62 



ordinary among quadrupeds ; and, he adds, that it alone would give the key to all the 

 anomalies in that of the Megatherium*. But this could only have been affirmed under 

 a misconception of the real nature of those anomalies. In the Dasypus gigas the fore- 

 foot is pentadactyle ; all the digits are unguiculate, and, in three of them, the claw- 

 phalanges furnish a bony sheath as well as core to the claws ; but these belong to the 

 third, fourth and fifth toes, not, as in the Mylodon, to the first, second and third, or, as 

 in the Megatherium, to the second, third and fourth toes ; they moreover successively 

 decrease in size from the radial to the ulnar aspect, instead of the reverse proportions 

 which they present in the Mylodon. No doubt the claw on the middle digit is the most 

 developed, as in the Megatherium, and the first and second phalanges of this digit have 

 coalesced ; but here ends the particular resemblance between the Megatherium and the 

 great Armadillo, in regard to the bony structure of the fore-foot. 



"We can state with confidence, what M. Laurillard suggests f, viz. that the fore-feet 

 of the Megatherium, as represented by the skeleton in the Madrid Museum, are not 

 transposed, the right being on the left and the left on the right side, as Cuvier was led 

 to suspect ; but that the articulation of those complex parts by the laborious Prosector 

 and Curator Bru, was in the main correct. 



The bony structure of the fore-limb of the Megatherium is now, indeed, as completely 

 understood, and the homologies of every constituent bone can be as exactly defined, as 

 in any existing species of quadruped. And, to the degree in which so important a part 

 of the frame throws light on the whole; the Naturalist may thereby trace the affinities, 

 and the Physiologist infer the habits, of the great extinct beast. 



§8. Of the Bones of the Posterior Extremity. 



In the description of the bones of the hind-limbs I commence with the ilium, as being 

 the homotype or correlative of the scapula in the fore-limb. The ischium, which is the 

 homotype of the coracoid, is confluent with the ilium, as the coracoid is with the sca^ 

 pula ; the pubis, which is the homotype of the clavicle, is confluent with both the ilium 

 and ischium. All the three bones on both sides become confluent with the sacrum, and 

 form therewith, in the full-grown Megatherium, a single bone — the pelvis — which is the 

 largest known among terrestrial Mammals, and forms the most striking feature in the 

 skeleton of the present gigantic extinct Sloth. 



As a like progressive ossification brings to pass a similar state of the pelvis in the small 

 existing Sloths, the limits of the primitive bony constituents of that of the Megatherium 

 can only be determined, at present, by analogy with the pelvis of its modern congeners, 

 studied at a period of immaturity. This I have had the opportunity of doing in the 



• " La main du taiou giant est une des plus extraordinaires qu'il y ait parmi les quadruples, et a elle 

 aeule elle expliquerait toutes les anomalies que nous verrons dans celle du Megatherium." — Ossemens Fos- 

 ■ue», ed. cit. torn. viii. p. 242. No qualifying note is appended by the editors to this statement. 



t See the note (1) appended by that able anatomist to the chapter on the Megatherium, in the posthu- 

 mous edition of the ' Ossemens Fossiles,' 8vo, t. viii. p. 355. 



