The Oculomotor Nerve (III)
leaves the brainstem between the cerebral peduncles and passes near the posterior communicating artery of the circle of Willis. Lateral to the pituitary gland, it is closely approximated to the optic tract, and here it pierces the dura to course in the lateral wall of the cavernous sinus.
As the nerve leaves the cavernous sinus, it divides into superior and inferior divisions. The superior division enters the orbit within the annulus of Zinn at its highest point and adjacent to the trochlear nerve. The inferior division enters the annulus of Zinn low and passes below the optic nerve to supply the medial and inferior rectus muscles.
A large branch from the inferior division extends forward to supply the inferior oblique. A small twig from the proximal end of the nerve to the inferior oblique carries parasympathetic fibers to the ciliary ganglion
The Trochlear Nerve (IV)
Although the thinnest of the cranial nerves, the trochlear nerve has the longest intracranial course, and it is also the only nerve to originate on the dorsal surface of the brain stem.
The nerve pierces the dura behind the sella turcica and travels within the lateral walls of the cavernous sinus to enter the superior orbital fissure medial to the frontal nerve. From this point it travels within the periorbita of the roof over the levator muscle to the upper surface of the superior oblique muscle.
The Trigeminal Nerve (V)
originates from the pons. The first (ophthalmic) of the three divisions passes through the lateral wall of the cavernous sinus and divides into the lacrimal, frontal, and nasociliary nerves.
The Abducens Nerve (VI)
originates between the pons and medulla
passes within the cavernous sinus. (All other nerves course through the lateral wall of the cavernous sinus.)
After passing through the superior orbital fissure within the annulus of Zinn, the nerve continues laterally to innervate the lateral rectus muscle.