The Trochlear Nerve (SE) It is a purely somatic motor nerve that supplies the superior oblique muscle.
The nerve exits the dorsal surface of the midbrain and sweeps around its side and passes between the posterior cerebral and superior cerebellar arteries.
It then approaches and pierces the dural roof of the cavernous sinus just anterior to the site where the margin of the tentorial notch crosses the petroclinoid ligament. The nerve then runs forward in the cavernous sinus, with its epineurium adherent to the dural wall. About halfway through the sinus, it encounters the upper border of the Ophthalmic division of the trigeminal nerve and then runs along with it out of the sinus toward the superior orbital fissure. It enters the orbit through the upper compartment of the superior orbital fissure along with the frontal and lacrimal branches of the ophthalmic division of the trigeminal nerve .