Comparative Anatomy
Digestive System
Kardong
Chapter 13
Part 11
Digestive System

Agnatha - a straight digestive tube
 Coiling of tube evolved with lengthening of
tract
Figure 11.1. Simple to complex digestive systems—lower verts and birds (book figure 13.27).
Figure 11.2. Simple to complex digestive systems—m ammals (book figure 13.28).
Digestive System
Six major subdivisions
 Buccal cavity
 Pharynx
 Esophagus
 Stomach
 Small & large intestine
 Rectum
Buccal Cavity
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Begins at mouth, ends
at pharynx
Tongue in floor of cavity
Palate in roof of cavity
Primary palate
Secondary palate
Teeth
Figure 11.3. Buccal cavity in
monkey and shark.
Palates

Primary palate in
anamniotes- nasal
passageways empty into
buccal cavity
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
Ex: Salamander
Secondary palate of
amniotes- extends to
pharyngeal cavity

Internal nares
Figure 11.4. Buccal cavity of
amphibian (a) and mammal (b).
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On jaws normally
Cheeks in mammals form pocket
Acrodont teeth- fish
Bicuspid- amphibians
Tricuspid- lizards
Pleurodont teeth- snakes
Thecodont teeth- crocodilians
Teeth
Figure 11.5. Types of cusps (book figure13.15).
Figure 11.6. Cross section of jaw (book figure 13.10).
Cheek and Jaw Teeth
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Used for storage- rodents and squirrels
Modified placoid scales- sharks
Polyphyodont- permanent replacement of
teeth
Diphyodont- two sets of teeth
Monophyodont- one set of teeth
Reptilian Egg Tooth

Egg tooth - reptiles and snakes
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Actual tooth
Upper jaw
To penetrate eggshell
Figure 11.7. Monitor egg tooth.
Egg tooth of the lizard,
Aspidoscelis sexlineata
(from Trauth 1988)
Bird Egg Tooth

Egg caruncle- all egg layers
Not actual tooth
 Structure epidermal, horny,
keratinized
 On tip of snout
 To penetrate eggshell

Figure 11.8. Egg caruncle of 15
day old owlet.
Specialized Modifications of
Snake Teeth
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Aglyphous- no modifications
for venom delivery
Solenoglyphous- retractable
teeth, fangs (e.g.,
rattlesnakes)
Proteroglyphous- fangs in
front of mouth - cobras
Opisthoglyphous- fangs in
back of mouth – rear-fanged
species (hognose snake)
Figure 11.9. Position, cross and
longitudinal sections of aglyphous (1),
opisthoglyphous (2), and
solenoglyphous (3) fangs.
Mammalian Teeth
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Incisors
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Canines
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For piercing
Ex: walrus tusks
Premolars & Molars
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For cutting
Ex: elephant tusks
To matriculate food
Diastema- have incisors
but no canines
Figure 11.10. Mammalian teeth specializations
(heterodont dentition).
Figure 11.11. Deciduous and
permanent teeth (carnassials
shaded). (book figure 13.7)
Dental Formula
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Catarrhines, including humans, have
2-1-2-3=16 x 2 = 32 total teeth
Canids: 3-1-4-2 and 3-1-4-3
If 0 is present, diastema is present
Figure 11.12. Dental formula
for mammals.
Tongue
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Immobile in jawed fish
Fleshy in higher vertebrates
 Frog- tongue shoots out and draws back
 Glandular field secretes sticky fluid
Immobile tongue- turtles, crocs, and some
birds
Flexible tongue- nectar-feeding bats and
snakes
 Forked tongue of snake
Figure 11.13. Jacobson’s organ (sensing
apparatus) of snake.
Oral Glands

Named based on location
Labial- near the lips
 Palatal- near palate
 Internasal
 Sublingual- releases venom
 Parotid- salivary gland
 Submaxillary
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Birds have few oral glands
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Swifts
Figure 11.14. Swift and nest.
Figure 11.15. Oral glands of reptiles
Pharynx

In embryo, exhibits series of lateral pharyngeal
pouches
 Gives rise to various glands
 Slits in pharyngeal region
Figure 11.16. Embryonic pharyngeal
arches and oral development.
Figure 11.17. Adult regions of pharynx.
Pharynx

Constant features in tetrapods
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Glottis-slit to larynx
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Covered by epiglottis
Eustachian tube- opening
 Esophagus- opening
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Pharynx further subdivided for food and air
passage
Foramen cecum- groove on back of tongue

Vestigial structure that leads to thyroid gland
Pharynx
Figure 11.18. (a) Upper respiratory tract of human showing phayrnx regions and
(b) hyoid and larynx.
Esophagus
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Muscular tube connecting
pharynx and stomach
Can be short
Crop - specialization in birds
Outpocketing of esophagus
 Used to store food
 Pigeon’s milk
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Figure 11.19. Esophagus, crop,
and stomach of bird (see book
figure 13.32).
Stomach
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Muscular chamber
Secretes gastric juices
Different lining of stomachs
 Esophageal-like epithelia
 Glandular epithelia
Ruminant stomach
 4 chambers: rumen, reticulum,
omasum, abomasum
Human stomach
 Cardiac sphincter- esophagus
meets stomach
 Mostly lined with gastric
epithelium
Figure 11.20. Stomach of mammals with
esophageal-like epithelia in gray and
glandular epithelia in red.
Stomach Structure
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Greater and lesser curvature
Mesentaries
Greater omentum
 Lesser omentum
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Cecum - increases surface area
2 parts in bird and croc stomach
Proventiculus - glandular portion – secretes
digestive enzymes
 Gizzard - grinding mill (gastroliths)
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Four-chambered Stomachs
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Rumen - food enters
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Reticulum - forms a bolus
Omasum - reswallowed
grass
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Bacterial action
Salivary action
Abomasum- food worked
out by gastric glands
Figure 11.21. Stomach of calf
(see book figure 13.43).
Small Intestine
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Duodenum - 1st portion
Bile and pancreatic ducts
Jejunum and ileum
subdivisions
Figure 11.22. Digestive tract
showing regions of small intestine
in humans.
Small Intestine
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Brunner’s Glands- mucous glands in duodenum
Peyer’s patches- lymphatic nodules in ileum
Crypts of Lieberkühn - intestinal glands at base of villi
Lacteals- in villi within interior lymphatic vessels
 Transport fat molecules to circulatory system
Valve of Kirckring- increases surface area
Small Intestine
Figure 11.23. Histology of alimentary canal of a mammal showing
various glands of small intestine (book figure 13.26).
Large Intestine
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Fish and amphibians - straight and short
Amniotes - divided into colon and rectum
Ileocecal valve - allows passage from small intestine into
large
Sigmoid flexure - S shaped at rectum
Cecum - aids in absorption
 Terminates at vermiform appendix
Cloaca - common chamber for
digestive, urinary, and reproductive
products to empty
Figure 11.24. Large intestine of human.
Liver
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Liver is endodermal diverticulum
Liver produces bile
 Bile stored in gallbladder
 Common bile duct (combines cystic and hepatic ducts)
 Ampulla of Vater - terminal portion of common bile duct
Figure 11.25. Development of liver and pancreas (book figure 13.38).
Pancreas
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Pancreas is a diverticulum
Most people have a single pancreatic duct
Duct of Santorini - small, dorsal (accessory)
Duct of Wirsung - large, ventral
- functional duct after small, dorsal
accessory duct disappears
Exocrine and endocrine glands

Islets of Langerhans- endocrine glands

Rectal gland – diverticulum off hindgut in
sharks
“Another Notable Duct”
 Duct of Cuvier or Common Cardinal
Georges Cuvier (1769-1832) was “father” of
Comparative Anatomy and Paleontology
 2 ducts of Cuvier in most vertebrates – See
Circulatory System
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