A patient has a drooping eyelid, dilated pupil, and the eye drifts outward-down. This is oculomotor nerve (CN III) palsy. CN III lifts the eyelid, constricts the pupil, and drives most eye movements (up, down, in). When it fails, the lid droops (ptosis), the pupil stays wide, and the unopposed lateral rectus (CN VI) and superior oblique (CN IV) pull the eye down-and-out. One nerve's functions explain all three signs together.