142 



AGE OF THE DOMESTIC ANIMALS. 



and the wearing surface is much softer ; the mastication is not 

 complete, and the animal shows the effect of a lessened nutrition. 

 Superior Jaw. — What has been said of the lower jaw ap- 

 plies to the upper, but the changes in them are less frequent. 



Fig. 149. 

 Lower molar arch of a very old horse. 



Fig. 150. 



Molar arches (right) of a very old horse. 



Lower jaw to the left of figure. 



The separation of the roots in the upper jaw is less common, as 

 these teeth are longer and contain a greater amount of enamel. 



/ EXCESS OF LENGTH OF THE CROWNS. 



Excess of length of the crowns or portions of them is of 

 rather common occurrence. As the upper molars are broader as 



