87 



robust Mylodon. The osteology of this part of the skeleton of the 

 Mylodon is replete with interest to the physiologist and student of 

 animal mechanics : the tarsal portion of the foot is a perfect specimen of 

 massive organic masonry. The analogical correspondence which may 

 be traced between the hind and fore-foot is very close ; since it is evident 

 that the two curtailed outer toes, whose extremities seem, as it were, to 

 have suffered amputation, were sunk in a hoof- like modification of the 

 integument of that part of the foot. 



454. The left astragalus of the Mylodon robustus. 



Abb. A portion of the right external cuneiform bone of the Mylodon robustus. 



456. A flattened ossicle, without any articular surface, with the margins 

 rounded, and the two sides with a striated or fibrous character : this may 

 either have been a dermal bone, imbedded in the substance of the co- 

 rium, or it may have been developed in a tendon like the palmar and 

 plantar sesamoid ossicles in the Armadillos : it does not resemble either 

 of those ossicles in shape. This and the three following specimens 

 were exhumed with the bones of the skeleton of the Mylodon robustus, 

 to which they most probably belong. 



457- A similar ossicle, apparently the analogue of the opposite side, and 

 forming with the preceding bone a symmetrical pair. 



458. A similar, but smaller ossicle, and of a different shape from either of the 



preceding. 



459. A similar, but larger ossicle. 



460. The left squamo-temporal bone of a foetal or newly-born Mylodon robustus. 



The air-cells have not begun to be developed in the diploe of this bone. 



461. The left os petrosum of the same fcetal or immature animal. 



462. A portion of the left parietal bone of the same fcetal or immature 



animal. The broad sutural surface, which unites with the squamo-tem- 

 poral, exhibits a more complicated junction of the two bones than is 



