494 
THE STRUCTURE AND RELATIONSHIPS OF ANCODUS. 
Tlie hind-leg of Ancodus is in all essentials like that of Oreodon. The proximal 
end of the feinnr is more expanded transversely, and the shaft is relatively longer. 
The patella is more massive; the internal malleolus of the tibia is less extended, 
while the distal end of the fibula has moved somewhat more completely beneath the 
tibia. The shaft of the libula is of about the same relative proportions in both 
genera. In A^riochceriis the knee-joint has acquired a curious resemblance to that 
of the carnivores, doubtless in correlation with the extraordinary character of the 
hind-foot. 
The tarsus of Ancodus is much more specialized than is the carpus; all its 
elements are notably higher than in Oreodon (though this is subject to considerable 
specific variation), and, therefore, much more so than in Agriochasrus. The special 
cliaracters of the tarsus, however, resolve themselves principally into the remark- 
ably complex and perfect articulations between the calcaneum and astragalus. 
These peculiarities are much more strongly marked in the American forms of Ancodus 
than in the European, and even among the former some species have these articula- 
tions more perfectly differentiated than others. Another notable feature is the 
great size and peculiar shape of the entocuneiform. There is a tendency, though a 
variable one in both the European and American species, for the meso- and ectocu- 
neiforms to ankylose, as in Oreodon. The tarsus of Agriochasrus does not differ in 
any noteworthy way from that of Oreodon, except in the greater relative breadth 
and height of its various elements. 
The metatarsus is more or less peculiar in each of the three genera. In Agrio- 
chnerus the pes is almost isodactyl, the median metatarsals not much exceeding the 
laterals in length. In Ancodus the hallux is reduced to a nodular rudiment of the 
metatarsal without phalanges, and the lateral metatarsals are so much shorter than 
the median pair that the second and fifth digits cannot have reached the ground. 
In Oreodon the hallux has entirely disappeared, but, on the other hand, the median 
digits do not exceed the lateral pair so much as in Ancodus. Here, again, Protore- 
odon serves to connect the two White River genera. In a recent paper (No 7 p 
267) Marsh has pointed out that Protoreodcni {Eomeryx) possesses a nodular rudi- 
ment of the first metatarsal. The tarso-metatarsal articulations are nearly the 
same in all four genera, except that the second metatarsal, which in Protoreodon, 
Oreodon and Ancodus has a small lateral contact with the mesocuneiform, is in 
Agriocharus excluded from that element. 
Fi-om this rapid corap.,rati,e survey of the osteology of Ar^odm .and Oreodon 
the numerous .mportant reseraUauces between them become at once obvious, thougli 
the oorrospondences are aocompanied and, to some extent, concealed by many Si 
ences. I he similarities between Ancodus and the oreodonts are so nmnerons^aiid so 
genera t at any reference of them to parallelism seems altogether ui.likl in the 
toioinmiuHroTdeTcenr'’ Tr'* fundamental and point 
of the pinbable European origin of .daWrrx, hut it Irt^em^b^rLT'a 
