TONGUE. Anatomically the tongue is divided into a main part, a base toward the pharynx, a dorsum or upper surface, a root by which it is attached to the hyoid bone and floor of the mouth, a tip which is free and an inferior free surface in contact with the front part of the floor of the mouth and with the lower incisor teeth. The dorsum is covered by stratified squamous epi thelium, and, when at rest, is convex both anteroposteriorly and transversely ; it is thickly studded with papillae, of which four kinds are recognized.
Filiform papillae are minute conical projections covering the whole of the dorsum as well as the tip and borders of the tongue. They are very numerous and contain a short core of subepithelial mucous membrane covered by a thick coating of epithelial cells, which coating may divide at its tip into a number of thread-like processes.
Fungiform papillae are less numerous than the last, and some what resemble "button mushrooms"; they generally contain spe cial taste buds.
Circumvallate papillae are usually from seven to ten in number and are arranged in the form of a V, the apex of which points down the throat. They lie quite at the back of the upper surface of the tongue and each consists of a little flat central mound sur rounded by a deep moat, the outer wall of which is slightly raised above the surface, and it is to this that the papillae owe their name. Both sides of the moat have taste buds embedded in them, while into the bottom small serous glands open.
Foliate papillae are only vestigial in man and consist of a series of vertical ridges occupying a small oval area on each side of the tongue near its base and just in front of the attachment of the anterior pillars of the fauces. (See PHARYNX.) The posterior surface or base of the tongue forms part of the anterior wall of the pharynx and has a different appearance from that of the dorsum. On it are found numerous circular or oval elevations of the mucous membrane caused by lymphoid tissue (lymphoid follicles), on the summit of the most of which is a mucous crypt or depression. The division between the superior or oral surface of the tongue and the posterior or pharyngeal is sharply marked by a V-shaped shallow groove called the sulcus terminalis which lies just behind and parallel to the V-shaped row of circumvallate papillae. At the apex of this V is a small blind
pit, the foramen caecum.
At the lower part of the pharyngeal surface three folds of mucous membrane, called glosso-epiglottic folds, run backward; the middle one passes to the centre of the front of the epiglottis, while the two lateral ones pass backward and outward to the fossa of the tonsil.
On the inferior free surface of the tongue there is a median fold of mucous membrane called the fraenum linguae, which is attached below to the floor of the mouth. On each side of this the blue outlines of the ravine veins are seen, while close to these a little fold on each side, known as a plica fimbriata, is often found. It must not, however, be confused with the plica sublingualis described in the article MOUTH AND SALIVARY GLANDS.
The substance of the tongue is composed almost entirely of striped muscle fibres which run in different directions. Some of these bundles, such as the superficial, deep, transverse and oblique linguales are confined to the tongue and are spoken of as intrinsic muscles. Other muscles, such as the hyo-glossus, stylo-glossus, etc. come from elsewhere and are extrinsic ; these are noticed under the head of MUSCULAR SYSTEM. The arteries of the tongue are derived from the lingual, a branch of the external carotid (see ARTERIES), while the veins from the tongue return the blood, by one or more veins on each side, into the internal jugular vein (see VEINS).
The nerves to the tongue are the (I) lingual or gustatory, a branch of the fifth (see NERVE: Cranial) which supplies the anterior two-thirds with ordinary sensation and also, by means of the chorda tympani which is bound up with it, with taste sensa tion ; the glossopharyngeal which supplies the circumvallate papillae and posterior third of the tongue with taste and ordinary sensation; (3) a few twigs of the superior laryngeal branch of the vagus to the pharyngeal surface of the tongue; and (4) the hypo glossal which is the motor nerve to the muscles.