tongue(redirected from on the tip of (one's) tongue)
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the unpaired growth on the floor of the mouth in humans and other vertebrates.
In fishes the tongue is a fold of the mucous membrane; it has no muscles (except in dipnoans) and moves with the entire visceral skeleton when the sublingual-branchial apparatus moves. In amphibians numerous mucous glands are found on the dorsum, that is, the superior surface of the tongue. All terrestrial vertebrates develop tongue musculature, derived from the sublingual parietal musculature. The tongue is able to move independently and serves to grasp food, move the food within the mouth, and swallow the food. Most tailless amphibians use the tongue to catch prey. In some amphibians the posterior end of the tongue is free; the tongue is ejected to catch insects, tipping downward with the free back edge. This feature is unknown in all other vertebrates.
In reptiles the anterior portion of the sublingual skeleton, the hyoid bone, lies at the base of the tongue. The tongue of crocodiles and turtles moves only inside the mouth. The long tongue of chameleons is covered with a sticky substance that aids in catching insects. The tongue of snakes and some lizards is bifurcated at the front and moves quickly; it is used to feel and analyze chemically (for taste) surrounding objects.
In birds the tongue is also connected to the hyoid bone. It usually is incapable of free movement, although it can be thrust forward in woodpeckers and hummingbirds. The tongue is covered by cornified epithelium. Parrots have a broad, fleshy, movable tongue. The shape of the avian tongue is extremely varied and is related to the diet of the particular species.
In mammals the tongue is capable of particularly free movement because of its complex musculature and reduction of the hyoid bone. In edentates and some ungulates the tongue is used to grasp food. In humans the tongue has also become an organ of speech. The mammalian tongue consists of the free part (or body), the apex, and the root (by which the tongue is attached to the lower jaw and hyoid bone). On the dorsum, between the body and the root, is situated the foramen cecum linguae, which is an atretic thyroid duct. The underside of the tongue is covered by a thin mucous membrane; salivary ducts open between the folds of the membrane and near the root of the tongue. The frenulum linguae, a fold of mucous membrane, descends from the middle of the tongue’s underside to the floor of the mouth.
The mucous membrane of the dorsum is thick and partly cornified. It has papillae of different shapes: filiform papillae for feeling and foliate, fungiform, and vallate papillae for perceiving taste stimuli. Serous and mucous glands located in the mucous membrane open between the papillae. The mucous membrane of the superior surface of the root of the tongue has protruding follicles, which make up the lingual tonsil.
The tongue musculature is striated, and the intertwining of muscle bundles ensures highly differentiated tongue movement. Three nerves enter the tongue: the hypoglossal is a motor nerve, and the glossopharyngeal and lingual are sensory, mainly gustatory, nerves. The tongue is supplied with blood by the paired lingual arteries; the blood flows out through several veins.
REFERENCESShmal’gauzen, I. I. Osnovy sravnitel’noi anatomii pozvonochnykh zhivotnykh, 4th ed. Moscow, 1947.
Prives, M. G., N. K. Lysenkov, and V. I. Bushkovich. Anatomiia cheloveka, 8th ed. Leningrad, 1974.
A. S. SEVERTSOV
Pathology. Congenital pathological conditions of the tongue include fissured tongue (presence of deep fissures on the dorsum that retain particles of food, thereby encouraging the development of erosions and cracks), shortened frenulum (manifested in infants by difficulty in sucking and later by impaired speech), and macroglossia (abnormally large tongue caused mainly by excessive muscle development). Some of these conditions, including macroglossia and shortened frenulum, can be corrected surgically. Injury to the tongue may be complicated by the development of an abscess or phlegmon requiring surgery. Specific and local treatment is used in case of tuberculosis or syphilis of the tongue. Tumors of the tongue may be benign (papillomas, fibromas, myomas, and hemangiomas) or malignant (carcinoma and sarcoma); therapy varies with the type of tumor (surgery, radiation, chemotherapy).
A. I. RYBAKOV