The hand is the most complex and variable form in the human body. No other form can respond with such extraordinary range and functional capability and with such case and grace. For example, the separate fingers can perform ¿in immense variety of actions, and the thumb, obliquely opposing the four long fingers and palm wedge, aids in actions such as grasping, prying, and supporting. However, not all the forms of the hand are as free to move as the fingers. Some fomis arc bound tightly by ligaments and have a very limited range of movement. In this chapter we will look at the hand in terms of some of the many maneuvers of which it is capable.
One of the hand's unique actions is palm rotation, it rotates in a 180-dcgrce arc, a full half circle. The drawing at left, with thumb in, shows puliation. and the one at right, w ith thumb out, shows supination. This is a simple action with the arm outstretched, but not so simple when the arm changes position. Put your hand to your head, shoulder, back, leg. or ankle, and rotate it. Note the difficulty in different positions.
When the palm bends downward with the fingers extended, the ultimate dee* lination from the line of tlx; forearm is an angle of 90 degrees—a right angle. The point at which the ami stops and the hand begins is show n by the horizontal arrow, the wristlinc juncture of the arm, not ihe carpal line of (he hand,,
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