THE STRUCTURE AND RELATIONSHIPS OF ANCODUS. 483 
the outer, but extends much farther distally, where it terminates upon the plantar 
face of the ridge separating the cuboid and navicular surfaces of the distal 
trochlea, while it does not extend so far proximallj by a corresponding amount. 
This accessory facet is inclined in position, facing obliquely toward the external and 
plantar sides. Of the external calcaneal facets, the proximal one is very unusually 
prominent and very deeply concave, describing almost a semicircle, which closely 
embraces the corresponding protuberance on the calcaneum. This facet is also 
divided by a sulcus into two parts, proximal and distal, which are separated by a 
considerable interval. The distal external facet for the calcaneum is large and 
plane. The whole mode of articulation between the calcaneum and astragalus is 
peculiar and implies a very uncommon freedom of movement. 
So far as can be judged from Filhofs figures (No. 1, PI. 26, figs. 132-3) these 
characteristics do not occur in the astragalus of Ancodtis leptorhy fichus, which is 
more like that of Oreodon, nor does Kowalevsky mention them in his description 
of tire other species. 
Tim calcaneum is correspondingly difterentiated to suit the changes of the 
astragalus. The tuber is long, compressed, and deep, with nearly parallel dorsal 
and plantar borders, somewhat expanded and club-shaped at the free end, which is 
marked by the sulcus plantaris, so general among the artiodactyls. The distal end 
is not, as in Oreodon, suddenly contracted to form the cuboidal facet, the plantar 
border remaining straight throughout. The sustentaculum differs markedly from 
that of all the oreodonts in its much greater prominence, and in the possession of 
an accessory facet for the astragalus. These two facets form a continuous articular 
surface, but being placed at different angles, their junction forms a distinct ridge 
which fits into the reentrant angle between the corresponding facets of the astraga- 
lus. The external facet of the sustentaculum is the larger of the two, is simply 
concave, and presents obliquely toward the distal and dorsal aspects of the bone; 
the inner facet is narrow, nearly plane, and presents distally and internally. It is 
this internal accessory facet which gives its great prominence to the sustentaculum, 
which in the European species does not project much more strongly than m Oreodon 
owing to tlie absence of the inner facet. The fibular facet forms a hrgh, elongate 
prominence, whicl., when seen in profile, has much the same shape and pi-oportions 
as in Fillrofs d, -awing of A. leplcrhy,uhus, but it is thicker transversely than ,n 
that sirecies, and on its internal side are two conve-X facets for the astragalus Be- 
low the Hhular prominence the calcaneum has a greater dorso-p an tar ‘ “ 
in the European sirecies, and the cuboidal facet is less oblique with reference to the 
"n axim bone, though more so than in Oreoim. This facet rs somewhat 
sadSle-shaped. being ch.cave in the dorso-plantar f 
transversely; the The dlutialarLet is unusually 
63 JOUEN. A. N. S. PHILA., VOL. IX. 
