86 NATURAL HISTORY OF THE HORSE. 



traced in the animated world. The grinders, or molars, are 

 twenty-four in number. They are teeth of great power. By 

 them the food is crushed or ground into small particles, and 

 prepared for the digestive action of the stomach. In order to 

 fit them for this office, they possess additional interlayers of 

 enamel, which prevent their too rapid wear. 



In common with most animals, the horse is provided with 

 two sets of teeth ; those appearing first are known as the tem- 

 porary, deciduous, or milk teeth, and are succeeded by the 

 permanent set. On comparing the different magnitudes of the 

 jaw-bones of the colt and the adult horse, the necessity of such 

 a change is at once apparent. By it the teeth are adapted to 

 the size of the maxillary bones. The teeth, from their peculiar 

 character and mode of growth, do not admit of any material 

 increase of dimension ; and nature was therefore forced either 

 to place the large permanent teeth in small and disproportionate 

 jaw-bones, or to adapt the size of the teeth by displacement to 

 the growth of the bones that contained them. The latter pro- 

 cess is adopted, and constitutes one of those remarkable 

 evidences of creative power, with which the living frame is 

 replete. 



Three substances enter into the structure of the teeth ; first 

 the enamel; secondly, the dental bone, or ivory ; and thirdly, 

 a cortical envelope, surrounding the fang. The enamel differs 

 but little in chemical constitution from the bony body of the 

 teeth ; and that principally results from the absence of animal 

 matter in it. It appears closely analogous to the univalve 

 porcellaneous shells, and is the hardest and most indestructible 

 substance of the body. The dental bone is distinctly tubular 

 in structure ; these tubuli taking a perpendicular direction, 



