Quadrupeds. 419 



hind-feet, the long and curved fore-claws, which are habitually flexed and fettered in 

 the movements of extension, would next be applied to the opposite sides of the loosen- 

 ed trunk of the tree : and now the Mylodon would derive the full advantage of those 

 modifications of its fore-feet by which it resembles the Bradypus ; the correspondence 

 in the structure of the prehensile instruments of the existing and extinct sloths, ex- 

 tending as far as was compatible with the different degrees of resistence to be overcome. 

 In the small climbing sloth the claws are long and slender, having only to bear the 

 weight of the animal's light body, which is approximated by the action of the muscles 

 towards the grasped branch, as to a fixed point. The stouter proportions of the pre- 

 hensile hooks of the Mylodon accord with the harder task of overcoming the resistance 

 of the part seized and bringing it down to the body. For the long and slender bran- 

 chial and anti-branchial bones of the climbing sloth we find substituted in its gigantic 

 predecessor a humerus, radius and ulna of more robust proportions, — of such propor- 

 tions, indeed, in the Mylodon robustus, as are unequalled in any other known existing 

 or extinct animal. The tree being thus partly undermined and firmly grappled with, 

 the muscles of the trunk, the pelvis and hind limbs, animated by the nervous influence 

 of the unusually large spinal cord, would combine their forces with those of the an- 

 terior members in the efforts at prostration. And now let us picture to ourselves the 

 massive frame of the Megatherium, convulsed with the mighty wrestling, every vibrat- 

 ting fibre reacting upon its bony attachment with a force which the sharp and strong 

 crests and apophyses loudly bespeak : — extraordinary must have been the strength and 

 proportions of that tree, which, rocked to and fro, to right and left, in such an era- 

 brace, could long withstand the efforts of its ponderous assailant.'' — p. 147. 



A few pages are occupied by elaborate observations on several re- 

 markable points, particularly the arrangement of the bones of the hind 

 feet, and the evidence, which appears irresistible, of the existence of 

 a large and powerful tongue, with which the animal, in all probability, 

 drew down the boughs before devouring them. The structure of the 

 feet is truly remarkable : the anterior pair, or hands, had five fingers, 

 of which the first, second and third were armed with immense claws, 

 the first being the shortest, and the third the longest ; the fourth and 

 fifth fingers, instead of claws, appear to have been furnished with 

 small hoofs : the hind toes were only four, the interior pair having 

 claws, the exterior pair hoofs. 



In the zoological summary, the natural affinities of the sloths are 

 briefly detailed, and their relation to the other tribes of Cuvier's Eden- 

 tata pointed out ; and a structural peculiarity of the teeth is used as 

 an argument against their approximation to the monkeys : but when 

 we find the microscopic structure of the teeth of fishes repeated in 

 mammals, as Professor Owen admits to be the case, we surely must 

 pause before we regard these characters as available to the important 

 subject of natural classification. The following paragraph is sufficient 

 to induce some hesitation in adopting the dental hypothesis. 



D2 



