This is a single bone composed of two flattened branches, which converge from above downward, and unite in front to form the body. It is the largest bone of the face. It carries six molar teeth, or grinders, on each side, and six incisor teeth in front. In addition, it also gives lodgment to two canine teeth or tusks in the male. Above it forms a hinge joint on either side, where its rounded prominences or condyles are fitted to corresponding depressions in the temporal bones by the interposition of a disc of cartilage. In front of the condyles are two long, thin, and flattened bony prominences, the "coronoid processes", which give attachment to muscles of mastication. On the inner sides above, and on the outer sides below, are two openings communicating with a long canal, through which pass an artery and a nerve to supply the teeth with blood and sensation. 0s Hyoides or Tongue Bone. - This bone is situated in the region of the throat, and is composed of five distinct pieces. One is formed like a spur, having a short, pointed process projecting forward, and embedded in the root of the tongue, and the heel - like branches directed backwards to be connected with the larynx or upper part of the windpipe. The others, two flat slender pieces on either side (superior and inferior cornua), are united together and attached above to the petrous temporal bone at the base of the cranium by means of a short rod of cartilage. The several parts composing the bone are joined together by articulations, some of which form free-moving joints, to which the extreme mobility of the tongue is due.

The Hyoid Bone and the Larynx.

Fig. 291. - The Hyoid Bone and the Larynx.

A, Superior or Long Cornu of 0s Hyoides. B, Inferior or Short Cornu. C, Thyroid or Heel-like Process. D, Spur Process.

E, Epiglottis. F, Glottis. G, Cricoid Cartilage. H, Thyroid Cartilage. I, First Ring of Trachea. J, Arytaenoid Cartilage.