58 



fracture or has not been completed, owing to the nonage of the indi- 

 vidual. The glenoid cavity is a long and narrow vertical ellipse. 



353. The cast of the humerus of a full-grown Megalonyx, from Big-bone-lick. 



It presents the general characters of this bone in the Megatherioid 

 animals ; the rotatory movements of the convex head were not inter- 

 rupted by any inordinate development of the outer or inner tuberosities, 

 although these are well marked. The large size of the supra-condyloid 

 plates, which gave attachment to the pronator and supinator muscles, 

 indicate, with the modifications of the distal articular surface, that the 

 fore-foot could be freely rotated. The most marked character by which 

 the humerus of the Megalonyx differs from that of the Megatherium, is 

 the perforation of the internal condyloid plate. The articular surface 

 presented to the ulna is convex, as in the Megatherium ; in the Mylodon 

 it is concave from side to side. 



354. The shaft of the humerus of the young Megalonyx, from Big-bone-cave, 



Tenessee. It has lost its terminal epiphyses ; but although the ridges 

 and condyloid plates are less developed than in the old animal, the cha- 

 racteristic perforation of the internal condyle remains. 



355. The ulna of the Megalonyx Jejfersonii, from the cavern in Green-briar 

 County, Virginia. The original specimen from which the present cast 

 was taken is described and figured by Cuvier, Annates du Muse'um, 

 torn. v. (1804) p. 372, pi. xiii. fig. 7. 



356. The shaft of the ulna of the young Megalonyx, from Big-bone-cave, Te- 



nessee. The olecranon and the distal extremity are broken off. The 

 original is figured in Dr. Harlan's Medical and Physical Researches, 

 pi. xiii. fig. 15. 



357- The radius of the young Megalonyx, from Big-bone-cave, Tenessee. The 

 head is concave and circular, as in the preceding specimen and in the 

 Megatherium ; the slight differences in the proportions of the shaft of 

 this bone, as compared with the preceding specimen, belonging to the 

 Megalonyx Jeffersonii, depend on the difference in the age of the indi- 



