the Megatherium. 351 



this resembling, in its bony structure, that of other Edentata 

 with a similar appendage, especially in the independency 

 of the two haemapophyses of the first caudal, a charac- 

 ter which obtains in the great Ant-eater and in some Arma- 

 dillos ; but this is no evidence of direct affinity to either of 

 these families ; the habits of the small arboreal Sloths render 

 their eminently prehensile limbs sufficient for their required 

 movements, and the tail is wanting. Had that appendage 

 been proportionally as large as in the Megatherium, we can- 

 not suppose that the caudal vertebrae would have materially 

 differed from those of other Edentata. 



In the coalescence of the anterior vertebral ribs with the 

 bony sternal ribs, the Megatherium resembles the Sloths. 

 This essential affinity is still more marked in the peculiari- 

 ties of the scapula and of the carpus. In the Myrmecophaga 

 jubata the scaphoid is distinct: in the Manis it coalesces 

 with the lunare : in the Dasypus gigas the trapezoides is an- 

 chylosed to the second metacarpal : in the Das. sexcincttis it 

 has coalesced with the trapezium. Not any of these charac- 

 teristics are manifested by the Megatherium ; its carpus 

 repeats the peculiarities of that in the Sloths, viz., the re- 

 duction of the number of carpal bones to seven, by the 

 coalescence of the scaphoid with the trapezium. The first 

 digit (pollex) which is retained in the Ant-eaters and Arma- 

 dillos, is obsolete in the Megatherium, as in the Sloths and 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 gi*ound-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 Bradypodidce. 



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, Megalonix^ and Scclidotheriumy a fact which 



