Cranial nerve IV, the trochlear nerve, is the smallest cranial nerve and has the longest intracranial path as it exits from the dorsal midbrain (at the level of inferior colliculus), crosses to the other side of the brainstem and travels along the lateral wall of the cavernous sinus, exiting the skull through the superior orbital fissure, and traveling all the way to the superior oblique muscle. Because of decussation of the intraparenchymal fibers after originating from the nucleus, the left trochlear nucleus eventually innervates the right superior oblique muscle and vice versa.