KOOF OF MOUTH IN THE HORSE. 17 



unlike the other parts entering into the animal frame. But 

 as dentition goes on in the horse during a period of five years, 

 it should be considered, during that age, whether all the 

 chemical materials entering into the teeth are sufficiently sup- 

 plied to the growing animal. Of the chemical substances 

 entering into the teeth, the fluate of lime, more properly 

 termed the fluoride of calcium, is the only one not universally 

 found in vegetable bodies. Small as is the proportion of this 

 substance in the teeth, it cannot be doubted that, were it not 

 supplied to the colt during the time of the formation of the 

 teeth, that process would either not take place at all, or be 

 carried on in an imperfect manner. 



The teeth are fixed, each in a separate socket of the jaw 

 to which it belongs, not by ossification or anchylosis, but 

 by a peculiar kind of connection likened to that of a nail 

 in a board. The periosteum or membrane of the bone lines 

 the alveolus or socket, and is reflected on the fang of the tooth, 

 which it invests up to the neck. This membrane blends with 

 the tissue of the gum. The gum is composed of a dense 

 fibrous tissue, covered by a red, not very sensitive, mucous 

 membrane, smooth in its general surface, but, where it closely 

 surrounds the teeth, beset with fine papillae. The action of 

 the teeth in cropping and mastication depends on the move- 

 ments of the lower jaw, of which hereafter. 



The bones which form the roof of the mouth are the inter- 

 maxillary bone, the upper jaw-bone, and the palatine plates of 

 the palate-bones. The intermaxillary bone belongs to mam- 

 mals, with the exception principally of man, in whom the 

 upper jaw-bones of the opposite sides unite in the mesian line 

 that is, in the middle line and support all the upper teeth. 

 On the other hand, in the horse and mammals generally, a 

 distinct bone lies behind the upper lip, interposed between the 

 fore parts of the opposite upper jaw-bones, so that these 



B 



