The triangular deltoid muscle covers the point of the shoulder like a cap, and can pull the humerus to the side (abduction), forward (flexion), or backward (extension). You already know the functions of the biceps brachii and triceps brachii, the muscles that form the bulk of the upper arm. Other muscles partially in the upper arm help bend the elbow (flexion). The muscles that form the bulk of the forearm are the flexors and extensors of the hand and fingers. You can demonstrate this yourself by clasping the middle of your right forearm with your left hand, then moving your right hand at the wrist and closing and opening a fist; you can both feel and see the hand and finger muscles at work. See table 3 for details.
