Right lateral 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 draining into the junction between the transverse and sigmoid sinuses. An emissary vein is also exposed. The roof of the internal auditory canal has been drilled out to reveal the facial and vestibulocochlear nerves and labyrinthine artery, a branch of the anterior inferior cerebellar artery. Laterally, these nerves pass between the cochlea anteriorly and the labyrinth posteriorly. Here, the facial nerve ends at the geniculate ganglion, which gives rise to the greater superficial petrosal nerve that courses anteriorly deep to the Gasserian (trigeminal) ganglion. The main trunk of the facial nerve is directed posteriorly within the facial canal, first along the medial wall of the tympanic cavity and then inferiorly along its posterior wall. Just before exiting the stylomastoid foramen it gives rise to the chorda tympani which passes through the middle ear cavity medial to the malleus. The anterior wall of this cavity has also been drilled out to show the tensor tympani muscle within a semicanal superior to the bony portion of the Eustachian tube. The lateral wall of the tympanic cavity is bounded by the tympanic membrane located at the 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 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. From its origin from the midbrain, the oculomotor nerve passes between the superior cerebellar and posterior cerebral arteries. The abducens nerve can be seen coursing within the cavernous sinus along the lateral surface of the internal carotid artery. The middle meningeal artery is shown emerging through the foramen spinosum on the floor of the middle fossa. (Image courtesy of AL Rhoton, Jr.)