Tongue, in the animal system, the organ, situated on the median line, at the commencement of the alimentary canal, ministering to the senses of touch and taste. Taking the tongue of man as an example, the organ is at-tached at its base to the movable hyoid arch of bones, and suspended and kept in place by muscles from the base of the skull, lower jaw, and hyoid bone; it is essentially composed of muscular fibres, which move freely its various portions; it is covered by sensitive mucous membrane, containing numerous mucous glands and follicles; fibrous, areolar, and fatty tissues enter into its structure, which is freely supplied with blood vessels and nerves. The size bears no relation to the height of the individual, but is proportioned to the capacity of the alveolar arch; it is, therefore, smaller in women than in men. From the base to the epiglottis extends a fold serving to limit the movements of the latter organ, and from the sides of the base to the soft palate two folds on each side, the pillars of the fauces, between which are the tonsils; under the anterior free extremity is the frenum, which connects it with the lower jaw, a fibrous and mucous lamina or ligament, sometimes so short congenitally as to prevent the free movements of the tongue and to require an operation for its division.

There is a more or less distinct longitudinal furrow on the median line, from which extend outward and forward numerous other lines whose angle of union points backward; the posterior third is smooth and without compound papillae, exhibiting a few simple ones and the nodular eminences of the numerous muciparous glands; in front of this is a V-shaped ridge, the angle directed backward, formed by two converging lines of button-like eminences, the circumvallate papillae; in front of these, and occupying the anterior two thirds of the organ, are the fungiform and conical or villiform papillae, the former spheroidal and scattered, the latter very numerous. The osseous support •of the tongue is the U-shaped or hyoid bone, consisting of a base or median body, two greater and two lesser cornua, and placed in the neck between the lower jaw and the thyroid cartilage; it is the homologue of a very complex apparatus in the lower vertebrates. The muscles constitute the chief bulk of the tongue; they are arranged in a complicated manner, so as to support each other, rendering the movements of the organ exceedingly varied and extensive; they are attached to the submucous fibrous tissue, which is firm and thick on the superior surface.

The mucous membrane is invested with a delicate scaly epithelium, the superficial layer of which readily and constantly falls off. The papillae are much like those of the skin, most being compound organs, in their nervous and vascular supply. The circumvallate papillae are G to 10 in number, and sometimes 1/8 in. in diameter; the fungiform are fa to fa in. in diameter, and vary greatly in number, perhaps accounting for the well known diversity in the acuteness of the sense of taste in different individuals; the filiform are the most numerous, closely set like the pile of velvet, covering the anterior two thirds of the tongue, and the seat of what is called the fur; their epithelium frequently breaks up into hair-like processes, having their imbrications directed backward, which mark a physiological distinction between the circumvallate and fungiform papillae and the filiform and conical ones. The conical papillae are generally regarded as tactile, the fungiform and circumvallate as gustatory (acutely tactile), and the filiform as the homologues of the recurved spines of the tongue of the cats, and as principally concerned in regulating the movements of the food in order to bring it within the reach of the muscles of deglutition.

The principal arteries of the tongue are the lingual branches of the external carotid; the sensory nerves are the lingual branch of the fifth-pair or trifacial and the glossopharyngeal, distributed respectively to the anterior and, posterior portions, and the motor nerve is the hypoglossal; for their functions see Taste. , The tongue in fishes is rudimentary, and not endowed with any great sensibility or motor power; in reptiles it varies greatly in length, size, and mov-ability, being in some immovable or short and thick, in some remarkablo for slenderness and length (as in serpents), and in others for pro-tractility (as in the chameleon and frog); in them it is usually an organ of prehension and not of sensation. The tongue in birds is also prehensile and not gustatory, and generally provided at the base with numerous spines directed backward to prevent the return of food; though itself incapable of elongation, it may be remarkably protruded by the action of the muscles attached to the very long and movable hyoid bones.

In some mammals, as the giraffe and ant-eater, it is capable of great elongation, and is an important organ of prehension; the recurved spines of the cats have been referred to, and constitute efficient instruments for cleaning flesh from bones and for combing their fur. In man the tongue keeps the food during mastication within the range of the teeth, collects it from all parts of the mouth preparatory to swallowing it, and is also concerned in the commencement of deglutition; and it is a principal organ of articulation. It is liable to inflammation, enlargement, atrophy, ulcerations, tumors, and malignant diseases. The fur in disease depends on a sodden and opaque condition of the epithelium of the filiform and conical papillae, arising from an alteration of the mucus and saliva of the mouth, the bright red color of the fungiform papillae presenting a striking contrast; the amount, color, and arrangement of the fur are symptomatic of various morbid changes in the system, of interest to the physician, though there is great variety within the limits of health.

The papillary surface is healed and repaired with great readiness and perfection.

Fig. 1. - Papilla circumvallata of Man, in transverse and vertical section. A. Proper papilla. B. Wall. a. Epithelium, c. Secondary papillae. b, b. Nerves of the papilla and of the wall. (Magnified about 10 diameters).

Fig. 2. - A. Fungiform Papilla, showing the secondary papillae on its surface, and at a its epithelium covering them over. (Magnified 25 diameters.) B. The capillary loops of the simple papillae of A, injected: a, artery; v. vein. The groove around the base of some of the fungiform papillae is represented, as well as the capillary loops (c. c) of some neighboring simple papilla?. (Magnified 18 diameters).