The muscles of this group which specially interest us are the masseter and the temporal. As regards the pterygoids, since they are situated within the borders of the inferior maxillary bone, and consequently do not reach the surface, we shall not require to occupy ourselves with them here.
Masseter ([Fig. 89], 2; [Fig. 90], 1; [Figs. 91], [92]).—For those who have studied the masseter of man, it is not difficult to recognise that of quadrupeds. Nevertheless, the particular aspect which it presents in different species gives to its study a certain interest.
Arising from the zygomatic arch, and passing downwards and backwards, it is inserted into the external surface of the ramus of the mandible and into its angle.
Its posterior border is in relation with the parotid gland ([Fig. 90], 14; [Figs. 91], [92]), this gland being situated between the corresponding border of the lower jaw bone and the transverse process of the atlas. Such are the general characters; the following are the particular ones:
In the carnivora it is thick and convex. In the horse it is flat, but more expanded; it forms the flat of the cheek. In the ox it is flat, as in the latter; but, while being less thick, it is more prolonged in the vertical direction.
The form of the osseous parts which give it origin is, besides, in relation with these differences, and explains the peculiar characters which the masseter presents.
Fig. 89.—Myology of the Dog: Masticatory Muscles (a Deeper Dissection than that shown in [Fig. 90]).
1, Zygomatic arch; 2, masseter; 3, temporal exposed by the suppression of the auricular and occipital muscles and the pinna of the ear; 4, auditory canal; 5, inferior maxillary bone; 6, digastric.