TONGUE, the principal organ of the sense of taste and an essential part of the ap paratus of speech in human beings. The name tongue is also given to various structures in invertebrates, as the proboscis of a lepidopter or the odontophore of a shellfish. In man the tongue is attached by its base or root to the hyoid bone and to the epiglottis. Its tip, sides, upper surface and part of its under surface are free. Its under surface is fixed to the lower jaw by the genio-hyoglossi muscles and from its sides the mucous membrane is reflected on the inner surface of the gums. In front of the under surface a fold of the mucous mem brane is specially developed and is named the frenum linguae. The upper surface is convex and bears a deep middle line, the raphe, which ends behind in a deep follicle or sac the foramen ccecum. Two-thirds of the forward portion of the organ are rough and bear the characteristic structures known as papilla', in which the sense of taste resides. The posterior third is smooth and exhibits the openings of numerous mucous glands. The substance of the tongue consists of numerous intrinsic muscles, which are named superior and inferior longitudinal and transverse muscles. The mucous membrane consists of an upper layer or cutis supporting papilla and covered with epithelium. This cutis supports the blood-ves sels.and nerves and into it the muscles of the tongue are inserted. The papilla, which cause the characteristic roughness of the tongue, are of three kinds. The circumvallate papilla num ber from eight to 10. They are of large size and are placed on the hinder part of the upper surface and extend from the raphe in two diverging lines. Each of these papilla consists of a rounded central and flattened disc, situ ated in a cup-shaped depression or fossa. The exposed part of the papilla is itself covered with numerous smaller papilla. The fungiform papilla are more numerous than the circum vallate and are scattered irregularly over the upper surface of the tongue, but are most plen tiful on its apex and sides. They are of large size, of rounded, projecting form and of a deep red color. The filiform or front papilla are of very small size and are arranged in rows corresponding with the rows of the circum vallate papilla. In structure the papilla are like those of the skin (q.v.) and contain loops of capillary vessels as well as nervous fila ments. The mode of termination of the nerves in the papilla is hardly determined. Numerous follicles and mucous or lingual glands exist on the tongue, the functions of these latter being the secretion of mucus (q.v.). The epithelium (q.v.) of the tongue is of the flat or scaly kind, resembling that of the epidermis or outer skin, but the deeper cells of the epithelial layer do not contain any pigmentary or coloring mat ter. The muscular halves or substance of the tongue are divided in the median line by a fibrous septum. The arteries are derived chiefly from the lingual and facial trunks and the nervous supply is distributed in the form of three main nerves to each half of the organ. The gustatory branch of the fifth nerve sup plies the papilla in front and those of the sides. The lingual branch of the glossopharyngeal nerve supplies the mucous 'membrane at the sides and base and also the circumvallate papilla, while the hypoglossal nerve is dis tributed to the muscular substance of the organ.
The gustatory nerves and glossopharyngeal branches are the nerves which provide the tongue with common sensation and also with the sense of taste, the hypoglossal nerve being that which invests the muscles of the tongue with the necessary stimulus. The conditions
which appear to be essential for the exercise of this sense are: (1) the solution of the matters to be tasted — that is, their presence in a form in which their particles may readily come in contact with the nerves of taste, there being thus a strong analogy between the sense of taste and that of touch, since the latter sense must be in a manner exercised before the taste of any substance can be perceived; (2) the presence of a specialized gustatory nerve, a necessary condition for the exercise of this sense. Occasionally it happens, however, that other stimuli than those produced by the actual contact of sapid substances sith the nerves of taste may excite that sense. If a current of cool air be directed on the tongue a saline taste is perceived; and a smart tap on the tongue will produce a taste analogous to that excited by electricity. A minute current of electricity can be detected by the tongue which is not ob servable by the contact of the hand. It appears necessary that the surface of the tongue itself should be moist, in order that the gustatory sense may be exercised, and hence the inability to taste substances when the palate and fauces are dry and parched. The tongue itself does not appear to be the exclusive seat of this sense. The soft palate, uvula, tonsils and upper part of the pharynx in all probability exercise this sense, although in a minor degree when compared with the tongue. The middle of the tongue appears to be most feebly.endowed with the sense of taste, the most sensitive region of the organ being the tip and edges. The tongue may occasionally lose its sense of taste and re tain its sensibility to touch, or vice-versa. Sur prising variations in taste occur. While some substances taste alike when touched by every part of the tongue, other substances taste dif ferently when applied to different parts of the tongue. Sensations of taste, or at any rate of the impressions of taste, may remain for long periods after the substances tasted have dis appeared, while the frequent repetition of the same taste dulls the sense. This sense may also be excited by internal stimuli as well as by those of external kind.
In the articulation of words, the modulation of sounds, the tongue plays an important part among the organs of speech; and in mastica tion, swallowing and nearly all the actions per formed by the mouth the tongue is more or less concerned.
Various mechanical devices and structures thought to resemble the human tongue in some respect are so named, as the pole of a wagon, the fastening pin of a buckle, a vibrating slip in a musical reed, the tang of a tool, a strip of leather for closing the front gap in a laced shoe, etc.
an English name, cor rupted frotn the French tangsse, ap.plied to young soles and other small edible flatfish found along the shores of the English Channel. The term has been applied by Jordan to the American genus Sympincrus of sole-like fishes occurring on both United States coasts.
an abnormal attachment or adhesion of some part of the tongue to some portion of the surrounding structures of the mouth. The ordinary form of tongue-tie' con sists in an abnormal development of the frenum. The tongue, in consequence, cannot be ex tended beyond the lips, and suction and masti cation, as well as speech, are impeded.