T02 AMERICAN PERMIAN VERTEBRATES 



of the flexor muscles. The outer condyle is less expanded, is more 

 thickened, and has considerable surface for the extensor muscles. 

 The shaft, near the middle of the bone, is much contracted and very 

 short, subrotund or prismatic in cross-section. 



Radius (Plate VII, Figs. 1-4). The radius is a slender bone, 

 about three-fourths the length of the humerus, with only moder- 

 ately expanded extremities. It was found in this specimen closely 

 articulated with both humerus and ulna, as shown in the figures 

 (Figs, i, 2). Its proximal articular surface is broader on the 

 dorsal than on the palmar side, shallowly concave above for the 

 capitellum. The shaft is curved, with the concavity on the ulnar 

 side, the outer margin thinner for the interosseous membrane. 

 The lower extremity is transversely oval, the end concave, the 

 dorsal side convex, the palmar more concave. 



Ulna (Plate VII, Figs, i, 2, 3, 6). The ulna is a little longer than 

 the radius, and is much more expanded at its extremities than that 

 bone; the shaft at its narrowest place, the lower third, is more 

 slender. The sigmoid surface is concave and is almost continuous 

 with that of the radius for the capitellum in the articulated condi- 

 tion. The olecranon is produced but little, and has also a concave 

 ligamentous surface for the attachment of the triceps. The 

 radial border is concave throughout, the inner border convex 

 for fully three-fourths its length, as far as the most slender part 

 of the shaft. The distal extremity, narrower than that of the 

 radius, is flattened oval and is concave in the end. 



That minor differences in the shapes of the bones of the skeleton 

 are not necessarily due to specific differences is apparent in many 

 of our specimens. In Plate VIII, I have figured the radius and 

 ulna of another skeleton, in which such differences are very 

 apparent, without corresponding differences in other parts of the 

 skeleton; they certainly belong in the same species. 



Front foot (Plate VIII; Plate VII, Fig. 5). The foot, as it is 

 figured in Plate VIII, is nearly wholly that of a single specimen, 

 but it has been completed in part and the position of various 

 bones determined by the aid of several other specimens. Unfor- 

 tunately many of the phalanges of the three middle bones have not 

 yet been found associated, though the most of them, as outlined, 



