DIGESTION. 



265 



The surface of the villas is clothed by columnar epithelium, which 

 rests on a fine basement membrane; while within this are found, reck- 

 oning from without inwards, blood-vessels, fibres of the muscularis mu- 

 cosw, and a single lymphatic or lacteal vessel rarely looped or branched 

 (Fig. 200); besides granular matter, fat-globules, etc. 



The epithelium is of the columnar 

 kind, and continuous with that lining the 

 other parts of the mucous membrane. 

 The cells are arranged with their long axis 

 radiating from the surface of the villus 

 (Fig. 199), and their smaller ends resting 

 on the basement membrane. The free 

 surface of the epithelial cells of the villi, 

 like that of the cells which cover the gene- 

 ral surface of the mucous membrane, is 

 covered by a fine border which exhibits 

 very delicate striations, whence it derives 

 its name, " striated basilar border." 



Beneath the basement or limiting 

 membrane there is a rich supply of Mood- 

 vessels. Two or more minute arteries are 

 distributed within each villus ; and from 

 their capillaries, which form a dense net- 

 work, proceed one or two small veins, 

 which pass out at the base of the villus. 



The layer of the muscularis mucosce in 

 the villus forms a kind of thin hollow cone 

 immediately around the central lacteal, 

 and is, therefore, situate beneath the blood- 

 vessels. It is without doubt instrumental 

 in the propulsion of ch} T le along the 

 lacteal. 



The lacteal vessel enters the base of 

 each villus, and passing up in the mid- 

 dle of it, extends nearly to the tip, where it ends commonly by a 

 closed and somewhat dilated extremity. In the larger villi there may be 

 two small lacteal vessels which end by a loop (Fig. 200), or the lacteals 

 may form a kind of network in the villus. The last method of ending, 

 however, is rarely or never seen in the human subject, although common 

 in some of the lower animals (A, Fig. 201). 



The office of the villi is the absorption of chyle and other liquids from 

 the intestine. The mode in which they effect this will be considered in 

 the next Chapter. 



II. The Large Intestine. The Large Intestine, which in an adult 



f 



FIG. 196. Vertical section of duo- 

 denum showing a, villi: b crypts of 

 Lieberkuhn, and c, Brunner's glands 

 in the submucosa s, with ducts, d; 

 muscularis mucosae, m; and circular 

 muscular coat /. (Schofleld.) 



