G, The venous plexus surrounding the nerves has been removed to expose the trigeminal divisions and the nerves coursing in the wall of the cavernous sinus. H, The ophthalmic nerve has been depressed to expose the abducens nerve, which passes under the petrosphenoid ligament roofing Dorello’s canal, and courses medial to the ophthalmic nerve. The abducens nerve crosses laterally below the ophthalmic nerve as it passes through the superior orbital fissure. I, The anterior clinoid process has been removed. The optic strut separates the optic canal and superior orbital fissure. The dura extending medially off the upper surface of the anterior clinoid forms the upper dural ring around the internal carotid artery, and the dura lining the lower margin of the clinoid extends medially to form the lower dural ring. The clinoid segment of the carotid artery, located between the upper and lower ring, is enclosed in the dura sheath, referred to as the carotid collar. J, The trigeminal nerve has been folded downward to expose the petrolingual ligament, which extends above the internal carotid artery, just proximal to where the artery enters the cavernous sinus. The abducens nerve passes around the internal carotid artery and courses medial to the ophthalmic nerve in the lower part of the cavernous sinus. The margins of the cavernous sinus are shown with a broken line. The cavernous sinus does not extend laterally into the area of the trigeminal impression where Meckel’s cave sets. K, Enlarged view. The optic nerve has been elevated to expose the ophthalmic artery coursing within the optic sheath. At the orbital apex, the artery penetrates the optic sheath and enters the orbital apex on the lateral side of the optic nerve. Removal of additional optic strut exposes the mucosa lining the sphenoid sinus on the medial side of the optic strut. L, The bone between the first and second and the second and third trigeminal divisions has been drilled to expose the lateral wing of the sphenoid sinus. The vidian nerve, which passes forward to enter the sphenopalatine ganglion in the pterygopalatine fossa, is exposed between the second and third trigeminal divisions. (Images courtesy of AL Rhoton, Jr.)