AGE OF THE HOESE BY ITS TEETH. 



443 



In America the horse died out, but the line continued in Europe 

 and Asia to the present day. 



Thus we have every gradation from a four-toed horse to the 

 existing one-toed animal. 



The Age of the Horse told hy its Teeth.— The teeth of the 

 horse vary with age, so that we can tell approximately their 

 age by an examination of the mouth. The incisors of the 

 upper jaw appear sooner than those 

 of the lower jaw. The front milk- 

 incisors come through the gum 

 about a week after birth, the middle 

 milk - incisors at the age of five 

 weeks. At nine months the corner 

 milk - incisors are apparent. The 

 permanent incisors appear as fol- 

 lows : the front when the horse is 

 two and a half, the middle when 

 three and a half, the corner ones 

 when four and a half years old. 

 The milk-incisors are distinguished 

 by being shorter and whiter and 

 with a narrower neck than the per- 

 manent ones ; they also become 

 gradually shorter, which is not the 

 case with the permanent incisors. 



The number of back teeth at 

 birth, or soon after, is twelve, 



three on each side of each jaw ; these are in the position of the 

 three first molars. The permanent molars appear as follows: 

 the 1st and 2nd at about two and a half years ; the 3rd at three 

 and a half years ; the 4th at from ten to twelve months ; 

 the 5th at two years, and the 6th at four years. The true 

 molars— that is, the fourth, fifth, and sixth double teeth- 

 have no milk-teeth in their place. 



The date of appearance of the canines — the tushes— in the 

 male is variable. 



Fig. 210.— Seotion of Horse'.s 

 Incisor Tooth. (Chauveau.) 



I, Dentine ; E, enamel ; c, cement. 



The dentine envelopes the pulp- 

 cavity ; in the complete tooth it is 

 yellowish ; it forms on the table the 

 dental star. The enamel covers the 

 dentine ; when worn down it pre- 

 sents two rings, an outer and an 

 inner. The cement lies over the 

 enamel, and is thickest in the hol- 

 lows and at the bottom of the i 



