FOSSIL MAMMALIA. 97 



Scelidothere. The protuberance from the inner surface of the astragalus is more 

 compressed laterally in the Megathere than in the Scelidothere. The correspon- 

 dence between the astragali of the Mylodon(?) (PI. XXVIII. fig. 6) and Megathere 

 in the conformation of the under surface is so close, that the few differences which 

 exist will be sufficiently appreciated by an inspection of the figures. 



In the Armadillo the astragalus, in consequence of the greater production of 

 its anterior part, presents more of an angular than a quadrate figure ; and the 

 scaphoid articular surface, being proportionally carried forwards, is altogether 

 separated from the anterior calcaneal surface. The posterior and inner calcaneal 

 surface resembles that in the Scelidothere, but is less inclined upwards ; and is 

 continuous with the posterior part of the tibial articular surface. 



Thus the astragalus in the structure of its two most important articulations, 

 viz. that which receives the superincumbent weight from the leg, and that which 

 transmits it to the heel, presents a closer correspondence in the Scelidothere with 

 that of the Dasypus, than with that of the Megathere or Mylodon. 



The ungueal phalanx of the Scelidothere before alluded to, is represented of 

 the natural size in PI. XXVII. The side-view, fig. 3. shows the position of the 

 articular surface on the proximal end, sloping obliquely towards the under surface, 

 and overtopped by an obtuse protuberance, calculated to impede any upward 

 retraction of the claw : the present joint, in fact, illustrates in every particular 

 the argument by which Cuvier established the true affinities of the allied extinct 

 genus Megalonyx.* 



The present phalanx is, however, less compressed, and less incurved than 

 those of the Megalonyx, which have been hitherto described ; but it more resem- 

 bles in these proportions one of the smaller, and presumed hinder, ungueal 

 phalanges of the Megatherium. The upper and lateral parts of the bone are 

 rounded, and it gradually tapers to the apex, which is broken off. The osseous 

 sheath for the claw is developed only at the under part of the bone : it presents 

 the form of a thick flat plate of bone, with the margin very regularly and obliquely 

 bevelled off, and having a vertical process of bone attached lengthwise to the 

 middle of its under surface. This process must have served for the insertion of a 

 very powerful flexor tendon. The figures of this bone preclude the necessity of 

 any further verbal description. 



M. Lund lays most stress upon the argument founded on the inward inflec- 

 tion of the sole of the foot in the Megalonyx, and appeals with greatest confidence 

 to this structure in support of his hypothesis of the scansorial habits of that 

 extinct Edental.f 



* Ossemens Fossiles, vol. v. part i. p. 163. 



t For the translation of the following passage, and of others alluded to in the present work, from the 

 original Danish Memoir of M. Lund, loc. cit., I am much indebted to the Rev. W. Bilton, M.A. &c. &c. : — 



O 



