An anatomic triangle formed by the clavicle (bone extending from the breastbone, sternum, at the base of the front of the neck to the shoulder), the deltoid, and the pectoralis major (a skeletal muscle that rotates the arm): The deltopectoral triangle or "clavipectoral triangle" contains the cephalic vein which is a large vein of the arm that empties blood into the axillary (armpit) vein.