24 PATAGONIAN EXPEDITIONS: PAL/EONTOLOGY. 



manus is an excellent example of what Kowalevsky has called the "ina- 

 daptive" method of reduction in the Artiodactyla. 



The scaphoid is a large, nearly cubical bone ; its proximal end is covered 

 by the radial facet, which is convex on the dorsal, concave on the palmar 

 side ; distally, it articulates with the trapezium, trapezoid and magnum ; 

 the facet for the trapezium is small, that for the trapezoid is the largest of 

 the three and deeply concave, while the articulation with the magnum is 

 quite extensive and is made by a process which descends below the level 

 of the trapezoid facet. 



The lunar is quite large, exceeding the scaphoid in proximo-distal length; 

 the radial facet consists of two parts, a dorsal portion, which is broad, 

 convex and oblique, rising quite steeply toward the ulnar side, and a much 

 narrower palmar extension, which is saddle-shaped. Distally, the lunar 

 rests entirely upon the magnum and is very widely separated from the 

 unciform. 



In proximo-distal diameter, the pyramidal is much the longest of the 

 carpal elements, almost equalling the combined lunar and magnum in 

 .length, but in width and thickness it is considerably inferior to the scaph- 

 oid ; the ulnar facet is of moderate size and slightly convex, and is 

 continuous with that for the pisiform, which is narrow, oblique and slightly 

 saddle-shaped. Distally, the bone is covered by a large, concave facet for 

 the unciform, while on the radial side of the distal end is a large surface 

 for the magnum, which is an unusual arrangement in an ungulate carpus. 



In the present genus the pisiform is still unknown. 



In view of the tridactyl and functionally monodactyl character of the 

 manus, the trapezium is quite large ; it is of an irregularly polygonal shape, 

 with the maximum diameter directed proximo-distally, and is so displaced 

 toward the palmar side as to be almost invisible when the manus is seen 

 from the front : the trapezium articulates with the scaphoid, trapezoid and 

 second metacarpal. The trapezoid is not very much larger than the tra- 

 pezium and, like the latter, its principal diameter is the proximo-distal one : 

 proximally it has a slightly convex facet for the scaphoid and on the ulnar 

 side are two facets, for the scaphoid and magnum respectively, which meet 

 at a very open angle ; distally, the trapezoid articulates only with mc. II. 



In correlation with the great enlargement of mc. Ill, the magnum is 

 much the largest bone of the distal row, but is quite unlike that of the 

 horses in shape, being longer proximo-distally and narrower transversly 



