Superior view of right middle fossa and trigeminal nerve. The trigeminal nerve has left the lateral pons and crossed the petrous apex and expands as the trigeminal ganglion within the trigeminal depression. From the ganglion margins arise the three branches: ophthalmic nerve to the superior orbital fissure and orbit, maxillary nerve to the foramen rotundum and pterygopalatine fossa, and mandibular nerve to the foramen ovale and infratemporal fossa. The greater superficial petrosal nerve, a branch of the facial nerve, emerges from its hiatus and passes beneath the trigeminal ganglion toward the foramen lacerum. Posterolateral to foramen ovale is the foramen spinosum and middle meningeal artery. The superior petrosal sinus courses in the tentorial attachment to the superior border of the petrous bone. The petrous segment of the internal carotid artery can be seen deep to the mandibular nerve and it continues into the cavernous sinus as the cavernous segment of this artery. Here, the abducens nerve courses on its lateral surface toward the superior orbital fissure. Also, the trochlear and oculomotor nerves are shown converging on this fissure. Posteriorly, on the anterior surface of the petrous bone is an elevation, the arcuate eminence that marks the location of the superior semicircular canal. Posterior to this is the tegmen tympani, a thin plate of bone that forms the roof of the tympanic cavity. (Image courtesy of AL Rhoton, Jr.)