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98 ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



It is quite true that the Quadrumana derive advantage from this position of 

 the foot in climbing trees, and that it is carried to excess in the Sloths, which can 

 only apply the outer edge of the foot to the ground. But we may ask, was the 

 inversion of the sole of the foot actually carried to such an extent in the Me<ra- 

 lonyx ? And, admitting its existence in an inferior degree, is it then conclusive 

 as to the scansorial habits of that species ? 



M. Lund expressly states that it is produced by a different structure and 

 arrangement of the tarsal bones, from that which exists in the Sloth, but he does 

 not specify the nature of this difference. 



If the astragalus, which I have referred with doubt to the Megalonyx, do not 

 actually belong to that genus, it is evidently part of a very closely allied species. 

 Now this astragalus, as w r e have seen, resembles most closely that of the Mega- 

 therium ; and since we may infer that the calcaneum, scaphoides, and cuboide 

 had a like correspondence, the inclination of the sole of the foot inwards must 

 have been very slight, as I have determined from examination of the structure and 

 co-adaptation of those bones in the incomplete skeleton of the Megatherium in the 

 London College of Surgeons. Such an inclination of the foot may be conceived to 

 have facilitated the bending of the long claws upon the sole, during the ordinary 

 progressive movements of the animal, but it is quite insufficient to justify the 



conclusion, that it related to an application of the hind feet for the purposes of 

 climbing. 



It is not without interest again to call to mind the deviation of the structure 



u Thus in every point of comparison we have instituted between the organization of burrowers and climbers ; 

 we have seen that the Megalonyx constantly differs from the former and resembles the latter ; but the point to 

 which I last alluded (the obliquity of foot), I consider to be quite decisive. 



" There is one other point in its organization, which is not quite without weight in reference to our present 

 inquiry, — I mean its unusually powerful tail. Now, it is certainly true that many animals which are not 

 climbers have a powerful tail, as e. g. Armadillos, while the others that climb well, have none, as Sloths and 

 Apes. But when we find a remarkably powerful tail attached to an animal that according to all probability 

 was a climber, we are led to infer that this organ must have served for that purpose : in other words, that 

 the Megalonyx was furnished with a prehensile tail. 



" How far the Megatherium is to be considered in the same light as the Megalonyx cannot be decided without 

 an accurate and scientific examination of its skeleton at Madrid. Pander and D' Alton do not mention any 

 distortion of the hind-foot, neither does their figure exhibit any. It is nevertheless quite possible that such 

 may exist, but that it is disguised by the faulty manner in which the skeleton is put up. It strikes me 

 as little probable that two animals which agree so well in the principal particulars of their organization should 

 differ so much in one of the most important. The Megatherium has been proved by later discoveries to 

 possess the same powerful tail as the Megalonyx, and as it corresponds also with the latter entirely in the con- 

 formation of its extremities, the same difficulties present themselves against the supposition of its having 

 been a burrower. But if the Megatherium was really a climber, it must have had still more occasion (on 

 account of its greater size), for that peculiar arrangement of the hind-feet which we have described in the 

 Megalonyx." 



