ACTION Ol^' THE LARGE INTESTINE 129 



the bottom of this ccecum is a wormUlie extension a few 

 inches in length called the vermiform appendix. Inflamma- 

 tion of this appendix produces the disease known as 

 appendicitis. The appendix has no known function, and 

 is supposed to represent a remnant left in man's develop- 

 ment. From the point where the small intestine enters 

 the caecum the intestine extends upward, along the right 

 side, of the abdomen, across the cavity just below the 

 stomach and down the other side. These portions of the 

 intestine have the gi'eatest diameter (2 J inches) of any 

 part of the intestine and are called the ascending, trans- 

 verse, and descending colons according to position. At 

 the base of the descending colon is an S-shaped bend 

 called the sigmoid flexure, and from this a straight 

 portion (the rectum) proceeds to the external opening or 

 anus. 



The large intestine shows the same number of coats as 

 the small intestine. The muscular layer, however, is not 

 uniformly developed but arranged in bands separated by 

 spaces where it is wanting. This arrangement gives the 

 tube a puckered appearance. The mucous coat has no 

 valvulse conniventes but is filled with closely set simple 

 glands similar to the crypts of Lieberkiihn. 



Action of the large intestine. — By contractions of the 

 small intestine its contents are forced through the ileo- 

 colic valve into the large intestine. Before these con- 

 tents reach the large intestine, however, nearly all the 

 nutrient part has been digested and absorbed, and what 

 passes through the ileocolic valve consists mainly of indi- 

 gestible material called faeces. These faeces consist mainly 

 of water, cellulose, elastic tissue, and mucin. With these 

 substances may be present some starch and fat. If this 



EDDY. PHYS. — 9 



