THE OSTEOLOGY OF HY.EN0D0N. 525 
Tlie tarsus m not at nil characteristicnlly crcodont in structure ,md altliou"h 
nivora a* in any of the cX 
I'l't- in all the American species of Hy^mdon displays certain con- 
fof . ?r'"“n ?"■ - ‘ (*■* No 9, n. 684. fij. 
587, tie ISIainvlIle, Osteographie, Subursus, PI. XII), the most important of which 
are the greater obliquity of the external calcaneal facet 
and the much greater length of the neck in the former. 
The amount of grooving exhibited by the trochlea varies 
according to the species. In H. cruentus the groove is 
deep, for a creodont astragalus, less so than in the recent 
digitigrade carnivores, but decidedly more so than in 
such White River genera as Dinicfis, Hoplophone^^s or 
Daphmius. In the little H. mustelinus the trochlea is 
more flattened, while in H. horridus the grooving is 
better marked than in the existing cats. Between these 
extremes the contrast is very notable. The degree of 
symmetry of the astragalar trochlea also differs in the 
different species. In H. horridus and H. cruentus the 
external condyle but slightly e.xceeds the internal in size, 
wdiile in the small undetermined species (marked H. sp. 
in the tables of measurements) and in H. miistehnus it 
does so considerably. The fibular facet of the astraga- 
lus is large and slightly concave; distally it becomes 
confluent with the external calcaneal facet, from which 
it is elsewhere separated by a deep sulcus. The facet on 
the inner side for the tibial malleolus has but little dorso- 
plantar depth, but extends well distally, where it termi- 
nates in the characteristic pit or fossa which occurs in so many creodonts. The 
neck is long, especially in H. mustelmus, and strongly everted toward the mtm-nal 
^ 1 ..1 it* K/V 1 f\ 
Kio. ». — Ifi/tr.iwdonsp. Right 
j)c» : a, astragalus, el, lalca- 
iieiiiii ; cb, cuboid ; c', e", 
e"', ent<>-, lueso- and ectocu- 
neiforniH. j natural size. 
side, so that there is no contact, or none 
but the most limited, with the cuboid. 
Tire head bears a rounded, simply convex facet for the navicular; there is no facet 
for the cubtiid (Zittel’s figure is incorrect in this regard) and, apparently^ the wo 
bones do not meet at all. The head is depressed and flattened, the transveise 
The external calcaneal facet is large 
diameter exceeding the dorso-piaiuai unc. -uuv. w ... 
and ilunply concave ; its position is obliqne with reference “ ^ 
plnntnr and prlvimonlisUl a.ve» of the astragalus, ^lis ^ 
slightly convex and is everywhere sepanated from the outer calcaneal facet by 
