The Digestive System
EFE Veterinary Science
Overview of Digestive System
Schematic representation of the digestive apparatus in the dog. 1, Mouth; 2, salivary
glands; 3, pharynx; 4, esophagus; 5, stomach; 6, liver; 7, duodenum; 8, pancreas; 9,
jejunum; 10, ileum; 11, cecum; 12, colon; 13, rectum; 14, anus.
The Mouth (Dog)
General view of the oral cavity of the dog. 1, Vestibule; 2, canine tooth; 2′, philtrum;
3, hard palate; 4, soft palate; 5, tongue; 6, sublingual caruncle; 7, palatoglossal arch;
8, palatine tonsil; 9, frenulum.
Hard and Soft Palates
Dog and Cow
The hard and soft palate of the dog. 1,
Philtrum; 2, incisive papilla; 3, hard
palate with rugae; 4, soft palate; 5,
palatoglossal arch; 6, intrapharyngeal
ostium; 7, palatopharyngeal arches; 8,
esophagus.
The hard palate of a cow. 1, Dental pad; 2,
incisive papilla; 3, rugae of hard palate; 4,
palatine raphe; 5, P2; 6, buccal papillae
The Tongue (Dog)
The tongue of the dog. The soft palate and the esophagus are sectioned in the median
plane. 1, Apex; 2, body; 3, root, forming floor of oropharynx; 4, median groove; 5,
vallate papilla; 6, fungiform papillae; 7, palatoglossal arch; 8, palatine tonsil in tonsillar
fossa; 9, epiglottis; 10, frenulum.
Tooth Structure
Figure 03-13. Schematic longitudinal section of a simple
tooth. 1, Enamel; 2, dentine; 3, cement; 4, pulp; 5, apical
foramen; 6, periodontal ligament; 7, socket (alveolus); 8, gum.
Equine Premolars
Figure 03-14. Premolar teeth exposed in the upper jaw of a horse. The part protruding
above the gum is the clinical crown (1); the whole enamel-covered part is the
anatomical crown or body (2) of the tooth.
Deciduous (“baby”) Teeth
Figure 03-15. Schematic drawings representing tooth eruption and replacement. A,
Eruption of a deciduous tooth. The primordium of the permanent tooth is located on the
lingual side of the deciduous tooth. B, The fully developed deciduous tooth within a
bony alveolus. The crown of the permanent tooth has already formed. C, The permanent
tooth is ready to break through. The root of the deciduous tooth has been resorbed;
formation of the root of the permanent tooth is in progress.
Permanent Dentition of the Dog
Dental Formula of the dog: I3/3, C1/1, P4/4, M1/2
Permanent Dentition of the Cat
Dental Formula of the Cat: I3/3, C1/1, P4/4, M1/1
Permanent Dentition of the Pig
Permanent dentition of the pig, upper (A) and lower
(B) jaws. 1, Lingual surface; 2, vestibular surface; 3,
distal surface; 4, mesial surface.
Dental Formula: I3/3, C1/1, P3/4, M4/3
Permanent Dentition of the Horse
Figure 03-19. Permanent dentition of the horse,
upper (A) and lower (B) jaws. 1, Wolf tooth (P1); 2,
diastema.
Dental Formula: I3/3, C1/1, P4/4,
M3/3
Permanent Dentition of the Cow
Figure 03-20. Permanent dentition of cattle,
upper (A) and lower (B) jaws.
Dental Formula: I0/4, C0/0, P3/3,
M3/3
Muscles of Mastication
Figure 03-21. The muscles of mastication of the dog, left lateral aspect (A), in section (B).
1, Temporalis; 2, masseter; 3, 3′, rostral and caudal bellies of digastricus; 4,
mylohyoideus; 5, medial pterygoid; 6, origin of lateral pterygoid; 7, tongue; 8, mandible;
9, zygomatic arch; 10, level of transection (B).
The Pharynx
Figure 03-27. Schematic drawing of the pharynx showing its rostral connection with
the nasal and oral cavities and caudal connection with the esophagus and larynx. 1,
Nasal cavity; 2, oral cavity; 3, soft palate; 4, nasopharynx; 5, root of tongue; 6, larynx
(protruding through pharyngeal floor); 7, laryngopharynx (piriform recess); 8, caudal
end of palatopharyngeal arch; 9, esophagus; 10, lamina of cricoid cartilage; 11,
trachea.
Structures of the Neck
Figure 03-29. Lateral view of the
bovine neck. In midneck the
esophagus lies on the left dorsolateral
aspect of the trachea. 1, Esophagus; 2,
trachea; 3, pharyngeal musculature; 4,
sternocephalicus muscle; 5, nuchal
ligament.
Esophageal Structure
Figure 03-30. Semischematic drawing of the
structure of the esophagus, sectioned
longitudinally and transversely. 1, Mucosa; 2,
muscular layer (longitudinal and circular); 3,
adventitia.
Abdominal Viscera (Dog)
Figure 14-05. Abdominal viscera of the dog
after removal of the greater omentum. 1,
Liver; 2, stomach; 3, spleen; 4, small
intestine; 5, bladder.
Abdominal Viscera (Dog)
Figure 14-07. Visceral projections on
the left (A) and right (B) canine
abdominal walls. 1, Diaphragm; 2,
liver; 3, stomach; 4, spleen; 5, 5′, left
and right kidneys; 6, descending
colon; 7, small intestine; 7′,
descending duodenum; 8, pancreas;
9, rectum; 10, female urogenital
tract; 11, bladder.
Radiographs of the Canine Abdomen
Figure 14-08. Lateral (A) and ventrodorsal (B)
radiographic views of the canine abdomen. 1,
Liver; 2, pyloric part of stomach; 2′, descending
duodenum; 3, spleen; 4, os penis; 5, cecum; 6,
fundus of stomach; 7, left kidney; 8, bladder.
The Stomach (Canine)
Figure 03-35. A, Visceral surface of stomach (dog). 1, cardia; 2, pylorus.
Interior of the Stomach (Canine)
Figure 03-35. B, Interior of stomach (dog). 1, cardiac opening; 2, fundus; 3, body; 4,
pyloric antrum.
Comparison:
Monogastric, Hindgut Fermenter and
Ruminant
Figure 03-36. Gastrointestinal tracts of the dog (A), of
the horse (B), and of cattle (C) laid out in one plane. 1,
Stomach; 2, small intestine; 3, cecum; 4, ascending
colon; 5, descending colon
The Digestive Tract and Aortic
Branches
Figure 03-39. Distribution of the celiac artery of the dog (ventral view). 1, Aorta; 2,
celiac artery; 3, hepatic artery; 4, splenic artery; 5, left gastric artery; 6, left
gastroepiploic artery; 7, gastroduodenal artery; 8, right gastric artery; 9, cranial
mesenteric artery; 10, pancreas; 11, spleen; 12, stomach; 13, liver.
Canine Intestinal Tract
Figure 03-40. Intestinal tract of the dog (schematic). 1, Stomach; 2, descending
duodenum; 3, caudal flexure; 4, ascending duodenum; 5, jejunum; 6, ileum; 7, cecum; 8,
ascending colon; 9, transverse colon; 10, descending colon; 11, rectal ampulla; 12,
jejunal lymph nodes.
Barium Radiographs (Dog)
Figure 14-12. Lateral (A) and
ventrodorsal (B) radiographic views of
the canine abdomen after
administration of a barium suspension.
1, Stomach; 2, pyloric part; 3,
descending duodenum; 4, caudal flexure
of duodenum; 5, jejunum.
Barium Radiographs (Cat)
Figure 14-14. Lateral (A) and ventrodorsal (B)
radiographic views of the feline abdomen after
administration of a barium suspension. 1, Liver; 1′,
fat-filled falciform ligament elevating the liver; 2, gas
and barium in stomach; 2′, fundus; 2″, pyloric part of
stomach; 3, descending duodenum—the striking
“string-of-pearls” appearance (characteristic of cats)
is due to segmental peristalsis; 4, jejunum; 5,
ascending colon; 6, transverse colon; 7, descending
colon; 7′, gas in descending colon; 8, kidneys
(superimposed).
Abdominal Organs (Dog)
Figure 03-41. Ventral view of the abdominal
organs of the dog after removal of the
greater omentum. 1, Liver; 2, stomach; 3,
spleen; 4, descending duodenum; 5,
jejunum; 6, bladder; 7, diaphragm.
Canine Abdominal Organs
Figure 14-15. The canine duodenum, cecum,
and colon in situ; ventral view. 1, Liver; 2,
stomach; 3, spleen; 4, pancreas; 5, descending
duodenum; 6, ascending duodenum; 7, ileum; 8,
cecum; 9, 10, 11, ascending, transverse, and
descending colon; 12, vessels in root of
mesentery; 13, duodenocolic fold; 14, bladder.
Intestinal Structure
Figure 03-42. Transverse section
through the gut. The artery and
vein reach the gut via the
mesentery; the larger branches
fail to reach the antimesenteric
border. 1, Mucosa; 2, submucosa;
3, muscle layer; 4, serosa; 5,
mesentery.
Duodenal Villi (Rat)
Figure 03-43. Scanning electron micrographs of rat duodenal villi (A) and of a
vascular cast of the same tissue demonstrating subepithelial capillary plexuses (B).
Intestinal Lymph Nodules
Figure 03-44. Patch of aggregated lymph nodules in ileum (horse).
Large Intestines
Figure 03-45. Schematic drawing of the large intestine of the domestic mammals:
carnivores (Car), the pig (su), ruminants (Ru), and the horse (eq). Cranial is to the upper
right. 1, Ileum; 2, cecum; 3, ascending colon; 4, transverse colon; 5, descending colon;
6, rectum and anus; 7, aorta; 8, celiac artery; 9, 9′, cranial and caudal mesenteric
arteries; 10, 10′, dorsal diaphragmatic and pelvic flexures of ascending colon; 11, 11′,
proximal and distal loops of ascending colon.
Mesenteric Arteries (Dog)
Figure 03-49. Distribution of the cranial
and caudal mesenteric arteries to the
intestines of the dog (dorsal view). a,
Jejunum; b, ileum; c, cecum; d, ascending
colon; e, transverse colon; f, descending
colon; g, rectum. 1, Aorta; 2, cranial
mesenteric artery; 3, ileocolic artery; 4,
middle colic artery; 5, right colic artery; 6,
colic branch of ileocolic artery; 7,
mesenteric ileal branch; 8, antimesenteric
ileal branch; 9, jejunal arteries; 10, caudal
mesenteric artery; 11, left colic artery; 12,
cranial rectal artery.
The Portal Vein
Figure 03-50. Semischematic dorsal view of
the formation of the portal vein (dog). 1,
Portal vein; 2, splenic vein; 3,
gastroduodenal vein; 4, cranial mesenteric
vein; 5, caudal mesenteric vein; 5′, ileocolic
vein; 5″, middle colic vein; 6, left gastric
vein; 7, right gastroepiploic vein; 8, cranial
pancreaticoduodenal vein.
Liver (Comparative)
Figure 03-51. Caudal surface of the
liver of the dog (A), pig (B), horse (C),
and cattle (D). The median planes are
indicated. The liver is asymmetrical,
less so in the dog, more so in the pig
and horse, and most in cattle, in
which the bulk of the organ is
displaced to the right. Note the
absence of a gallbladder from the
horse liver.
Canine Liver
Figure 03-52. A, Visceral surface of liver (dog). 1, Gallbladder; 2, hepatic ducts.
Pig Liver
Hepatic Lobules (Pig)
Pig Liver
Figure 03-54. B, Liver (pig) (28×). 1, central v.; 2, interlobular a.; 3, hepatic lobule; 4,
interlobular connective tissue; 5, centrolobular venule.
Bile Drainage (Dog)
Figure 03-55. The bile drainage system of the dog. 1, Gallbladder; 2, bile duct; 3, cystic
duct; 4, hepatic ducts.
The Pancreas (Canine)
Figure 03-56. The pancreas of
the dog (caudal view). 1,
Esophagus; 2, stomach; 3,
cranial flexure of duodenum; 4,
descending duodenum; 5, left
lobe of pancreas; 6, body; 7,
right lobe; 8, caudal flexure of
duodenum; 9, bile duct; 10,
mesoduodenum.
Canine Abdominal Viscera
Abdominal Viscera (Horse)
Figure 21-06. Visceral projections on the left abdominal wall (including the
diaphragm). 1, Cut edge of diaphragm; 1′, rib 6; 2, stomach; 3, liver; 4, spleen; 5,
descending colon (banded); 6, jejunum (smooth); 7, left dorsal colon; 8, left ventral
colon.
Abdominal Viscera (Horse)
Figure 21-07. Visceral projections on the right abdominal wall (including the
diaphragm). 1, Cut edge of diaphragm; 1′, rib 6; 2, liver; 3, right kidney; 4, descending
duodenum; 5, body of cecum; 6, right ventral colon; 7, right dorsal colon.
Equine Digestive Tract
Figure 21-11. The intestinal tract
seen from the right, schematic. The
caudal flexure of the duodenum and
the cranial mesenteric artery (17)
have been displaced to the right of
the animal to lie over the base of
the cecum. 1, Stomach; 2, 3,
descending and ascending
duodenum; 4, jejunum; 5, ileum; 6,
cecum; 6′, cecocolic fold; 7, right
ventral colon; 8, ventral
diaphragmatic flexure; 9, left ventral
colon; 10, pelvic flexure; 11, left
dorsal colon; 12, dorsal
diaphragmatic flexure; 13, right
dorsal colon; 13′, ascending
mesocolon; 14, transverse colon; 15,
descending (small) colon; 16,
rectum; 17, cranial mesenteric
artery.
The Equine Stomach
Figure 21-09. B, Notice the white mucosa
of the fundus. The Gastrophilus larvae
are an incidental finding in this part of
the stomach. 4, Margo plicatus is clearly
visible.
The Equine Cecum
Figure 21-13. The cecum in situ. 1, Base of cecum; 2, body of cecum; 3, apex of
cecum; 4, right ventral colon.
Bovine Abdominal Viscera
Figure 28-04. Topography of the abdominal viscera. A, Relationship of abdominal
viscera to the left abdominal wall. 1, Esophagus; 2, outline of spleen; 3, reticulum; 4,
dorsal sac of rumen; 5, ventral sac of rumen, covered by superficial wall of greater
omentum; 6, fundus of abomasum, covered by superficial wall of greater omentum.
Interior of the Bovine Stomach
Figure 28-04. Topography of the abdominal viscera. B, The interior of the stomach seen
from the left. 3, reticulum; 4, dorsal sac of rumen; 7, reticular groove; 8, body of
abomasum; 9, atrium ruminis; 10, caudodorsal blind sac; 11, caudoventral blind sac;
12, ventral sac of rumen (opened).
Bovine Stomach (left)
Figure 28-07. A, Bovine stomach, left side. 1, Reticulum; 2, omasum; 3,
abomasum; 4, rumen.
Bovine Stomach (right)
Figure 28-07. B, Bovine stomach, right side. 2, omasum; 3,
abomasum; 4, rumen.
Rumen (papillated mucosa)
Figure 28-16. A, Rumen papillated mucosa taken from a Waterbuck (left) and a lesser
Kudu.
Reticulum
Figure 28-16. B, Reticulum: mucosal ridges outlining “cells” characteristic of the
reticular mucosa (cow).
Stratification of Ingesta
Figure 28-17. Stratification of ingesta in the ruminoreticulum, left lateral view. 1, Gas
bubble; 2, coarse forage (“floating mat”); 3, more finely ground material with higher
specific gravity than 2; 4, liquid zone; 5, atrium ruminis; 6, reticulum; 7, esophagus
The Omasum
Figure 28-21. A, Internal surface of omasum (cow). 1, Omasal
laminae
The Abomasum
Figure 28-21. B, Internal surface of abomasum (cow). 1, Abomasal
folds.
The Abomasum
Figure 28-22. Opened abomasum as seen from behind, above, and slightly from the
left. 1, Omasoabomasal opening through which the omasal laminae can be seen; 2,
abomasal folds; 3, fundus; 4, body; 5, pyloric part; 6, torus pyloricus; 7, pylorus.
Bovine Intestinal Tract
Figure 28-26. Right lateral view of the bovine intestinal tract, schematic. 1, Pyloric
part of abomasum; 2, duodenum; 3, jejunum; 4, ileum; 5, cecum; 6, ileocecal fold; 710, ascending colon; 7, proximal loop of ascending colon; 8, centripetal turns of
spiral colon; 9, centrifugal turns of spiral colon; 10, distal loop of ascending colon;
11, transverse colon; 12, descending colon; 13, rectum; 14, jejunal lymph nodes; 15,
Avian Oropharynx
Figure 37-14. Oropharynx opened by the
reflection of the lower jaw. 1, Median
and lateral palatine ridges; 2, openings of
salivary glands; 3, choana; 4, infundibular
cleft; 5, body of tongue; 6, root of
tongue; 7, “mechanical” papillae; 8,
laryngeal mound; 9, glottis; 10, branchial
cornu of hyobranchial apparatus; 11,
esophagus; 12, position of trachea.
The Avian Neck
Figure 37-15. Ventral view of the dissected
neck. B, Detail of neck with crop. 5, trachea; 7,
esophagus; 8, crop.
Avian Viscera
Figure 37-16. Viscera after
removal of ventral body wall,
ventral view. 1, Esophagus; 2,
trachea; 3, pectoralis, cut; 4,
crop; 5, sternotrachealis; 6,
coracoid bone, cut; 7, right
cranial vena cava; 8, heart; 8′,
common carotid artery; 8″,
subclavian artery; 9, 9′, right
and left lobes of liver; 10,
gizzard (its caudal blind sac);
11, duodenal loop, enclosing
pancreas; 12, vent; 13, one of
the ceca.
Avian Stomach
Figure 37-17. Stomach, ventral surface (A) and opened ventrally (B). 1, Esophagus;
2, proventriculus; 3, papillae; 4, deep proventricular glands, visible on cut surface;
5, lumen of gizzard; 6, caudal blind sac; 7, cranial blind sac; 8, pyloric orifice; 9,
cranioventral muscle mass; 10, duodenum.
The Avian Stomach
Figure 37-18. Stomach of chicken. 1, Esophagus; 2, spleen; 3, proventriculus; 4,
gizzard with aponeurosis (4′); 5, duodenum.
Opened Avian Stomach
Figure 37-19. Opened stomach. Note grit inside gizzard (right).
Avian Intestinal Tract
Figure 37-20. Isolated intestinal tract with
detail of ileocolic junction. 1, Pylorus; 2,
2′, dorsal and ventral lobes of pancreas; 3,
duodenal loop; 4, bile and pancreatic
ducts entering duodenum; 5, jejunum; 6,
vitelline diverticulum; 7, ileum; 7′, ileum
opened; 8, ileocecal fold; 9, ceca; 9′,
cecum opened; 10, cecal tonsil; 11, colon;
11′, colon opened; 12, cloaca; 13, vent.
The Avian Cloaca
Figure 37-22. Median section of the cloaca,
semischematic. 1, Colon; 2, coprodeum; 2′,
coprourodeal fold; 3, urodeum; 3′,
uroproctodeal fold; 4, proctodeum; 5, vent;
6, ureteric orifice; 7, papilla of deferent
duct; 8, position of oviduct orifice (only on
left side); 9, cloacal bursa; 9′, dorsal
proctodeal gland; 10, skin; 11, tail feather;
12, uropygial gland; 12′, papilla of uropygial
gland; 13, muscles surrounding caudal
vertebrae.