552 THE SENSE OF TASTE. 



over the fungiform papillae forms a thinner layer than else- 

 where, so that these papillae stand out more prominently than 

 the rest. The epithelium covering the filiform papillae has 

 been shown by Todd and Bowman to have a singular arrange- 

 ment ; being extremely dense and thick, and, as before-men- 

 tioned, projecting from their sides and summits in the form of 

 long, stiff, hair-like processes. Many of these processes bear 

 a close resemblance to hairs, and some actually contain minute 

 hair-tubes. Bloodvessels and nerves are supplied freely to the 

 papillae. The nerves in the fungiform and circurnvallate pa- 

 pillae form a kind of plexus, spreading out brush-wise (Fig. 

 203), but the exact mode of termination of the nerve filaments 

 is not certainly known. 



Such, in outline, is the structure of the sensitive surface of 

 the tongue. But the tongue is not the only seat of the sense 

 of taste ; for the results of experiments as well as ordinary ex- 

 perience show that the soft palate and its arches, the uvula, 

 tonsils, and probably the upper part of the pharynx, are en- 

 dowed with taste. These parts, together with the base and 

 posterior parts of the tongue, are supplied with branches of the 

 glosso-pharyngeal nerve, and evidence has been already ad- 

 duced (p. 437 et seq.) that the sense of taste is conferred upon 

 them by this nerve. 



In most, though not in all persons, the anterior part of the 

 tongue, especially the edges and tip, are endowed with the 

 sense of taste. The middle of the dorsuni is only feebly en- 

 dowed with the sense, probably because of the density and 

 thickness of the epithelium covering the filiform papillae of 

 this part of the tongue, which will prevent the sapid substances 

 from penetrating to their sensitive parts. The gustatory prop- 

 erty of the anterior part of the tongue is due, as already said 

 (p. 431 ), to the lingual branches of the fifth nerve. 



Besides the sense of taste, the tongue, by means also of its 

 papillae, is endued, especially at its sides and tip, with a very 

 delicate and accurate sense of touch, which renders it sensible 

 of the impressions of heat and cold, pain and mechanical pres- 

 sure, and consequently of the form of surfaces. The tongue 

 may lose its common sensibility, and still retain the sense of 

 taste, and vice versa. This fact renders it probable that, al- 

 though the senses of taste and of touch may be exercised by 

 the same papillae supplied by the same nerves, yet the nervous 

 conductors for these two different sensations are distinct, just 

 as the nerves for smell and common sensibility in the nostrils 

 are distinct ; and it is quite conceivable that the same nervous 

 trunk may contain fibres differing essentially in their specific 

 properties. Facts already detailed (p. 430) seem to prove that 



