84 



he classed, like the humerus of the Mole, with the flat instead of the long hones 

 of the skeleton. Viewed from the inner or ulnar side, it presents the form of an 

 elongated inequilateral triangle, with one of the angles scooped out for the hu- 

 meral articulation, and the other two angles obhquely truncated : the inner sur- 

 face of the bone is smooth, and concave to near the distal end, where it is tra- 

 versed by an oblique ridge. The compressed shaft of the ulna is more irregular 

 on the outer side*, which is traversed by a thick and strong ridge, running 

 parallel with the posterior border, from the radial angle of the proximal articular 

 surface to the corresponding side of the distal end. Along this broad and rough 

 ridge the shaft of the radius was evidently connected with the ulna by strong 

 ligaments. The surface between this ridge and the posterior border is deeply 

 concave at its proximal half, slightly convex at the distal half, which is traversed 

 obliquely by a narrow ridge, and supports near its extremity a large oblong pro- 

 tuberance. 



The olecranon, a process of great length, breadth and thickness, is bent ob- 

 liquely inwards ; the broad and rough back part of the olecranon gradually con- 

 tracts into the postei'ior flattened border of theulnaf- The great sigmoid, or 

 rather reniform articular surface, extends almost transversely across the base of 

 the olecranon, and plays upon the inner and back part of the outer condyle of 

 the humerus, being divided by a median convexity into two compartments : the 

 inner portion is produced forwards upon the anterior angle of the ulna, and is 

 very slightly concave : the outer division is more deeply excavated. The arti- 

 cular surface is continued for a few lines upon the large rough depression for the 

 head of the radius. Much of the non-articular surface of the ulna is sculptured 

 by fine reticular ridges. The distal extremities of the bones of the fore-arm 

 were attached to each other by syndesmosis : below the rough surface for this 

 union the ulna is obliquely truncated, leaving a triangular space between it and the 

 radius : it then terminates by a flat smooth articular surface applied to the os 

 cuneiforme, which surface is continued for half an inch upon the ulnar side of the 

 distal end, where a part of the pisiform bone plays upon the ulna. 



Cuvier, in pointing out the nearer resemblance of the ulna of the Megathe- 

 rium to that bone in the Ant-eaters than in the Sloths, indicates the difierences 



* Plate XIII. I Plate XII. fig. 2. 



