278 Elementary Biology. 



layer. It is from the blood circulating in the capillaries 

 that the secretory cells lining the glands obtain the materials 

 for the formation of gastric juice, the most important con- 

 stituent of which is a ferment called pepsin. In the intestinal 

 mucous membrane there are similar glands, known there by 

 the name of Lieberkiihnian follicles, and having a similar 

 function to those in the gastric wall. In addition, however, 



FIG. 141. VERTICAL SECTION OF THE SMALL INTESTINE. (Qualn.) 



/, /, submucous layer containing blood-vessels d, c, and large lacteal, a, a; 

 ~, g", mucous layer with Lieberkiihnian follicles ; e, e : , epithelial layer; 

 a, lacteal in the interior of a villus ; b, network of blood-capillaries in 

 the subepithelial tissue (/) of the villus. 



the mucous membrane is elevated between the mouths of 

 the follicles into long papillae, or villi, which are, structurally 

 speaking, follicles turned inside out. Each villus is covered 

 by columnar cells resting on a basement membrane, and 

 covering a core of submucous tissue, consisting of lymphatics, 

 or, as they are here termed, lacteals, nerves, blood-capilla- 

 ries, and connective tissue. Among the columnar cells are 

 found many wide-mouthed goblet-shaped cells, whose func- 



