Natural Position of Standing
Again, it will be found that in the natural position of standing
we are not perfectly flat-footed, but tend to press much more on
the outer than on the inner edge of the foot. This tendency,
surviving after ages of living on the level ground, is a
lingering effect of the far-off arboreal days.
A more curious reminiscence is seen in the fact that the very
young infant, flabby and powerless as it is in most of its
muscles, is so strong in the muscles of the hand and arm that it
can hang on to a stick by its hands, and sustain the whole weight
of its body, for several minutes. Finally, our vestigial
tail--for we have a tail comparable to that of the higher
apes--must be mentioned. In embryonic development the tail is
much longer than the legs, and some children are born with a real
tail, which they move as the puppy does, according to their
emotional condition. Other features of the body point back to an
even earlier stage. The vermiform appendage--in which some recent
medical writers have vainly endeavoured to find a utility-- is
the shrunken remainder of a large and normal intestine of a
remote ancestor. This interpretation of it would stand even if it
were found to have a certain use in the human body. Vestigial
organs are sometimes pressed into a secondary use when their
original function has been lost. The danger of this appendage in
the human body to-day is due to the fact that it is a blind alley
leading off the alimentary canal, and has a very narrow opening.
In the ape the opening is larger, and, significantly enough, it
is still larger in the human foetus. When we examine some of the
lower mammals we discover the meaning of it. It is in them an
additional storage chamber in the alimentary system. It is
believed that a change to a more digestible diet has made this
additional chamber superfluous in the Primates, and the system is
slowly suppressing it.
Other reminiscences of this earlier phase are found in the many
vestigial muscles which are found in the body to-day. The head of
the quadruped hangs forward, and is held by powerful muscles and
ligaments in the neck. We still have the shrunken remainder of
this arrangement. Other vestigial muscles are found in the
forehead, the scalp, the nose--many people can twitch the
nostrils and the scalp--and under the skin in many parts of the
body. These are enfeebled remnants of the muscular coat by which
the quadruped twitches its skin, and drives insects away. A less
obvious feature is found by the anatomist in certain
blood-vessels of the trunk. As the blood flows vertically in a
biped and horizontally in a quadruped, the arrangement of the
valves in the blood-vessels should be different in the two cases;
but it is the same in us as in the quadruped. Another trace of
the quadruped ancestor is found in the baby. It walks "on all
fours" so long, not merely from weakness of the limbs, but
because it has the spine of a quadruped.
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