Abduction and adduction of the fingers are defined with respect to the long axis of the middle finger (Fig. 7.93). In the anatomical position, the long axis of the thumb is rotated 90° to the rest of the digits so that the pad of the thumb points medially; consequently, movements of the thumb are defined at right angles to the movements of the other digits of the hand.
The hand is a mechanical and sensory tool. Many of the features of the upper limb are designed to facilitate positioning the hand in space.