158 VIEW OF THE FAUNA OF BRAZIL 



ileum ; which last, therefore, entirely differ from those of all 

 other mammals, in the form and position of their anterior 

 articular surfaces. 



Inasmuch as the mechanism of the sloth's movements, so 

 far as I am aware, is not very well known, I may take the 

 liberty of recording the observations I made on the three- 

 toed sloth, Bradypus torquatus, which I kept in my house 

 for a considerable time. This animal climbs with remark- 

 able sureness and aptitude, although, as is well known, with 

 a degree of slowness which, however, may be called rapidity 

 in comparison with its terrestrial movements. The manner in 

 which it moves is this : — Lying on its belly, with all its four 

 extremities stretched out from the body ; it first presses one 

 of its hind feet with all its might against the ground, whereby 

 the corresponding side of the body is a little raised. The 

 fore-leg on the same side thus becomes sufficiently free for 

 the animal to advance it a trifle forward. It then hooks its 

 powerful claws fast in the earth, and so drags its body a little 

 onwards. The same manoeuvre is next repeated on the op- 

 posite side ; and thus the poor creature progresses in the 

 slowest and most laborious manner possible. But this mode 

 of progression requires certain conditions of the surface ; for 

 if it is not soft enough to admit the insertion of the claws, 

 or if there are no inequalities for them to hold by, the sloth 

 is completely deprived of the power of changing its position. 

 For instance, when I laid it on a table of polished mahogany, 

 it could not advance the least, notwithstanding all its exer- 

 tions. But in proportion as the sloth's organization unfits it 

 for terrestrial progression, is it wonderfully adapted to climb- 

 ing trees. With its long arms it reaches high up, and clings 

 fast to the branches with its strong crooked claws. The m- 

 verted position of the soles of its hind feet gives it a power 

 of grasping the trunk of the tree, which no other mammal 

 possesses. So that truly, when we see it climbing a tree, 

 we can scarcely believe it to be the same animal that lies so 

 helpless on the ground. Hence we see, that the sloth's organ- 

 ization is entirely adapted for living in trees. Compared 

 with the slowness of its motions, it is the best climber among 

 mammals, while it is the worst walker ; or rather, it is the 

 only mammal that can neither walk nor stand. These pecu- 

 liarities depend on three principal points in its organiza- 

 tion : — 1st, the great length of its anterior extremities, in 

 comparison with the posterior ; 2dly, its powerful, crooked 

 claws ; and 3dly, the irregular podtion of its hind feet. 



Let us now see how far the results to which we have been led 

 by the consideration of the living sloth's structure and habits 



