350 



STOMACH AND INTESTINE. 



laries of the neighbouring villi. And the 

 venous radicles of these latter processes usually 

 unite with the branches formed by their con- 



t Fig. 2.58. 



Capillaries occupying the surface of the mucous mem- 

 brane of the small intestine ; as seen on examining 

 an injected specimen by reflected light, with a mag- 

 nifying power of about 50 diameters. 



a, b, capillaries around the orifices of the intes- 

 tinal tubes. At a their meshes are more numerous 

 and complex than at b, where they are almost re- 

 duced to single capillaries ; c, calibre or cavity of 

 the intestinal tube. 



flux in a small vein ; that sinks vertically 

 through the mucous membrane, to join the 

 sub-mucous plexus which gives origin to the 

 portal vein. 



Villi. The interior of almost all the small 

 intestine presents to the naked eye a texture 

 very like that of velvet. For it is soft and 

 shaggy : yields readily to pressure : and, on 

 close examination, is evidently composed of 

 innumerable short filaments, which are placed 

 more or less vertically to the general inner sur- 

 face of the tube. These filaments, the dense 

 arrangement of which on a common surface 

 causes this general velvety appearance, are 

 thence usually named villi. Their form, and 

 their situation, or office, might also be denoted 

 by the name of intestinal or chyliferous papilla. 



We have seen that, in the stomach, the con- 

 fluent ridges intervening between the tubes are 

 here and there raised into slight projec- 

 tions. These are rendered more prominent by 

 artificial injection of the subjacent vessels, 

 or even by that afflux of blood which ordi- 

 narily attends the digestive act. In the pylo- 

 ric extremity of the organ, these projections 

 become more distinct. And just at its termi- 

 nation, some of them often assume the form 

 of bluntly triangular and flattened folds. 



In the upper part of the duodenum, the 

 villi begin; by processes which somewhat 

 resemble the gastric elevations just alluded 

 to, and occupy an analogous situation with 

 respect to the intestinal tubes. At first, they 

 may be described as flattened folds, the out- 

 line of which is a very obtuse triangle, that 

 has a broad base about four or five times 

 its height ( T o tn of an inch). In the lower 

 part of the duodenum, this rudimentary form 



for the most part disappears ; and the villi, 

 which are still more or less flattened, have 

 about twice the length, and half the width, of 

 those present in the upper part. But it is 

 in the upper part of the jejunum that they 

 attain their greatest number ; being placed so 

 closely together that their interstices scarcely 



Fig. 259. 



Villusfrom the upper part of the jejunum, as seen in 

 the fasting state. Magnified 140 diameters. 



a, epithelium of the villas ; 6, parenchyma or sub- 

 stance of the same. 



equal their own bulk. Here they also acquire 

 their maximum length, which ranges from 

 about ^yth to ^th, or even T ^th or T \th of 

 an inch. Their form, however, is still that of a 

 flattened cone (compare Jig. 259. and Jig. 257. 

 p. 347.) ; the breadth of the base of which is 

 about Jth, and the depth about -j^th, its height. 

 In the remainder of the intestine, the length of 

 the villi gradually recedes to that which they 

 possess in the lower part of the duodenum ; 

 while their number also diminishes to a some- 

 what smaller extent. Throughout all this 

 extent, the shapes and sizes of contiguous 

 villi often present great varieties. But as a 

 rule, the lower we descend in the examina- 

 tion of the intestine, the greater is the number 

 of cylindrical- forms we meet with. While 

 towards the extremity of the ileum, the gradual 

 diminution of their size renders many of them 

 scarcely more than ^^o^ 1 f an m ch in dia- 

 meter. 



The villi cover the whole surface of the 

 mucous membrane of the small intestine, in- 

 cluding its valvulae conniventes ; and they 

 extend to the free margin of the valve 

 which marks the commencement of the caecum 

 and colon. The only exception to their pre- 



