Right posterolateral view of middle fossa and auditory complex following subtotal petrosectomy. The superior petrosal sinus can be seen coursing along the superior border of the petrous bone within the attachment of the tentorium cerebelli. The roof of the internal auditory canal has been drilled out to reveal the fundic end of the facial nerve, which ends at the geniculate ganglion. The greater superficial petrosal nerve arises from the ganglion and courses anteriorly deep to the Gasserian (trigeminal) ganglion. The main trunk of the facial nerve (cut) is directed posteriorly within the facial canal. The roof of the tympanic cavity has also been drilled out to show the malleus (attached to the tympanic membrane) and the incus. The tympanic membrane bounds the medial end of the external auditory meatus. Crossing the apex of the petrous bone is the cisternal part of the trigeminal nerve, which expands within Meckel's cave as the Gasserian (trigeminal) ganglion, a sensory ganglion of this nerve. From the ganglion, the three nerve divisions (ophthalmic, maxillary, mandibular) arise. The ophthalmic and maxillary nerves course within the lateral wall of the cavernous sinus (lateral to the cavernous segment of the internal carotid artery) as do the oculomotor and trochlear nerves located superior to the ophthalmic nerve. The abducens nerve can be seen coursing within the cavernous sinus along the lateral surface of the internal carotid artery. The oculomotor, trochlear, ophthalmic, and abducens nerves enter the orbit through the superior orbital fissure. (Image courtesy of AL Rhoton, Jr.)