THE TONGUE. 



1575 



face of the mucous membrane. The anterior two-thirds of this surface are rough 

 with fjingiform and filiform papillce ; the former, less numerous, appear as red 

 points chiefly near the edges, while the filiform are everywhere, but arranged in par- 

 allel rows continuing forward the lines of the circumvallate papillae. At the edges of 

 the tongue, just in front of the end of the anterior pillar of the fauces, close inspec- 

 tion, especially with a lens, will generally show a small series of minute transverse 

 parallel ridges, corresponding to ^h^ papillce foliatce of rodents in a rudimentary con- 

 dition. The papillce circumvallatce are fungoid papillae surrounded by a depression 

 bounded externally by a low annular wall. The usual number of these papillae is 

 from nine to ten, ranging from six to sixteen (Munch). The sides of the V in which 

 they are disposed are not very symmetrical. Usually there is at least one median 

 papilla behind the apex, and very rarely one or two before it. The circumvallate 

 papillae are of especial interest as being the most important seat of the gustatory end- 



FiG. 1335. 



Filiform papilla 



Surface epithelium covering 

 tungiform papilla 



Pto lections of tunica pro- 

 [iiia constituting basis of 

 papilla 



Connective-tissue stroma of 

 mucous membrane 



Muscular tissue of 

 tongue 



Section of lingual nuicous membrane, showing filiform and fungiform papillae. X 75. 



organs, or taste-buds, which lie embedded within the epithelium lining the groove 

 encircling the central elevation. A detailed description of the taste-buds, is given 

 with the organs of special sense (page 1433). 



The surface of the vertical posterior third of the tongue is smooth, in the sense 

 that there are no papillae nor roughnesses, but it is studded with masses of lymphoid 

 tissue, sometimes called the liiigual tonsil {Y\^. 1334), which make numerous eleva- 

 tions on its surface. The mucous membrane of the back of the tongue is continued 

 in a thinner layer onto the front of the epiglottis. It presents the 9nedian glosso- 

 epiglottic fold, containing fibro-elastic tissue and muscular fibres of the genio-glossi, 

 which separate two little depressions, the glosso-epiglottic fossce. These may be with- 

 out any definite lateral boundary, or may be embraced by the small lateral glosso- 

 epiglottic folds, the internal borders of which are concave. The mucous membrane 

 is firmly attached to the subjacent muscles in the anterior two-thirds of the tongue, 

 but less firmly behind. 



Glands of the Tongue. — The lingual glands include both serous and mucous 

 varieties, which are distributed as three groups : (i) serous glands, (2) posterior 

 mucous glands and (3) anterior mucous glands. 



