38 AMERICAN PERMIAN VERTEBRATES 



Radius,' ulna. — The radius and ulna are very like those of 

 Diadecfes and Eryops, rather short and stout bones. The two 

 lie in position on each side, as shown in the figure, the upper end 

 of the radius partly lodged in the lower end of the sigmoid fossa, 

 and the two are in one plane. The radius has the capitulum trun- 

 cated and hollowed for articulation with the humerus, the extremity 

 strongly convex on the dorsal, flattened on the ventral side. The 

 shaft of the bone is moderately narrowed, and its two borders are 

 nearly symmetrically concave. The lower extremity is more 

 expanded, with its end truncate and flattened for articulation with 

 the radiale and intermedium, the inner side the thicker. Just above 

 the inner distal angle there is a characteristic protuberance, which 

 evidently came in close contact with the ulna. The ulna is a more 

 slender bone and is a Httle longer; it is thick and massive at its 

 upper end, the shaft more slender than that of the radius, and the 

 lower end moderately expanded. Its radial border is deeply con- 

 cave, its inner border nearly straight to the lower fifth. The sig- 

 moid fossa is deep, winding obliquely about the bone, and fits 

 accurately the curved trochlear surface on the distal and dorsal 

 side of the humerus. Evidently the elbow joint was a strong and 

 firm one. The distal extremity of the ulna is subtruncate, its 

 border somewhat oblique to that of the radius, but with the angle 

 broadly rounded for articulation with the pisiform. Both radius 

 and ulna have the dorsal side convex, the ventral more flattened. 



Front foot. — ^Lying in close articulation with the radii and ulnae 

 are the proximal carpal bones, four in number on each side, the 

 radiale, intermedium, ulnare, and pisiform. The pisiform is a 

 small bone, thinned along its free border and articulating in its 

 usual position between the ulna and ulnare. The ulnare, the 

 largest of the carpal elements, is an irregularly oval bone, articulat- 

 ing rather broadly with the ulna and the intermedium, but without 

 distinct facets for the other carpal elements. The smaller inter- 

 medium is much thickened, articulating with the ulna, ulnare, 

 and the radius, with a very small free border between the ulna 

 and the radius. The radiale is the smallest of the three, almost 

 vestigial in fact, elongate, ovate in shape, with the radial border 

 straight and flattened, the outer end obtusely pointed; it merely 



