Extradural exposure of the right cavernous sinus. For orientation, anterior is toward the left border of the image; inferior is toward the top border. The temporalis muscle has been divided near the zygomatic arch. A large transtemporal craniotomy with elevation of the temporal lobe and division of the tentorium cerebelli has enabled visualization of the middle cranial fossa and the cavernous sinus, the latter adjacent to the body of the sphenoid bone. The oculomotor (CNIII) and trochlear (CNIV) nerves leave the midbrain and pass through the subarachnoid space before penetrating the dura mater on the superolateral wall of the cavernous sinus. The trigeminal (CNV) nerve leaves the lateral pons, travels in the prepontine cistern before passing over the apex of the petrous temporal bone, and entering Meckel's cave, a CSF-filled dural recess that contains the trigeminal (Gasserian) ganglion. This ganglion rests upon the trigeminal impression on the petrous apex. From the margin of the ganglion arise the ophthalmic (CNV1), maxillary (CNV2),  and mandibular (CNV3) divisions. The oculomotor, trochlear, and ophthalmic nerves are arranged in the posterolateral wall of the cavernous sinus in a rostral-to-caudal orientation before they  converge on the superior orbital fissure to enter the orbit. The abducens (CNVI) nerve leaves the caudal midline of the pons near the pontomedullary junction, traverses the prepontine cistern, and penetrates the dura on the clivus. It ascends in a lateral direction and passes beneath the petrosphenoid (Gruber's) ligament traversing Dorello's canal to enter the cavernous sinus. The petrosphenoid ligament extends from the anteromedial most portion of the petrous bone to the posterior clinoid process. The abducens nerve passes along the lateral surface of the cavernous segment of the internal carotid artery before passing through the superior orbital fissure. The maxillary nerve enters the pterygopalatine fossa through the foramen rotundum, while the mandibular nerve passes through foramen ovale to enter the infratemporal fossa. (Image courtesy of PA Rubino)