DEVELOPMENT OF TEETH IN THE HORSE. 



15 



The effect of this triturating edge may be judged of from 



GRINDING SURFACES OF THK UPPER AND LOWER MOLARS IN THE HORSE. 



The pattern presented in a is by the six molars on one side of the upper jaw in the 

 horse, owing to the unequal wearing of the dentine, enamel, and cement. The 

 same in b in the six molars on one side of the lower jaw. In both a and 6 the front 



molar is to the left hand. 



The mode in which each tooth forms in the gum, illustrates 

 the structure which it is afterwards to exhibit. There is pro- 

 duced, corresponding to each tooth, a pulp contained within a 

 capsule. The pulp is converted subsequently into dentine, 

 the capsule into cement. Thus the original relative position 

 of the pulp contained within the capsule answers to the rela- 

 tive position of the interior dentine and the exterior cement. 

 When the tooth is besides to possess enamel, a peculiar pro- 

 duct appears on the inner surface of the capsule, which is 

 finally developed into enamel. When a tooth is to be dis- 

 placed at a fixed age by a permanent tooth, the original 

 matrix gives origin to a germ, which finally passes into a pulp 

 contained, in like manner, within a capsule. When no germ 

 is detached from the first matrix, no second tooth ever arises. 

 The original pulp of each tooth assumes the figure of the den- 

 tine into which it is to be converted, so that the pulp of a 

 grinding or molar tooth resembles a stem with short expand- 



