432 



DIGESTIVE SYSTEM OF THE DOG 



to the ileum. It is situated usually against the middle of the upper part of the right 

 flank, below the duodenum and the right branch of the pancreas/ 



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 ascendens) is very short. It 

 begins at the junction of the ileum and caecum, and passes forward along the inner 

 surface of the duodenum and the right branch of the pancreas till it reaches the 

 pyloric part of the stomach; here it turns inward and crosses the median plane, 

 forming the transverse part (Colon transversum). The thirtl or left part (Colon 

 descendens) passes backward in the sublumbar region along the inner border or 

 ventral surface of the left kidney; then inclines toward the median plane and joins 



the rectum.^ The caliber of the colon 

 ^-\.-,_ is about the same throughout. It has 



no bands nor sacculations. 



The mucous membrane of the 



caecum contains numerous solitary 



glands; they are found also in the first 



part of the colon. 



The rectum is almost completely 



covered with peritoneum, the line of peri- 



FiG. 337. — Cecum op Dog. 

 1, Ileum; .?, csecum; S, colon. (From Leisering's Atlas.) 



Fig. 333. — Ti:rmin.\tion of Ileum of Dog. 

 a. Colon; b, ca?cuni; c, ileum; d, ileo-csecal open- 

 ing; e, circular depression arouml end of ileum, (.\fter 

 P. Schumann.) 



toneal reflection being under the second or third coccygeal vertebra. At the junc- 

 tion 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 alwut 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-glantls. Fur- 

 ther 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 

 first coccygeal vertebrae and the sphincter ani externus. The retractors, together 

 with the coccygei, form a sort of pelvic diaphragm, analogous to that of man. 



THE LIVER 



The liver is relatively large, weighing usually about 5 per cent, of the body- 

 weight. It is divided into six or seven lobes by fissures which converge at the portal 

 fissure. When the gland is examined in the soft condition, all the lobes are visible 

 on the visceral surface, but usually only four on the parietal surface. 



The left lateral lobe is the largest, and is oval in outline. The left central lobe 



' Ellenberger and Baum state that the ca>cum may reach a length of 20 cm. in very large dogs. 



^ When the stomach is very fvill, it pushes the left portion of the colon over to the right, 

 producing an acute angle in place of a transverse branch. The terminal part of the colon is thus 

 oblique in direction. 



