405 



to bend on the leg, there exists a conical pit in the top of the astragalus, 

 in which the extremity of the fibula is inserted, like a pivot, the foot 

 turning round like a vane on its staff. Added to this, when the leg is 

 vertical, the foot is nearly in a similar direction, standing on its edge, so 

 that the animal cannot place the soal of the foot on the ground, but 

 by stretching out the leg until it has placed it in almost a horizontal 

 direction. 



The toes of the animal are inclosed, quite to the nails, in a stiff skin, 

 which will allow only of their being bent and straightened all together. 

 And to add to its difficulty in motion, several bones, which, in other ani- 

 mals, are always distinct, are here joined together. Thus the first pha- 

 langes of all the feet are united to the bones of the metacarpus and me- 

 tatarsus. In this manner one bone fills the place of eleven, or even of 

 seventeen. The nails, which are of an enormous length, are bent, when 

 the animal does not use them, under the foot, with their convex side 

 towards the ground. 



The nails are of a monstrous length, and are weapons which, by ena- 

 bling the animal to defend himself with considerable success, may be 

 regarded as the only compensation for the disadvantages of the rest of its 

 organization. But these animals, unable to draw back their nails, as 

 the cats do, are obliged to curve them underneath, when they do not 

 use them, and thus place their convex surfaces downwards. As in cats, 

 so in the sloths, each claw is set, and retained in a bony glove-like 

 sheath ; but in the cats the upper part of this sheath is most advanced ; 

 whilst in the sloths, the lowest part is most forward. 



In the Ai, different from all other quadrupeds, are nine vertebrae; an 

 extraordinary singularity, characteristic of this particular species, and not 

 an accidental or monstrous formation. Thus in the same genus exists 

 a most essential difference of structure. 



The sloths, different from other animals, have no incisors. In the 

 Ai, those teeth which might be regarded as the canine teeth, are not 

 pointed, but are rubbed down obliquely : the upper ones backwards, and 



