354 Zoological Summary of Extinct and Living Animals 



and doubt. Of tho happy influence of Palaeontology in the 

 resolution of such problems in natural history, the present ap- 

 plication of the osteology of the Megatherioids afibrds a good 

 example. 



The genera Bradypus and Choloepus have been regarded by 

 all zoologists as forming one of the most anomalous and isolated 

 groups in the mammiferous class, of which no other proof is 

 needed than the fact, that whilst Cuvier, in the '* Regne Ani- 

 mal,*' has placed the Sloths in the lowest order of Unguiculata, 

 his successor* in the celebrated French school of zoology has 

 seen reason for raising to the highest, or quadrumanous order, 

 agreeably with an old opinion of Linnaeus. 



Our present knowledge of the extinct Megatherian quadru- 

 peds leads us to contemplate the natural affinities of the Sloths 

 from a vantage ground not attained before, yet essential to a 

 correct and coiriprehcnsive view of them. The tardigrade and 

 scansorial Edentata appear to the classifier conversant only 

 with existing forms as a very restricted and aberrant group ; 

 but they may now bo recognisable by the palseontologist as 

 the small remnant of an extensive tribe of leaf-devouring and 

 tree- destroying animals, of which the larger extinct species 

 were rendered equal to the Herculean labours assigned to them 

 in the economy of an ancient vyorld, by a gigantic development 

 of the unguiculate type of structure, combined with such mo- 

 difications as unequivocally demonstrate that they were at the 

 lowest step of the series of Mammals furnished with claws, 

 and that they completed the transition to the ungulate division 

 of the class. 



It harmonizes well with this general view of the affinities of 

 the Megatherioid quadrupeds, that whilst they brought the un- 

 guiculate type, both by modifications of structure and predo- 

 niinance of size, most closely to that of the great-hoofed her- 



* M. de Blainville, Prodrome d'une NouveUc Zoodassie, 181G ; quoted by the 

 author in his recent splendid Osteograpliie, in which he adduces the following 

 qsteological characters as common to the Sloths and Quadrumanes: — " Ce sont 

 ies Primates : — Par I'etat complet de I'avant-bras ; la rotondite de la tete du 

 radius ; la raobilite du carpe sur I'avant bras. — Par I'etat 6galement complet de 

 1^ jambe dans ses deux os ; la grand mobilite du tarsc sur les os de la jambe. — 

 Vax la f9i'm9 generale du trouc, pre^que bans queue, large et deprinie plutut quo 

 comprime a la poitrine ; — par la largeur du bassiu." — Ostco'jraphic dc Parcsscnoc, 

 4to, 1840, p. 58, 



