346 



PALAEONTOLOGY. 



(lb, i) are subcompressed laterally, with the fore part of their 

 base a little broader than the back part. The two inner cones 

 (p, p) have their inner surface convex, with their summits 



slightly inclined forwards. The 

 fore part of the base of the 

 hinder cone is prolonged ob- 

 liquely towards the centre of 

 the crown, beyond the con- 

 tiguous end of the base of the 

 front cone, so as to cause an 

 arrangement like that of the 

 two outer cones (0, 0), the ob- 

 liquity of the posterior cone 

 Fig. 116. of both the outer and the 



Stereognathus ; upper view of portion inner pairs being such that 

 of jaw (nat. size), and magnified view 



of the middle tooth, B (Stonesfield they slightly converge as they 

 0olite )- extend forwards. 



This type of tooth differs from that of all other known 

 recent or extinct Mammals. The nearest approach to it is 

 made by the middle lower true molar (fig. 124, m, 2) of Plio- 

 lophus yulpiceps, a small extinct herbivorous Mammal from 

 the London clay. 



That the fragment in question is the jaw of a Mammal is 

 inferred from the implantation of the tooth by two or more 

 roots. Most Mammals are known to have certain teeth so 

 implanted. Such complex mode of implantation in bone has 

 not been observed in any other class of animals. Why two 

 or more roots of a tooth should be peculiar to viviparous 

 quadrupeds, giving suck, is not precisely known. That a 

 tooth, whether it be designed for grinding hard or cutting soft 

 substances, should do both the more effectually in the ratio of 

 its firmer and more extended implantation, is intelligible. 

 That a more perfect performance of a preliminary act of 

 digestion should be a necessary correlation, or be in harmony, 



