On the external surface of the body are found the three mental foramina. The superior border is hollowed out by alveoli.
With regard to the branches (_rami_), they terminate in two processes: one, the posterior, is the condyle; the other, situated more forwards, is the coronoid process, which gives insertion to the temporal muscle. These two processes are separated by the sigmoid notch.
For reasons which we will explain further on (see p. 127, movements of the lower jaw), the condyle presents differences of form. In the carnivora, it is strongly convex from before backwards, expanded transversely, and firmly mortised in the glenoid cavity of the temporal bone; in the ruminants, it is less convex from before backwards, it is more slightly concave in the transverse direction; in the rodents--we give as an example the hare (Fig. 64)--the condyle is still convex from before backwards, but it is flattened from without inwards.
In the animals in which the muscles of mastication are very highly developed, and especially in the carnivora, the osseous regions occupied by these muscles are more extensive and more deep than in the human species. The length of the coronoid process, the depth of the temporal fossa, the extent of the zygomatic arch, the appearance of the external surface of each of the rami of the lower jaw, deeply hollowed out for accommodation of the masseter, and to provide extensive surfaces of insertion for this muscle, are sure proofs furnished by the skeleton of the occasionally enormous development of the muscles of mastication.
In the carnivora, a rather strong process, which is directed backwards, occupies the angle of the inferior maxilla; it is, accordingly, situated below the region of the condyle.
[Illustration: FIG. 64.--SKULL OF THE HARE: LEFT LATERAL ASPECT.
1, External occipital protuberance; 2, occipital condyle; 3, parietal bone; 4, frontal bone; 5, orbital process; 6, orbital cavity; 7, zygomatic process; 8, external auditory canal; 9, superior maxillary bone; 10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior opening of the nasal fossa; 13, malar bone; 14, inferior maxillary bone; 15, condyle of the inferior maxillary bone; 16, incisor teeth; 17, molar teeth.]