THE HEAD AND NECK 



105 



the cranium, the 'glenoid' cavities, or, rather 3 surfaces 

 (7), to which the two branches of the mandible arc 

 articulated, must be mentioned. They are placed just 

 below the hinder end of the zygomatic arch. They are 

 wide transversely, concave from side to side, convex 

 from before backwards in front and hollow behind, and 

 bounded posteriorly at the inner part by a prominent 

 ' post-glenoid ' process, which effectually prevents the 

 jaw from being dislocated backwards. 



The lower jaw, or '' mandible/ consists of two halves 

 or branches (' rami originally distinct, but firmly 

 united in adult horses by their front ends (the sym- 

 physis). Each is articulated to the corresponding 

 glenoid surface of the cranium by its 1 condyle/ 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 surfaces 

 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, backward- 

 curving, c coronoid process' (co, fig. 15), for the attach- 

 ment of the temporal muscle, which aids in closing the 

 jaw. Below it is a flat, broad, expanded surface, reaching 



