SENSE OF TASTE. 537 



digestive canal. In higher animals, the Tongue is the principal seat of 

 it ; but other parts of the mouth are also capable of receiving the 

 impression of certain savours. The mucous membrane which covers the 

 tongue is copiously supplied with papillae, of various forms and sizes. 

 Those of simplest structure closely resembje the cutaneous papillae; But 

 there are others, which resemble clusters of such papillae, each being 

 composed of a fasciculus of looped capillaries (Fig. 159), with a bundle 



Fig. 159. 



Capillary network of fungiform papillae of the Tongue. 



of nerve-fibres, whose precise- mode of termination it has not yet been 

 found possible to ascertain. These fungiform papillae, Which are 

 covered with a very thin epithelium, are probably the special instru- 

 ments of the sense of taste ; for the exercise of which it seems probable 

 that the sapid substances must penetrate, in solution, to the interior of 

 the papilla. When these papillae -are called into action by the contact 

 of substances having a strong savour, they not unfrequently become 

 very turgid, by a distension of their vessels analogous to that which 

 occurs in erection; and they rise up from the surface of the mucous 

 membrane, so as to produce a decided roughness of its surface. The 

 conical papillae, on the other hand, are furnished with thick epithelial 

 investments, which are sometimes prolonged into filamentous appen- 

 dages ; and, looking, to their higher development among other animals, 

 and the offices to which they are there subservient, it seems probable 

 that their functions are purely mechanical, and that they serve especially 

 to cleanse the teeth from adhering particles. The nerve-fibres can be 

 seen to form distinct loops in their interior, at some distance from the 

 apex. 



944. There has been much discrepancy of opinion as to the nerve 

 which is specially concerned in the sense of Taste. The tongue of Man 

 is supplied by two sensory nerves : the lingual branch of the Fifth pair ; 

 and the Glosso-pharyngeal. The former chiefly supplies the upper sur- 

 face of the front of the' tongue, and is copiously distributed to the 

 papillae near the tip. The latter is mostly distributed upon the mucous 

 surface of the Fauces, and upon the back of the tongue ; but it sends a 

 branch forwards, beneath the lateral margin on each side, which supplies 

 the edges and inferior surface of the tip of the tongue, and -inosculates 

 with the preceding. There is reason to believe, from experiment, that 

 the gustative sensibility of the tongue is not destroyed by section of 

 either of these nerves ; though the operation produces a total or partial 

 loss of sensibility over certain parts of the surface. There seems good 

 reason to conclude, that the lingual branch of the Fifth pair is the 



