THE ALIMENTARY CANAL 



177 



are goblet cells. These appeal- in \aryinu- miinhcrs and hccoiiic 

 more markedly abundant in the ileum. Within the epitheHum of 

 each villus there is loose connective tissue, a basketwork of blood 

 capillaries, a nerve net, and soin(> ditt'use lym])lioi(l tissue. A dilated 

 blind lym])h cai)illary, a lacteal, occu])ies the central portion. The 

 villi vary in sha])e, size, and number in various mammals. From the 

 bases of the villi extend simple tubular glands which formed as 

 invaginations of the embryo gut epithelium. These are called 

 Liel)erkiihn glands and extend down to the nuiscularis mucosa. 

 The epithelium lining them is continuous with that covering the 



-^l — Epithelium 



Capillary network 



Connective tissue 



After II 



^~ I ein 



-^Lymphatic 



Fig. 114. — Diagram of a villus. 



villus, but the cells are shorter and have no striated border. Near 

 the base of these glands occur coarsely granular, basally striated 

 cells, the cells of Paneth, which secrete a serous fluid containing an 

 enzyme. These cells are widely- distributed throughout the epithe- 

 lium of the digestive canal of higher vertebrates. Another type, 

 which reduces silver, is called an argentaffin cell and has a finely 

 granular basal portion of cytoplasm. It has been demonstrated 

 scattered among the cells lining the crypts and rarely among those 

 covering the villi, but as yet its nature is not full>- understood. 

 The tunica propria, or stroma, as it max- be called, ])acks in between 

 the Lieberkiihn glands, as well as forming the core of the villi. Its 

 light, loose reticular network and denser fibroelastic tissue supports 



12 



