FIFTH PERIOD. 



WEARING AWAY OF THE CROWNS. 



After this time, wliicli is commonly known as " past mark 

 of mouth," commencing- at nine years and extending to old age, 

 the regularity of the wearing of the teeth and the certainty of 

 the sisrns of ao-e furnished hv them become more variable. The 

 uncertainty increases greatly after fifteen years, and a year or 

 two later the estimation of age from the teeth can only be a 

 conjecture, based upon experience and subject to error of one, 

 two, or even several years, which becomes greater the older the 

 animal is. 



The changes of this period are : The successive alteration 

 in shape of the tables of the teeth ; the position of the cups in 

 the incisors of both jaws ; the form and location of the dental 

 stars in the tables ; the obliquity or degree of incidence in the 

 incisive arches ; the convergence of the crowns and the narrow- 

 ness of the jaw holding the roots ; the thickness of the enamel 

 on the anterior and posterior faces of the teeth ; the appearance 

 of the cement around the roots ; and, the shape of the bones of 

 the face and jaw. 



At nhie years, the pinchers are round ; their cups are tri- 

 ansfular and their dental stars are more distinct, but narrower. 

 The intermediate teeth commence to become round and the 

 corners oval ; the superior pinchers are often leveled ; the 

 notches on the superior corners often disappear. 



At ten years, the tables of the pinchers are decidedly round ; 

 the cups are very small and distinctly triangular. The interme- 

 diate teeth assume the shape of the pinchers the previous year. 

 The dental star is nearly in the middle of the table. 



At eleven years, the corner teeth are rounded. The cups 

 are only small spots near the posterior borders of the tables ; 

 the dental stars are in the middle of the tables. The inferior 

 (100) 



