AGE, AS INDICATED BY THE TEETH. 



307 



ored than milk teeth. The discoloration is due to the lodgment of 

 the juices and other matters connected with the food in the grooves. 

 The object of the external grooving probably is to enable the animal to 

 get a better grip on grass and such-like food. The plumpness and cir- 

 cularity of the jaw is less than in the younger animal, and it gradually 

 decreases, until in old age the teeth are arranged in a nearly straight 

 line. 



The Temporary or Milk Incisors.— The foal is born with his 

 teeth in a rudimentary state in the gums. At various periods during the 

 first ten months the different temporary incisors appear. (Figure 138.) 



Fig. 138. 

 Teeth of a Foal. 



Under one year old, the foal is also clearly distinguished by a woolly tail. 



The yearling is complete in all six incisors, but several well-marked 



signs distinguish his mouth from that of the two-year old. The teeth 



at this period show but little signs of wear. The corner teeth are mere 



Fig. 139. 

 Teeth at One Year. 



shells, having no inner walls, and all the teeth are in close juxtaposition. 

 (Figure 139.) 



At two years old, the inner wall of the corner teeth has grown up 

 level with the outer wall. The centre teeth show considerable signs of 



