No: 2. 
THE HARD PARTS; OF THE MAMMALIA. 187 
oblique articulation between the tibia and astragalus ; and second, 
by a rotation of the navicular on the rounded extremity of the 
astragalus. 
second in the Meg- 
alonyx and Myrme- 
cophaga, and both 
combined in the 
sloths (Bradypodi- 
dz). The incurva- 
tune, OL the’ Loot 
naturally resulted 
from the 
amd size of the 
claws, which ren- 
dered a truly planti- 
grade walk difficult 
or inconvenient, and 
thus compelled the 
animal to walk on 
the outside of its 
fee=’ In’ the mod- 
ern sloths the lat- 
eral position of the 
tibio-tarsa] articula- 
tion is an exact adap- 
tation to the trans- 
verse direction 
assumed by the foot 
in hanging or walk- 
ing while holding 
the body suspended 
beneath the branch 
on which the ani- 
mal lives. The di- 
rection of the foot is 
at right angles to the 
longitudinal axis of 
the body, and across 
the branch to which 
it is suspended. 
leon othe 
SSQ Qo \ 
The first mode is seen in the Megatheriidz ; the 
\ 
\, 
fl 
ff 
\ woop” 
Ws 
SS 
he. 
Figure 26.— Cholepus hoffmanii, in progression; 
three positions of the limbs; from Muybridge, Animal 
Locomotion, 
