163 



class, of which no other proof is needed than the fact, that whilst Cuvier, in the 

 ' R^gne Animal,' has placed the Sloths in the lowest order of Unguiculata, his 

 successor* in the celebrated French school of zoology has seen reason for raising 

 them to the highest or quadrumanous order, agreeably with an old opinion of 

 Linnaeus. 



Our present knowledge of the extinct Megatherian quadrupeds leads us to 

 contemplate the natural affinities of the Sloths from a vantage-ground not at- 

 tained before, yet essential to a correct and comprehensive 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 be re- 

 cognizable by the Palaeontologist 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 world, by a gigantic development of the unguiculate type of structure, 

 combined with such modifications 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 unguiculate type, both by modifications 

 of structure and predominance of size, most closely to that of the great hoofed 

 Herbivora, they hkewise were, of all the quadrupeds provided with formidable 

 claws, the most strictly vegetable feeders. 



And if we have reason to view the structural differences or superadditions 

 which the Megatherioids present, compared with the Sloths, as being the neces- 

 sary consequences of an identity of diet in quadrupeds too bulky to climb, and 

 therefore requiring new powers for the attainment of the foliage, such an inter- 

 pretation of the peculiarities of their organization, whilst it confirms the close 



* M. de Blainville, Prodrome d'une Nouvelle Zooclassie, 1816 ; quoted by the author in his recent 

 splendid Osteographie, in which he adduces the foDowing osteological characters as common to the 

 Sloths and Quadrumanes : — " Ce sont des Primates : — ' Par I'etat complet de I'avant-bras ; la rotondite 

 de la tete du radius ; la mobilite du carpe sur I'avant-bras. — Par I'etat egalement complet de la jamte 

 dans ses deux os ; la grand mobilite du tarse sur les os de la jambe. — Par la forme generale du tronc, 

 presque sans queue, large et deprime plutot que comprime a la poitrine ;— par la largeur du bassin." 

 — Osteographie de Paresseux, 4to, 1840, p. 58. 



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