Upper limb: posterior muscle groups

Triceps (1) arises by two heads from the humerus and one from the scapula (infraglenoid tubercle) to insert into the olecranon of the ulna. With a little help from anconeus, triceps extends the elbow. It is supplied by branches of the radial nerve (C6,7,8) that arise high in the axilla. The triceps reflex tests C7 and C8.