222 MANUAL OF MODERN PARKIER Y. 



upper incisors are less liable to friction and wear than those 

 of the under jaw, in consequence of the lower jaw alone 

 being moved in the act of chewing, and the upper jaw- 

 being fixed and without motion : its office is only to resist 

 the pressure of the under jaw in eating. 



The tushes are of no use whatever in enabling us to 

 determine the age of a horse, because the change of their 

 form is very uncertain. They will sometimes be blunt at 

 one year, and in other cases will remain pointed to eighteen 

 or even twenty. They do not rub against each other like 

 the teeth, and are consequently less liable to be worn down. 



After eight, we are best enabled to judge of the age of 

 a horse from the form of the upper surface of the incisors. 

 At this time all of them are transversely oval, that is, the 

 length of the oval extended from one tooth to another. As 

 the animal advances in years, they diminish in size, the 

 width being the first affected, and not their thickness,, 

 They soon grow a little apart from each other, and their 

 surface rounded, which continues to be the case up to 

 thirteen years ; after this they assume a new character, and 

 become triangular in the same order in which they had 

 become oval and rounded. 



At nine, the nippers or middle incisors are rounded, and 

 the next teeth or dividers begin to assume that form ; the 

 remainder of the funnel of these four teeth is round, and 

 quite close to the inner edge of the tooth ; they also ex- 

 hibit the septum of the root. 



At ten, the incisors will be considerably shortened in 

 their oval form. There is merely a rudiment of the funnel 

 of the nippers, as well as in the dividers, and the remainder 

 of the central enamel touches the inner edge of the table of 

 the tooth. The nippers and dividers are rounded, and the 

 corner teeth exhibit an oval form. (Plate v. fig. 3.) 



