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422. The opposite section of the same bone. Purchased. 



The following bones, from No. 423 to No. 440 inclusive, belong to the same 

 right fore-foot of the Mylodon ?-obuslus, are from the same stratum and locality 

 as the skeleton, and were purchased by the College. 



423. The scapho-trapezial bone. 



The os scaphoides, besides its usual relations to the radius, lunare and 

 trapezoides, sends down a process which represents the os trapezium, and 

 supports the metacarpal bone of the thumb. This process, or con- 

 fluent bone, gives to the scaphoid an unciform figure. It is short or de- 

 pressed in the direction of the axis of the limb, broad from side to side, 

 convex towards the back of the corpus, and made concave on the opposite 

 side by the production of the two angles, and especially of that formed 

 bv the anchylosed trapezium. The articulation of the radius covers all 

 the proximal surface save the trapezial angle. The articular surface is 

 continued at right angles to its radial portion upon part of the ulnar 

 side of the scaphoid for the junction with the os lunare. The distal 

 surface of the scapho-trapezial bone is excavated by two concave arti- 

 cular surfaces for the os magnum and trapezoides : these surface's are 

 separated by a rough concavity from the small and nearly flat one, at 

 the outer side of the trapezial process, for the metacarpal bone of the 

 thumb. 



424. The os cuneiforme. 



The os cuneiforme, or triquetrum, is the largest of the carpal bones and 

 approaches to the cubical figure : the rough quadrilateral dorsal surface 

 is nearly flat, with an oblong protuberance near the radial margin, and 

 a concavity above the edge of the lower articular surface. The upper or 

 proximal end presents an almost square, flat articular surface for the 

 truncated distal end of the ulna, which surface bends over upon the outer 

 and posterior surface of the bone, to form the slightly convex semi-oval 

 articulation for the os pisiforme. The articular surface of the opposite 

 side for the lunare is divided by a rough tract from the ulnar surface, 

 but is continuous with the broad and slightly sinuous one, by which the 



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