STRUCTURE OF TEETH IN THE HORSE. 13 



shed the three last grinding teeth above and below on each 

 side of the mouth, for they are also permanent teeth. By 

 attention to the varying state of the mouth, owing to the 

 changes on the teeth, much may be learned as to the age of 

 the animal ; but to enter into any detail on this point is 

 foreign to the immediate purpose of the present treatise. It 

 should be remarked, however, that during the period between 

 the shedding of the central milk-nippers and the protrusion of 

 the corresponding permanent nippers, between the second and 

 third year, the colt may fall away in condition, owing to the 

 difficulty of grazing, in which case mashes and corn or cut 

 meat should be provided. 



The part of a tooth which appears beyond the jaw is named 

 the crown, that part which is sunk in the jaw is called the root 

 or fang, while a narrow space between the crown and the fang 

 is known as the neck of the tooth. 



The substance of a tooth is not homogeneous that is, its sub- 

 stance is not throughout of one character. The textures which 

 enter into the composition of the teeth, in such animals as the 

 horse, are termed respectively enamel, dentine, and cement 

 the last formerly called the petrous crust. The dentine forms 

 the body of the tooth, and is more, or less allied to bony sub- 

 stance. The cement forms the outer crust of the tooth. The 

 enamel is the hardest of the whole, and has its place between 

 the dentine and the cement. Even on what is so well known 

 as the enamel on the crown of the human front teeth, there 

 is, at least originally, a very thin layer of cement. The teeth 

 of mammals in general consist of hard unvascular dentine, 

 defended at the crown by an investment of enamel, and every- 

 where surrounded by a coat of cement. In man, the monkey 

 tribe, and common carnivorous quadrupeds, the coronal cement 

 is of extreme tenuity. It is thicker in herbivorous quadru- 

 peds, particularly in the grinders of the elephant. In the 



