2io TEXT-BOOK OF PHYSIOLOGY. 



portion of the large intestine below the orifice of the small intestine. 

 The posterior and inner wall presents a small opening which leads 

 into a narrow round process about four inches in length the vermi- 

 form appendix. The opening of the small intestine into the cecum is 

 narrow and elongated and bordered by two folds of mucous mem- 

 brane strengthened by fibrous and muscle-tissue. These folds 

 constitute the so-called ileo-cecal valve. When the cecum is dis- 

 tended the margins of these folds are approximated and effectually 

 prevent the return of material into the small intestine. 



The colon ascends to the under surface of the liver, where it bends 

 at a right angle, crosses the abdominal cavity to the spleen, bends 

 again, and descends to the left iliac fossa. At this point it turns upon 

 itself to form the sigmoid flexure. The rectum is a dilated pouch, 

 situated within the true pelvis. It measures from 15 to 18 centi- 

 meters in length. Within an inch of its termination at the anus it 

 presents a constriction formed by a circular band of muscle-fibers 

 the internal sphincter. 



The walls of the large intestine consist of three coats: viz., serous, 

 muscular, and mucous. 



The serous is a reflection of the general peritoneal membrane. 



The muscular is composed of both longitudinal and circular 

 libersi^The longitudinal fibers are collected int" tbrrr fiflTflW 

 bands which are situated at points equidistant from one another. 

 At the rectum they spread out so as to completely surround it. 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 sac- 

 culf; 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 valvuke eonniventes. It contains a large number of tubules 

 consisting of a basement membrane lined by eolumnar epithelium. 

 They resemble the follicles of Lieberkuhn. The secretion of these 

 glands is thick and viscid and contains a large quantity of mucin. 



Contents 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, 

 proteid, starches, sugars, and fats, undergo chemic changes and are 

 transformed into peptones T dextrose, soap and glycerin, fatty acids, 

 under which forms they are absorbed. After the 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 



