310 PAL/EONTOLOGY 



the middle true molar of Pliolophus vulpiceps, a small extinct 

 herbivorous Mammal from the London clay (fig. 96, m, z). 



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 sub- 

 stances, 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, with a 

 more complete conversion of the food into chyle and blood, — 

 and that such more efficient type of the whole digestive ma- 

 chinery should be correlated, and necessarily so, with the hot 

 blood, quick-beating heart and quick-breathing lungs, with the 

 higher instincts, and more vigorous and varied acts of a Mam- 

 mal, as contrasted with a cold-blooded reptile or fish, — is also 

 conceivable. To the extent to which such and the like reason- 

 ing may be true, or in the direction of the secret cause of the 

 constant relations of many-rooted teeth discovered by observa- 

 tion, — to that extent will such relations ascend from the em- 

 pirical to the rational category of laws. 



The interest which the above-described fossil from the 

 Stonesfield oolitic slate excites is not exclusively due to its 

 antiquity, its uniqueness, or its peculiarity ; much is attached 

 to its relations as a test in palaeontology of the actual value of 

 a single tooth in the determination of other parts of the organ- 

 ization of the animal. According to our opinion of these un- 

 seen parts, we frame our expression of the nature and affinities, 

 or of the place in the zoological system, of the extinct species. 

 Fr<»m the resemblance of the lower molars of Stereognathus to 



