Lateral exposure of the right cavernous sinus. 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 tentorium cerebelli attaches anteriorly to the anterior clinoid process of the sphenoid bone. Just medial to it is the intradural portion of the internal carotid artery. Medial to this is the optic nerve and canal. The oculomotor nerve is shown here entering the roof of the cavernous sinus. It lies superior to the trochlear nerve. These two nerves along with the ophthalmic nerve enter the orbit through the superior orbital fissure. The cavernous sinus drains blood from the orbit via the ophthalmic veins. It, in turn, is drained by the superior petrosal vein (and inferior petrosal vein, not shown) to the transverse sinus. (Image courtesy of PA Rubino)