MEGA THERIIDjE 187 



1 iack wan Is from the extremity of the upper surface of the pre- 

 maxilhe. 



The vertebral column consists of seven cervical, sixteen dorsal, 

 three lumbar, five sacral, and eighteen caudal vertebrae. The 



spinous processes are much better developed than in the Sloths, 

 and are all directed backwards, there being no reversing of the 

 inclination near the posterior end of the dorsal series, as in most 

 active-bodied mammals. In the lumbar region, the accessory zyga- 

 pophyses, rudimentary in Sloths, are fully developed, as in the 

 Ant eaters. 



The tail is large, and its basal vertebra? have strong lateral and 

 spinous processes and chevron bones, indicating great muscular 

 development. The scapula resembles that of the Sloths in the 

 union of the acromion with the coracoid, and in the bridging over 

 of the supra-scapular notch. The clavicle is complete and very 

 huge, much resembling that of man on a large scale. The fore 

 limbs are longer than the hind limbs. The humerus has no ent- 

 epicondylar foramen. The radius and ulna are both well developed, 

 and have a considerable amount of freedom of movement. The 

 hand is singularly modified. The pollex is represented only by a 

 rudimentary metacarpal, but the next three digits are large, and 

 terminate in phalanges adapted for the support of immense claws, 

 the middle one being especially large. The outer or fifth digit has 

 no claw, and it may be considered as certain that the weight of the 

 foot was, in standing and walking, chiefly thrown upon this one, 

 which was protected by a callous pad below, as in the existing 

 great Anteater, while the other toes were curved inwards towards 

 the palm, and only came in contact with the ground by their outer 

 surfaces. The mechanical arrangements by which the weight of the 

 body was thrown entirely upon the outer side of the foot are very 

 curious, and are fully described in Owen's memoir. The pelvis is 

 remarkably wide, even more so than that of the Elephant, but it is 

 formed on the same principle as in the Sloths. The femur is 

 extremely broad and flattened ; the tibia and fibula are short and 

 strong, and united together at each end. The hind foot, contrary 

 to the usual rule in the Edentata, is even more singularly modified 

 than the hand. Thus the ankle-joint is formed upon a peculiar 

 plan, quite unlike that of the Sloths, or of any other mammal, except 

 the Megatherium's nearest allies ; and the calcaneum projects nearly 

 as far backwards as the fore part of the foot does forwards. There 

 is no trace of great toe or hallux, or of its corresponding cuneiform 

 bone ; the second toe is rudimentary ; while the third has an enor- 

 mous ungual phalanx, which, as in those of the hand, is remarkable 

 for the immense development of the bony sheath reflected from 

 its proximal end around the base of the claw. The two outer toes 

 have large and very peculiarly-shaped metatarsals, but only small 



