1 835 . ] Transactions of the Linnean Society of London . 39 1 



well defined and useful end) and the result of these deviations pre- 

 senting an animal structure not less perfect, in reference to its state, 

 than those slender and graceful forms of light and active quadrupeds 

 with which we usually, and perhaps more justly, associate our ideas 

 of perfect symmetry and beauty. 



The stiffness of the toes and fingers of this animal, which fit it for 

 the habit of constantly living and feeding upon trees ; and the diffi- 

 culty of motion in other joints become advantageous and a source of 

 strength to an animal living as it does, while to one moving on the 

 ground, they would be a source of great inconvenience. The claws 

 of the Sloth are of unusual length, and so powerful that they are 

 capable of strangling a dog, holding him at arm's length. On trees 

 the Sloth is surprisingly tenacious of its hold. 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. All 

 mammalia, from the Giraffe and Camel down to the Cetacea, have 

 , invariably seven cervical vertetrse, while the Sloth was considered to 

 have nine. Mr. T. Bell has, however, shewn that the two lowest 

 are really dorsal, but their position so far in advance of the clavicle 

 and scapula, enables them to co-operate with the seven true cervical 

 vertebrae, in increasing the rotatory motion and flexibility of the neck. 

 Hence, the animal has the power of looking backward over its own 

 shoulder. Mr. Burchell has observed, that this animal can turn 

 its head quite round, and stare a person in the face who is directly 

 in its rear, while at the same time the body and limbs are unmoved. 

 He also noticed, that his captive Sloths assumed during sleep, a 

 position of perfect ease and safety on the fork of a tree ; their arms 

 embracing the trunk, their backs resting in the angle of a branch, 

 and their heads reclining on their own bosom, the animal being thus 

 rolled up nearly in the form of a ball, with the vertebral column bent 

 circular. The Sloth has no incisor teeth, because the leaves are 

 brought to the mouth, being collected from the branches by the 

 powerful claws. 



Besides the four canine teeth, there are on each side four molars 

 in the upper and three in the lower jaw. The construction of these 

 teeth is the most simple that exists ; they are .composed of a cylinder 

 of bone encased with enamel and hollow at the two extremities, the 

 upper cavity being produced by the act of mastication, which wears 

 away the softer bony texture of the interior more readily than the 

 exterior enamel, and the lower cavity being filled with gelatinous 

 pulp which maintains the continual growth of the tooth, these simple 

 teeth being employed exclusively in the mastication of buds and 

 leaves are fully adequate to the wants of an animal which has no 

 need of more complicated teeth. Mr. Waterton states, that he " in 

 crossing the Esquibo one day, saw a large two-toed sloth on the 

 ground upon the bank, though the trees were not twenty yards from 

 him, he could not make his way through the sand time enough to 

 make his escape before we landed, he threw himself on his back and 

 defended himself with his fore legs. I took a long stick and held it 

 for him to hook on, and then conveyed him to a high and stately 

 mora, he ascended with wonderful rapidity, and in about a minute he 

 was almost at the top of the tree ; he now went off in a side direc- 



