272 THE ORGANS OF DIGESTION 



front of it are the belly wall and some coilsof small 

 intestine. The peritoneum forms a loose mesocolon 

 for it. It is the narrowest part of the colon. 



The Rectum. This is the lowest part of the large 

 intestine, and extends from the sigmoid flexure to the 

 anus. It has been divided into three parts: the first 

 part extends from the left sacro-iliac joint to the 

 centre of the third piece of the sacrum; the second 

 part, to the tip of the coccyx; and the third part, to 

 the anus. 



The rectum is about 8 inches long and somewhat 

 cylindrical in form, narrower above than the sigmoid 

 flexure, but it enlarges as it descends, and just above 

 the anus is remarkably dilated, forming the ampulla. 

 The first part has a mesorectum; the second part is 

 covered by peritoneum in front and laterally; the third 

 part has no peritoneal covering. 



The cul-de-sac of Douglas (rectovaginal pouch) is the 

 space in front of the rectum and behind the cervix 

 of the uterus and upper fourth of the vagina. It is 

 formed by the peritoneum reflected over the rectum 

 to the vagina and uterus. In the male it is the space 

 formed between the rectum and bladder, and is called 

 the rectovesical space or pouch. 



The Structure of the Large Intestine. The large 

 intestine has three coats comprising its w^all: A serous, 

 muscular, and mucous. Its mucous membrane does 

 not possess the valvulse conniventes nor villi; it is lined 

 by columnar epithelium, and contains a large number 

 of tubules lined by columnar epithelium; they resemble 

 the glands of Lieberkiihn, and secrete a viscid fluid, 

 rich in mucin. (See Fig. 83, page 204, for blood- 

 supply of the large intestines.) 



