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the Megatherium already discussed, have proved that only the middle digit 

 could have supported a claw-bone so large as belongs to that digit, and that 

 those of the other unguiculate digits of the fore -foot were much smaller : the ex- 

 istence of an ungual phalanx of almost equal size with, but of a different form 

 from that of the middle toe of the fore-foot, in the collection of Megatherian bones 

 transmitted by Sir W. Parish, proves, therefore, that the hind-foot must have 

 been similarly armed ; and the evidence of the navicular and cuneiform bones, 

 with the analogy of the Mylodon, concur in referring such phalanx to the third 

 toe, or that which adjoins the two outer ungulate toes supported by the os 

 cuboides. This induction establishes, therefore, the accuracy in this respect 

 of the figures of the hind-foot of the Madrid Megatherium. The ungual pha- 

 lanx of the third hind-toe of the Megatherium presents the same differences, in 

 its greater relative depth, and compression, as compared with that of the My- 

 lodon, which have been pointed out in the comparison of the corresponding bones 

 of the fore-foot of these extinct Edentata. The great claw-bone, as it may be 

 emphatically termed, of the hind-foot differs from that of the fore-foot in the 

 Megatherium, in its somewhat smaller size, being shorter in proportion to its 

 depth, in the deeper articular cavities, in the downward production of a rough 

 tuberosity from the base of the osseous sheath anterior to the foramina of the 

 ungual arteries, in the greater breadth of the upper part of the claw-sheath, and 

 in the straighter cone which supported the claw. This latter character accords 

 well with the position of the bone on the hind-foot, which must have been more 

 habitually resting on the ground than the fore-foot, and therefore perhaps re- 

 quired its claw to be less curved. 



The middle phalanx supporting the great claw-bone of the hind-foot is singu- 

 larly compressed from before backwards in the Megatherium. Its vertical dia- 

 meter is more than twice the antero-posterior diameter or length of this phalanx. 

 At the upper half of the anterior surface are the two convexities which are re- 

 ceived into the double trochlear cavity of the ungual phalanx. The posterior 

 surface for the proximal phalanx is concave above, convex below : the inferior 

 prolongation of the middle phalanx is deeply and obliquely notched, and 

 the inner surface of the notch is smooth and probably articulated with a large 

 sesamoid : it thus differs considerably from the corresponding phalanx in the 

 Mylodon. 



We have next to compare the second, which is the innermost toe in the My- 



