502 DIGESTIVE SYSTEM OF THE DOG 
The large intestine is two to two and a half feet (ca. 60 to 75 em.) long in 
average. Its caliber is about the same as that of the small intestine, and it has 
neither longitudinal bands nor sacculations. 
The cecum averages about five or six inches (ca. 12.5-15 em.) in length, and 
is flexuous (Fig. 442). The flexures are maintained by the peritoneum, which 
attaches it also to the ileum. It is situated usually about midway between the 
right flank and the median plane, ventral to the duodenum and the right branch of 
the pancreas.!_ Its anterior end opens into the origin of the colon, lateral to the 
ileo-colic orifice. The other end is pointed and blind. 
The colon is attached to the sublumbar region by a mesentery—the mesocolon. 
It presents three parts, which correspond to the ascending, transverse, and descend- 
ing colon of man. The first or right part (Colon 
dextrum s. ascendens) is very short. It passes for- 
ward along the medial surface of the first part of the 
duodenum and the right branch of the pancreas till 
it reaches the pyloric part of the stomach; here it 
turns to the left and crosses the median plane, 
forming the transverse part (Colon transversum). 
The third or left part (Colon sinistrum s. descen- 
dens) passes backward in the sublumbar region 
along the medial border or ventral surface of the 
left kidney; it then inclines toward the median 
plane and is continued by the rectum. The cali- 
ber of the colon is about the same throughout. It 
has no bands nor sacculations. The mesen- 
tery of the colon is termed the mesocolon; it is 
given off from the left side of the common mesen- 
tery.? 
The mucous membrane of the caecum con- 
tains numerous solitary lymph nodules which are 
circular, with a central depression; some are 
present also in the first part of the colon. 
The rectum is almost completely covered with 
peritoneum, the line of peritoneal reflection being 
under the second or third coecygeal vertebra. At 
the junction of the rectum and anus the mucous 
membrane has a stratified squamous epithelium, 
and contains the anal glands. A small opening on 
Fic. 443.—Secrionat View or ILeum, 
Cacum, axp Coton oF Dos, either side leads into two lateral anal sacs (Sinus 
1, Ileo-colie orifice; 2, exco-colic orifice; paranales); these are usually about the size of 4 
3, apex of cecum. . 2 : * y 
hazel-nut, and contain a dirty gray, fatty substance, 
which has a peculiar and very unpleasant odor. 
The skin which lines these pouches contains coil-glands. Further back the skin 
contains large sebaceous glands and peculiar circumanal glands. 
The retractor ani muscle is extensive. It arises from the shaft of the ilium, 
the pubis, and the symphysis pelvis, and passes upward and backward to end on the 
1 Jn large dogs (e. g., St. Bernard or Great Dane) the cecum may reach a length of 45 em. 
(measured along its curves) and a diameter of 83cm. Its position is somewhat variable. It may 
be closer to the lateral wall, or more medial than is stated above. Its anterior end is usually 
in a transverse plane through the ventral end of the last rib if the stomach is not very full. 
2The arrangement of the colon is variable. The transverse part may be quite long and 
extend across from the angle of junction of the two branches of the pancreas to the dorsal end of 
the spleen. On the other hand, a transverse part may be absent, the colon forming instead an 
acute angle or flexure. When the stomach is empty and contracted, the transverse part of the 
colon may be separated from the ventral wall by the omentum only. 
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