The |deltoid| is a large, thick powerful muscle. It is triangular in form with a coarse texture. On its broad side, it originates from the clavical (collar bone) and from the |spine| of the |scapula| (shoulder blade) covering the outer side of the |shoulder joint|, giving the shoulder its rounded appearance, and inserts in the |humerus| (upper arm bone). This muscle moves the |humerus| bone and is used to raise the arm outward from the side. It works with the |pectoralis major| to move the arm forward and works with the |teres major| and |latissimus dorsi| to move the arm back.
