TEETH OF DIPHYODONTS. 339 



A large extinct carnivorous animal {Machairodus, fig. 293, vi.), 

 had the upper canine teeth, c, developed to almost the same dis- 

 proportionate length as in the Walrus, whereby they were also 

 compelled to pass outside the lower jaw when the mouth was shut. 

 But these teeth were shaped after the type of the feline canines, 

 only with more compressed and trenchant crowns ; and they were 

 associated with other teeth in number and kind demonstrating 

 the feline affinity of the genus Machairodus. Its remains occur 

 in newer tertiary deposits and in caves. 1 



In older tertiary formations, remains of carnivorous Mammals 

 have been found with the three true molar teeth as expressly 

 modified for the division of flesh, and as worthy the term of 

 6 sectorials ' as the teeth so called in the lion. These teeth 

 were associated with conical premolars, long canines, and short 

 incisors, so as to exemplify the typical formula, e.g. — 



.3.3 1.1 4.4 3.3 

 l 3T3 ;C lTI^4l ;7n 3r3 = 44 - 



The extinct Hycenodon and Pterodon of the upper eocene forma- 

 tions of Hampshire and of France, manifest this interesting and 

 instructive character of dentition. 



A reduced view of the lower jaw of the Hycenodon Requieni is 

 given in fig. 266. After the canines, c, come four successively 

 enlarging conical com- 266 



pressed premolars, p 

 1—4; then, instead of 

 a single carnassial re- 

 presenting the first 

 true molar, there are 

 three of these singu- 

 larly modified teeth — 

 the first, m l, being of 



11 . Dentition, lower jaw, of Hycenodon. 



suddenly small size, 



as compared with the antecedent premolar, and obviously illustra- 

 ting its true nature as a continuation of the deciduous series, with 

 which, doubtless, it agreed in size. It became a permanent tooth 

 only because there was no premolar developed beneath it, so as to 

 displace it. The succeeding carnassial true molars, m 2 and 3, 

 progressively increase in size. The symbols in fig. 266 denote the 

 homologies of the teeth. The marks of abrasion on the lower 

 teeth in the Hycenodon prove the upper series to have been the 

 same in number. 



A second form of equally ancient Carnivore was a mixed- 



1 Kent's Hole, Devonshire, e. g.; cxvi". p. 174. 

 z 2 



