I20 The American Naturalist. [March, 
supports the weight of the animal, thus removing it from the 
ungues. This cushion has relieved the metapodials from im- 
pacts and torsion, a fact which I have regarded as explaining 
the absence of the trochlear keel from the extremity and 
front of those elements in the Camelidae. We must then sup- 
pose that the development of the elastic foot-pad of the camels 
began in the Miocene period before this character appears, 
and caused a divergence from the Booid line in the foot struct- 
ure. This divergence probably took place before the devel- 
opment of the third stomach, and the addition of water com- 
partments in the paunch maybe supposed to have commenced 
at about the same time. 
Existing Camelidse pace, yet they have more or less dis- 
tinct episphenal processes to the vertebrae. These are dis- 
tinctly visible in Procamelus. We must suppose that their 
ancestors, as the Poebrotheriidae, were trotters, and that the 
habit has been changed in later periods. 
With the Tragulid/E we commence the great, mostly 
modern division of the Booidea, or Ruminantia. As already 
related, most of the characteristic peculiarities of the special- 
ized Artiodactyla commence with this family. The trochlear 
cylinder and crest of the humerus appear here for the first 
time, for the Suoid and Cameloid series never develop more 
than traces of either. The naviculocuboid bone is character- 
istic. How variable the conditions of the other bones of the 
limbs are in the Tragulidai may be gathered from the accom- 
panying table. A few species of two genera, Dorcatherium 
and Tragulus, still exist in the warm parts of Africa and Asia. 
These agree with the Camelidae in the absence of the third 
stomach, the other three being present. 
I. Both metatarsals and metacarpals distinct ; molars brachyodont (Hyper- 
a. Lateral toes behind. 
Anterior internal cresent of inferior molars represented by a conical cusp. 
Lophiomeryx Pom. 
Interior crescnts of inferior molars developed Dorcatheriiun Kaup. 
aa. No lateral toes behind. 
Diastemata in both iavvs ffypcrtragulus Coft. 
II. Metatarsals forming a cannon bone ; metacarpals distinct; molars bra- 
chyodont (GelocinK). 
