Lateral view of a left petrosectomy. For orientation, the left border of the image is rostral. The external auditory canal has been drilled out but the tympanic membrane is intact. The handle of the malleus is visible on the membrane and its head articulates with the incus. The chorda tympani can be seen coursing through the middle ear cavity between these two bones. Also, the tendon of tensor tympani is seen attaching to the malleus near the upper part of the handle to help dampen loud sounds. The semicircular canals of the inner ear are dissected. The internal carotid artery is visible within the cavernous sinus deep to the Gasserian ganglion of the trigeminal nerve. The mandibular nerve (V3) is visible arising from the ganglion. The facial and vestibulocochlear nerves course together in the internal auditory canal. At the fundus, the facial nerve ends at the geniculate ganglion. From here, the greater superficial petrosal nerve (cut) arises and courses anteriorly. The facial nerve continues by entering the facial canal and courses along the medial wall just inferior to the lateral semicircular canal before descending within the posterior wall of the tympanic cavity. Posterior to the bony labyrinth is the sigmoid sinus, which continues as the jugular bulb and then internal jugular vein through the jugular foramen in company with the vagus nerve. The right and left vertebral arteries are shown uniting to form the basilar artery within the posterior fossa. (Image courtesy of AL Rhoton, Jr.)