Lateral exposure of the right trigeminal nerve and Gasserian ganglion. The dura over the lateral wall of the cavernous sinus and floor of the middle cranial fossa has been removed.  The trigeminal nerve has crossed the apex of the petrous temporal bone and expanded as the Gasserian ganglion within Meckel's cave. The ganglion gives rise to its three divisions or branches. The ophthalmic nerve courses forward to enter the orbit via the superior orbital fissure. The maxillary nerve passes through foramen rotundum to enter the pterygopalatine fossa. The mandibular nerve passes through the foramen ovale to enter the infratemporal fossa. Just posterolateral to this foramen is foramen spinosum transmitting the middle meningeal artery. The oculomotor nerve is shown here entering the roof of the cavernous sinus. It lies superior to the trochlear nerve. The trochlear nerve courses along the lateral wall of the cavernous sinus superior to the ophthalmic nerve. All three nerves enter the orbit through the superior orbital fissure. (Image courtesy of PA Rubino)