HUMAN ANATOMY. - The human tongue (in common with that of all mammalia) consists of, first, an osseous basis, itself movable, to which it is attached, and with which and on which it moves ; secondly, a muscular system, in part extrinsic, serving to attach it to certain fixed points and to move it on them, and in part intrinsic, constituting the hulk of its substance and moving it on it self; thirdly, a mucous investment, variously modified in different parts ; fourthly, a pro per system of mucous glands ; fifthly, a small quantity of fibrous and areolar tissue ; sixthly, a still smaller quantity of fit; seventhly, a large vascular supply ; and eighthly, an abun dant distribution of nerves from three separate MUMS.
Size. — The size of the tongue is very va rious. I have examined some tongues of adults that certainly were not more than half the size of others, and there does not seem to be any relation between the size of the tongue and that of the individual; but between it and the size of the alveolar arch there is a close relation, and hence we see it generally much smaller in women than in men. It has been generally stated that certain obscurities in speech are caused by too large a tongue, but there do not seem to be any well authen ticated cases to prove that this supposition is correct. It may in some degree be explained by the fact, that paralysis, which would cause a thickness of speech, would also cause a flaccid half-protruded condition, and, there fore, an apparent increase of size, of the tongue.
Direction. — In its anterior half it follows pretty much the direction of the lower jaw, that is, it tends forwards and a little down wards, but behind this it curves downwards and backwards, and ere it reaches the os hyoides has become quite vertical, so that the average of its direction would be downwards and backwards, and its posterior extremity much lower than its anterior.
tongue is of an ovoidal shape, the broad part being behind ; and the character of the curvature in front is parabolic, coin ciding with the parabolic curve of the lower jaw : it possesses an exact lateral symmetry, and is flattened from above downwards, being thickest towards its base, and thinnest in front. When taken out of the body it seems
to be flat, and in the same plane longitudin ally, but when in situ it possesses a double curvature ; one longitudinal, the most consi derable, by which the upper surface is rendered convex, and by which the posterior part of the tongue is bent from a horizontal to a ver tical direction ; the other, less considerable, affects the tongue transversely, and renders its posterior part concave in that direction : it is much increased by the contraction of the genioglossi, which draw the centre of the tongue down, or by that of the styloglossi, which draw its sides up. The longitudinal curvature, too, is very much affected by the position of the tongue, for when it is thrust forward, and the hyoid bone raised, the whole organ is much more horizontal, and the cur vature almost effaced.
General description. — In consequence of its possessing a long axis, and being vertically flattened, the tongue presents for description a superior and inferior surface, two lateral borders, and an anterior and posterior extremity.
The superior surface, borders, anterior ex tremity, and anterior third of the inferior sur face are free ; the posterior extremity and posterior two thirds of the inferior surface are attached. Along the line where the free and attached surfaces meet, we see the investing membrane leaving the tongue, and passing off to neighbouring structures, investing the loose areolar tissue by which in these situations it is underlaid, and forming a system of yielding and movable attachments. Thus at the base the mucous membrane passes off to the an terior surface of the epiglottis, the sides of the pharynx, and upwards to the soft palate and posterior parts of the cheeks. As we proceed forwards we find it investing the sides, and gradually more and more of the under surface, reflected thence over the hyoglossi and ge nioglossi muscles, the sublingual glands, vessels, and nerves, and much areolar tissue, which separate it from the mylohyoid muscle, to the inner surface of the alveoli of the lower jaw, where it becomes continuous with the mucous membrane covering the gums.