248 THE DIGESTIVE ORGANS. 



are several classes of lingual papillae the filiform, the fungiform, 

 and the circumvallate papillae. The most numerous are the thread- 

 like or filiform papillcz (from 0.7 to 3 mm. long). These are scat- 

 tered over the entire upper surface of the tongue, and consist of 

 conic projections of the epithelium and of the mucosa. The con- 

 nective-tissue portions of these papillae are very thin and long. The 

 basal layers of the epithelium can not be distinguished from the 

 same layers covering the surrounding mucosa, but the more super- 



"Papilla filiformis. 



*vTT.^ -Tongue epithe- 

 lium. 



-Connective-tissue 

 papilla. 



,';;, ;/."</ '-': : ;' ' 

 '' \! ';.'.;..'-' ;,; 



. , --'.._- - / Miu-osii. 



: ,. ; 



Basal epithelial 

 layer. 



Fig. 192. From a cross-section of the human tongue, showing short, thread-like papillae 



(filiform) ; X I 4- 



ficial layers are differentiated, in that their cells are arranged parallel 

 to the long axes of the papillae and overlap each other like tiles 

 (Fig. 192). Their free ends are often continued into several spine- 

 like processes. Less numerous than the filiform are the fungiform 

 papillcs (from 0.7 to 1.8 mm. in height) scattered here and there 

 between the former. They are nearly hemispheric in shape, and are 

 joined to the surface of the tongue by a slightly constricted base. 

 At times they are even partly sunk into the mucous membrane. 

 The mucosa is raised under the epithelium to form connective-tissue 

 papillae (Fig. 191). On the free surface of the fungiform papillae 



