TEETH OF SEALS. 299 



should be sought for in the substance of the jaw below 

 these, and above their opponents in the upper jaw; and 

 thus the true characters of the permanent dentition may 

 be ascertained. 



The deciduous molars are three in number on each 

 side, and, being succeeded by as many premolars, the 



g Q Q Q 



ordinary permanent molar formula is p ^ -, m : 



o — o o — o 



but there is a rudiment of an anterior milk-molar, rZl, in 

 the embryo fallow-deer, and in one of the most ancient 

 of the extinct ruminants (dorcatheriiaii, Kaup) the normal 

 number of premolars was fully developed. 



The molar series of all the Diphyodonts is naturally 

 divisible into only two groups, premolars and molars; 



A. A. ^ Q 



the typical number of these is , _; and each 



individual tooth may be determined and symbolized 

 throughout the series, as is shown in the instances under 



Cut 75. 



SEAL TKIBE. 



(Phocicke). — There is a tendency to deviate from the 

 ferine number of the incisors in the most aquatic and 

 piscivorous of the Musteline quadrupeds, viz., the sea- 

 otter (e/iA?/(im), in which species the two middle incisors of 

 the lower jaw are not developed in the permanent denti- 

 tion. In the family of true seals, the incisive formula is 



further reduced, in some species even to zero in the lower 



g g 



jaw, and it never exceeds . All the j^hockke possess 



powerful canines; only in the aberrant walrus are they 

 absent in the lower jaw; but this is compensated by the 



