IV N. Trochlearis
—The fourth nerve, the trochlearis (or patheticus), arises from the lateral border of the velum medullare anterius, as already described (Fig. 141, n). It passes craniad, emerges through the orbital fissure in company with the oculomotor, abducens, and ophthalmic, passes dorsad of the superior rectus muscle, and reaches (Fig. 154, l) the caudal border of the belly of the superior oblique muscle near its middle. It supplies only the superior oblique.