36 A COURSE ON ZOOLOGY. 



function is to retard the progress of the food and present 

 a larger surface for absorption. This membrane bristles 

 all over with a sort of little hairs or villi, which give it 

 the appearance of velvet, and which are true absorbent 

 organs. The serous membrane, or mesentery, is a pro- 

 longation of the peritoneum, a general serous membrane 

 which lines the abdomen. The mesentery forms loops 

 which sustain at various points the small as well as the 

 large intestine, thus separating the folds, and preventing 

 the tube from twisting and becoming tangled. Without 

 knowing the arrangement, it would be difficult to under- 

 stand how the food can pass through a tube so long and 

 so many times coiled on itself. It is also through the 

 mesentery that the nerves and the various vessels pass 

 to or from the intestines. 



Although the small intestine possesses about the same 

 form and the same structure throughout its entire length, 

 it has been arbitrarily divided into three sections, named 

 duodenum, jejunum, and ileum. The duodenum is the 

 portion directly connected with the stomach, and into it 

 empty two ducts, one of which carries the bile, and the 

 other the pancreatic juice. 



The large intestine is much shorter than the small 

 one, but it is much greater in diameter ; it also differs by 

 having numerous enlargements, by the very small num- 

 ber of absorbent organs, and by the absence of convolu- 

 tions. It is considered as made up of three portions: 

 first, the caecum, which is simply an enlargement into 

 which the small intestine opens ; then the colon, which 

 first passes upward in a straight line, bends over in 

 front of the stomach, and turns down, forming a letter 

 S. The rectum forms the end of the large intestine and 

 of the digestive tube. 



