LOWER JAW OF THE HORSE. 23 



cutaneous, a muscular, and a mucous layer, besides fat, areolar 

 (called also cellular) tissue, and glands. The principal muscle 

 in the cheek is the alveolo-labialis or buccinator. The mus- 

 cular substance of the cheeks powerfully contracts the cavity of 

 the mouth. 



Lower Jaw. To complete the notice of the parts concerned 

 in the changes of the aliment within the mouth, the lower jaw 

 has still to be spoken of. It is the movement of the lower jaw 

 which gives efficiency to the teeth. The mode of its motion 

 depends on the kind of articulation between it and the temporal 

 bone, into a cavity of which its head, called its condyle, is re- 

 ceived. In the horse, however, the temporal bone divides into 

 two separate bones the squamous bone and the petrous bone. 

 It is with the squamous bone that the lower jaw articulates. 

 The lower jaw itself somewhat resembles the letter V with its 

 two upper extremities bent to an angle with the upper surface 

 of the sides. The part which is bent out of the original direc- 

 tion is known on each side, particularly in human anatomy, 

 as the ramus. This ramus ends in two processes the ante- 

 rior, the coronoid ; the posterior, the condyloid. It is this last 

 which articulates with the squamous bone ; the anterior pro- 

 cess or coronoid is for the attachment of the powerful muscle 

 named the temporal muscle, which makes the teeth of the under 

 jaw strike against the teeth of the upper jaw. Here, in the lan- 

 guage of natural philosophy, the power is between the fulcrum 

 and the resistance. If the coronoid process were behind the 

 condyloid process, while the temporal muscle had its attach- 

 ment as now, it is plain the contraction of that muscle would 

 separate the jaws by drawing the lower jaw downwards, for 

 then the fulcrum would be between the power and the resist- 

 ance. The simplest movement of the lower jaw is that which 

 belongs to carnivorous animals, such as the dog : in these the 

 movement is merely up and down, like that of the blades of a 



