During routine dissection studies, we encountered an aberrant muscle in the neck region of a 50 year-old female cadaver. The accessory muscle was on the left side. It arose from the superior angle of the scapula and lay over the brachial plexus and brachial artery then inserted to the first rib's cartilage. According to its origin and insertion, the aberrant muscle was considered to be the subclavius posticus. The accessory muscle was innervated by a branch coming from the suprascapular nerve.