61 



of the carpus. In the Myrmecophagajubata, the scaphoid is distinct: 

 in the Manis it coalesces with the lunare : in the Dasypus gigas 

 the trapezoides is anchylosed to the second metacarpal : in the Das, 

 sexcinctus it has coalesced with the trapezium. Not any of these 

 characteristics are manifested by the Megatherium : its carpus re- 

 peats the peculiarities of that in the Sloths, viz. the reduction of the 

 number of carpal bones to seven by the coalescence of the scaphoid 

 with the trapezium. The first digit (poUex), which is retained in 

 the Anteaters and Armadillos, is obsolete in the Megatherium as 

 in the Sloths and Orycteropus : three digits are fully developed and 

 armed with claws, as in the Bradypus tridactylus ; and the fifth, 

 though incomplete in the Megatherium, is better developed, because 

 it was required in the ponderous terrestrial Sloth for its progression 

 on level ground. In no existing ground-dwelling Edentate is the 

 fifth digit deprived of its ungual phalanx, as in the Megatherium. 

 The bones of the fore-foot of that extinct animal are thus seen to be 

 modified mainly after the type of the BradypodidcB. 



The long bones of all the limbs are devoid of medullary cavities, as 

 in the Sloths. The femur lacks the ligamentum teres as in the Sloths. 

 The fibula is anchylosed to the tibia at both ends in Megatherium, 

 as in Dasypus but this is not the case in the closely- allied extinct 

 Megatherioids called Mylodon, Megalofiyx and Scelidotherium, a 

 fact which diminishes the force of the argument which Cuvier de- 

 duced from the coalesced condition of the bones in the Megatherium 

 in favour of its affinities to the Armadillos. The semi- inverted but 

 firm interlocking articulation of the hind-foot to the leg shows the 

 peculiarities of that joint in the Sloths exaggerated, and departs 

 further from its characteristics in other Edentata. In all the existing 

 Edentata, save the Sloths, the hind-foot is pentadactyle, and four of 

 the toes have a long claw, even in the little arboreal Myrmecopkaga 

 didactyla : the departure by degradation from the pentadactyle type 

 is a peculiar characteristic of the Sloth-tribe in the order. It is 

 carried further in the same direction in the great extinct terrestrial 

 Sloths. In these the mutilation of the foot has commenced on the 

 outer side by the removal of the ungual phalanx from the fifth and 

 fourth toes ; but this accompanied by modifications which adapt these 

 toes to the important office of support and progression of the body on 

 level ground. In the scansorial Sloths, the three middle digits being 

 equally developed for prehension, one toe on the outer and one on 

 the inner side of the foot, are reduced to their metatarsal basis. In 

 the Megatherium the mutilation of the foot on the inner side is 

 carried to a greater extent; the innermost toe or hallux, with its 

 entocuneiform bone, is wholly removed : the second toe is repre- 

 sented, like the first in the Sloths, by its cuneiform bone and a 

 coalesced rudiment of the metatarse : and it is only the third toe or 

 medius that repeats the condition of the claw-bearing toes in the 

 climbing Sloths. 



Finally, the author enters upon the question of the habits and food 

 of the Megatherium. Guided by the general rule that animals 

 having the same kind of dentition have the same kind of food, he 



