158 COPE. [Vot. IIT. 
ternal digit of the manus is necessarily the support of the body 
when in the act of climbing out of the water and is used in such 
progress as they make when on the shore. The hind feet are 
used in the same way ; but I must note here, that I do not know 
to what use the external digit is put which shall account for its 
superior development. Observation on the living animal only 
ean furnish the explanation. 
In the heavy Ungulata the longitudinal diameter of the 
phalanges is greatly reduced in relation to their transverse. 
The successive increase in depression in the bones of the feet 
with the advance of time is to be most readily seen in the order 
Amblypoda, where we pass from Pantolambda to Coryphodon 
and Uintatherium (Fig. 8). A similar successive reduction is 
to be seen in the lines of the Perrisodactyla, as we om (ii 
pass from the smaller and lighter to the heavier and 
more bulky types. Such series are those which com- 
mence in the Lophiodontidz, and terminate in the 
Menodontidz on the one hand, and the rhinoceroses 
on the other. The elephants display the end of a 
similar line, which 
commences in the 
Condylarthra. In 
all of these bulky 
mammals the 
weight in progres- 
sion is borne on 
Hi 
iw 
(i 
Figure 8.—a, Pantolambda bathmodon, digit of posterior foot. 4, Right posterior 
foot of a species of Coryphodon from New Mexico, one-half nat. size. From Report 
Expl. W. of tooth Mer., G. M. Wheeler, IV., Pl. LIX. c, Uintatherium mirabile, 
right posterior foot; from Marsh, Dinocerata, 
