THE HEAD AND NECK. 113 



The lower jaw, or " mandible/ 7 consists of two 

 halves or branches ("rami 77 ), originally distinct, but 

 firmly united in adult horses by their front ends (the 

 symphysis). Each is articulated to the correspond- 

 ing glenoid surface of the cranium by its " condyle/ 7 

 placed at the hinder and upper end of the ramus. The 

 smooth, articular surface of this is very wide trans- 

 versely, but narrow and convex from before back- 

 wards. The principal action at this joint is that of 

 a simple hinge, but the form of the contiguous sur- 

 faces allows a certain amount of motion in other 

 directions, far more, for instance, than is permitted 

 in the very -complete interlocking hinge-joint of the 

 Carnivora. 



In front of the condyle, and separated from it by 

 a notch, rises a somewhat small and slender, back- 

 ward-curving "coronoid process 77 (co, Fig. 15), for 

 the attachment of the temporal muscle, which aids in 

 closing the jaw. Below it is a flat, broad, expanded 

 surface, reaching down to the "angle 7 ' (where the 

 horizontal and vertical or ascending portions of the 

 jawbone meet), for the attachment of the huge mas- 

 seter muscle, arising from the zygomatic arch, and 

 from a well-marked ridge running horizontally for- 

 wards on the cheek in continuation of the lower bor- 

 der of the arch. This muscle is the main agent in 

 closing the mouth, and therefore in crushing the 



