The wrist or joint between the hand and arm lessens on closing the hand, and grows larger when it opens. The contrary happens in the arm, in the space between the elbow and the hand, on all sides; because in opening the hand the muscles are extended and thinned in the arm, from the elbow to the wrist; but when the hand is shut, the same muscles swell and shorten. The tendons alone start, being stretched by the clenching of the hand.