THE DIGESTIVE SYSTEM 1 67 



of these portions. The ileum terminates, at an obtuse 

 angle, near the right pelvic or haunch bone by a valvular 

 opening into the colon, which is guarded by the ileocecal 

 valve. This arrangement prevents the passing of sub- 

 stances from the colon into the ileum. The jejunum and 

 ileum are surrounded above and at the sides by the colon. 

 The small intestine, like the stomach, has three coats 

 (some writers include a fourth, or submucous coat). The 



FIG. 84. Mucous membrane of the jejunum, highly magnified (sche- 

 matic) : i, i, Intestinal villi; 2, 2, closed or solitary follicles; 3, 3, orifices 

 of the follicles of Lieberkuhn (Testut). 



inner or mucous coat is thrown into folds or valves. In 

 consequence of this valvular arrangement the mucous 

 membrane is more extensive than the other tissues, and 

 gives a greater extent of surface with which the aliment 

 comes in contact. Protruding from the surface of the 

 mucous coat are .an immense number of projections which 

 are called villi and give the surface the appearance of 

 velvet; for this reasonthis membrane is sometimes called 

 the villous coat. 



