TASTE, ORGAN AND SENSE OF. The principal seat of the sense of taste is the mucous membrane of the tongue, in which dissection reveals a cults or chorion, a papillary struc. Lure, and an epithelium. Of the cubs, it is sufficient to remark that it is tough, but thin ner and less dense than in most parts of the cutaneous surface, and that it receives the insertions of the intrinsic muscles of the tongue, which will be described when we treat of that organ generally. The papillary structure differs from that of the skin in not being concealed under the epithelium, but in projecting from the surface like the villi of the digestive canal, and it thus gives to the tongue its well-known roughness. The epithe lium (q.v.) is of the scaly variety, as on the skin, but is much thinner on the tongue than on the skin. It is most dense about the middle of the upper surface of the tongue, and it is here that, in disordered digestion, there is the chief accumulation of fur, which in reality is simply a depraved and over-abundant formation of epithelium. The papilla on the surface of the tongue are either simple or compound. The former, which closely resemble those of the skin, are scattered over the whole surface of the tongue in parts where the others do not exist, and they likewise participate in the formation of the com pound which, from their forms, are respectively termed (1) the circumvallate or ettlyatform, (2) the fungiform, and (3) the conical or filiform.
The circumvallate papillm are not more than eight or ten in number, and are situated in the form of a V at the base of the tongue. Their function seems to be to secrete mucus, as well as to take part in the act of tasting. They consist of "a central flat tened projection of the mucous membrane of a circular figure, and from sic to of an inch wide, surrounded by a tumid ring of about the same elevation."—Todd and Bow man, Physiological Anatomy and Physiology of Alan, 2d ed. vol. i.•p. 437. The fungi form papillm are scattered over the surface in front of the circumvallate papillae, and about the sides and apex. They are usually narrower at the base than at the apex, where they are about of an inch in diameter. They are covered with simple or secondary papillm, and their investing epithelium is so thin• that the blood circulating in them gives them a red color, which is not seen in the conical papillae, among which they are distributed. They contain nerves terminating in loops. The shape of the conical or
filiform papillae is indicated by their names; and even if they take little part in the sense of taste directly, it is convenient to describe them here. Their average length is about of an inch. The papillm terminate in long pointed processes, which are bathed by the mucus of the mouth, and are capable of moving in any direction, although they arc generally inclined backward. Some of the stiffer of these epithelial processes inclose minute hairs. Messrs. Todd and Bowman surmise, on structural grounds, that the fili form papillae "can scarcely share in the reception of impressions which depend on the contact of the sapid material with the papillary tissue. The comparative thickness of their protective covering, the stiffness and brush-like arrangement of their filamentary pro ductions, their greater deyelopment in that portion of the dorsum of the tongue which is chiefly employed in the movements of mastication, all evince the subservience of these papillm to the latter function rather than to that of taste; and it is evident' that their isolation and partial mobility on one another must render the delicate touch with which they are endowed more available in directing the muscular actions of the organs. The almost manual dexterity of the tongue in dealing with minute particles of food is proba bly provided for, as far as sensibility conduces to it, in the structure and arrangement of these papillm."—Phys. Anat. and Phys. of Man, vol. i. p. 441. Notwithstanding the difference in their outward form and mode of arrangement, the simple papillae, which have been detected by Todd and Bowman as scattered over the whole dorsum of the tongue (although concealed under the common sheet of epithelium), and those clothing the circumvallate and fungiform papillae, do not seem to present any structural differ ence; and their epithelium, which is very thin, readily permits the transudation of sapid substances dissolved in the mucus of the mouth. With regard to the use of the singular configuration of the circumvallate and fungiform " it may be conjectured that the fissures and recesses about their bases are designed to arrest on their passage small portions of the fluids in which the sapid materials are dissolved, and thus to detainthem in contact with the most sensitive parts of the gustatory membrane."—Op. cit. p. 441.