equals the total area devoted to arms, trunk,
and legs (3). This circumstance ensures great
potentiality for coordinated movement and
for learning new activities. Similarly, the
sensory areas are large, so that they determine
such advanced functions as stereognosis, the
ability to recognize the shape of an object
simply by holding it in the hand. The great
tactile sensitivity of the hand is, of course, in
large part due to the rich supply of sense organs
in the hand surface itself. The threshold for
touch in the finger tip, for example, is 2 gm.
per sq. mm., as compared to 33 and 26 for the
forearm and abdomen respectively (2).
The three major types of movement described
by Stetson and McDill (11) are in part
represented in the hand. They include fixation
movements including cocontractions; movements
ranging from slow to rapid with control
of direction, intensity, and rate; and ballistic
movements.