Reflex movements are followed by instinctive, and
these by voluntary. The latter are first shown by grasping at objects,
which took place in Preyer's child during the nineteenth week. The
opposition of the thumb to the fingers, which in the ape is acquired
during the first week, is very slowly acquired in the child, while, of
course, the opposition of the great toe is never acquired at all;
in Preyer's child the thumb was first opposed to the fingers on
the eighty-fourth day. Up to the seventeenth month there is great
uncertainty in finding the mouth with anything held in the hand--a
spoon, for instance, striking the cheeks, chin, or nose, instead of at
once going between the lips; this forms a striking contrast to the case
of young chickens which are able to peck grains, etc., soon after they
are hatched. Sucking is not a pure reflex, because a satisfied child
will not suck when its lips are properly stimulated, and further, the
action may be originated centrally, as in a sleeping suckling. At a
later stage biting is as instinctive as sucking, and was first observed
to occur in the seventeenth week with the toothless gums. Later than
biting, but still before the teeth are cut, chewing becomes instinctive,
and also licking.
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