that, while the position of the bird's limb is natural, that of the
crocodile is not so. In the bird, the thigh-bone lies close to the body,
and the metatarsal bones of the foot (ii., iii., iv., Fig. 6) are,
ordinarily, raised into a more or less vertical position; in the
crocodile, the thigh-bone stands out at an angle from the body, and the
metatarsal bones (i., ii., iii., iv., Fig. 6) lie flat on the ground.
Hence, in the crocodile, the body usually lies squat between the legs,
while, in the bird, it is raised upon the hind legs, as upon pillars.

In the crocodile, the pelvis is obviously composed of three bones on
each side: the ilium (_Il._), the pubis (_Pb._), and the ischium
(_Is._). In the adult bird there appears to be but one bone on each
side. The examination of the pelvis of a chick, however, shows that
each half is made up of three bones, which answer to those which remain
distinct throughout life in the crocodile. There is, therefore, a
fundamental identity of plan in the construction of the pelvis of both
bird and reptile; though the difference in form, relative size, and
direction of the corresponding bones in the two cases are very great.

[Illustration: FIG. 6.--BIRD. ORNITHOSCELIDAN. CROCODILE.

(The letters have the same signification in all the figures. _Il._,
Ilium; _a_, anterior end; _b_, posterior end _Is._, ischium; _Pb._,
pubis; _T_, tibia; _F_, fibula; _As._, astragalus; _Ca._, calcaneum;
_i_, distal portion of the tarsus; i., ii., iii., iv., metatarsal
bones.)]

But the most striking contrast between the two lies in the bones of the
leg and of that part of the foot termed the tarsus, which follows upon
the leg. In the crocodile, the fibula _(F)_ is relatively large and its