of the Sloths to their peculiar Mode of Life. 21 



that it never can be placed flat or have a firm tread upon the ground, but if set 

 on the earth would rest on its outer edge. Now there is not one of these 

 peculiarities that is not admirably adapted to render complete the mechanical 

 power of the liind-leg and foot as organs by which the animal is enabled to 

 attach itself most firmly, and as it were with pincers and grappling-hooks, to 

 the trunk and branches of a tree. 



The unusual stiffness of the toes and fingers is another peculiarity of the A'i, 

 not less fitted to assist its habits of constantly living and feeding upon trees ; 

 all the bones of the fingers and toes, except the claw-bones, are inclosed in an 

 undivided skin, and can only move together ; tlie claws alone are separate. 

 The first joints of the fingers and toes are united to those of the metatarsus and 

 metacai-pus ; the bones of the metacai-pus also being consolidated with them 

 into a single piece, which represents what in many animals are 14 small bones. 

 In the hind-foot there is a similar union of the first joints with the bones of 

 the metatarsus, one bone representing what in the more active animals are I7. 

 This stiffness of the parts, which would be inconvenient to an animal moving 

 on the ground, becomes advantageous and a source of strength to one whose 

 constant position and occupation are almost stationaiy upon a tree. The 

 claws of the Sloth are of unusual length, and form a powerful instrument of 

 defence ; with these a Sloth has been known to strangle a dog, holding him 

 at arm's length : on trees also it is most surprisingly tenacious of its hold, and 

 the limbs, though possessing great capability of motion, can fix themselves 

 almost with the rigidity of iron. Mr. Burchell has seen the limbs, even just 

 after death, continue fast clinging round the object to which they were 

 adhering before the animal expired. 



The Sloth has till very recently been supposed to present a most extraordi- 

 nary deviation from the normal character of all Mammalia in the number of 

 its cervical vertebrae ; all other Mammalia, from the Giraffe and Camel, down 

 to the Cetacea, have invariably seven, while the Sloth was considered to have 

 nine. Mr. T. Bell* has lately ascertained, by the dissection of two specimens 

 of the Bradypus tridactylus, that the two lowest of these supposed cervical ver- 

 tebrae are in reality dorsal, having two small and short rudimentaiy ribs 

 attached to each of them, which have been hitherto overlooked in the dissec- 

 * See paper read before the Zoological Society of London, August 13th, 1833. 



