88 



THE NATURAL HISTOEY EEVIEW. 



COMPAEATIYE MeASUEEMENTS OF MiLK TeETH. 



Succession. In the upper jaw figured above, (fig. 1, 2,) immedi- 

 ately in front of Dm. 1, is a small conical tooth, almost equally far 

 advanced in growth. This is the small conical one-fanged Premolar 

 1, which appears in the alveolar border, while the other premolars and 

 the canine exist as mere germs buried deeply in their alveolar cavi- 

 ties, and while the milk series are unworn. The small calcified cap 

 of enamel, which is to compose the crown of Premolar 2, lies hid 

 deep in the jaw at the point where the palatal process joins the 

 maxillary, very much to the inner side of the Dm. 1, which it is to 

 displace. The large conical cap of enamel, on the other hand, which 

 represents Premolar 3, is situated immediately underneath the ante- 

 rior portion of Dm. 3, which it displaces at the same time that the 

 anterior portion of the permanent sectorial displaces the posterior 

 half. The posterior blade displaces the third and last milk molar at 

 nearly the same time that Dm. 2 is shed. 



Coincident with the^ appearance of Premolar 4 on the alveolar bor- 

 der in the lower jaw, is that of the Canine, Dm. 1 and 2, remaining 

 a little later, and being pushed out nearly at the same time. The 

 lower sectorial makes its appearance very early, while the milk series 

 is in place, and worn but little. 



The teeth first to disappear in the adult hyena are — as one would 

 expect— the large bone crushers. Premolars 2 and 3 of the upper, 

 3 and 4 of the lower jaw. These are always very much worn in the 

 middle aged adult, while the upper Premolar 1, and the lower Pro- 

 molar 2, exhibit scarcely any trace of wear. 



§ 3. D. In the permanent dentition the crowns of the Incisors 

 one and two of the upper jaw are divided into two cusps by a deep 



