The Mandible, forming the lower jaw, is horseshoe in shape, with vertical processes at the ends. The body supports on its upper border the lower row of teeth, and near the middle line on the outer surface is the mental foramen through which the mental nerve emerges. In the middle line of the body a faint ridge can be seen, the symphysis, indicating that the bone was developed in two halves and fused in the middle line. On the inferior border on each side of the symphysis is the digastric fossa, a small concave surface for the digastric muscle, and on the inner surface of the bone is found an oblique line or ridge the mylo-hyoid ridge, slanting from above downwards and forwards.

Fig. 44. - The Inferior Maxilla (Mandible).

The posterior vertical portions are called rami; they pass upwards from the posterior extremities of the body of the bone forming the angle of the jaw, which varies with different individuals. On the inner surface of the bone is a large foramen for the inferior dental nerve, and overhanging it a small spur of bone, called the lingula. The ramus ends above in two processes-the coronoid anteriorly and the articular condyle posteriorly. Between them is a notch-the sigmoid notch.

The mandible articulates with the temporal bone.

The Hyoid bone is a small U-shaped bone lying between the mandible and the larynx, and connected to the skull by ligaments from the styloid process of the temporal bone; it is not articulated with any bones.

The bone consists of a small body with two large processes, the great cornua projecting backwards and, where the great cornua join the body, two small pointed processes, the lesser cornua, projecting obliquely upwards.

The hyoid bone has a large number of muscles attached to it, and owing to its loose connection with the skull gives great mobility to this region.