78 



liarities 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 Dasypm 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 repeats 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 first digit (pollex), which is retained in the Anteaters and Armadillos, is obsolete in the 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 terres- 

 trial Sloth for its progression on level ground. In no existing ground-dwelling member 

 of the Bruta 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 the Megatherium, as in Dasypus ; but this is not the case in the closely- 

 allied extinct Megatherioids called Mylodon, Megalonyx, and Scelidotherium, a fact 

 which diminishes the force of the argument which Cuvier deduced from the coalesced 

 condition of the bones in favour of the affinities of the Megatherium 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 Bruta. In all the existing members of the order, save the 

 Sloths, the hind foot is pentadactyle, and four of the toes have a long claw ; this is even 

 the case with the little arboreal Myrnxecoplmga didactyla. The departure by degrada- 

 tion 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 Megatherium and other great 

 extinct terrestrial Sloths. 



Guided by the general rule that animals having the same kind of dentition have the 

 same kind of food, I conclude that the Megatherium must have subsisted, like the Sloths, 

 on the foliage of trees ; but that the greater size and strength of the jaws and teeth, 

 and the double-ridged grinding surface of the molars in the Megatherium, adapted it to 

 bruise the smaller branches as well as the leaves, and thus to approximate its diet to 

 that of the Elephants and Mastodons. The Elephant and the Giraffe are specially modi- 

 fied to obtain their leafy food ; the one being provided with a proboscis, the other with 

 much elongated cervical vertebrae ; the entire frame of the lofty ruminant being con- 

 currently modified to adapt it to browse on branches above the reach of its largest con- 

 geners. If the Megatherium had possessed, as Cuvier conjectured, a proboscis, it could 

 not, judging from the suborbital foramina, have exceeded in size that of the Tapir, and 

 must have been able to operate only upon branches brought near the mouth. Of the 



* Plate, Bradypus didactylus, st. 



