514 THE NERVOUS SYSTEM. 



be especially connected with the perception of savors, there is thus far 

 no certainty in this respect ; and in any case the tactile and gustatory 

 sensibilities are closely intermingled in the mucous membrane. The 

 sensibility of taste, furthermore, is not confined to the fibres of a single 

 nerve, but resides in portions of two, which also supply general sensi- 

 bility to the corresponding parts ; and lastly, though some gustatory 

 impressions are of a distinctly special character, others, like the taste of 

 oily or mucilaginous substances, differ but little from those of tactile 

 sensibility. 



The sense of taste is localized in the mucous membrane of the tongue, 

 the soft palate, and the pillars of the fauces. The tongue is a flattened, 

 leaf-like muscular organ, attached to the symphysis of the lower jaw in 

 front, and to the os hyoides behind. It has a vertical sheet of fibrous 

 tissue in the median line serving as its framework, and is provided with 

 longitudinal, transverse, and radiating muscular fibres, by which it can 

 be protruded or retracted, or moved in a lateral direction. 



The lingual papillae are of three kinds. First the filiform papillae, 

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

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

 with horny epithelium, and usually prolonged into filamentous tufts. 

 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 tig of the tongue, but may be seen 

 elsewhere on the surface of the organ, scattered among the filiform 

 papillae. Thirdly, the circumvallate papillae. These are the rounded 

 eminences, eight or ten in number, which form the V-shaped figure near 

 the foramen caecum. Each consists of a central eminence, surrounded 

 by a wall or circumvallation, from which they derive their name. The 

 circumvallation, as well as the central eminence, has a structure similar 

 to that of the fungiform papillae. 



The sensitive nerves of the tongue are two in number, namely, the 

 lingual branch of the fifth pair, and the lingual portion of the glos- 

 sopharyngeal. 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 muscular 

 bundles of the organ, until they reach its mucous membrane, where 

 their fibres penetrate the lingual papillaB. 



The lingual portion of the glossopharyngeal nerve passes into the 

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

 divides into 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 

 secretion by which its surface is lubricated. The muscles of the tongue 

 are animated exclusively by filaments of the hypoglossal nerve. 



The exact seat of the sense of taste has been determined by placing 



