3. THE LIMBS.

TWO SETS OF LIMBS branch from the trunk, viz.: the upper, and the lower.
They closely resemble each other. The arm corresponds to the thigh; the
forearm, to the leg; the wrist, to the ankle; the fingers, to the toes.
The fingers and the toes are so much alike that they receive the same
name, _digits_, while the several bones of both have also the common
appellation, _phalanges_. The differences which exist grow out of
their varying uses. The foot is characterized by strength; the hand, by
mobility.

FIG. 10.

[Illustration: _The Shoulder Joint._ a, _the clavicle;_ b,
_the scapula._]

1. THE UPPER LIMBS.--THE SHOULDER.--The bones of the shoulder are the
collar bone (clavicle), and the shoulder blade (scapula). The
_clavicle_ (_clavis_, a key) is a long, slender bone, shaped
like the Italic _f_. It is fastened at one end to the breastbone and
the first rib, and, at the other, to the shoulder blade. (See Fig. 1.) It
thus holds the shoulder joint out from the chest, and gives the arm
greater play. If it be removed or broken, the head of the arm bone will
fall, and the motions of the arm be greatly restricted. [Footnote: Animals
which use the forelegs only for support (as the horse, ox, etc.), do not
possess this bone. "It is found in those that dig, fly, climb and seize."]

THE SHOULDER BLADE is a thin, flat, triangular bone, fitted to the top and
back of the chest, and designed to give a foundation for the muscles of