Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/91

Rh 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 anus 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 permit 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 lobe 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 referred to as the right and left central 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