THE ABDOMEN, INTERIOR. 477 



downward to become the descending- colon. This bend is 

 the splenic flexure. At this point the transverse mesocolon 

 is seen to be continued to the under surface of the tenth 

 rib, forming the costocolic ligament or the sustentacu- 

 lum splenis, as it supports the spleen. 



The descending colon is covered like the ascending, 

 front and sides, the peritoneum at the right passing into 

 the left lower surface of the mesentery, to the left, to line 

 the lateral abdominal wall. In both the posterior surface 

 is usually bare ; this allows the bowel to be entered from 

 the back without opening into the general peritoneal cavity. 

 The large loop of intestine following the descending colon 

 is the omega loop, or the sigmoid flexure. It has a dis- 

 tinct mesentery about three inches long and the same 

 width. This allows the gut to hang free in the pelvic 

 cavity. When the hollow of the sacrum is reached the 

 peritoneum passes around to cover in the front of the rec- 

 tum, descending to a point about an inch above the level 

 of the tip of the coccyx, then reaches upward, covering in 

 the back and sides of the bladder until its top is attained, 

 from which point it is continued on to the anterior abdomi- 

 nal wall. The cavity between the rectum and bladder is 

 the rectovesical fossa. The peritoneal folds formed around 

 the rectum and bladder are termed the ligaments of those 

 organs. 



In the female the condition is altered by the interposition 

 of the uterus and vagina between the bladder and the 

 rectum. 



Posteriorly the peritoneum reaches as low as the upper 

 part of the vagina, anteriorly only to the lower part of the 

 uterus. The hollow behind the uterus is the rectovaginal 

 fossa, Douglas's pouch, the one in front of it the utero- 

 vesical. Laterally from the uterus the peritoneal folds 



