168 COPE. [Vov. III. 
plantation, the rotation of the foot is arrested at the moment of 
contact with the ground, with the result of producing a torsion 
of the segments of the limb on each other. The energy of the 
torsion is directly as 
the distance from the 
moving body, since 
its cause resides in the 
inertia ‘af ithe fvec 
hoof, which is that of 
the animal of which it 
is a part. 
The mechanical ef- 
fect of this torsion is 
seen at various points 
on the length of the 
lim Dy «sin. the store 
limb (I.) the distal ex- 
tremity of the radius 
has spread outwards so 
as to cover almost the 
entire carpal articula- 
tion, and the ulna has 
been excluded from it. 
That torsion with im- 
pacts, the’ Cornect 
explanation of this 
divergence from the 
condition of lower land 
vertebrates is rendered 
probable by the large 
ulnar carpal articula- 
tion in primitive plan- 
tigrade types with 
taxeopodous carpus, as 
Figure igp — Boicharus humerosus, Cope; distal Elephas, Hyrax, and 
extremity of radius, showing oblique intercarpal keels; Ph d IL Th 
do. of humerus; also left fore foot from front and : enacoaus. : e€ 
from inside; one-fifth nat. size. lines of mutual contact 
in the zodlogical garden of Philadelphia. The horse turns the toes out but little, and 
frequently turns them in; but the tapir, which represents the horse’s ancestors, turns 
them out. The llama also turns the hind toes out very little, or not at all. 
