A, The lateral wall of the cavernous sinus extends downward from the tentorial edge and blends into the dura covering Meckel’s cave and the middle fossa. The oculomotor and trochlear nerves enter the roof of the cavernous sinus. The carotid artery exits the cavernous sinus on the medial side of the anterior clinoid process. B, The outer layer of dura has been peeled away from the lateral wall of the cavernous sinus and Meckel’s cave. This exposes the oculomotor and trochlear nerves entering the roof of the cavernous sinus and passing forward through the superior orbital fissure. The thin layer covering Meckel’s cave consists in part of the arachnoid membrane extending forward from the posterior fossa and surrounding trigeminal nerve to the level of the trigeminal ganglion. The superior petrosal sinus passes above the ostium of Meckel’s cave and joins the posterior part of the cavernous sinus. C, The oculomotor nerve enters a short cistern in the sinus roof (red arrow) and does not become incorporated into the lateral wall until it reaches the lower margin of the anterior clinoid process (yellow arrow). The arachnoid covering of Meckel’s cave, which extends forward around the posterior trigeminal root to the level of the midportion of the ganglion, has been removed. The cavernous sinus extends from the superior orbital fissure to the petrous apex. It is located medial to the upper third of the gasserian ganglion. The pericavernous venous plexus surrounds the maxillary and mandibular nerves in the region of the foramen rotundum and foramen ovale. D, The remaining dura covering the lateral wall has been removed. The oculomotor, trochlear, and ophthalmic nerves pass forward to converge on the superior orbital fissure. The segment of the superior petrosal sinus above the posterior trigeminal root has been removed. E, The posterior trigeminal root has been reflected forward to expose the posterior part of the lower margin of the cavernous sinus (yellow arrow) in the area medial to the trigeminal impression on the petrous apex, in which Meckel’s cave sits. The superior ophthalmic vein exits the orbit through the superior orbital fissure and passes posteriorly below the ophthalmic nerve to enter the cavernous sinus. F, The trigeminal nerve and its three divisions have been reflected forward to expose the venous spaces of the cavernous sinus. The lower margin of the cavernous sinus (broken line) is located at the site where the internal carotid artery exits the carotid canal by passing below the petrolingual ligament. The venous spaces in the cavernous sinus communicate posteriorly with the inferior and superior petrosal and basilar sinuses. In addition, the cavernous sinus communicates with the superior ophthalmic veins and the venous plexus around the maxillary and mandibular nerves and pituitary gland. (Images courtesy of AL Rhoton, Jr.)