THE VALVUL^E CONNIVEKTES. 



299 



Fig. 73-* 



middle of the ileum. In structure they are formed by a 

 doubling inwards of the mucous membrane, the crescentic, 

 nearly circular, folds thus formed being arranging- trans- 

 versely with regard to the axis of the intestine, and each 

 individual fold seldom extending around more than J or f 

 of the bowel's circumference. Unlike the rugse in the 

 stomach, they do not disappear on distension. Only an 

 imperfect notion of their natural position and function can 

 be obtained by looking at them after the intestine has been 

 laid open in the usual manner. To understand them 

 aright, a piece of gut should be distended either with air 

 or alcohol, and not opened until the tissues have become 

 hardened. On then making a section, it may be seen that 

 instead of disappearing, as the rugae in the stomach would 

 under similar circumstances, they stand out at right angles 

 to the general surface of the mucous 

 membrane (fig. 73). Their functions 

 are probably these Besides (l) offer- 

 ing a largely increased surface for 

 secretion and absorption, they proba- 

 bly (2) prevent the too rapid passage 

 of the very liquid products of gastric 

 digestion, immediately after their es- 

 cape from the stomach, and (3), by 

 their projection, and consequent inter- 

 ference with an uniform and untrou- 

 bled current of the intestinal contents, 

 probably assist in the more perfect 

 mingling of the latter with the secre- 

 tions poured out to act on them. 



Glands of the Small Intestine. The glands are of three 

 principal kinds, named after their describers, the glands of 

 Lieberkiihn, of Peyer, and of Brunn. The glands or fol- 



* Fig. 73. Piece of small intestine (previously distended and hardened 

 by alcohol) laid open to show the normal position of the valvulse con- 

 niventes. 



