% THE SENSES. 169 



as electricity and mechanical impressions. Thus, Henle observed that a 

 small current of air directed upon the tongue gives rise to a cool saline 

 taste, like that of saltpetre; and Baly has shown that a distinct sensation 

 of taste, similar to that caused by electricity, may be produced by a smart 

 tap applied to the papillae of the tongue. Moreover, the mechanical irri- 

 tation of the fauces and palate produces the sensation of nausea, which is 

 probably only a modification of taste. 



Seat of Sensation. The principal seat of the sense of taste is the 

 tongue. But the results of experiments as well as ordinary experience 

 show that the soft palate and its arches, the uvula, tonsils, and probably 

 the upper part of the pharynx, are endowed 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 adduced that the sense of taste is conferred upon them by this 

 nerve. In most, though not in all persons, the anterior parts of the 

 tongue, especially the edges and tip, are endowed with the sense of taste. 

 The middle of the dorsum is only feebly endowed with this sense, prob- 

 ably 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. 142, 

 Vol. II.), to the lingual or gustatory branch of the fifth nerve. 



Structure of the Tongue. The tongue is a muscular organ covered 

 by mucous membrane. The muscles, which form the greater part of the 

 substance of the tongue (intrinsic muscles) are termed linguales; and 

 by these, which are attached to the mucous membrane chiefly, its smaller 

 and more delicate movements are chiefly performed.. 



By other muscles (extrinsic muscles) as- the genio-hyoglossus, the 

 styloglossus, etc., the tongue is fixed to surrounding parts; and by this 

 group of muscles its larger movements are performed. 



The mucous membrane of the tongue resembles other mucous mem- 

 branes (p. 322, Vol. I.) in essential points of structure, but contains 

 papillce, more or less peculiar to itself; peculiar, however, in details of 

 structure and arrangement, not in their nature. The tongue is beset with 

 numerous mucous follicles and glands. The use of the tongue in relation 

 to mastication and deglutition has already been considered (pp. 226 and 

 238, Vol. I.). 



The larger papillw of the tongue are thickly set over the anterior two- 

 thirds of its upper surface, or dorsum (Fig. 349), and give to it its char- 

 acteristic roughness. In carnivorous animals, especially those of the cat 

 tribe, the papillae attain a large size, and are developed into sharp re- 

 curved horny spines. Such papillae cannot be regarded as sensitive, but 

 they enable the tongue to play the part of a most efficient rasp, as in 

 scraping bones, or of a comb in cleaning their fur. Their greater promi- 



