A Rare Accessory Clavicular Muscle With Clavicular Origin and Insertion in the Right Posterior Cervical Triangle: A Cadaveric Case Report

Variations in cervical and supraclavicular musculature have been documented, including the cleidooccipital, levator claviculae, levator scapulae, sternocleidomastoid (SCM), and trapezius muscles.In this report, we describe a rare accessory clavicular muscle with both right clavicular origin and insertion, identified during dissection of an approximately 35-year-old male cadaver.The muscle was located in the right posterior cervical triangle, originating from the superior surface of the clavicle immediately medial to the trapezius insertion and inserting on its superoposterior surface, posterior to the lateral margin of the clavicular head of the sternocleidomastoid.The muscle had close anatomical relationships with the anterior and posterior branches of the supraclavicular nerve and the external jugular vein (EJV).This rare anatomical variant has potential clinical relevance and may influence local neurovascular relationships.Recognition of such variants may improve anatomical interpretation and reduce diagnostic errors.