OP TUE CLASS MAMMALIA. 35 



short strong jaws, become, thereby, more powerfully and effectively 

 destructive than the eocene Hyamodon with its typical dentition 

 and three carnassial teeth on each side of its concomitantly pro- 

 longed jaws could have been. 



Much additional and much truer insight has, doubtless, been 

 gained into the natural grouping of the Mammalia since palae- 

 ontology has expanded our survey of the class ; but our best-cha- 

 racterized groups do but reflect certain mental conceptions, which 

 must necessarily relate to incomplete knowledge, and that as ac- 

 quired at a given period of time. Thus the order which Cuvier 

 deemed the most natural one in the class Mammalia becomes 

 the debris of a group, known at a subsequent period to be a more 

 natural order. 



We cannot avoid recognizing, in the scheme which I now 

 submit, the inequality Avhich reigns amongst the groups, which 

 our present anatomical knowledge leads us to place in one line or 

 parallel series as orders. I do not mean mere inequality as re- 

 spects the number and variety of the families, genera, and species 

 of such orders, because the paucity or multitude of instances 

 manifesting a given modification or grade of structure in no 

 essential degree affects the value of such grade or modification. 



The order Monotremata is not the less ordinally distinct from 

 the Marsupialia, because it consists of but two genera, than is the 

 order Bimana from that of Quadrumana, because it includes only 

 a single genus. So likewise the anatomical peculiarities of the 

 Proboscidia, Sirenia, and Toxodontia call, at least, for those general 

 terms, to admit of the convenient expression of general proposi- 

 tions respecting them ; and some of these general propositions are 

 of a value as great as the organic characters of more expanded 

 orders. 



There are residuary or aberrant forms in some of the orders, 

 which, to the systematist disagreeably, compel modifications of the 

 characters that would apply to the majority of such orders. The fly- 

 ing Lemurs ( Galeopitlieci) , the rodent Lemurs (Cheiromys), the slow 

 Lemurs (Boris, Otolienus), forbid any generalization as to teeth or 

 nails in the Quadrumana, whilst they continue associated with that 

 order by the character of the hinder thumb ; which, by the way, they 

 possess in common with the pedimanous Marsupials. The large, 

 volant, frugivorous Bats (Pteropus) are equally opposed to the ap- 

 plication of a common dental character to the Cheiroptera. They are 

 associated with the insectivorous Bats on account of the common 

 external form arising out of the modification of their locomotive 



3* 



