THE DIGESTIVE SYSTEM 



169 



The ileocecal valve (Fig. 86) is formed by two longi- 

 tudinal semilunar folds of mucous membrane at the ter- 

 mination of the ileum in the cecum, opening toward the 

 large intestine and guarding against reflux from the large 

 into the small intestine. 



The colon is divided into three parts the ascending, 

 the transverse, and the descending. The ascending colon 

 passes upward from the right hip-bone to the under surface 

 of the liver. It then bends inward and crosses the upper 

 part of the abdomen, below the liver and stomach, to the 



FlG. 86. The cecum, vermiform appendix, and ileocecal valve : A, The 

 ileocecal valve (Campbell). 



left side, under the name of transverse colon. At the 

 left side it turns and descends to the left hip-bone, and is 

 here called the descending colon. At this point it makes 

 a peculiar curve upon itself, called the "sigmoid flexure," 

 from its resemblance to the letter Si On its internal sur- 

 face the colon has many sac-like folds, which serve to 

 retain the contents in its passage for a long period. 



The rectum is the lowermost or last portion of the large 

 intestine, and terminates in the anus; at this point it is 

 surrounded by a sphincter or circular muscle that keeps 

 the orifice closed except during defecation. 



