The Digestion of Food 



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166. The Coats of the Small Intestine. Like the stomach, 

 the small intestine has four coats, the serous, muscular, sub- 

 mucous, and mucous. The serous is the peritoneum. By the 

 contraction of the muscular coat the food is forced along 

 the bowel. The blood vessels and nerves are distributed in 

 the submucous coat. The inner, or mucous surface, has a 

 fine, velvety feeling, due to a countless number of tiny, 

 thread-like projections called villi. They stand up some- 

 what like the "pile" on velvet. It is through these villi 

 that the digested food passes into the blood. 



The inner coat of a large part of the 

 small intestine is thrown into numerous 

 transverse folds called valvulce conniventes. 

 These serve to increase the extent of the 

 surface of the bowels and to delay mechani- 

 cally the progress of the intestinal contents. 



167. The Peritoneum. The intestines 

 do not lie in a loose mass in the abdominal 

 cavity. Lining the walls of this cavity, just 

 as in a general way a paper lines the walls 

 of a room, is a delicate serous membrane 

 called the peritoneum. It envelops, in a 

 greater or less degree, most of the viscera 

 in the cavity, and forms folds by which 

 they are connected with one another, or are 



attached to the posterior wall. Its arrange- (Villi are seen sur- 



ment is therefore very complicated. When 



the peritoneum comes in contact with the 



large intestine, it passes over it just as 



the paper of a room would pass over a gas 



pipe which ran along the surface of the wall, and in passing 



over it binds it down to the wall of the cavity. 



The small intestines are suspended from the back wall of the 

 abdomen by a double fold of the peritoneum, called the mes- 

 entery. The bowels are also protected from external cold by 

 several folds of this membrane loaded with fat. This is known 

 as the great omentum. 



y 168. The Large Intestine. The large intestine begins in 

 the right iliac region and is about five or six feet long. It 

 is much wider than the small intestine, which opens into 



FIG. 55. A Small 

 Portion of the Mu- 

 cous Membrane of 

 the Small Intes- 

 tine. 



rounded with the 

 openings of the tubu- 

 lar glands. Magni- 

 fied 20 diameters.) 



