TONGUE, TrrE, is a symmetrical muscular oroan, extending from the hyoid bone backward and downward, to the lips in front, and occupying the buccal cavity. The superior surface, borders, and anterior third of the inferior surface are free; while the remaining parts are attached to adjacent parts by the investing mucous membrane and subjacent structures. At certain points, this membrane, on leaving the tongue, forms distinct folds, containing fibrous or muscular tissue, which act to a certain extent as ligaments to the tongue. The most considerable of these folds is termed the frcenum (or bridle) of the tongue, and connects its anterior free extremity with the lower jaw. It acts as a strong ligament, and limits the backward movement of the tip of the tongue. In rare cases, this ligament extends abnormally to the tip, so as to interfere with speech and mastication, and the child is said to be tongue-tied; recourse must be then had to divis iou of the frrenurn, popularly known as cutting the tongue. Other folds of mucous mem brane (the glosso-epiglottid folds) pass from the base of the tongue to the epiglottis; while from the sides of the base, passing to the soft palate, are seen two folds on either side, known as the pillars of the fauees. See PALATE. The superior surface of the tongue is divided into two symmetrical lateral parts by a median longitudinal furrow, commenc ing at the tip, and extending back about two-thirds of the tongue's length. The various kinds of papillae which are seen on their surface are described in the article TASTE, ORGAN AND SENSE OF. At the back of the surface, just behind the circumvallate papilla;, are large mucous glands, extending into long and capacious canals, and helping to secrete the fluid that moistens the tongue. On the inferior surface, the longitudinal furrow, which extends from the tip to the frxnurn, is deeper than on the upper surface; on each side of it veins are seen running forward; and immediately beneath the tip is a cluster of mucous glands, known as the glands of Nuck (their discoverer in 1690). The posterior extremity or base, is flattened and extended laterally before it is inserted into the hyoid bone (known also as the lingual or tongue bone), which, with certain liga ments, must be regarded as the basis or framework of the tongue. The muscles of the tongue are usually divided into two groups—viz: the extrinsic muscles, which attach the tongue to certain fixed points external to it, and move it on them; and the intrinsic muscles, which pass from one part of the tongue to another, constitute its chief hulk, and move it on itself. These intrinsic muscular fibres run vertically, transversely and longitudinally, and are so interlaced as mutually to support one another, and to act with the greatest advantage. By the action of the various muscles, the upper surface of the
tongue may be made concave or convex, or may be pressed against the roof of the mouth; the tip may be protruded straight out or laterally, upward and downward, and to any recess (as for instance, a hollow tooth) within the mouth where food might lodge; and the whole organ may be drawn back. The organ is freely supplied with blood, mainly by the lingual artery, which is given off by the external carotid. With regard to the nerves, the glosso-pharyngeal and certain branches of the third division of the fifth nerve are concerned in the special sense of taste (q.v.); other branches of the fifth nerve are concerned in ordinary sensation, while the hypoglossal nerve on each side is the motor nerve of the tongue.
The various uses or functions of the tongue cannot be thoroughly understood with out a brief reference to its comparative anatomy. The tongue in mammals does not differ very materially from that of man; but in-general there is a close coincidence both in size and form between this organ and the lower jaw. In the rodents the tongue has a wedge-like shape. In the giraffe and the ant-eater, the tongue is much prolonged, being an important prehensile organ iu the former; while in the latter it is driven into ant hills, and the victims are secured by its viscid secretion. In the feline races the conical papillae are converted into recurved spines of great size and strength, which the animal uses in scraping bones and in combing its fur. Except in mammals, the tongue is prob ably not an organ of taste. For a good description of the tongue in birds, reptiles, and fishes, the reader is referred to prof. Owen's Anatomy of the Vertebrates, vols. i. and ii. Among the mollusca, the gasteropoda are provided with a very singular apparatus known as the tongue, and consisting generally of a thin membrane, long and narrow, and rolled, except at its anterior extremity, into a tube. This mer-brane is covered on its upper surface with transverse rows of minute teeth, or mo commonly with plates having tooth-like siliceous projections. These teeth present a great variety of patterns, which are constant in the different genera, and even characterize the species. Two eminent naturalists, Messrs. Loven, a Swede, and Troschel, a German, have independently made the teeth of the mollusca a basis of classification. The articulata do not present any thing like a true tongue, although in insects a certain oval appendage is described as a lingua.