Fig 4. Superior oblique muscle. The reflected tendon of the superior oblique muscle courses at an angle of 51° to the medial wall of the orbit, giving a cyclovertical action in the primary position (B) that becomes principally intorsion in abduction (C) and depression in adduction (A). Slight abduction action is also produced, because the pulling power is exerted along a line posterior to the center of rotation. (Parks MM, Parker JE: Atlas of Strabismus Surgery. Philadelphia, Harper & Row [in press]. Courtesy of John E. Parker)