SENSE OF TASTE. 601 



papillae, which are the most numerous, and which cover most uniformly 

 the upper surface of the tongue. They are long and slender, and are 

 covered with horny epithelium, usually prolonged into filamentous tufts. 

 At the edges of the tongue they are often united into parallel ranges 

 or ridges of the mucous membrane. Secondly, the fungiform papillae. 

 These are thicker and larger than the foregoing, of a club-shaped 

 figure, and covered with soft epithelium. They are most abundant 

 at the tip of the tongue, but may be seen elsewhere on the surface of 

 the organ, scattered among the filiform papillae. Thirdly, the circum- 

 vallate papillae. These are the rounded eminences, eight or ten in 

 number, which form the V-shaped figure near the situation of the fora- 

 men caecum. Each consists of a central eminence, surrounded by a wall 

 or circumvallation, from which they derive their name. The circum. 

 vallation, as well as the central eminence, has a structure similar to that 

 of the fungiform papillae. 



The sensitive nerves of the tongue, as above mentioned, are two in 

 number, namely, the lingual branch of the fifth pair, and the lingual 

 portion of the glossopharyngeal. The lingual branch of the fifth pair 

 enters the tongue at the anterior border of the hyoglossal muscle. Its 

 branches pass from below upward and from behind forward, between the 



Fig. 187. 



DIAGRAM OP THE TONGUE, with its sensitive nerves and papillae. 1. Lingual branch 

 of the fifth pair. 2. Glossopharyngeal nerve. 



muscular bundles of the organ, until they reach its mucous membrane. 

 The nerve fibres then penetrate the lingual papillae, where they termi- 

 nate, partly in the " terminal bulbs" already described (p. 594), and 

 partly in a manner not yet distinctly ascertained. 



The lingual portion of the glossopharyngeal nerve passes into the 

 tongue below the posterior border of the hyoglossus muscle. It then 

 divides into various branches, which pass through the muscular tissue, 

 and are distributed to the mucous membrane of the base and sides of 

 the organ. 



The mucous membrane of the base of the tongue, of its edges, and 

 of its under surface near the tip, as well as that of the mouth and fauces 

 generally, is also supplied with mucous follicles furnishing a viscid 

 39 



