THE OSTEOLOGY OF HYiENODON. 515 
with one another and marked only by a change of shape. Of these facets the 
largest is the internal one, which is convex transversely and concave antero-poste- 
riorly ; the median one is a shallow, rounded pit for the intercondylar protuberance 
of the humerus, while the external facet is small and nearly plane. Such an elbow 
joint as that here described cannot have allowed any greater degree of pronation 
and supination than exists among the dogs. The ulnar facet of the head is a single 
broad, convex band, uninterrupted by any sulcus. The bicipital tubercle is so in- 
conspicuous that its position is somewhat uncertain. The proximal portion of the 
shaft is wide but very thin, gradually increasing in thickness and decreasing in 
width downward, until it becomes nearly cylindrical in shape. The distal portion 
of the shaft is much heavier than the proximal and of more trihedral section, having 
a 8 har[) edge on the external or ulnar side, and on the inner side is a broad and deep 
tendinal sulcus. As a whole, the radius has an irregular double curvature, both 
anterior and lateral. The carpal surface is a simple concavity, which shows no sign 
of a division into facets for the scaphoid and lunar ; it is deepest on the outer side, 
contracting toward the inner, and the inner angle is prolonged into a recurved hook, 
which jm)jects over the tendinal sulcus already mentioned. The radius is relatively 
heaviest and best developed in H. horridus ; in the smaller species it is more slender 
in proportion, and in H. mustclinus is exceedingly so, much less heavy than the 
ulna. The slenderness of the radius and the large 
size of the ulna in Hycenodon are in notable con- 
trast to the proportions which are to be found in 
the recent Carnivora. 
The carpus of the American species of Hyce- 
nodon has some constant differences from that of 
the European species. In the latter the scaphoid, 
lunar and central appear to be always united, 
while in the American forms they are as constantly 
separate and show no tendency to ankydosis. In 
my former paper I stated that de Blainville’s draw- 
ing [Taxotherium parisiense, Ostdographie, Subur- 
sus, PI. XII) seemed to show the impression of a 
distinct lunar. Since writing that suggestion, 
however, I have had an opportunity of examining 
the original specimen in the Paris museum and 
find the supposed lunar to be a displaced magnum. 
Of the American forms I have seen the carpus in 
H. horridus and H. crueiiius and, except 111 the 
matter of size, find no noteworthy difference be- 
tween the two species. , - . 
The scaphoid is wide and thick in the dorso- 
palniar direction, but very low vertically; seen from -^etds Tow 
67 JOURX. A. N. S. PHILA., VOL. IX. 
Fig. 5. — Hi/wnodon horridus; Ijcft 
maiius, from the dorsal side, s, sca- 
phoid ; I, lunar; cn, cuneiform ; ( 771 , 
trapezium ; t, trapezoid ; ti, unci- 
form. The central appears between 
the lunar and trapezium. One-half 
natural size. 
