Chap, xviii.j THE RECTUM. 417 



the connections of the bowel loose, prolapsus ani is 

 much more common in children than in adults. 

 Children are, besides, especially liable to such exciting 

 causes of prolapse as worms and rectal polypi. 



The rectum is about eight inches in length. Its 

 upper pai't, for some three inches, is entirely invested 

 by peritoneum. The serous membrane gradually 

 leaves its posterior surface, then its sides, and lastly 

 its anterior surface. Anteriorly, the peritoneum, in 

 the form of the recto-vesical pouch, extends in the 

 male to within three inches of the anus, while on 

 the posterior aspect of the gut there is no peritoneum 

 below a spot five inches from the anus. Thus, in 

 excision of the rectum, more of the bowel can be 

 removed on the posterior than on the anterior part of 

 the tube. It will be seen, also, that carcinomatous 

 and other spreading ulcers are more apt to invade the 

 peritoneal cavity when they are situated in the anterior 

 wall of the intestine. The internal sphincter 

 surrounds the lower part of the rectum, an inch above 

 the anus, and extends over about half an inch of the 

 intestine. Mr. Cripps has shown that the posterior 

 edge of the levator ani forms a distinctly felt free 

 border, which crosses the rectum, neai-ly at a right 

 angle at a point from one and a half to two inches 

 from the anus. 



By inserting the finger into the rectum the pro- 

 state and seminal vesicles can be readily felt and 

 examined, and that triangular surface of the bladder 

 explored through which puncture per rectum is made 

 (page 396). 



It will be understood that the prostate, when 

 enlarged, may encroach upon the cavity of the rectum 

 and greatly narrow its lumen. The position of the 

 seminal vesicles with regard to the bowel is such that 

 in violent attempts at defsecation they may be pressed 

 upon by the rectal contents, and so in part emptied. 

 B B 4 



