1911 Encyclopædia Britannica/Tongue
TONGUE (O. Eng. tunge), in anatomy, a movable organ situated in the floor of the mouth, and serving for the sensation of taste besides helping in the mastication of food, in articulate speech, and in feeling the exact position of any structure within the mouth.
The tongue is divided into a main part or body, a base which looks backward 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. Owing to the large amount of muscle in its composition the shape of the tongue varies considerably from time to time. The dorsum of the tongue is covered by stratified squamous epithelium, 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, by which term the true upper surface is meant, 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 somewhat resemble “button mushrooms”; they generally contain special 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 surrounded 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 quite different appearance to 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, in modern anatomy often called pharyngo-epiglottic folds, pass backward and outward to the fossa of the tonsil.
On the inferior free surface of the tongue, that is to say, the surface which is seen when the mouth is looked into and the tongue turned up, 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 ranine 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, &c. 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 (1) lingual or gustatory, a branch of the fifth (see Nerves: Cranial) which supplies the anterior two-thirds with ordinary sensation and also, by means of the chorda tymphani which is bound up with it, with taste sensation; (2) 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 hypoglossal which is the motor nerve to the muscles.
The mucous membrane covering the second and third visceral arches fuses to form the furcula (see Respiratory System). Just in front of this a rounded eminence appears at an early date in the ventral wall of the pharynx to form the tuberculum impar which is separated from the furcula by the depression known as the sinus arcuatus. This tuberculum impar gradually grows to form the central part of the tongue in front of the foramen cæcum, while the anterior part of the organ is derived from two lateral swellings which appear in the floor of the mouth and surround the tuberculum impar antero-laterally. The posterior third, or pharyngeal part, is developed from the anterior part of the furcula in the middle line, that is to say from the third visceral arch. The V sinus arcuatus becomes gradually shallower as these two parts of the tongue grow together and eventually is indicated by the sulcus termina is; in the mid line, however, the isthmus of the thyroid grows down from it, forming the thyro-glossal duct the remains of which are seen in the foramen caecum (see Ductless Glands). It will be seen that the tongue is developed in connexion with the first, second and third visceral arches, and it is therefore to be expected that the fifth, seventh and ninth nerves which supply those arches would help to supply it, but the vagus from the fourth arch reaches it in addition, while the fact that most of the muscular substance of the tongue is supplied by the hypoglossal nerve is explained on the theory that some of the cervical skeletal musculature has grown cephalad into the tongue and has carried its nerve with it.
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- (From Ambrose Birmingham in Cunningham's Text Book of Anatomy.)
- Horizontal Section through Mouth and Pharynx at the Level of the Tonsils.
The tongue is present in fishes but it is an immovable swelling in the floor of the mouth and is practically devoid of muscles. In the hag (Myxine) among the Cyclostomata, and pike (Esox) among the Teleostei, teeth are developed on the tongue. In the Amphibia the tailed forms (Urodela) usually have tongues like fishes, though in the genus Spelerpes the organ is very free and can be protruded for a great distance. In the majority of the Anura the tongue is usually attached close to the front of the floor of the mouth so that it can be Happed forward with great rapidity. There are, however, two closely allied families of frogs (Xenopodidae and Pipidae) which form the order of Aglossa, because in them the tongue is suppressed.
In the reptiles the tongue is generally very movable, though this is not the case in the Crocodilia and many of the Chelonia. The forked tongues of snakes and many lizards and the highly specialized telescopic tongue of the chameleon are familiar objects.
In birds the tongue is usually covered with horny epithelium and is poorly supplied with muscles. When it is Very protrusile, as in the woodpecker, the movement is due to the hyoid, with the base of the tongue attached, moving forward.
In the Mammalia the tongue is always movable by means of well developed extrinsic and intrinsic muscles, while papillae and glands are numerous. The filiform papillae reach their maximum in the feline family of the Carnivora where they convert the tongue into ahrasp by which bones can be licked clean of all flesh attached to them.
Foliate papillae are best seen in the rodents, and when they are well developed the circumvallate papillae are few, often only one on each side.
In the lemurs an under tongue or sub lingua is found, which is probably represented by the plicae fimbriatae under the human tongue, and by some morphologists is regarded as the homologue of the whole tongue of the lower vertebrates, the greater part of the mammalian tongue being then looked upon as a new formation.
For further details and literature see R. Wiedersheim’s Comparative Anatomy of Vertebrates, translated by W. N. Parker (London, 1907); C. Gegenbaur, Vergleich. Anat. der Wirbelthiere (Leipzig, 1901); A. Oppel, Lehrb. vergleich. mikroskop. Anat. der Wirbelthiere, Teil 3 (Jena, 1900); Parker and Haswell, Text Book of Zoology (London, 1897). (F. G. P.)
Surgery of the Tongue.
During infancy it is sometimes noticed that the little band of membrane (fraenum) which binds the under part of the tongue to the middle line of the floor of the mouth is unusually short. The condition will probably right itself as the front part of the tongue takes on its natural growth. In some children the tongue is so large that it hangs out of the mouth, scratching itself upon the teeth. This condition is likely to be associated with weak intellect.
Acute inflammation of the tongue may be caused by the sting of a wasp or by the entrance of septic germs through a wound, and the trouble may end in an abscess.
Chronic inflammation of the tongue may be caused by syphilis, by the irritation of decayed teeth or of a badly-fitting plate of artificial teeth, or by excessive smoking. The condition is one of danger in that it may lead eventually to tie tongue becoming the seat of cancer. The treatment demands the removal of every source of irritation. The teeth must be made sound and smooth and must be kept so. Smoking must be absolutely and entirely given up, and salt, mustard, pickles, spirits, aerated waters, and everything else which is likely to be a cause of irritation must be avoided. Cancer of the tongue is the result of chronic irritation which produces an excessive growth of the scaly covering of the tongue and causes an invasion of the deeper parts of the tongue by the scales. It is more often found in men than women and is usually associated with a hard swelling at one side of the tongue-perhaps near a jagged tooth or at the spot where the end of the pipe-stem approaches the tongue. The nerves of the tongue being caught and compressed in the growth, pain is constant and severe, and the movements during mastication cause great distress. The swelling gradually increases in size and, spreading to the floor of the mouth, hinders the free movements of the tongue. In due course it breaks down in the middle and a hard-walled ulcer appears. All this time the small scales of the cancer are finding their way along the lymph-channels and causing a secondary enlargement in the glands just below the jaw and along the side of the neck. Enlargement of the cervical glands is a very serious complication of cancer of the tongue.
The only treatment for cancer of the tongue which is at present known in surgery is the early removal by operation. It not seldom happens that because there is a certain amount of doubt as to the exact nature of the growth in the early weeks delay in operatin is reasonably permitted, but during this time there is the risk of the cells of the disease finding their way to the lymphatic system. Still, inasmuch as there may ie great difficulty in determining the diagnosis from tertiary syphilitic disease, a course of treatment by iodide of potassium may well be recommended. Syphilis is often the precursor of lingual cancer, and it is impossible tc say exactly when the syphilitic lesion becomes malignant. In the case of a cancerous tumour of the tongue being so deeply or so widely attached that its removal cannot be recommended, relief may be afforded by the extraction of most, or all of the teeth, by limiting the food to the most simple and unirritating kinds, and possibly by dividing the great sensory nerves of the tongue.
Cancer of the tongue is now operated on in advanced cases such as in former years would not have been dealt with by a radical operation. An incision is made beneath the jaw and through the floor of the mouth, by which the tongue is drawn out and rendered easily accessible, the arteries being leisurely secured as the tissues are cut across. The upper part of the gullet is plugged by a sponge so that no blood can enter the lungs, and unimpeded respiration is provided for by the preliminary introduction of a tube into the windpipe. Through the incision which is made below the jaw the infected lymphatic glands are removed. To Dr Kocher of Berne the profes- sion and the public are indebted for this important advance in the treatment of this disease. (E. O*.)