204 THE TEETH AS INDICATORS OF AGE. 



perhaps less reliable, during the same period, and for 

 about four or five years longer (say the twelfth or thir- 

 teenth), and the change in shape,* color, and position 

 from about the seventh year till old age. The change 

 in the shape of the teeth is caused by their wear and 

 growth, the wear counteracting the growth and the 

 growth the wear. 



In foals and young horses the marks are probably 

 the surest guides by which to judge of the age. One 

 peculiarity of them is that, as the teeth wear down, 

 they approach the posterior edge. Besides their utility 

 in indicating age being composed of enamel (the ad- 

 amantine substance) they greatly enhance the dura- 

 bility of the teeth that is, during the first third of 

 the horse's life. As a rule the variations in the size 

 and appearance of the mark will be 

 as follows : 



At six months they are oblong and 

 distinct in the centrals, and the 

 cavities are plain in the dividers. 



At one year they are short in the 

 centrals, are becoming so in the di- 

 viders, but are large in the corners. 

 At a year and a half they are rep- 

 resented by a small spot in the cen- 

 trals, are diminished in the dividers, 

 but are still large in the corners. 



At two years they are no longer 

 visible in the centrals (in some cases 

 are even shed) ; are smaller and 

 rounder in the dividers, but still 

 plain in the corners. 



* Surg. Cherry says the shape and general character of the 

 teeth are better criterions of age than the marks. 



