THE LARGE INTESTINE. 315 



rich supply of Hood-vessels. Two or more minute arteries 

 are distributed within each villus ; and from their capil- 

 laries, which form a dense network, proceed one or two 

 small veins, which pass out at the base of the villus. 



The layer of organic muscular fibres forms a kind of 

 thin hollow cone immediately around the central lacteal, 

 and is, therefore, situate beneath the blood-vessels and 

 much of the granular basis of the villus. The addition 

 of acetic acid to the villus brings out the characteristic 

 nuclei of the muscular fibres, and shows the size and 

 position of the layer most distinctly. Its use is still un- 

 known, although it is impossible to resist the belief, that it 

 is instrumental in the propulsion of chyle along the lacteal. 

 Kolliker has lately shown that this layer is continuous with 

 a layer of organic muscular fibres situated within the mu- 

 cous membrane of the intestine. 



The lacteal vessel enters the base of each villus, and pass- 

 ing up in the middle of it, extends nearly to the tip, where 

 it ends commonly by a closed and somewhat dilated ex- 

 tremity. In the larger villi there may be two small lacteal 

 vessels which end by a loop (fig. 80), 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. 80). 



The office of the villi is the absorption of chyle from the 

 completely digested food in the intestine. The mode in 

 which they effect this will be considered in the chapter on 

 ABSORPTION. 



*> 

 Structure of the Large Intestine. 



The large intestine, which in an adult is from about 4 to 

 6 feet long, is subdivided for descriptive purposes into three 

 portions, viz.: The ceecum, a short wide pouch, commu>- 

 nicating with the lower end of the small intestine through 

 an opening, guarded by the ileo-c&cal valve; the colon, 



