Transtemporal craniotomy and extradural exposure of the right cavernous sinus wall and middle cranial fossa. 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 lateral wall of the cavernous sinus. Several triangles of the cavernous sinus (supratrochlear, infratrochlear) and middle fossa (anteromedial, anterolateral) are also demonstrable. 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 conduit connects the posterior cranial fossa to the middle fossa. The trigeminal ganglion rests upon the trigeminal impression on the petrous apex. The petrous segment of the internal carotid artery lies medial to the ganglion within the petrous bone. From the convex margin of the ganglion arise the ophthalmic (CNV1), maxillary (CNV2),  and mandibular (CNV3) divisions. The supratrochlear triangle is bounded by the oculomotor and trochlear nerves, the tentorial edge, and the dura between the entry points of these two nerves. The infratrochlear triangle is bordered by the trochlear and ophthalmic nerves and the tentorial edge. Deep to this triangle is the abducens nerve and cavernous segment of the internal carotid artery. The anteromedial triangle is bounded by the ophthalmic and maxillary nerves and a line between the superior orbital fissure and the foramen rotundum. The anterolateral triangle is bounded by the maxillary and mandibular nerves and a line between the foramen rotundum and ovale. The oculomotor, trochlear, and ophthalmic nerves converge on the superior orbital fissure to enter the orbit. 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)