gastrocnemius and soleus. In the standing posture the heel slopes
downwards and backwards, and is thus in a position, as regards its
piston cord, considerably beyond the point of maximum leverage. As the
heel is lifted by the muscles, it gradually becomes horizontal and at
right angles to its tendon or piston cord. As the heel rises, then, it
becomes a more effective lever; the muscles gain in power. The more the
foot is arched, the more obliquely is the heel set and the greater is
the strength needed to start it moving. Hence, races like the European
and Mongolian, which have short as well as steeply set heels, need large
calf muscles. It is at the end of the upward stroke that the heel
becomes most effective as a lever, and it is just then that we most need
power to propel our bodies in a forward direction. It will be noted that
the heel, unlike the crank-pin of an engine, never reaches, never even
approaches, that point of powerlessness known to engineers as a dead
centre. Work is always performed within the limits of the most effective
working radius of the lever. It is a law for all the levers of the body;
they are set and moved in such a way as to avoid the occurrence of dead
centres. Think what our condition would have been were this not so; why,
we should require revolving fly-wheels set in all our joints!

[Illustration: Fig. 8.--The arch of the foot from the inner side,
showing some of the muscles which maintain it.]

Another property is essential in a lever: it must be rigid; otherwise it
will bend, and power will be lost. Now, if the foot were a rigid lever,
there would be missing two of its most useful qualities. It could no
longer act as a spring or buffer to the body, nor could it adapt its
sole to the various kinds of surfaces on which we have to tread or
stand. Nature, with her usual ingenuity, has succeeded in combining
those opposing qualities--rigidity, suppleness, and elasticity or