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articular surface for the inner condyle of the femur is relatively larger. The 

 large tendinous groove which crosses obliquely the back of the inner malleolus, 

 is less deep and further from the distal margin than in the Mylodon robustus. The 

 excavation for the astragalar tubercle is more sloping, but relatively deeper and 

 wider. 



The proximal articulation of the tibia of the Scelidotherium closely resembles 

 that of the Mylodon, and the articular surface below the outer expansion in- 

 dicates that the fibula was likewise a separate bone in this species. The repetition 

 of the separate state of the bones of the leg in three different genera of Mega- 

 therioids much diminishes the value of the evidence which Cuvier deduced from 

 their anchylosed condition in the Megatherium in favour of its affinities to the 

 Armadillos, although, as this structure is known among existing quadrupeds 

 only in the loricated family of Edentata, it forms an interesting additional proof 

 of the essential relations of the huge extinct animals under consideration to that 

 anomalous order of Mammalia. 



Astragalus. — It is worthy of observation, that, although the astragalus of the 

 Sloth differs much from that of the Mylodon, it offers modifications as peculiar 

 and as distinct from those of the same bone in any other mammalian genus. The 

 outer part is excavated by a deep cell in which the pivot-like end of the fibula 

 rotates ; the inner side is applied, as usual, against a malleolar process of the 

 tibia. In the Ant-eaters and Armadillos the upper surface of the astragalus has 

 the normal configuration, and is sunk deeply, as in most other mammals, into a 

 tibio-peroneal mortice. Other recent mammals offer, in this bone, no compari- 

 sons by which further light can be thrown on the peculiarities of the Megatherian 

 race. 



The astragalus and distal articulation of the leg-bones being coadapted, the 

 principal modifications of that tarsal bone in the Megatherian family relate to 

 the peculiarities already pointed out in the tibia ; and, as its mode of articulating 

 with the OS naviculare is almost as peculiar, it forms the most characteristic 

 single bone in the skeleton of the Megatherioid quadrupeds. The chief and most 

 distinctive character of the astragalus is the convex protuberance on the inner 

 half of the upper articulation already described; but, with this modification 

 common to all the known Megatherioids, the astragalus presents striking and 

 recognisable differences in the different genera. Different species of the same 



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