OF THE CLASS MAMMALIA. 11 



delphes.' His orders are in the main a return to the Linnean sy- 

 stem and nomenclature, with some peculiar views, as e.g. of the 

 quadrumanous or primatial affinity of the Sloths, which have never 

 gained acceptance. But his system indicates a clearer apprecia- 

 tion or stronger conviction of the value of the character of parity 

 and imparity in the number of toes of the Ungulata, first sug- 

 gested by Cuvier*, than was subsequently entertained by the 

 originator of the idea. 



The position of the marsupial and monotrematous quadrupeds at 

 the bottom of the class Mammalia^ and the higher value assigned 

 to the group which they constituted, than that in the 'Eegne Ani- 

 mal ' of Cuvier, were ideas also in closer conformity with nature. 

 They were, however, but surmises, unsustained by anatomical 

 knowledge ; and, as such, failed to carry conviction, or gain ac- 

 ceptance. Nor was it until comparative anatomy had shown that 

 the Marsupials and Monotremes agreed in differing from all other 

 mammals in the absence of a placenta, and of the great commissure 

 of the brain, in certain bird-like characters of the heart f, and from 

 all other diphyodont Mammals in a less number of premolars, and 

 a greater number of true molars, — depending essentially on the 

 retention of a milk-tooth (w. 4), which is displaced and changed 

 in the placental diphyodonts,— that the true affinities of the didel- 

 phid and ornithodelphid mammals to each other, and their true 

 position in the class Mammalia, were finally recognized. 



In the ' Systema Yertebratorum,' communicated in 1840 to the 

 Linnean Society by that accomplished and indefatigable zoologist 

 Prince Charles Lucien Bonaparte, the primary subdivision of the 

 Mammalia according to developmental and generative characters 

 is adopted; and the first division or series Flacentalia is sub- 

 divided, agreeably with M. Jourdan's distribution of Mammalia in 

 the Leyden Museum, into the two subclasses Educalilia and 

 Ineducahilia, the latter including the orders Bruta, Cheiroptera, 

 Insectivora and Bodentia, with the common character of 'cere- 

 brum unilobum.' This I regard as the most important improve- 

 ment in the classification of the Mammalia, which has been pro- 

 posed since the establishment of the natural character of the 

 implacental or ovo-viviparous division. 



Cuvier had early noticed the relation of the Australian mam- 

 mals, as a small collateral series, to the unguiculate mammals of 



* Ossemens Fossiles, 4to. ed. 1812, p. 9 j torn. iii. ed. 1822, p. 72. 

 t On the Classification of the Marsupialia, Zoological Transactions, vol. ii, 

 p. 315 (1839). 



