THE ARTIODACTYLA. 
(Continued from page 1095, Vol. XXII., 1888.) 
IN passing from the lower to the higher Artiodactyla we en- 
counter a succession of modifications of the skeleton 
which give the suborder a higher specialization than any other 
among mammals. These may be considered under three 
heads : First, the consolidation of the bones of the carpus and 
tarsus ; second, the development of a tongue and groove of 
the humero-cubital and metapodio-phalangeal articulations ; 
and third, increased complexity of the intervertebral articula- 
Of consolidation of the bones of the feet we have first, the 
coossification of the larger two elements of the distal row of 
the carpus and tarsus ; viz. ; the trapezoides and magnum in 
the former^ and the meso- and ectocuneiform in the latter. 
This commences in the Oreodontidae (Scott) and continues 
throughout the succeeding familfes. The next modification of 
this kind is the coossification of the cuboid bone with the 
navicular. This commences with the Tragulidae, and con- 
tinues throughout the remaining families. The fusion of the 
metapodials into cannon bones first appears in geological 
time in the Tragulidae, as does also the fusion of the ulna and 
radius (in Hypertragulus ), and also in the contemporary Poe- 
brotheriidae. The reduction in the number of the digits pro- 
gresses with varying correlation with the other changes, 
from five in Oreodon to two in Camelus and Bos. As already 
explained, similar reductions took place in the Eocene mem- 
bers of the suborder, Anoplotherium having the digits 3-3, 
and Xiphodon 2-2. 
The mechanical cause of these coossifications must be re- 
garded as strains incurred in the act of rapid locomotion. 
Where not sufificient to produce actual flexure, strain is met 
by resistance and increased nutrition of the tissue, resulting in 
a strengthening of material at the point of resistance. With 
such coossifications comes increased mechanical effective- 
