530 



DIGESTION. 



not, like them, float loosely in the abdomen. In its course to its termi- 

 nation in the jejunum, it describes a kind of Italic <?, the concavity of 

 which looks to the left. From this shape it has been separated into 

 three portions ; the first situate horizontally beneath the liver: the 

 second descending vertically in front of the right kidney; and the third 

 in the transverse mesocolon. Its mucous membrane presents a number 

 of circular folds or rugse, very near each other, which have been called val- 



vulse conniventes. (Figs. 230 and 231.) 

 By some anatomists, however, this name 

 is not given to the irregular rugse of 

 its mucous coat; but to those of the 

 lining membrane of the jejunum. The 

 valvulse are not simple rugse, passively 

 formed by the contraction of the mus- 

 cular coat. They are dependent upon 

 the original formation of the mucous 

 membrane; and are not effaced, what- 

 ever may be the distension of the in- 

 testine. On and between these dupli- 

 catures, the different exhalant and 

 absorbent vessels are situate, forming, 



in part, the villi of the intestine, which are from a quarter of a line to 

 a line and two-thirds in length. 1 These villi give to the membrane a 

 velvety appearance, and are not simply composed of exhalants and 

 absorbents, but of nerves; all of which are distributed on an areolar 

 and perhaps erectile tissue. In its healthy state, when successfully- 

 injected, the membrane appears to consist almost entirely of a cribri- 

 form intertexture of veins. It was formerly believed, that the villi 

 are not supplied with bloodvessels. In each villus, however, there is 



Muscular Coat of the Ileum. 



m different parts of the intestine. 



Fig. 233. 



Fig. 234. 



Distribution of Capillaries in the 

 Villi of the Intestine. 



Distribution of Capillaries around 

 Follicles of Mucous Membrane. 



a minute vascular plexus, the larger branches of which, when distended 

 with blood, may be seen even by the naked eye. Marginal illustra- 

 tion, Fig. 235, exhibits the vessels of one of the intestinal villi of the 

 hare, from Wagner, after an extremely beautiful dry preparation by 

 Dollinger, magnified about 45 diameters. The most obvious use of 

 these villi is to increase the surface from which the secretion is pre- 

 pared, and from which absorption is effected. Within the membrane 



1 J. Muller, Elements of Physiology, by Baly, 2d edit., p. 285, Lond., 140. 



