THE DIGESTIVE SYSTEM 77 



and ileum, to the region of the stomach. Here the colon 

 (transverse colon) circles dorsally and to the left as far 

 as the sagittal plane of the body. The descending colon 

 follows approximately the sagittal plane of the body back 

 to the rectum. The ascending limb of the duodenum lies 

 at the right of the descending colon, and both are close 

 to the dorsal surface of the abdominal cavity. The rectum 

 is the continuation of the colon through the pelvis. It 

 terminates posteriorly at the anns^ where the feces are 

 expelled. There is no sharp boundary between colon and 

 rectum. The dark fecal matter in the colon forms pellets 

 shaped like cotton seeds. Wherever these masses occur 

 the inner surface of the colon is smooth. Elsewhere the 

 lumen is practically devoid of feces and the surface is 

 thrown into prominent folds, the colic ridges. The absence 

 of ridges and the greater diameter of the colon where the 

 fecal pellets occur shows that at least one purpose of the 

 ridges is to x>ermit distension of the mucous membrane of 

 the colon without undue strain upon it. 



The liver is a firm, bulky, dark red organ lying in the 

 anterior region of the abdominal cavity. Its convex, 

 cranial surface rests against the concave posterior face 

 of the diaphragm. Ventrally it rests upon the abdominal 

 wall. Its caudal surface is concave and is in contact with 

 the stomach and intestines. The organ is deeply cleft 

 into several very distinct lobes and lobules. 



The median lohe occupies a median position in front of 

 the other lobes of the liver. A longitudinal fissure near 

 the sagittal plane of the body partly divides this into two 

 lateral lobules, approximately equal in size, sometimes re- 

 ferred to as the right and left <^entral lobes. This fissure 

 extends from the thin posterior edge of the lobe nearly to 

 the ventral border of the diaphragm, where it receives the 

 round ligament. Dorsal to this point the two lobules are 



