1856.] OWEN — STEREOGNATHUS OOLITICUS. 5 



an unknown IMammal from a fragment of jaw with a tooth cannot 

 be wholly useless. 



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

 from the implantation of the tooth hy two or more roots. ]\lost 

 Mammals are known to have certain teeth so implanted. Such 

 complex mode of implantation in hone has not been observed in any 

 other class of animals. The rule is deduced from the number of 

 observations, positive and negative. Why two or more roots of a 

 tooth should be peculiar to viviparous quadrupeds, givins; 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 })reliminary 

 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 machinery 

 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 Mammal, as contrasted with 

 a cold-blooded reptile or fish, — is also conceivable. To the extent 

 to which such and the like reasoning may be true, or in the direction 

 of the secret cause of the constant relations of many-rooted teeth 

 discovered by observation, — to that extent will such relations ascend 

 from the empirical to the rational category of laws. So much, briefly, 

 at present, for the grounds of reference of the Stereognathiis to the 

 Mammalian class. 



The broad sex-cuspid crowns of the molar teeth of the Stereogna- 

 thiis niight crush vegetable matter or insect-cases : a recognition of 

 their adaptability to uses observable in the nearest resembling 

 teeth of existing animals leaves the above wide field of choice, 

 or guess, as to the nature of the food of the oolitic animal. Let us 

 take the latter hypothesis, and endeavour to work cut more of the 

 Stereognathiis on the basis of its multicuspid and assumed insecti- 

 vorous tooth. Insects fill the air, creep on the ground, burrov/ in the 

 earth, move on and in the waters. In the living v»orld of animals 

 we have insectiA'orous molars associated with a frame and limbs mo- 

 dified for flying, running, burrowing, and diving. The principle of 

 the mechanism for crushing insects being the same, it is secondarily 

 modified in each genus of Insectivora ; and so modified, though 

 without affecting the crushing power of the tooth, that the odonto- 

 logist discriminates at a glance the grinders of the Bat, the Hedge- 

 hog, the Shrew, or the ?>Iole. 



At present we can only refer such secondary modifications, as 

 we do those of the more complex grinding teeth of the Herbivora, 

 to that principle of variety in non-essentials which makes the leaf 

 in each kind of tree unlike, and, as it is affirmed, which makes no 

 two leaves, in any single tree, exactly alike. 



If the tooth of the Stereognathiis were like those of any known 

 recent or fossil Insectivore, we should infer that the rest of its orga- 

 nization was like such Insectivore, and so classify it according to the 

 degree of similitude. But as we know of no sufficient ground for 



