Il8 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



From the posterior and inner aspect of the cecum runs off the 

 appendix vermiformis. The diameter of the colon gradually 

 decreases from two and a half to three and a half inches in the 

 cecum to the beginning of the rectum. The ascending colon 

 passes upward from its beginning in the right iliac fossa to the 

 under surface of the liver, where it bends upon itself almost at a 

 right angle (hepatic flexure). The transverse colon runs di- 

 rectly across the upper part of the abdominal cavity to the lower 

 border of the spleen, where an abrupt turn downward (splenic 

 flexure) begins the descending colon. The lower part of the 

 descending colon occupies the left iliac fossa in the shape of the 

 letter S, and is the sigmoid flexure. 



The rectum, which receives the contents of the sigmoid, is 

 not straight, as its name indicates. It curves (i) to the right to 

 reach the median line, (2) forward to follow the contour of 

 the sacrum, and (3) backward in the last inch of its course. 

 It has the shape of a dilated pouch, its lower termination at the 

 anus being guarded by the powerful external sphincter of stri- 

 ated muscle. Its diameter is greatest below. 



The vermiform appendix has the three coats common to the 

 intestine, but its muscular coat is ill-developed. The peritoneal 

 coat generally forms a short meso-appendix at the root of the 

 organ. The blood supply of the organ is not abundant. It is 

 greater in the female than in the male, a part of it coming 

 through the appendiculo-ovarian ligament. The appendix has 

 no function. 



The ileo-cecal valve, guarding the opening between the large 

 and small intestines, is made of two folds, upper and lower, of the 

 muscular and mucous coats, which folds project into the large 

 intestine. The serous coat runs directly over from the small 

 to the large intestine at their point of junction, without being 

 folded inward upon itself, as are the others. This prevents 

 obliteration of the folds by distention. By this arrangement the 

 two portions of the gut communicate only by a buttonhole slit, 



