2 oo TEXT-BOOK OF PHYSIOLOGY. 



The serous is a reflection of the general peritoneal membrane. 



The muscle is composed of both longitudinal and circular fibers. The 

 longitudinal fibers are collected into three narrow bands which are situated 

 at points equidistant from one another. At the rectum they spread out so 

 as to surround it completely. As the longitudinal bands are shorter than 

 the intestine itself, its surface becomes sacculated, each sac being partially 

 separated from adjoining sacs by narrow constrictions. The circular fibers 

 are arranged in the form of a thin layer over the entire intestine. Between 

 the sacculi, however, they are more closely arranged. In the rectum they 

 are well developed, and at a point an inch above the anus they form, as 

 stated above, the internal sphincter. 



The mucous membrane of the large intestine possesses neither villi nor 

 valvulae conniventes. It contains a large number of tubules consisting of a 

 basement membrane lined by columnar epithelium. They resemble the 

 follicles of Lieberkiihn. The secretion of these glands is thick and viscid 

 and contains a large quantity of mucin. 



The Movements of the Large Intestine. As a result of the actions of 

 saliva, of gastric, intestinal, and pancreatic juice, and of the bile, the food is 

 disintegrated and liquefied. The nutritive principles, protein, starches, sugars, 

 and fats, undergo chemic changes and are transformed into amino-acids and 

 peptids, dextrose, soap and glycerin, fat acids, under which forms they are 

 absorbed. After the more or less complete digestion and absorption of these 

 nutritive substances the residue of the food, comprising the indigestible and 

 undigested matter, passes out of the small intestine into the large intestine 

 and forms a portion of its contents. This residue consists of the hard parts 

 of the cereals, vegetable seeds, cellulose, etc., the quantity and variety of 

 which depend on the nature of the food. These substances, passing into 

 the large intestine along with the excrementitious matter of the bile, become 

 incorporated with the mucous secretions and assist in the formation of the 

 feces. 



Under the influence of a peristaltic movement similar to that wit- 

 nessed in the small intestine, all this excrementitious matter, deprived by 

 absorption of the excess of its contained water and nutritive material, is 

 gradually carried downward to the sigmoid flexure, where it accumulates 

 prior to its extrusion from the body. The effects of the peristaltic waves are 

 to some extent interfered with by anti-peristaltic waves which beginning in the 

 transverse colon run toward and to the cecum. An anti-peristaltic wave 

 occurs in the cat about every fifteen minutes and lasts for about five minutes. 

 The intestinal contents are thereby driven back toward the cecum. The 

 effect is a still further admixture with the secretions and exposure to the 

 absorbing mucosa. There is some evidence also that the anti-peristaltic 

 waves may force some of the liquefied contents through the ileo-colic opening 

 into the small intestine because of the relaxation of the ilio-colic sphincter 

 muscle. It is questionable if this ascending movement is a true peristalsis 

 inasmuch as the advancing contraction is apparently not preceded by an area 

 of inhibition or relaxation. It resembles rather the corresponding move- 

 ment manifested by the small intestine to which the term anastalsis has been 

 given, and is propagated along the muscle coat independently of the myen- 

 teric plexus. 



