Inferior surface. — This surface is attached in its posterior two thirds by the muscles passing from it to the hyoid bone and lower jaw. The most posterior part of this attach ment is as wide as the tongue itself, so that there no portion of the inferior surface is free ; but in front of this the attachment narrows, so that the lateral portions become increasingly free till they meet at the frxnum, in front of which they involve the whole surface. The longitudinal furrow is much more distinctly marked here than above, and is constant : it passes from the tip, on which it is continued, to the frxnum. On each side of the furrow the ranine veins are seen pass ing forwards, and immediately beneath the tip is a little cluster of mucous glands first de scribed by nick*, and also by Nuhn.t The mucous membrane here is quite smooth and free from any visible papillm.
The edges of the tongue, which separate its upper and under surface, are thick behind and gradually become thinner in front ; they are marked by a series of vertical ridges, separated by corresponding furrows, very dis tinct on the upper, and gradually becoming lost as they approach the under, surface. They are very conspicuous at the posterior part, but disappear anteriorly, and they differ very much in their development in different subjects. They are, essentially, fused conical papilla. At the upper and posterior part of the edges are also a series of small mucous glands.
The anterior extremity, apex, or point (fig. 745. b.), is flattened or rounded, blunt or pointed, according to the movements of the tongue, and slightly impressed by the median furrow which is continued on it : it is not marked by any of those vertical ridges that characterise the edges.
The posterior extremity, or base. — Ere the tongue reaches the os hyoides it becomes very flat and thin, and this from two causes — di minution in the quantity of the intrinsic mus cles, and the passing off of the extrinsic in other directions ; so that instead of being very thick, as is generally described, the base is in reality the thinnest part of the whole organ. It is flattened antero-posteriorly and much extended laterally, and by its attach ment to the hyoid bone is curved in a horse shoe shape, which, however, is much effaced by the insertion of the epiglottis in the area of the curvature. It is constituted laterally by the hyoglossi, centrally by the hyoglossal liga ment, anteriorly by some fibres of the germ glossus, and behind and above by the mu cous membrane passing from it over the epiglottis. It contains less muscular and more fibrous tissue than any other part of the tongue.
Such, then, is a general description of the tongue, — such are the appearances that pre sent themselves to the eye, on regarding its ex ternal surface and configuration. Let us now
examine these structures more minutely, and, to facilitate that examination, arrange the parts that contribute to the formation of the organ, according to the office they fulfil, or their absolute nature.
Regarding the tongue in this light, we find that it may be considered as consisting of three systems,— I.
A basis, or system of support.
2. A muscular system, or system of move ment.
3. A tegumentary investment, or system of sensation and protection.
1. Basis, or framework of the tongue.—This consists of the hyoid bone, the hyoglossal membrane or ligament, the median fibrous septum (the cartilaginous lamina of M. Blan din), and, fourthly, to these may perhaps be added, on account of its density, and its giving attachment to most of the intrinsic muscles, the compact fibrous tissue, or cutis, beneath the mucous membrane.
a. The hyoid bone (os hyoides, —lingualis,— lingua), called also the lingual or tongue bone, has received its name from its resemblance to the Greek v ; it is the homo logue in man of a very complex mechanism in the lower vertebrata, from which circum stance it is sometimes called the hyoid ap paratus. It consists of a bony arch, with a curvature nearly approaching a parabola, the convexity being in front ; — situated in an almost horizontal position behind and rather below the lower jaw. In the lower ver tebrata -the hyoid bone is connected to the rest of the skeleton by bony media ; in man, by the substitution of a ligament (the stylo hyoid) for a part of this osseous connection ; it is isolated, and disconnected from all the other bones.* It performs the triple office of a basis of the tongue, a point of support to the larynx, and a point d'appui or fulcrum, by which the contractions of the intrinsic muscles of the tongue and larynx may be impressed on those organs : it may also be looked upon as the first part of that framework (afterwards generally continued by cartilage) which secures the permanent patulence of the respiratory passages. It is retained in its place by muscles and ligaments, which, converging to it from different direc tions, effectually prevent its displacement : thus it is tied upwards and backwards by the ligament and muscles from the styloid process, in front by the muscles from the chin and lower jaw, below by those from the thyroid cartilage, sternum, and scapula. Placed be tween the tongue and larynx, it impresses on each the movement of the other, and is the medium by which the motions of these two organs are so intimately associated.