162 



My theory of the Megatherian animals, in assigning to them the Herculean 

 labour of uprooting and prostrating trees, for the acquisition of the food which 

 is unequivocally indicated by their dental and maxillary organs, explains and re- 

 quires all the other characteristics of their organization, and assumes no unknown 

 condition of the vegetable world. Whoever is acquainted with the energy and 

 rapidity of the growth of trees in the intertropical regions of the American con- 

 tinents, or with the enormous quantity of timber annually floated away by the 

 great American rivers, can have little difficulty in conceiving that the intermi- 

 nable and by man unpenetrated forests of the primaeval world would yield suste- 

 nance to many generations of huge quadrupeds, even though they might uproot 

 the trees on the foUage of which they fed. 



In fine, whatever be the value of such collateral evidence as may be deduced 

 from the known conditions of the vegetable kingdom, a searching and impartial 

 review of the anatomical facts and analogies detailed in the foregoing part of the 

 present Memoir has led me to the conclusion, that : — All the characteristics 

 which co-exist in the skeleton of the Mylodon and Megatherium conduce and 

 concur to the production of the forces requisite for uprooting and prostrating 

 trees ; of which characteristics, if any one were wanting, the effect could not be 

 produced ; and that this hitherto unknown and most extraordinary mode of 

 obtaining food, is the condition of the sum of such characteristics, and of the 

 concourse of so great forces in one and the same animal. 



Zoological Summary. 



The light which is thrown on the nature of animals belonging to extinct spe- 

 cies by the comparison of their fossil remains with recent skeletons is very often 

 reflected back, so as to elucidate affinities of existing species which were before 

 obscure, and which must otherwise have remained subjects of debate and doubt. 

 Of the happy influence of Paleontology in the resolution of such problems in 

 natural history, the present apphcation of the osteology of the Megatherioids 

 affords a good example. 



The genera Bradypus and Cholcspus have been regarded by all zoologists as 

 forming one of the most anomalous and isolated groups in the mammiferous 



