Q, Overview. The posterior wall of the cavernous sinus extends laterally from the dorsum sellae to the medial edge of the ostium of Meckel’s cave. The floor of the middle fossa has been removed to expose the infratemporal fossa, which contains the branches of the maxillary artery and the mandibular nerve, the pterygoid venous plexus, and the pterygoid muscles. The infratemporal fossa opens medially into the pterygopalatine fossa. The maxillary nerve passes through the foramen rotundum to enter the pterygopalatine fossa and send branches along the orbital floor. The ophthalmic nerve passes through the superior orbital fissure and sends branches along the orbital roof. R, Lateral view of the left cavernous sinus. The oculomotor, trochlear, and trigeminal nerves are all enclosed in an arachnoid sac that surrounds the nerve for a short distance after they enter into the dura. The lateral wall of all three cisterns has been removed. Meckel’s cave, the cistern around the posterior trigeminal root, extends forward to the middle portion of the gasserian ganglion. The oculomotor cistern extends forward in the roof of the cavernous sinus to where the nerve passes under the anterior clinoid process. The thin cistern around the trochlear nerve extends forward below the oculomotor cistern. S, The posterior trigeminal root has been removed to expose the trigeminal impression and the lower margin of the cavernous sinus, which is located at the level of the upper and middle thirds of the trigeminal ganglion (arrows). (Images courtesy of AL Rhoton, Jr.)