IN THE LOWER ANIMALS, ETC. 235 



These muscles have an extensive surface for 

 insertion in the large coronoid process, which 

 forms the entire vertical ramus of the lower jaw. 

 (See Fig. 32.) 



To admit of the free action of the muscles, the 

 temporal fossa is continuous with the orbit, the 

 frontal and malar bones not being united as in 

 many other animals ; and the zygomatic process 

 extends very widely at a right angle from the 

 temporal bone, in order to give room for the tem- 

 poral muscle, and to form the long transverse 

 glenoid cavity to receive the condyle, constituting 

 a perfectly hinge-like articulation. 



The zygomatic arch being very large and power- 

 ftil, and convex above, is carried forward beneath 

 the orbit, the condyle being situated very far 

 back, and in a direct line with the cutting surface 

 of the teeth. This arrangement enables the 

 masseter muscle to act with immense force, its 

 place of insertion being, like that of the temporal 

 muscle, so far in advance of the articulation of the 

 jaw. (See Fig. 31.) 



Not only is the muscular power of these ani- 

 mals proportioned to their active habits, but, in 

 accordance with the greater intelligence required, 

 the cranial cavity is large, as compared, for 

 instance, with that of the sheep, while the face is 

 shorter and broader. 



The infra-orbital foramen is very large, supply- 

 ing nervous energy to the powerful levator muscles 



