NOTES OjST THE CANID.E OF THE WHITE RIVER OLIGOCENE. d4o 



IV. The Fore Limb. 



Of the scapula no part has yet been recovered. 



The humerus (PI. XX, Fig. 15) differs in several important respects from that of 

 the recent Canidw. Unfortunately, in all of the specimens the j)roximal end of the bone 

 is broken away, so. that nothing can be determined with regard to the head, tuberosities, 

 or bicipital groove. The shaft is rather short and stout, and is arched strongly forward, 

 though less so than in Canis ; the deltoid ridge descends low upon the shaft and is very 

 prominent, much more so than in the existing canines or felines, though it does not attain 

 the exaggerated development seen in the early Machairodonts, such as Dinietis and 

 Hoplophoneus. The distal end of the humerus is remarkably cat-like in appearance, and 

 does not suggest any relationship with the modern Canidce. The supinator ridge is very 

 prominent and extends far up upon the shaft, while in Canis this ridge is almost obso- 

 lete. The internal epicondyle is very much larger, more rugose and more prominent 

 than in the modern genus, quite as much so, indeed, as in the cats, and there is a large 

 entepicondylar foramen, bridged over by a stout, straight bar of bone. The anconeal 

 fossa is lower, broader, shallower, and altogether more cat-like than in Canis, and does 

 not perforate the shaft to form a supratrochlear foramen. The humeral trochlea is 

 extremely low, its vertical diameter being conspicuously less than in Canis and less even 

 than in Felis, resembling in this respect the humerus of the sabre-tooth Hoplophoneus. 

 The shape of the trochlea is of feline appearance, having a simply convex surface for the 

 capitellum of the radius, and no such distinctly marked intercondylar ridge or convexity 

 as is found in the recent Canidce. The internal border of the trochlea is prolonged 

 downward into a large flange. 



The radius (PL XX, Fig. 16) is also singularly cat-like in structure and in all its 

 parts is much more feline than canine. The proximal end bears an oval and somewhat 

 concave capitellum, for articulation with the humerus ; its transverse diameter only 

 slightly exceeds the antero-posterior dimension. • The anterior notch of the humeral 

 surface is somewhat more deeply incised than in Felis, but not more so than in Hop- 

 lophoneus, which has an entirely similar capitellum. The articular facet for the ulna 

 surrounds more than half the circumference of the head of the radius, which is in 

 remarkable contrast to the small size of this facet in Canis. The shape and mode of 

 articulation of the bones which enter into the formation of the elbow-joint show that 

 Daphcenus possessed unimpaired powers of pronation and supination of the manus. In 

 the existing members of the Canidce, on the contrary, this power is lost, the head of the 

 radius being so much expanded transversely, as to occupy nearly the whole width of the 

 humeral trochlea, and interlocking with it in such a way as to allow only the movements 

 of flexion and extension. 



A. P. S. — VOL. XIX. 2 R. 



