brachial plexus of a hawksbill (ventral view). The inferior

brachial nerve of the brachial plexus travels along the ventral and anterior aspect of

the flipper. The ulnar nerve is seen branching off. The other main nerve of the arm,

the median nerve, is deep to the inferior brachial nerve and cannot be seen.
NERVOUS SYSTEM

Fig. 206. Diagram of the right brachial plexus

based upon cheloniids. The three roots of the

brachial plexus and their interconnections to the

flipper and shoulder musculature are shown.

Branches to ventral muscles go to the pectoralis,

biceps superficialis, biceps profundus, and the

deltoideus Larger branches are shown as thicker

lines. The most distal branches are not shown.

The Anatomy of Sea Turtles 143

The sacral plexus (Figs. 207-208) arises as 4

(sometimes 5-6) rami (branches) from spinal

nerves XVII-XXI, located on the last dorsal and

sacral vertebrae. These nerves interconnect and

subdivide several times as they send nerves to the

inguinal, pelvic, and hind leg muscles (Table 1).

Many muscles receive multiple innervations. The

more posterior nerves roots give rise to the

obturator nerve, going to the ventral pelvic

muscles, and the ichiadicus nerve, which runs

medial to the ilium and then divides to form the

peroneal and sciatic nerves. The anterior two

nerve roots interconnect provide major

innervations (via crural, femoral, and tibial

nerves) to the inguinal muscles, thigh adductors,

and leg extensors. 

to anterior

shoulder

to radial side

of flipper

to ulnar side

of flipper

to humerus

to coracobrachialis

to

respiratory

muscles

VI VII VIII

to ventral muscles }

}

to subscapularis
NERVOUS SYSTEM

sciatic nerve

iliofemoralis muscle

iliofibularis

muscle (cut) femorotibialis (cut)

peroneal nerve

ambiens

muscle

obturator nerve

femoral nerve

crural

nerves

tibial nerve

tail

XX IXX

XVII

XVIII

Fig. 208. Diagram of the right sacral plexus

(lateral view) based upon cheloniids. The roots

of the sacral plexus and their interconnections

to the pelvic, inguinal, and hind limb

musculature are diagrammed. Thicker lines

represent larger branches. The most distal

branches are not shown. The lone branch

medial to the ilium is the oburator nerve to the

ventral pelvic muscles.

144 The Anatomy of Sea Turtles

Fig. 207. The sacral plexus

of a hawksbill. This lateral

view of the sacral plexus

shows four roots giving rise

to the interconnecting

nerves that innervate the

hind limb and respiratory

muscles of the inguinal

region. The most posterior

branch of the sacral plexus

extends posteriorly, medial

to the ilium, and then

travels along the posterior

hind limb. It gives rise to

the sciatic, tibial and

peroneal nerves that

innervate many of the distal

hind limb muscles.

ilium

XXI XX IXX XXVIII

XXVII

to

posterior

foot

to ventral

foot

to posterior leg & leg flexors

to anterodorsal lower leg

to dorsal

& anterior thigh

to inguinal & thigh muscles

to inguinal muscles

}
NERVOUS SYSTEM

Brachial Plexus Innervations

Inferior brachial nerve Tractor radii

Superficial radial nerve Latissimus dorsi

Deep radial nerve Latissimus dorsi

Supracoracoideus

Testoscapularis

Supracoracoideus nerve Supracoracoideus

Pectoralis major

Biceps brachii (profundus and superficialis)

Subscapular nerve Subscapularis

Axillary (= Deltoideus) nerve Deltoideus (ventral parts)

Brachialis

Radial nerve Latissimus dorsi

Teres major

Tractor radii

Triceps brachii (humeral head)

Respiratory muscles

Ulnar nerve Deltoideus (dorsal head)

Latissimus dorsi

Subscapularis

Extensor radialis

Medial flipper muscles

Extensors of digits

Median nerve Coracobrachialis

Flexor carpi ulnaris

Flexors of digits

Sacral Plexus Innervations

Crural nerve Inguinal muscles

Thigh protractors (Triceps femoris complex)

Femoral nerve Puboischiofemoralis

Dorsal hip muscles

Obturator nerve Ventral hip muscles

Caudi-ilioformoralis

Ischiotrocantericus

Adductor femoris

Flexor tibialis (internus & externus)

Pubotibialis complex

Ischiadicus nerve Posterodorsal hip muscles

Sciatic nerve Gastrocnemius

Iliofemoralis

Ventrolateral foot extensors

Peroneal nerve Triceps femoris (ambiens, femorotibialis, Iliotibialis)

Gastrocnemius

Foot flexors

Tibial nerve Flexor tibialis (internus & externus)

Ambiens

Pubotibialis Inguinal muscles

Foot extensors

Table 1. Major innervations by the nerves of the brachial and sacral plexuses. Nerves are named using

mammalian nerve terminology.

The Anatomy of Sea Turtles 145
146 The Anatomy of Sea Turtles

SENSE ORGANS

Sense Organs

Chemical, visual, acoustic, and vestibular senses

of sea turtles are concentrated in the head. 

The tongue (Fig. 209) is a muscular organ covered

by a mucous membrane. Taste buds are present but

are poorly characterized. The tongue lacks obvious lymphoid tissue at its posterior, as is seen in

mammals.

The nose includes external nares leading to an

olfactory (nasal) sacs. The olfactory sac communicates via the nasopharyngeal duct to the internal

choanae (internal nares; Figs. 195 and 210). The

olfactory sacs and choanal folds are covered with a

ciliated sensory epithelium. The olfactory epithelium, located posterodorsally in the nasal cavity, is

innervated by the olfactory nerve leading to the

olfactory bulb (Figs. 189, 193-201). The

vomeronasal organ (Jacobsen's organ) of turtles is

not typical in its structure. This specialized sense

organ, usually associated with detection of airborne

and substrate-borne odor molecules, is not recessed

in a separate pit as in snakes and some lizards. It is

widely distributed anterolaterally and ventrally in

the olfactory sac. The vomeronasal organ is distinguished from olfactory epithelium by region and

histological characteristics rather than gross

appearance. It is innervated by nerves running to

Fig. 210. The sense organs of a

green turtle. The nares lead to

large pigmented olfactory sacks.

There are several choanal folds

on the walls of the olfactory sac,

which lack bony supports. The

olfactory sac leads, via the

nasopharyngeal duct to the

internal choanae. The olfactory

nerve is cut in this dissection and

has fallen ventrally. The inner

cavity is cut ventral to the brain;

the cochlea is also cut and part

is exposed at the ends of the

inner ear pointers. The middle

ear is located more laterally and

hence is not seen in this view.

inner ear nasopharyngeal duct

salt gland

olfactory

sac

nares

eye

(medial view)

Fig. 209. Dorsal view of the tongue of the Kemp's ridley. The tongue is muscular and attached to the floor

of the mouth. The surface is grossly smooth. The

epithelium is covered in small, short, flat papillae.

glottis
SENSE ORGANS

the accessory olfactory bulb (effectively the dorsal

part of what is grossly called the olfactory bulb).

A series of small spike-like papillae line the

lateral margin of the internal choane in C. mydas.

These papillae are absent or poorly developed in

other species.

The anterior tissue lining the nares is highly vascular

and erectile in adult sea turtles. It appears not to

have a sensory function but instead has the ability

to seal the nostrils when the turtles are submerged. 

The eyes of sea turtles are round and housed in

bony orbits. The eye is protected by dorsal and

ventral lids. The ventral lid is continuous with the

conjunctiva, which forms its inner surface. The

nictitating membrane, at the anterior and ventral

corner of the eye, also is continuous with the

conjunctiva (Figs. 198-200). 

iris

palpebral

scales

dorsal lid

secondary

lid

ventral lid

nictitating

membrane

pupil

sclera

Figs. 211a and 211b. Eye and

lids of a loggerhead. The eyes

are located dorsally and

anterolaterally. They have

overlapping fields of view

(hence, binocular vision). The

dorsal and ventral lids are

keratinized and mobile. The

secondary lid is also keratinized

but not mobile. The cornea,

not labeled, is a clear portion

of the sclera that overlies the

iris and pupil. Palpebral

scales are found in the margins

of the ventral lid in cheloniids,

but not in Dermochelys.

The Anatomy of Sea Turtles 147

a

b
148 The Anatomy of Sea Turtles

SENSE ORGANS

Figs. 212a and 212b. Leatherback eye. The lids of the leatherback eyes are

positioned as more anterior and posterior lids than dorsal and ventral lids.

sclera

iris

pupil

nictitating

membrane

posterior

(ventral) lid

external

nares

anterior

(dorsal) lid
Fig. 213. Leatherback eye dissection. The lids of this leatherback eye were removed

to show the extent and position of the nictitating membrane. 

sclera

iris

conjunctiva

(cut)

external

nares

nictitating

membrane

conjunctiva

(cut)

SENSE ORGANS

The Anatomy of Sea Turtles 149
150 The Anatomy of Sea Turtles

SENSE ORGANS

The wall of the eye (or globe) is composed of 3

major layers: the sclera, uvea, and retina,

surrounding the viscous vitreous body. The eye is

supported medially by cartilage and laterally by

scleral ossicles (Figs. 82-84). The outer-most

layer is the sclera. The eye muscles attach to the

sclera (Figs. 215-216). The superior oblique

muscle inserts dorsally and it is innervated by the

trochlear nerve. The superior rectus muscle

attaches posteriorly. Ventral to these muscles is the

attachment of the internal rectus muscle.

Anteriorly, the pyramidalis muscle extends from

the eye to the eyelids and nictitating membrane.

Deep and ventral to the pyramidalis muscle are the

inferior oblique and inferior rectus muscles. The

external rectus muscle is located posteriorly and

ventrally and is innervated by the abducens nerve.

The superior rectus, inferior rectus, inferior oblique

and internal rectus muscles are all innervated by

the oculomotor nerve.

Fig. 214. Sagittal section

of a loggerhead eye. The

eye is cut into medial and

lateral halves. The retina

and back of the eye are on

the left. The inside of the

iris, lens, and pupil are in

the middle of the photo.

Part of the vitreous body

was removed and placed

on the right.

Fig. 215. Lateral view of a loggerhead

left eye. The extrinsic eye muscles are

extended radially in this picture to show

their relative insertion points. Normally

their origins would converge on the

interorbital septum.

retina

sclera

iris

vitreous body

(cut)

lens

coroid

(of uvea)

superior

oblique

Harderian

gland

medial

rectus

ANTERIOR

DORSAL superior

rectus

lateral

rectus

external

rectus

salt gland

(cut)

inferior

oblique
SENSE ORGANS

The sclera, often termed the "white of the eye" in

vertebrates, is partially pigmented in most sea

turtles. The sclera is clear at the front of the eye;

there it is termed the cornea. Internal to the sclera

is the uvea, composed of the choroid, tapetum

lucidum, ciliary body, and the iris (Fig. 199). The

choroid is pigmented and extends from the iris to the

retina. It includes the reflective material (tapetum

lucidum) that is responsible for "eye-shine”. The

reflective material enhances the eye's sensitivity

under low light conditions. The ciliary body (not

shown), is responsible for changing lens shape

during visual accommodation. It extends from the

choroid near the front of the eye, to the attachments

that suspend the lens. The iris is pigmented brown

or black and extends from the choroid across the

front of the eye. The limbus (= limbas) is the tissue

between the cornea and the sclera. Because the

cornea and sclera are continuous with one another,

the limbus represents a transitional zone that is

usually described histologically (not labeled in the

figures). The free border of the iris forms the edge of

the pupil. The lens is strongly curved in sea turtles

(Fig. 214). It is suspended behind the pupil and iris

by "ligaments" attached to striated muscles of the

ciliary bodies. The chamber of the eye is filled with

a clear viscous liquid, the vitreous body. 

The eyes are photoreceptors that are capable of

color and shape discrimination. The retina is the

sensory layer of the eye; it detects color as well as

brightness. The retina is composed of several cell

layers and includes several types of rods and

cones, each containing photopigments. 

The ears of sea turtles are responsible for hearing

and equilibrium. Each ear consists of an external

tympanum covered by a tympanic scale that

stretches across the otic notch (= auditory canal)

formed by the quadrate, quadratojugal and

squamosal bones (Fig. 28). There is middle and

inner ear but no outer ear. The middle ear is

involved in sound transduction while the inner ear

functions in sound reception and the detection of

Fig. 216. Loggerhead left eye (medial

view) showing extrinsic eye muscles.

The extrinsic eye muscles are

responsible for eye movements. Also

shown is the Harderian gland, which

lubricates the eye and a portion of the

salt gland (an organ primarily

responsible for salt excretion and

maintaining water balance). The

retractor muscle surrounds the optic

nerve and positions the eye deeply or

shallowly in the orbit.

lateral

rectus

superior rectus

superior

oblique

optic

nerve

Harderian

gland

medial

rectus

external

rectus

retractor

muscle

salt gland

(cut)

inferior

oblique

ANTERIOR

DORSAL

The Anatomy of Sea Turtles 151
152 The Anatomy of Sea Turtles

position and acceleration. The middle ear contains a

single ear bone, the stapes (= columella). The stapes

extends from the tympanum via an extrastapedial

process of cartilage (Fig. 217), through the

tympanic cavity and recessus cavi tympani, to

articulate via an expanded footplate (also cartilage)

on the vestibular window of the cochlea (Fig. 218).

A Eustachian tube extends to each middle ear from

the mouth near the jaw joints (Fig. 165).

The inner ear of turtles is composed of the cochlea

and 3 semicircular canals, all of which are encased

in bone. The cochlea is involved in sound

transduction and is innervated by the auditory

nerve; it transmits sound information to the brain.

The semicircular canals sense the head's position

and movement by detecting changes in acceleration

in the three planes. One canal resides in each plane

(sagittal, coronal, and axial) in each ear.

Fig. 217. The tympanum of a ridley ear. The

tympanic scale has been removed to expose the

tympanum and the distal-most aspect of the

extrastapedial process (at arrow).

Fig. 218. Ventral view of a ridley

ear. The coronal section exposes

the tympanic cavity (= the otic

notch of a skull) and, more medially

the recessus cavi tympani. The

footplate of the stapes articulates

with the vestibular window. 

SENSE ORGANS

tympanum

stapes

tympanic cavity

brain

cochlea

recessus cavi

tympani
UROGENITAL SYSTEM

Urogenital Anatomy

The urogenital system (UG) is made up of the

kidneys, ureters, gonads and their ducts, the urinary

bladder, and derivatives of the genital papilla

(penis or clitoris) in the floor of the cloaca. The

kidneys function in removal of nitrogenous wastes

(excretion) and maintaining water and electrolyte

balance (osmoregulation). The ureters transport

nitrogenous wastes to the cloaca where it either drains

into the urinary bladder or is eliminated. The gonads

(ovaries or testes) produce gametes and their ducts

transmit eggs or sperm to the cloaca. They are

reproductive structures. The urinary bladder

functions in water and urine storage. The cloaca is

the common chamber into which the ureters,

gonadal ducts, rectum, and bladder empty. The

cloaca leads to the outside of the body via the vent.

Excretory System. The kidneys are paired, lobular,

elliptical red structures that are located

retroperitoneally (between the peritoneum and the

shell). Sea turtle kidneys are metanephric,

meaning (1) they arise from the posterior part of

the nephric ridge in the embryo and (2) the kidney

tubules are drained by ureters (metanephric ducts).

The ureters extend from the kidney, through the

peritoneum and empty into the dorsal cloaca on

each side. Ureters are located on the ventral

surface of each kidney. They drain uric acid,

ammonia, and water to the cloaca. Each ureter

enters the cloaca with a gonadal duct via a

urogenital papilla in the urodeum portion of the

cloaca (Figs. 219 - 220). 

Fig. 219. Diagram of the Urogenital System. The

relative positions of the kidneys, gonads

(undifferentieted for diagrammatic purposes),

accessory ducts, urinary bladder, rectum and

cloaca are shown. Anterior is to the left. 

The Anatomy of Sea Turtles 153

gonadal duct

urinary bladder

plastron

anus

urodeum

urogenital

papilla

rectum

carapace

kidney

ureter

cloaca

genital papilla vent

tail

accessory

urinary bladder

gonad

lung
UROGENITAL SYSTEM

Fig. 220. Lateral view of the cloaca of an immature hawksbill. The lateral wall of

the cloaca has been cut away to show the urogenital papillae from the oviducts and

ureters, the opening to the urinary bladder, and the dorsally positioned anus from

the rectum. The urinary and genital ducts enter the cloaca adjacent to one another

in females. They are small and located as the lateral walls of the urogenital papillae. 

The kidneys of sea turtles lack a distinct cortex

and medulla. Sea turtle nephrons are composed

of a renal capsule, proximal tubule (which is

linked to water transport and protein synthesis), an

intermediate segment (function unknown), distal

convoluted tubule (responsible for fluid

reabsorption) and collecting tubule (draining to

the ureters). There is no loop of Henle as is found

in mammalian nephrons. Unlike higher

vertebrates, marine turtles retain the ability to

form new functional nephrons as they mature (and

perhaps throughout life).

Blood flows through the kidneys from afferent

vessels entering (renal arteries and iliac veins),

and efferent vessels leaving (renal portal and renal

veins) the kidneys. Water and mineral waste (a

filtrate) is removed from the blood at the renal

corpuscle (glomerulus plus renal capsule).

The urinary bladder is a highly elastic, single,

sack-like structure located along the midline of the

pelvis. It opens via a single opening to the ventral

floor of the cloaca (Figs. 219-221). The bladder is

located ventrally and urine, water, and sometimes

other waste products may enter it via the cloaca.

This anatomical position and the connection of the

cloaca to the outside sometimes allows materials

other than urine (e.g., fecal material, parasites, or,

in females, eggs) to enter opportunistically.

Sea turtles have two small accessory urinary

bladders connected to the urinary bladder; each

located lateral to the neck of the urinary bladder

and dorsal to the pubis (Fig. 221). They are seldom

filled and often are missed in dissections.

Gonads. The gonads of both species are located

dorsally in the body cavity, posterior to the lungs,

and ventral to the kidneys and peritoneal wall

Figs. 222 and 223). 

clitoris

anus

urogenital

papilla

neck of

urinary

bladder

kidney

154 The Anatomy of Sea Turtles

POSTERIOR
UROGENITAL SYSTEM

Fig. 221. Dorsal view of the

urinary bladder and dorsal pelvis

of a male loggerhead. The empty

urinary bladder and accessory

bladders are shown free of

connective tissues. The ilia are

found laterally; the sacral and

proximal caudal vertebrae are

present dorsally. The sacral

plexus is exposed in part. 

pubis

tail

urinary

bladder

sacral

plexus

accessory

urinary

bladder

The Anatomy of Sea Turtles 155

Figs. 222a and 222b. Testes of an immature green

turtle. The testes are attached to the peritoneal wall

by their flat dorsal surface. Lateral and slightly

dorsal to each testes is an epididymis, which leads

to a vas deferens. The surface of the testis is smooth

in immature turtles.

lung

dorsal

aorta

epididymis

mesorchium

testes

a vas deferens b
immature

oviduct mesotubarium

mesovarium

immature

ovary

dorsal

aorta

lung

Figs. 223a and 223b. Ovaries of an immature

green turtle. The ovaries are attached to the

peritoneal wall by their lateral edges. The surface

of the ovary is granular. Lateral to the ovary is the

immature oviduct, which is suspended by the

mesotubarium.

156 The Anatomy of Sea Turtles

UROGENITAL SYSTEM

Female: The female reproductive tract consists of

paired ovaries, oviducts (also called Müllerian

ducts), and the suspensory ligaments or

mesenteries (mesovarium, mesosalpinx, and

mesotubarium). The ovary and oviduct change

in size and composition with age and between

breeding and nonbreeding seasons. 

The cranial pole of the ovary is located just

posterior to the lung and extends posteromedially

toward the cloaca. Along its medial and dorsal

surface, it is attached by the mesovarium to the

peritoneum that overlies the kidney (Fig. 224)

Another ligament, the mesotubarium, extends from

the ovary to the oviduct. The oviduct lies lateral to

the ovary and extends anteriorly, before curving

medially and ending in a funnel shaped opening,

the ostium. The ostium, which receives ovulated

follicles, is supported by the mesosalpinx. There

are no tubules connecting the ovary directly to the

oviduct. The posterior end of each oviduct joins the

urodeum of the cloaca (Fig. 225). 

a b
Figs. 224a and 224b. Ovary and accessory ducts of a juvenile green turtle,

(ventral view). This immature ovary has a granular surface. Its follicles have not

yet added significant amounts of yolk. The immature oviduct is a thin, flat tube

supported in the mesentery (mesotubarium). Engorged renal arteries and veins

can be seen extending from the kidney, anatomically dorsal to the ovary, and

toward the midline. 

The Anatomy of Sea Turtles 157

UROGENITAL SYSTEM

right

lung liver

right lobe

renal

arteries

and vein

kidney

ovary

immature

oviduct

pelvis

mesotubarium

a b
158 The Anatomy of Sea Turtles

UROGENITAL SYSTEM

peritoneum

immature

oviducts

colon

(cut)

right

lung

left lung

pelvis

(reflected posteriorly

and ventrally)

ovaries

urinary

bladder

Figs. 225a and 225b. Immature ovary and oviduct (ventral view). The immature

ovary is thin and located more medially than the oviduct. The immature oviduct

extends anteriorly then turns posteriorly. The ostium is formed at the expanded end.

The oviduct, mesotubarium, and mesosalpinx are reflected laterally. 

a

b
In hatchlings, the ovaries are difficult to

distinguish from testes. If histology is unavailable,

the attachment of the mesovarium to the ovary

edge and the lack of a coiled vas deferens suggest

that the gonad is an ovary. In older turtles, the

gonad will be pink and will have a grainy texture

as small follicles become more distinct. As turtles

approach maturity, some follicles increase in size

and start to accumulate bright yellow yolk. In

sexually mature turtles, mature follicles tend to

cluster along the cranial aspect of the ovaries.

Immature follicles are most concentrated in the

posterior third of the ovary. Mature turtles that

have nested previously will have large follicles

that are ~2-3cm in diameter and scars from

previously ovulated follicles, corpora albicans

(Fig. 226). Recently ovulated follicles leave active

scars, each is called a corpus luteum. The corpus

luteum becomes a corpus albicans after it ceases to

produce the hormone progesterone. The ages of

corpora albicans are difficult to judge, however

larger ones are generally more recent than smaller

ones. It is safest to use this information simply to

determine if the turtle had nested previously or not.

The Anatomy of Sea Turtles 159

UROGENITAL SYSTEM

oviduct with

shelled eggs

corpora

albicans

mature &

maturing

folicles

shelled

eggs

Figs. 226a and 226b. Eggs, follicles, and corpora

albicans in a reproductively active loggerhead.

This oviduct holds shelled eggs. Above the oviduct

are several sizes of maturing follicles and the

scars (corpora albicans) remaining from the sites

of ovulated follicles. 

a b
The oviduct of immature turtles is a thin walled

tube (Figs. 224-225). As females mature, the walls

of the oviduct thicken and the lumen increases in

diameter. It appears folded along its length when

not active (Fig. 227). The oviduct can be described

functionally (but not in gross structure) as having 5

regions: the ostium (or infundibulum), aglandular

segment, magnum, shell gland, and vagina. The

ostium remains thin-walled but increases in size

(Figs. 228-229). The oviduct of mature females is

muscular and mobile. It is assumed that the ostium

migrates across the ovary surface collecting the

ovulated follicles. 

160 The Anatomy of Sea Turtles

UROGENITAL SYSTEM

distal

oviduct

urodeum

mesotubarium

proximal

oviduct

Figs. 227a and 227b.

Mature oviduct of a

leatherback. The mature

oviduct has a large

lumen and the walls

have undulatory folds.

The mesosalpinx and

mesotubarium enlarge to

accommodate the mature

structures. The distal

ends would normally

enter the cloaca. The

proximal end is the site

of the ostium.

a

b
UROGENITAL SYSTEM

Figs. 228a and 228b. The ostium of an immature oviduct. The ostium is flattened when

not active; the funnel-shaped opening is small in young turtles.

The Anatomy of Sea Turtles 161

mesosalpinx

ostium

immature

oviduct uterine

veins

a

b
162 The Anatomy of Sea Turtles

UROGENITAL SYSTEM

ostium of

mature

oviduct

Figs. 229a and 229b. The ostium of a mature

oviduct. The ostium of this leatherback's oviduct

is large, funnel-shaped and thin walled. The base

of the ostium opens into the aglandular part of the

proximal oviduct.

In preparation for nesting, an entire clutch of

follicles matures and ovulates together. Once in the

ostium, each follicle travels past the aglandular

segment and into the magnum (anterior glandular

region) where it is coated with layers of albumen.

After about 3 days, the follicles pass to the shell

gland where the protein and carbohydrate shell

membrane (chorion) and the aragonite shell matrix

are secreted. The shell calcification takes about 6 to

7 days. Eggs pass to the vagina where they remain

until deposition, several days later. During

deposition, the posterior oviduct allows eggs to pass

to the cloaca, then out the vent into the nest. The

cloaca forms a tubular orifice in nesting turtles. The

structures that form this "egg tube" are unknown.

Males: The male reproductive tract consists of

paired testes, epididymi, deferent ducts (vas

deferens = ductus deferens), suspensory ligaments

(mesorchium from the body wall to the testis),

and a single penis. Müllerian ducts may persist as

a pair of small, flat, thin-walled tubes in some

males. When present, they are located along the

lateral body wall (suspended by a mesotubarium)

from the duct to the testis or peritoneum overlying

the kidney. They will often extend toward the

anterior third of the body, lateral to the lung. 

The testis is fusiform shaped (Fig. 222). The

cranial pole is located just posterior to the lung; it

extends posteromedially toward the cloaca. Along

its dorsal surface, it is attached by the mesorchium

to the peritoneum overlying the kidney. The testis

is light tan or yellow in some species and gray to

pink in others. Sperm are produced in the testis

and are conveyed via very small efferent ductules

to the epididymis, which lies lateral or

posterolateral to the testis. The vas deferens leads

from the epididymis to the cloaca at the base of the

penis, demarked by the corpra cavernosum (Fig.

222). The testis, epididymis, and vas deferens

change in size and form with age and between

a b
breeding and nonbreeding seasons (Fig. 230).

Testes in mature breeding males are often twice as

long as their diameter and filled with white fluid

(sperm and accessory gland fluid).

The genital papilla elongates into the penis during

maturation. The penis is retracted except during

mating, trauma, or death; it lies in the ventral floor

of the cloaca. It is composed of a pair of corpora

cavernosa and a "urethral groove" (= sulcus

spermaticus; Fig. 231). During mating, the corpora

cavernosa are supplied with blood via the

hypogastric and internal iliac veins. When erect,

the walls of the urethral groove meet dorsally to

form a functional tube through which sperm and

fluids pass. Some species have ornamented

structures (e.g., spines or flaps that have a

triradiate form) on or near the glans penis at the

distal tip (Fig. 232).

Fig. 230. Mature loggerhead

testis and accessory ducts

(posteroventral view). The

testes, epididymis, and vas

deferens in a mature male

during breeding season. The

vas deferens lead to the base of

the penis in the ventral floor of

the cloaca.

Fig. 231. Adult loggerhead penis

(dorsal view). The marine turtle

penis is part of the ventral floor

of the cloaca. The two corpora

cavernosa function in penile

erection and elongation. The

urethral groove, between the two

cavernous bodies conveys sperm

during mating. The penis is

completely housed within the

cloaca when not erect.

UROGENITAL SYSTEM

The Anatomy of Sea Turtles 163

vas

deferens

epididymis cloaca

rectum

glans penis

urethral groove

corpus

cavernosum

cloacal floor

and musculature
164 The Anatomy of Sea Turtles

UROGENITAL SYSTEM

Fig. 232. Tail and penis of a Kemp's ridley.

The long tail and distally positioned vent

are distinctive of adult male turtles. This

animal has a semi-erect penis with a

subterminal horn on the ventral lobe of the

glans penis. Not all species have

ornaments on the penis. Generally,

maturing males have a more distally

positioned vent than a female of the same

body size. However, not all males start

maturation at the same size, so the

combination of tail length and cloacal

position should be used with caution when

identifying the sex of the turtle.

Fig. 233. Tail of an adult female Kemp's

ridley. The short tail and cloaca located

proximally are characteristic of females

and immature males. This female

protruded the cloacal opening as is seen in

nesting turtles. 
UROGENITAL SYSTEM

Fig. 234. Sexually mature male ridley. Male sexually

dimorphic characteristics include an elongated

tail, long curved claws, and, during breeding

season, the midventral plastron becomes soft.

The Anatomy of Sea Turtles 165

Sexual dimorphism. Adult females differ little in

external morphology from large, immature males.

Typically, females have a short tail and the cloacal

opening (vent) is located roughly half way

between the tip of the tail and the plastron's anal

scute (Fig. 232). Within the cloaca, the genital

papilla remains small as the clitoris on the floor of

the cloaca. (Fig. 219).

In the Western North Atlantic, female loggerheads

mature at an average SCL of 92 cm (range: 75-104

cm). Green turtle females mature and nest at an

average SCL of 97 cm (range: 83-113 cm) and

leatherback females are about 155 cm CCL (very

few nesting females have been measured on U.S.

beaches). The minimum size of a nesting female

leatherback in the USVI was 133 cm CCL.

Adult males are characterized by a long tail with

the cloacal opening near the tip, and strongly

curved claws on the second digit. During breeding

season, a decornification of the plastron occurs

along and to each side of the midline (Fig. 233).

The plastron becomes increasingly vascular and

edematous. Male leatherbacks, have slightly

concave plastrons. There is no evidence of

decornification or increased plastral vascularization

during leatherback breeding season. 
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168 The Anatomy of Sea Turtles
INDEX

A

abdominal scutes, 1-2, 4, 31

abdominal vein, 72, 74- 75, 79, 100, 101

abductors, 59-61

abducens nerve, 127-128, 150, see cranial

nerves

accessory urinary bladder, 153-156

acoustic nerve, 151, 152

acetabulum, 54-56, 152-155

acromion processes, 35-37, 51-52, 59, 61-63,

74-75, 111, 116

adductor femoris, 71, 73, 145

adductors, 56, 60, 65, 68, 70-73, 143

adenohypophysis, see pituitary

adrenal arteries, 78, 83-84

adrenal gland, 42, 84, 106, 124

afferent renal vessels, 154

aglandular segment, 160, 162

airway, 105-107, 109

albumen, 162

albumin, 119

alveolar surface, 26-27

ampulla of Vater, 111, 113

anal scutes 1-2, 4, 31

anatomical position, 1

anatomical terminology, 1

angular, 9, 11

anterior pancreatic veins, 103

anterior pancreaticoduodenal artery, 78, 80

anterior subscapular arteries, 77, 141

aortas, 37-38, 74, 76, 83, 117, 124, 156,

arteries, 37-38, 41-42, 59, 62-63, 74, 76-86,

95, 101, 103, 105, 116 - 118, 124, 154, 156

astragalus, 56-58

atlas, 9, 44-45, 136, 139

atria, see atrium

atrium, 38, 74, 121

auditory canal, 9, 11, 151

auditory nerve, 152

axial muscles, 68

axial skeleton, 43

axillary artery, 38, 77

axillary nerve, 145

axillary scale, 122

axillary vein, 79, 85

axis, 9, 45, 139

azygos artery, 86

azygos vein, 79, 85-86

B

basisphenoid, 9, 12, 125

BD, see body depth

beak, see rhamphotheca

biceps brachii, 59, 61-63, 65, 67, 86, 145

biventer cervical, 68, 87, 89-93

bladder, 40-41, 153-155

body depth, 31

brachial artery, 77, 99

brachial plexus, 59, 64, 141-143, 145

brachial vein, 79, 85

brachiocephalic artery, see brachiocephalic

trunk

brachiocephalic trunk, 38, 74, 76-78, 116,

brain, 8, 42, 105, 115-116, 125-141, 146, 152

braincase, 8-9, 12, 41, 115-116, 125, 130,

139-140

bronchi, see bronchus

bronchus, 40-41, 85, 105-107

C

calcaneum, 56-58

carapace scutes, 1-2, 4-8, 26-27, 102

carapace length, 28-29

carapace width, 28, 30

carapace, 1-2, 4-7, 26-30

Caretta caretta, 4, 6-7, 16-17, 25, 27, 41-

46, 50-51, 55, 71, 80, 86, 92, 94, 97, 101,

106, 108, 112, 120, 125, 129-132, 147,

150-151, 155

carotid artery, 69, 70, 76-78, 80, 117-118, 136

caudal artery, 83-86, see vertebral artery

caudal veins, 79, 102

caudal vertebrae, 45-46, 155

cavernous bodies, 161

cavum arteriosum, 74, 104

cavum pulmonae, 74, 104

cavum venosum, 74, 104

CCL, see carpace length

CCLmax, see curved carapace length

CCLmin, see curved carapace length

CCW, see curved carapace width

central nervous system, 125-141

centrale, 52-54

cerebellum, 42, 126-129, 131-141

cerebral aqueduct, 126-128, 132, 134

cerebral hemispheres, see cerebrum

cerebrum, 42, 127, 129, 131-141

cervical vertebrae, 9, 44-45, 66, 80, 94,

141-142

Chelonia mydas, 4-5, 13-15, 25-26, 46, 94,

98, 104, 110, 112, 119-121, 122-123,

126, 130, 133-134, 146, 156-157

Cheloniidae, 2

Cheloniids, 2-5, 11, 26-27, 35, 42, 46, 49,

51-53, 55, 62, 64, 71, 88, 104, 106, 110,

116, 129, 136-137, 141, 143-144, 147

choroid, 151

ciliary body, 151

circulation, 41, 74-104

circulatory system, 41, 74-104

CIRCUM, see circumference

circumference, 32

claws, 1-2, 5-7, 52, 165

clitoris, 154, 164-165

cloaca, 32, 39-42, 75, 83, 102, 108, 114,

153-154, 157, 160, 162-165

cloacal veins, 79, 102

CNS, see central nervous system

cochlea, 146, 152

coeliac artery, 78, 80, 82

collecting tubules, 154

colon, 39-41, 108, 111-112, 114, 121, 158

columella, see stapes

common bile duct, 39, 108, 111-113, 119-121

common cardinal vein, see precava

common carotids, 77-78

common iliac arteries, see iliac arteries

common mesenteric vein, 79, 100, 103

cones, 151

conjunctiva, 147, 149

coracoid processes, 35-37, 51-52, 59, 61-

64, 66-68, 74-75, 100, 111, 114

cornea, 147, 151

corporus albicans, see corpora albicans

corporus luteum, see corpora luteum

corpora albicans, 159

corpora luteum, 159

corpus albicans, see corpora albicans

corpus luteum, see corpora luteum

corpus cavernosum, 162-163

cortex, 154

costal arteries, 78-79, 83, 124

costal scutes, see lateral scutes

costal veins, 78-79, 83, 10, 102

cranial nerves, 42, 68, 98, 127-129, 131-

140, 150-151

crural nerve, 143-145

crural veins, 79, 100-101

CT images, 43, 50

curved carapace length, 28-29

curved carapace width, 30

curved plastron length, 31

D

deferent ducts, see vas deferens

dentary, 9, 11, 23, 44, 68, 131-132, 135

dermal ossicles, 49

dermochelyid, 4-5

Dermochelyidae 4-5

Dermochelys coriacea, 4-5, 23-25, 42,

107-108, 111-112, 115, 127, 129-130,

139-141, 148-149, 160, 162, 165

descending vena cava, see precava

diencephalon, 126-127

digital arteries, 77-78

digital veins, 85

distal convoluted tubule, 154

dorsal aorta, 41, 78, 80, 83-86, 124, 156

dorsal brachial vein, 78

dorsal muscles, 65-67, 87-93, 102

duodenal veins, 79, 100, 103

duodenum, 39, 80, 82, 108, 111-113, 119-121

dura mater, 42, 125, see meninges

E

ear, 109, 126, 129-130, 146, 151-152

efferent ductules, 162

efferent renal vessels, 79, 154

entoplastron, 50-52

epididymi, see epididymis

The Anatomy of Sea Turtles 169
epididymis, 156, 162-163

epigastric arteries, 78, 83-85, 102

epigastric vein, 79, 102

epimeningeal veins, 125

epiphysis, see pineal

epiplastron, 50

Eretmochelys imbricata, 4, 6-7, 21-22, 25-

26, 46, 94, 105, 108, 112, 120, 122, 129-

130, 137-138, 142, 144, 154

epiphysis, see pineal

esophageal arteries, 77-78

esophageal veins, 98

esophagus, 38-39, 69-70, 77, 83, 98, 108-

111, 117, 131, 135, 137-140

ethmoid, 125

Eustachian tube, 109, 152

excretory system, 153-155

external iliac arteries, 78, 84

external iliac vein, 100, 102

external jugular vein, 83, 85-98

external nares, 146, 148

external rectus muscle, 150

extrastapedial process, 152

eye muscles, 150-151

eyelids, 147-149 see lids

eyes, 42-43, 59, 115, 125-126, 130, 133,

146-151

F

facial nerve, 68-69, see cranial nerve

femoral scutes, 1-2, 4, 30

femoral artery, 78, 84, 101

femoral nerve, 142-145

femoral vein, 79, 100

femur, 55-58, 70

fibula, 55-58, 70

flexor tibialis, 71-73, 101-102, 144-145

flippers, 2, 5-7, 31-32, 35, 37-38, 43, 51-54,

59, 61-62, 65-67, 77, 99, 141-143, 145

follicles, 41, 157, 159-160, 162

fontanelles, 46, 48, 50

foot extensors, 71, 145

forebrain, 126-127, 139

forelimb muscles, 62, 65

fourth ventricle, 127, 132, 134, 138

frontal bone, 9, 125, 131, 139

frontal scale, 3

frontoparietal scale, 3, 116

G

gallbladder, 39-40, 80, 113, 119

gastric artery, 78, 80-82

gastric vein, 79, 82

gastropulmonary ligament, 106, 111

genital papilla, 153-154, 163

genital papillae, see genital papilla

glandular segment, 160-162, see oviduct

glenoid fossa, 51-52

glomerulus, 154

glossopharyngeal, 68, see cranial nerves

glottis, 38, 44, 105, 108, 134-140

gonadal arteries, 78, 83-84

gonadal ducts, 85, 153, see vas deferens,

oviducts,41, 156-163

gonadal veins, 79, 100

gonads, 40-42, 83, 85, 100, 153, 155, 159

great vessels, 35, 37-38, 76-77, 80, see

aortas, pulmonary trunk

greatest length, 29, see carapace length

green turtle, see Chelonia mydas

gubernaculum cordis, 37, 38, 74, 76

gular, 4

H

haemorrhoidal artery, 78, 85

Harderian gland, 114, 150-151

hawksbill, see Eretmochelys imbricata

head length, 30

head scales, 3, 130

head width, 30

heart, 35, 37, 38, 72-80, 85, 104, 111, 116-

117, 119

hepatic portal system, 100, 102-103, 119

hepatic portal vein, 85, 100, 102-103, 119

hepatic vein, 79, 100, 119

hepatopulmonary ligament, 106

hind limbs, 2, 43, 102, 145

hindbrain, 126-127

hip muscles, 71-73, 102, 145

HL, see head length

humeral, 1-2, 4, 31

humerus, 52-55, 59-60, 64, 67, 77, 141, 143

HW, see head width

hyoid, 9, 38, 43-44, 68-70, 95, 105, 109,

131, 138-141

hyoplastron, 50, 121

hypogastric vein, 79, 102

hypoglossal, 68, 127-128, see cranial nerves

hypoplastron, 50, 121

hypothalamus, 127

I

identification, 4-8, 13-27, 50-51

ileum, 39, 103, 108, 112

iliac arteries, 78, 84-86

iliac veins, 79, 100, 102, 154, 163

ilium, 46, 54-56, 71, 143-144

imbricate, 7

inferior mesenteric vein, 103

inferior oblique muscle, 150-151

inferior rectus muscle, 150-151

inframarginal, 4-5, 7-8, 34, 64, 120-122

infundibulum (brain), see pituitary

infundibulum (oviduct), see ostium

inner ear, 146, 151-152

interanal, see anal scutes

intergular scute, 1-2, 31

intermediate segment, 154

intermedium, 52-54

internal brachial vein, 79, 85

internal choanae, see internal nares

internal iliac arteries, 78, 84-85

internal iliac veins, 163

internal nares, 10, 13, 21, 22, 109, 146

internal rectus muscle, 150

interparietal scutes, 3

iris, 147-150

ischiadic veins, 102

ischiadicus nerve, 145

ischial tuberosity, 72

ischium, 54-56, 71

J

Jacobsen's organ, see vomeronasal organ

jaws, 3, 6, 8, 9, 13, 16, 18-19, 21, 23, 26-

27, 44-46, 61, 71

jejunum, 41, 110, 114

jugal, 9, 11-12

jugular vein, 72, 81, 84, 87-100, 120

K

Kemp's ridley, see Lepidochelys kempii

kidney, 40-42, 83-84, 86, 100, 102, 104,

106, 114, 124, 153-155, 157, 162

L

lamellar bone, 52, 55

large intestine, 38-39, 41, 84, 108

lateral scutes, 1-2, 4-9, 49

lateral ventricles, 132, 134

leatherback, see Dermochelys coriacea

left aorta, 38, 40, 74, 76, 78, 80, 82-83, 118

lens, 150-151

Lepidochelys kempii, 4, 7-8, 18, 20, 25, 27, 

41, 46, 51, 67, 94, 106-107, 129, 135-

136, 146, 164-165

Lepidochelys olivacea, 4, 7-8, 19-20, 25,

27, 67

leptomenix, 125

lids, 147-149

limbus (= limbas), 151

lipoidal veins, 79, 100

liver, 37-40, 74-75, 80-81, 102, 106, 108,

111, 113-114, 119, 121, 157

loggerhead, see Caretta caretta

longus colli muscles, 68, 70, 80, 98

loop of Henle, 154

lumbosacral plexus, see sacral plexus

lung, 38-42, 74, 76, 83-85, 104-107, 156-

158, 162

lymphatic vessels, 74

M

magnum, 160, 162

marginal scutes, 1, 6-7, 28-29, 34, 46, 49,

89-90, 92, 95, 97, 102, 121

marginocostal artery, 77-78, 83

marginocostal vein, 79, 100, 102

maxilla, 9-11, 16-19, 21, 23, 135-136

maxillary, see maxilla

170 The Anatomy of Sea Turtles

INDEX
maximum head length, 30

maximum head width, 30

maximum length, 29

Meckel's cartilage, 11

medulla, see brain or kidney

meninges, 94, 125, 134, 137, 139-140

menix, see meninges

mesencephalon, 127

mesenteric arteries, 103

mesenteric vein, 79, 100, 103

mesentery, 39, 103, 120, 157

mesorchium, 156, 162

mesosalpinx, 157-158, 161

mesotubarium, 156-158, 160, 162

mesovarium, 156-157, 158

metacarpal, 52-54

metanephric duct, 152

metatarsal, 56-58

metencephalon, 126-127

methods for dissection, 32-42

midbrain, 126-127, 139

middle ear, 109, 152

minimum length, 29

Müllerian ducts, see oviducts

muscle function, 59, 145

muscles, 35-37, 43, 52-53, 59-72, 85-87,

90, 92-94, 96-99, 101-102, 107, 132,

141-145, 150-151

myelencephalon, 126-127

N

nares, 9, 10, 13, 21-22, 111, 116, 134, 148-151

nasal sac, see olfactory sac

nasopharyngeal duct, 126, 133, 146

neck flexors, 68

nephrons, 154

nerves, 42, 59, 64, 68-69, 71, 73, 127-129,

141-145

nervous system, 59, 71, 125-145

neural bones, 45, 47-48

neurocranium, 8-9, 12, 115

neurohypophysis, see pituitary

nictitating membrane, 147-150

nostrils, see external nares

notch-to-notch length, see minimum length

over-the-curve length, see carapace length

nuchal bone, 45, 48, 51

nuchal scute, 2, 6-7, 28-29, 49, 89-95, 97

O

oculomotor nerve, see cranial nerves

olfactory bulb, 42, 127, 129, 131-140, 146

olfactory nerve, 127-128, 131-132, 134-

141, 146

olfactory sac, 105, 125-126, 131-140, 146

olfactory tracts, 42, see olfactory nerve

olive ridley, see Lepidochelys olivacea

opisthotic, 12, 68, 125

optic chiasma, 127, 132

optic lobes, 42, 126-127, 129, 131-137, 141

optic nerve, 127-129, 131-138, 140, 151,

see cranial nerves

orbits, 16, 18-20, 23, 42-43, 147

ostium, 157-158, 160-162

otic notch, 9, 11, 151

ovaries, 41, 83, 153, 156-160, see gonads

over-the-curve measurements, 28-30

over-the-curve length, 28

oviducts, 41, 154, 156-162

P

palate, 8, 10, 13-19, 21-27, 109, 132-134, 139

palatine, 10, 131

palpebral scales, 147

pancreas, 38-39, 80, 82, 103, 109, 111,

119-120

papilla (esophageal), 110-111, 139-141, 146

papilla (urogential), 114, 163, 153-154, 165

parathyroid, 116-118

parietal bone, 9, 11-12, 16, 68, 125, 131, 139

parietal notch, 16, 19, 21, 23

parietal scale, 3, 11-12, 16

pectoral apparatus, see pectoral girdle

pectoral artery, 63-64, 77-78

pectoral girdle, 35, 37, 43, 51, 59-60, 64,

107, 111

pectoral muscles, 36, 59-62, 66, 76-77, 82,

85-86, 100, 111, 121, 141-143, 145

pectoral scute, 1-2

pectoral vein, 63, 79, 86, 100

pelvic girdle, 43, 54-55, 59-60, 107, 114

pelvic muscles, 100, 102, 143-145

pelvic vein, 61, 100

pelvis, see pelvic girdle

penis, 102, 153, 162-164

pericardial sac, 74,

pericardial veins, 79, 100

pericardium, 37-38, 63, 74-76, 111

peripheral bones, 42, 45-46, 48, 50, 64

peripheral nerves, 141-145

peritoneum, 35-37, 40, 74, 76, 100, 106,

114, 119, 121, 153, 157, 162

peroneal nerve, 71, 73, 143-145

phalanges, 43, 52-54, 55-58

pia mater, see leptomenix

pineal, 116, 127, 129, 131-132, 134-140

pisiform, 52-54, 67

pituitary, 42, 115-116, 127-128, 131-132,

134, 136, 140

PL, see plastron length

plastron length, 31

plastron,1-2, 4-6, 31-32, 34-35, 42-43, 46,

50-51, 59, 110, 121-123, 165

pleural bones 2, 45, 48, 64

popletial veins, 100-101

pores, 4, 7-8, 35, 121-123

portal systems, 79, 100, 119

postcava, 79, 84, 100

postcentral scutes, 2, 28, see suprapygal scute

posterior muscles, 58-60, 71-74, 102

posterior pancreatic veins, 79, 103

posterior pancreaticoduodenal artery, 80

postorbital bone, 9, 11-12, 18

precava, 76, 79, 85, 88, 98-99

prefrontal bone, 9

prefrontal scale, 2, 4-6

premaxilla, 9-11, 16, 18-19, 21, 131, 134, 139

prootic, 12, 68, 125

proximal tubule, 154

pterygoid, 9-10, 12, 19, 131, 136

pterygoideus muscle, 70

PVTL, see tail length

pubis, 41, 54-56, 59, 61, 111, 154-155

puboischiofemoralis, 71-73, 145

pubotibialis, 71-73, 101, 145

pulmonary artery, 37-38, 74-78, 104-105

pulmonary system, 105-107

pulmonary trunk, 38, 76-78, 84, 104

pulmonary veins, 79, 85, 104

pupil, 147-151

pygal, 45, 48

pyloric sphincter, 39, 81, 108, 111-113

pyramidalis muscle, 150-151

Q

quadrate, 11

quadratojugal, 11-12, 69, 151

R

radial artery, 77-78

radial nerve, 64, 141-143, 145

radiale, 52

radius, 52-54, 59, 67

Rathke's glands, 120-123

Rathke's pores, 8, 35, 121-123

recessus cavi tympani, 152

rectum, 38-41, 102, 108, 112, 114, 153-

154, 163

renal arteries, 78, 83-84, 86, 154, 156

renal capsule, 154

renal corpuscles, 154

renal portal vein, 79, 100, 102, 154

renal veins, 114, 154, 157

respiratory muscles, 59, 62, 64, 141, 142-145

rete system, 85

retina, 150-151

rhamphotheca, 6, 26-27, 30, 131, 132

ribs, 43, 45-51

right aorta, 38, 40, 75-78, 83, 118

rods, 151

S

sacral plexus, 71, 141, 143-145, 155

sacral vertebrae, 45-46, 54-55, 143, 155

salt gland, 42, 115, 125, 139-140, 146, 150-151

scales, 1-8, 13, 116, 122-123, 151-152

scapula, 37, 51, 52, 59, 64-67, 77, 83, 85,

88, 99

scapular vein, 79, 85, 99

sciatic artery, 78, 84-85, 101

The Anatomy of Sea Turtles 171

INDEX
sciatic nerve, 73, 101, 143-145

scleral ossicles, 43, 150

SCLmax, see carapace length

SCLmin, see carapace length

scutes, 1-2, 4-7, 29, 31, 34, 46, 49, 102,

120-122, 165

SCW, see carapace width

secondary palate, 16-18, 21-23

sella tursica, 115-116, 128, 132

semicircular canals, 152

sense organs, 8, 146-152

sexual dimorphism, 164-165

shell gland, see glandular segment

shell membrane, 162

shoulder muscles, 62, 64, 66-67, 99, 107,

140, 143

sinus venosus, 38, 74, 76, 79, 85, 100, 111, 119

skull, 8-25, 42-44, 115, 128-129, 132-

140, 152

small intestine, 38-39, 103, 108, 111-112,

120-121

snout, 5, 8, 13, 16, 18, 20-21, 26-27, 42

species identification, 1-27, 50-51

spinal accessory nerves, 127-129, see

cranial nerves

spinal cord, 47, 127, 129, 138-139, 141

SPL, see plastron length

splanchnocranium, 8-9

spleen, 39, 82, 103, 108, 119-120

splenial, 9, 11

splenic vein, 79, 103

squamosal, 9, 11-12, 17, 68-69, 151

standard carapace length, 28

standard measurements, 28-32

stapes, 12, 152

statoacoustic nerve, see cranial nerves,

acoustic nerve

stomach, 38-39, 80-82, 102-103, 106, 108-

112, 119-121

straightline carapace lengths 28-29

straightline measurements, 28-31

subclavian arteries, 38, 76-78, 99, 115-118

subclavian vein, 79, 84, 88

sulcus spermaticus, see urethral groove

superficial limb retractors, 61, 72

superior mesenteric artery, 78, 80

superior oblique muscle, 150-151

superior rectus muscle, 150-151

superior vena cava, 85, 88, see precava

supernumery scales, 3

supracaudal scute, 2, 28, 49

supraoccipital, 9, 16, 30, 68, 70, 125, 131,

134, 137, 139

supraocular scales, see scales

suprapygal bone, 45, 48

suprapygal scutes, see supracaudal

T

tail length, 32, 164

tail, 46, 68, 72-73, 83, 85

tapetum lucidum, 151

tarsals, 56, 57

taste buds, 148

tela choroidea, 125-126, 131-132

telencephalon, 126-127

temporal bone, see squamosal

temporal scale, 3

tendons, 59, 64-65, 67-68, 71, 101

terminology, 1, 85, 145

testes, see testis, gonads

testis, 40-41, 82, 100, 114, 153, 156, 159,

162, 163, see gonads

thalamus, 127

third ventricle, 127, 132, 134

thoracodorsal artery, 99

thymus, 35, 38, 76, 116-118

thyroid artery, 38, 76-78, 116

thyroid, 35, 37-38, 76-77, 85, 116-117

thyroscapular vein, 79, 85

tibia, 57-58

tibial nerve, 71, 143-145

tibial vein, 100

TTL, see tail length

tongue, 38, 44, 68, 105, 108-109, 131, 133,

135-136, 138-140, 146

tools, 33

trachea, 37-41, 69- 70, 76, 95-96, 105-106,

109, 111, 117, 131, 133, 135, 137-139

transverse branch, see transverse cervical

branch

transverse cervical branch, 87, 94-95

transverse cervical muscles, 68, 86-97

trigeminal nerve, 68, 127-129, see cranial

nerves

trochlear nerve, 127, 150, see cranial nerves

tympanic cavity, 152, see otic notch

tympanic scale, 3, 151

tympanum, 151-153

U

ulna, 52-54

ulnar artery, 77-78

ulnar nerve, 141-143, 145

ulnare 52-54

ultimobranchial bodies, 116-118

ureters, 41-42, 114, 153-154

urethral groove, 163

urinary bladder, 40-41, 114, 153-155, 158

urinary papilla, 114, 153-154

urodeum, 114, 153, 157, 160

urogenital papilla, 153-154

urogenital system, 41, 153-165

uvea, 150-151

V

vagina, 160, 162

vagus nerve, 98, 127-128, see cranial

nerves

vas deferens, 41, 156, 159, 162-163

vascular circumflex, 85

veins, 79, 82, 85-98, 100-104, 114, 119,

125, 153, 157, 161, 163

ventral cervical arteries, 77, 95, 117-118

ventral hip muscles, 71-73, 145

ventral muscles, 59-60, 62, 65, 107, 143

ventral neck muscles, 68-69

ventricle (of brain), 126-128, 132, 134,

136, 138

ventricle (of heart), 38, 74-77, 102-104,

111, 118, 121

vertebrae, 47-48, 141-143, 155

vertebral arch, 45, 47

vertebral artery, 78, 84-85, 95

vertebral body, 9, 45, 47

vertebral branches, 83, 88-96

vertebral column, 41-42, 45, 102, 106-107

vertebral scutes, 1-2, 4, 6, 8, 49

vertebral vein, 79, 88-89, 93, 102

vesicular veins, 78, 100

vestibular, 146, 152

vision, 147-151

vitreous body, 150

vomer, 10, 18-19, 21

vomeronasal organ, 146

VTTL, see tail length

X

xiphiplastron, 50

172 The Anatomy of Sea Turtles

INDEX