145 



;ular masses of unwonted force diverged to act upon the trunk, the tail, and the 

 hind-legs*. Those muscles originating from the sacrum and the broad and ex- 

 tended lip of the ilium, as the sacro-lumbalis, the longissimus and latissimus 

 dorsi, &c., and which pass forwards to extend the trunk and retract the an- 

 terior limbs, have left the most marked evidence of their size and energy of 

 action in the long and strong spinal crest of the sacrum, and in the broad, rugged, 

 and anteriorly produced margin of the ilium. The fore-limbs being well adapted 

 for grasping the trunk or larger branches of a tree, the forces concentrated upon 

 them from the broad posterior basis of the body are manifestly adequate, and are 

 precisely such as might be expected to have cooperated in the act of uprooting 

 the tree or of wrenching off the branch so seized. But in order that the pelvis 

 should possess stability and resistance equivalent to the due effect of the forces 

 acting from it and so applied, it was necessary that it should be bound down as 

 it were, and supported by members of corresponding strength. 



Accordingly, we tind a thigh-bone, which, though surpassing the humerus in 

 length, is yet not less than half as broad as it is long, and provided with tro- 

 chanters and ridges, the fit attachments of the tendinous insertions of muscular 

 masses which expanded upon the back-part and on the fore-part of the broad 

 and capacious pelvis, and have there left, in strong and numerous inter-fascicular 

 bony crests, unequivocal evidence of the power by which they resisted the 

 efforts of the antagonizing muscles attached to the trunk and fore-limbs to draw 

 forwards the pelvis and hind-legs. The preponderating weight of both these 

 parts and the extraordinary power of the muscles connecting them together, are 

 quite inexplicable on the scansorial hj^othesis of the Megatherioid animals ; 

 since, if they attained their food by climbing, the fore-legs would be the fixed 

 point when the muscles attaching these to the pelvis were called into action, and 

 the hind-extremities, needing only the requisite prehensile power, ought to have 

 had their bulk reduced as far as was consistent with such power, in order to 

 facilitate their being drawn upwards towards the fore-legs. 



* The muscles of the Megatherioid animals, besides their mass and the mechanical advantages af- 

 forded by the peculiar development of their bony attachments, were most probably characterized by 

 the great energy of their vital contractility ; since this quality of the muscles of the Sloth is so 

 striking as to have forced itself upon the notice of the Marquis de Montmirail, who, in describing the 

 habits of a living Unau in his menagerie, says " la force de ses muscles est incroyable." — BufFon, 

 Hist. Naturelle, 4to, t. xiii. p. 48. 



T 



