Rhomboid major ORIGIN: spinous processes of T2-T5. INSERTION: medial border of the scapula. ACTION: Rhomboid minor and Rhomboid major are working together as a whole to perform the movement. retract scapula (squaring shoulders), synergist with middle fibers of Trapezius. rotate glenoid cavity downward (lowering arm against resistance). stabilize scapula. NERVE SUPPLY: Dorsal scapular nerve