262 



DIGESTION. 



measuring here from ^ to ^ of an inch in length by T V to -^ of an inch in breadth at 

 their base. 



The structure of the villi shows them to be simple elevations of the mucous mem- 

 brane, provided with blood-vessels, and probably also with lacteals, or intestinal lym- 

 phatics. Externally is found a single layer of long, columnar epithelial cells, resting on 



FIG. 66. Intestinal mllus. (Leydig.) FIG. 67. Capillary net-work of an intestinal villus. (Frey.) 



a, a, a, epithelial covering- ; 6, 6, capillary net-work ; a, venous trunk ; &, arterial trunk, 



c, c, longitudinal muscular fibres ; d, lacteal. 



a structureless basement-membrane. These cells, though closely adherent to the sub- 

 jacent parts during life, are easily detached after death and are almost always destroyed 

 and removed in injected preparations. They adhere firmly to each other and are isolated 

 with difficulty in microscopical preparations. Kolliker has shown that the membranes on 

 the free surfaces of these cells are thickened and finely striated, forming, as it were, a 



special membrane covering the villus and exter- 

 nal to the cells. This membrane may be raised 

 up from the cells and exhibited by the action 

 of water. 



The substance of the villus is composed of a 

 strom a of amorphous matter, in which are em- 

 bedded nuclei and a few fibres, fibro-plastic 

 cells, and numerous non- striated muscular 

 fibres. The blood-vessels are very numerous; 

 four or five, and sometimes as many as twelve 

 or fifteen arterioles entering at the base, ram- 

 ifying through the substance of the villus, 

 but not branching or anastomosing, or even 

 diminishing in caliber until, by a slightly wavy 

 turn or loop, they communicate with the ven- 

 ous radicles, each of which is somewhat larger 

 than the arterioles. The veins all converge 

 to two or three branches, finally emptying into a large trunk situated nearly in the 

 axis of the villus. 



FIG. S&.Epithdi-wm of the small intestine of the 

 rabbit. (Funke.) 



