STRUCTURE OF THE SMALL INTESTINE. 



223 



valvulae conniventes are the mill (Fig. 117), which are so numerous 

 as to give to it a velvety appearance. Between them open the 

 glands of Lieberkiihn. The villi are prominences, some triangular, 

 some conical, and some filiform in shape, and in length are about 

 0.5 to 0.7 mm., and in width at their base about one-fourth their 

 length (Fig. 118). They are most numerous in the duodenum and 

 the jejunum, although present throughout the whole extent of the 



Epithelium 

 of villus. 



Epithelium 

 of villus. 



Goblet-cell. 



Gland (crypt) 

 of Lieber- 

 kiihn. 



Mucosa. 



Muscularis 



mucosae. 



FIG. 118. Section through raucous membrane of human small intestine ; X88: at 

 a is a collapsed chyle-vessel in the axis of the villus (Bohm and Davidoff ). 



small intestine. It has been estimated that there are no less than 

 4,000,000 of these villi in an intestine. 



Each villus is composed of retiform tissue, and is covered with 

 a single layer of columnar epithelium resting upon a basement- 

 membrane consisting of a layer of endothelial cells. Between the 

 cells of columnar epithelium, at their bases and in the retiform 

 tissue, are numerous lymph-corpuscles. Between adjoining epithe- 

 lial cells and also between the endothelial cells is interstitial 



