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DIGESTIVE SYSTEM OF THE DOG 



The large intestine is two to two and a half feet (ca. 60 to 75 cm.) long in 

 average. Its cahber is about the same as that of the small intestine, and it has 

 neither longitudinal bands nor sacculations. 



The caectim averages about five or six inches (ca. 12.5-15 cm.) 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 right 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 coccygeal 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 

 either side leads into two lateral anal sacs (Sinus 

 paranales) ; these are usually about the size of a 

 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 



Fig. 443. — Sectional View of Ileum. 



Cecum, and Colon of Dog. 



1, Ileo-colic orifice; 2, caeco-colic orifice 



3, apex of caecum. 



1 In large dogs (e. g., St. Bernard or Great Dane) tlie caecum may reach a length of 45 cm. 

 (measiired along its curves) and a diameter of 3 cm. 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. 



- The 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. 



