Muscles of arm movement. Illustration of the skeleton of the chest and upper arms showing the major muscles responsible for arm movement. Bones (brown) and cartilage (grey) of the breastbone (sternum) and ribcage, and upper arms are shown. Attached to the left of the sternum is the pectoralis major (fan-shaped) which draws the arm across the body. Underlying it is the pectoralis minor (shown at right) which moves the shoulder and raises some ribs. The deltoid (rounded, upper left) raises sideways and twists the arm. Below it is the biceps of the upper arm. This muscle bends and twists the forearm. Its two heads are shown clearly at right.