It is a diamond-shaped quadrilateral Muscle. The trapezius has three functional parts: an upper (descending) part which supports the weight of the arm; a middle region (transverse), which retracts the scapula; and a lower (ascending) part which medially rotates and depresses the scapula. ORIGIN: occipital bone, ligamentum nuchae, spines of C7 - T12. INSERTION: spine & acromion ofscapula, lateral 3rd of clavicle. ACTION: stablizes, raises, retracts & rotates scapula. adducts & retracts scapula (middle). elevates scapula or synergist to head extension (suprior). depresses scapula & shoulder (inferior). NERVE SUPPLY: Accesory nerve