238 



INTESTINAL DIGESTION. 



FIG. 69. Intestinal villus (Ley- 

 dig). 



a, a,'a, epithelial covering ; 6, 6, 

 capillary net- work ; c, c, longi- 

 tudinal muscular fibres ; d, 

 lacteal. 



FIG. 70. Capillary net-work 

 of an intestinal villus 



(Frey). 



cells, resting on a structureless basement-membrane. These cells, though 

 closely adherent to the subjacent 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 diffi- 

 culty in microscopical prep- 

 arations. The borders of 

 the free surfaces of these 

 cells are thickened and fine- 

 ly striated, forming, as it 

 were, a special membrane 

 covering the villus and ex- 

 ternal to the cells. Between 

 the cylindrical cells are a 

 few of the so-called goblet- 

 cells similar to those found 

 on the mucous membrane of 

 the stomach (see Fig. 60, 

 page 214). 



The substance of the 

 villus is composed of amor- 

 phous matter, in which are 

 embedded nuclei and a few fibres, fibro-plastic cells and non-striated mus- 

 cular fibres. The blood-vessels are very abundant ; four or five, and some- 

 times as many as twelve or fifteen arterioles entering at the base, rami- 

 fying through the substance of the vil- 

 lus, but not branching or anastomosing 

 or even diminishing in caliber until, by 

 a slightly wavy turn or loop, they com- 

 municate with the venous 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 long axis of the villus. 



The muscular fibres of the villi are 

 longitudinal, forming a thin layer sur- 

 rounding the villus, about half-way be- 

 tween the periphery and the centre, 

 and continuous with the muscular coat 

 of the intestine. 



In the central portion of each villus, is a small lacteal, one of the vessels of 

 origin of the lacteal system, with an extremely delicate wall composed of 

 endothelial cells with frequent stomata, or small openings, between their 



a, venous trunk ; 

 trunk, 



6, arterial 



FlO. 71. Epithelium of the small intestine of 

 the rabbit (Funke). 



