The |deltoid| muscle is a thick triangular muscle which cups the |shoulder joint|. It is attached to the |clavicle| (collar bone) and |scapula| (shoulder blade) at its upper end, and to the shaft of the |humerus| (upper arm bone) at its lower end. The muscle is divided into three portions: an ~anterior~ (clavicular) portion, and acrominal (middle) portion, and a ~posterior~ portion. The ~posterior~ portion is located on the back of the shoulder. Almost any movement of your shoulder and upper arm involves the |deltoid| muscle. The ~anterior~ portion is used to raise the arm from the body and to lower it again. The acrominal portion is a powerful abductor and the ~posterior~ portion is used to move the arm backward.
