THE SENSES. 557 



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

 dowed with the sense of taste. The middle of the dorsum is only feebly 

 endowed with this 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 sensi- 

 tive parts. 



The Tongue. 



Structure. The tongue is a muscular organ covered by mucous mem- 

 brane. 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-hyoglossas, 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 in essential points of structure, but contains papillce, more or less 

 peculiar to itself; peculiar, however, in details of structure and arrange- 

 ment, 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. 



The larger papilla of the tongue are thickly set over the anterior 

 two-thirds of its upper surface, or dorsum (Fig. 369), and give to it 

 its characteristic roughness. In carnivorous animals, especially those of 

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

 recurved 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 fur. Their greater promi- 

 nence than those of the skin is due to their interspaces not being filled 

 up with epithelium, as the interspaces of the papillae of the skin are. 

 The papillae of the tongue present several diversities of form; but three 

 principal varieties, differing both in seat and general characters, may 

 usually be distinguished, namely, the (1) circumvallate, the (2) fungi- 

 form, and the (3) filiform papillae. Essentially these have all of them 

 the same structure, that is to say, they are all formed by a projection of 

 the mucous membrane, and contain special branches of blood-vessels and 

 nerves. In details of structure, however, they differ considerably one 

 from another. 



