THE VILLL 



147 



the " pile" on velvet and known as the villi (Fig. 51). In 

 structure a villus is somewhat complex. Covering it is a 

 single layer of cells, beneath which the villus may be re- 

 garded as made up of a framework of connective tissue sup- 

 porting the more essential constituents. Near the surface 

 is a network of plain muscular tissue. In the centre is an 

 offshoot of the lymphatic or absorbent system, sometimes 



FIG. 51. Villi of the small intestine; magnified about 80 diameters. In the 

 left-hand figure the lacteals, a, 6, c, are filled with white injection; d. blood ves- 

 sels. In the right-hand figure the lacteals alone are represented, filled with a 

 dark injection. The epithelium covering the villi, and their muscular fibres are 

 omitted. 



in the form of a single vessel with a closed dilated end, and 

 sometimes as a network formed by two main vessels with 

 cross-branches. During digestion these lymphatics are 

 filled with a milky white liquid absorbed from the intestines, 

 and they are accordingly called the lacteals. They com- 

 municate with larger branches in the outer coats of the in- 



Describe the structure of a villus. What is found in its lymphatics 

 during digestion? 



