TASTE. At the back of the surface, just be hind the circumvallate pa pilhe, are large mu cous glands, extending into long and capacious canals, and helping to secrete tie- fluid that moistens the tongue. On the inferior surface, the longitudinal furrow. whit•h extends from the tip to the fnenum, 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 'Suck (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 ligaments, must be re garded as the basis or framework of the tongue. The muscles of the tongue are usually divided into two groups—viz. the extrinsic muscles, which at tach 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 bulk, and move it on itself. These intrinsic muscular fibres run ver tically, transversely, and longitudinally, and arc 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 month ; the tip may be protruded straight out or later ally, upward and downward, and to any recess (as for instance, a hollow tooth) within the mouth where food might lodge; and the whole or gan may be drawn back. The nerve supply to the
tongue is rz.otor and sensory. The motor nerve is the hypcglossal. The sensory nerves are the lingual (or gustatory) branch of the fifth, which confers sensibility on the mucous membrane of the anterior two-thirds of the tongue; the lin gual branch of the glosso-pharyngeal, which con fers ordinary sensibility and the sense of taste on the posterior third of the tongue; the chorda tympani, which is the special nerve of taste for the anterior two-thirds of the tongue.
The functions of the tongue are gustation, pre hension (in man and monkeys this function is supplied by the hand), mastication, insalivation, deglutition, and speech; to which may be added spitting and whistling, and in the ease of the Gnsteropoda, trituration of the food.
The tongue is subject to several diseases, among which may be mentioned: Glossitis, or inflamma tion of the tongue, tuberculosis, and syphilis; new growths, usually malignant in nature; cer tain affections which the mucous membrane of the tongue shares with the skin, such as herpes, lichen, and leucopathia. It is also subject to ex eoriations, ulcers, and fissures. Macro-glossia is a term applied to certain chronically enlarged conditions of the tongue. It is a condition often found in cretins and is probably due in this case to alytnphangioma.
Hypertrophy and also cancer may attack the tongue.