146 THE HUMAN BODY. 



The Mucous Coat of the Small Intestine. This is pink, 

 soft, and extremely vascular. It is throughout a great por- 

 tion of the length of the tube raised up into permanent 

 transverse folds in the form of crescentic ridges, each fold 

 running transversely for a greater or less way round the in- 

 testine (Fig. 50). These folds are the valvulce conniventes. 

 They are first found about two inches from the pylorus, and 

 are most thickly set and largest in the upper half of the 

 jejunum, in the lower half of which they become gradually 

 less conspicuous; they finally disappear altogether about the 

 middle of the ileum. The folds of the mucous membrane 



Fio. 50. A portion of the small intestine opened to show the valvulce conni- 

 ventes. 



serve to greatly increase its surface both for absorption and 

 secretion, and they also delay the food in its passage; it 

 collects in the hollows between them, and so is longer ex- 

 posed to the action of the digestive liquids. 



The Villi. Examined closely with the eye or, better, with 

 a hand lens, the mucous membrane of the small intestine is 

 seen not to be smooth but shaggy, being covered everywhere 

 (both over the valvulse conniventes and between them) with 

 closely packed minute elevations standing up somewhat like 



Give the general characteristics of the mucous membrane of the 

 small intestine. What are the valvulse couniventes? Where do 

 they commence? Where are they most developed? Where do they 

 cease? What purposes do they subserve? What are the villi? 



