PAPILLAE OF THE TONGUE. 701 



The larger papilla of the tongue are thickly set over the 

 anterior two-thirds of its upper surface, or dor sum (fig. 195), 

 and give to it its characteristic roughness. Their greater 

 prominence than those of the skin is due to their interspaces 

 not being filled up with epithelium, as the interspaces of 

 the papillae of the skin are. The papillae of the tongue 

 present several diversities of form ; but three principal 

 varieties, differing both in seat and general characters, 

 may usually be distinguished, namely, the circumvallate or 

 calyciform, the fungiform, and the filiform papillae. Essen- 

 tially these have all of them the same structure, that is to 

 say, they are all formed by a projection of the mucous 

 membrane, and contain special branches of blood-vessels 

 and nerves. In details of structure, however, they differ 

 considerably one from another. 



All the three varieties of papillse just described have 

 been commonly regarded as simple processes, like the 

 papillae of the skin ; but Todd and Bowman have shown 

 that the surface of each kind is studded by minute conical 

 processes of mucous membrane, which thus form secondary 

 papillae. These secondary papillae also occur over most 

 other parts of the tongue, not occupied by the compound 

 papillae, and extend for some distance behind the papillae 

 circumvallatae. The mucous membrane immediately in front 

 Fig. 196 * 



* Fig. 196. Vertical section of the circumvallate papillse (from 

 Kolliker). \ q . A, the papillae ; B, the surrounding wall ; a, the epithe- 

 lial covering ; b, the nerves of the papilla and wall spreading towards 

 the surface ; c, the secondary papillae. 



