Shoulder Girdle Muscles 1) Trapezius O: base of skull, occipital protuberance, spinous process of C7- T12 I: clavicle and scapular spine A: elevation of scapula, extension and rotation of the head and neck/ elevation upward rotation, and adduction of the scapula/ depression, adduction, and upward rotation of the scapula N: CN XI and C3,4 2) Levator Scapulae O: transverse process of C1-4 I: medial scapula above scapular spine A: elevates medial margin of scapula N: Dorsal Scapula 3) Rhomboid O: spinous process of C7-T5 I: medial scapula below spine A: adduction, downward rotation, and elevation N: Dorsal Scapula 4) Serratus Anterior O: upper 9 ribs at side of chest I: Anterior aspect of medial border of scapula A: Abduction, upward rotation