THE OSTEOLOGY OF SINOFA— MATTHEW. 229 



what more elongate proportions. The pes is by no means as long 

 or compressed as in most modern Carnivora, and this, with the differ- 

 ence in symmetry, involves nmiierous small differences in construc- 

 tion and arrangement of the bones. 



Tritemnodon closely resembles Slnopa in the structure of the hind 

 limb, as shown by comparison of Doctor Wortman's description of 

 the parts known to him and of the more complete specimens in the 

 American Museum collections. 



Compari>«>ns of the appendicular skeleton. — In the characters of the 

 fore and hind limb, Slnopa is in the main of the primitive creodont 

 type, but shows an earlier stage of the cursorial adaptations of Ilyeeno- 

 don^ and shares with that genus a number of peculiarities probably 

 characteristic of the family. The long, narrow scapula, the expanded 

 ilium, the depth of the distal end of the femur, the reduction of the 

 deltoid and supinator ridges of the humerus, the squaring of the 

 carpus and deepening of the astragalar trochlea and head, and in 

 general the elongation of the limb bones, elongation and compression 

 of the feet, are all differentiations from the primitive tj^pe, carried to 

 but a slight extent in Sinojya, to a considerably greater extent in 

 Hy»nodon,, paralleled in all the cursorial Carnivora and in the Con- 

 dylarthra, and carried to a much greater extent in the cursorial 

 Ungulata. On the other hand, the retention of the coracoid process 

 and long acromion of the scapula, the comparatively long post- 

 acetabular region of the pelvis, the entepicondylar foramen on the 

 humerus and the third trochanter on the femur, the stout ulna with 

 its long olecranon, the unreduced fibula, the distinct centrale, the 

 astragulo-cuboidal articulation, the large size of the lateral digits, and 

 the moderately compressed claws, are apparently primitive creodont 

 features not yet modified by the cursorial adaptation which had begun 

 to show itself in the appendicular skeleton. Some of these characters 

 are still retained by Hyienodooi, and they are retained to a varying 

 extent by the other creodont families and by the more primitive mod- 

 ern Carnivora. The mesaxonic manus and ])es, the fibulo-calcanear 

 articulation, and the broad flange on the radial side of the ulnar shaft, 

 are apparentl}^ family characters of the Hyfenodontidti?. The first 

 and the last characters are also seen in the PhenacodontidjB, and the 

 relative conditions of the appendicular skeleton in Sinopa and Hy»- 

 vodon are exactly paralleled by the relative conditions in Euprotogmiia 

 and Phenncodus. 



ANALYSIS OF THE CHARACTERS OF SKULL AND 



SKELETON. 



Priinitive mammalian features.— '^knW elongate, brain-case small, 

 sagittal and occipital crests strong, orbits situate above molars, hence 

 lachrymal and superior process of jugal moderately expanded upon 



