A, The sella is located between the cavernous sinuses. The diaphragm, which usually separates the sella from the suprasellar cisterns, is absent in this case. The oculomotor nerves enter the roof of the cavernous sinus where there is a narrow cistern around the nerve. The oculomotor triangle, the triangular patch of dura through which the oculomotor nerve enters the dura in the cavernous sinus roof, is positioned between the anterior and posterior clinoid processes and the petrous apex. The roof of the cavernous sinus extends forward under the anterior clinoid process. B, The dura covering the anterior clinoid process and optic canal has been removed. The outer layer of dura in the lateral wall of the cavernous sinus has been removed to expose the thin inner layer of the lateral sinus wall and the lateral surface of Meckel’s cave. The falciform ligament, the dural fold extending above the optic nerve proximal to the nerve’s entrance into the optic canal, extends from the anterior clinoid to the tuberculum. C, The inner layer of the lateral sinus wall has been removed to expose the nerves coursing in the wall of the cavernous sinus and middle fossa. The oculomotor nerve enters the narrow oculomotor cistern in the sinus roof and passes forward along the lower margin of the anterior clinoid process. D, Enlarged view. A probe has been passed between the optic nerve and the falciform ligament. The dissector can be seen through the dura proximal to the osseous optic canal. The anterior clinoid is located lateral to the optic nerve and internal carotid artery and above the oculomotor nerve. E, The dura covering the dorsum sellae, basilar sinus, and posterior clinoid process has been removed. The oculomotor nerve passes forward lateral to the posterior clinoid and below the anterior clinoid. An abnormal bony projection extends laterally from the right posterior clinoid below the oculomotor nerve toward the petrous apex. The basilar sinus crosses the back of the dorsum and upper clivus and communicates widely with the posterior edge of the paired cavernous sinuses. The abducens nerve passes through the lower margin of the basilar sinus. An anterior intercavernous passes along the anterior margin of the sella. F, The posterior part of the cavernous sinus has been cleared to expose the abducens passing through Dorello’s canal, which is roofed by the petrosphenoid ligament. (Images courtesy of AL Rhoton, Jr.)