Il8 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



caput coli. 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 directly across the upper part of 

 the abdominal cavity to the lower border of the spleen, where 

 an abrupt turn downward (splenic flexure) begins the de- 

 scending colon. The lower part of the descending colon oc- 

 cupies 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 ter- 

 mination at the anus being guarded by the powerful external 

 sphincter of striated 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 pro- 

 ject 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 dis- 

 tention. By this arrangement the two portions of the gut 

 communicate only by a buttonhole slit, which is easily 



