THE AGE. 



117 



Sia. 4. 



represented at the 

 tops of fig ares 2 

 and 3, the six nip- 

 pers together form- 

 ing nearly a semi- 

 circle ; and their 

 general appearance 

 is similar to that 

 represented in fig 

 lire 4. 



As the horse becomes older his teeth are worn away by 

 use, and it is to this cause only are due the changes by 

 which we determine his age. The effect of this wearing 

 down is the same as would be that of cutting or sawing 

 off a portion of the teeth. They are sjipposed to be worn 

 down about one twelfth of an inch per year, though the 

 precise amount must depend very much on circumstances, 

 such as crib-biting, vigorous feeding, etc. If we look at 

 the 'mouth of a horse eight or nine years old, we shall see 

 that his corner teeth have been so woi'n down that the 

 mark, or superficial cav- 

 ity, is entirely destroy- 

 ed, and that the surface 

 has descended to the 

 point marked by the 

 lines a. a., figures 2 and 

 3 ; still later the upper 

 surface of the tooth descends to the point marked by the 

 lines b. b., figures 2 and 3. The folding in of the enamel 

 has now almost entirely disappeared, leaving very little dis- 

 coloration on the teeth, while the upper surface of the 

 tooth is almost triangular instead of being long from side 

 to side, as was the original surface. The teeth of the 

 lower jaw now present the appearance shown in figure 5. 



Fig. 5. 



