THE DIGESTIVE SYSTEM 



231 



surrounded by a groove or trench and wall (whence the name circum- 

 vallate). The wall is somewhat lower than the paj)illa, thus allowing 

 the latter to project slightly above the surface. Secondary papillae 

 are confined to the upper surface of the papilla, the sides being free 

 from secondary papilla;. The surface of the papilla and the borders 

 of the groove and wall are covered by stratified squamous epithelium. 

 Lying in the epithelium of the side wall and sometimes of the opposite 

 trench wall are oval IkxHcs. the so-called taste buds, which serve as 



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Fig. 136. — Vertical Section through a Circumvallate Papilla of Human Tongue. 

 X37. (Szymonowicz.) a, Secondary papilla; b, wall; c, trench; d, epithelium of 

 tongue; e, stroma;/, submucosa; g, Ebner's glands. 



organs for the nerves of taste (see nervous system) . Into the trench 

 surrounding the circumvallate papilla open the ducts of serous glands 

 (Ebner's glands). 



The lymph follicles of the tongue have been already described 

 (page 184) under the head of the lingual tonsils. 



For glands of the tongue see page 227. 



The larger blood-vessels run in the connective- tissue septa. 

 These give off smaller branches, which break up into capillary net- 

 works surrounding the muscle fibres and forming a plexus just be- 

 neath the epitheUum. From the latter are given off capillaries to 

 the papillae. The capillaries converge to form veins, which in general 

 follow the course of the arteries. 



