62 Classification of the Mammalia. 



In many existing genera of different orders there is a more 

 specialized structure, a greater deviation from the general type, 

 than in the answering genera of the miocene and eocene periods ; 

 such later and less typical Mammalia do more effective work by 

 their more adaptively modified structures. The Ruminants, e.g. 

 more effectually digest and assimilate grass, and form out of it a 

 more nutritive and sapid kind of meat, than did the antecedent 

 more typical or less specialized non-ruminant Herbivora. 



The mono:lacty!e Horse is a better aud swifter beast of draught 

 and burthen than its tridactyle predecessor the miocene Hippa- 

 rion could have been. The nearer to a Tapir or a Rhinoceros in 

 structure, the further will an equine animal be left from the goal 

 in contending wiih a modern Racer. The genera F.elis and Ma- 

 chairodus, with their curtailed and otherwise modified dentition 

 and short strong jaws, become, thereby, more powerfully and effec- 

 tively destructive than the eocene Hycenodon with its typical den- 

 tition and three carnassial teeth on each side of its concommitantly 

 prolonged 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 which 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 families, genera, and species of 

 such orders, because the paucity or multitude of instances mani- 

 festing 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, nor 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 ge- 

 neral terms, to admit of the convenient expression of general pro- 

 positions respecting them ; and some of these general propositions 



