106 THE STRUCTURE OF THE HORSE 



down to the c angle ' (where the horizontal and vertical 

 or ascending portions of the jawbone meet), for the at- 

 tachment of the huge masseter muscle, arising from the 

 zygomatic arch, and from a well-marked ridge running 

 horizontally forwards on the cheek in continuation of 

 the lower border of the arch. This muscle is the main 

 agent in closing the mouth, and therefore in crushing the 

 food between the molar teeth. The horizontal portion 

 of the jaw, long, straight, and flattened from side to side, 

 carries the great molar teeth, and gradually narrows 

 towards the symphysis, where it expands laterally, to 

 form, with the united opposite ramus, the wide, semi- 

 circular, shallow alveolar border for the lower incisor 

 teeth. 



The Teeth 



The next parts to which attention may be called 

 are the teeth, which in the horse, though founded upon 

 the same general type as the primitive Ungulates of the 

 Eocene period, have undergone a remarkable amount of 

 specialisation, fitting them in an eminent degree for the 

 purpose they have to fulfil. 



Number of the Teeth. — For convenience of description 

 teeth are divided, according to their situation in the 

 mouth and other characters, into four sets, called (be- 

 ginning from the front) incisors, canines, premolars and 

 molars. As mentioned in the first chapter, all the early 



