A, The dura covering Meckel’s cave and cavernous sinus has been removed. The cavernous sinus is located medial to the upper third of the gasserian ganglion and extends down to the lower margin of the ophthalmic nerve. The superior ophthalmic vein exits the orbit and passes below the ophthalmic nerve to enter the anterior part of the cavernous sinus. The superior petrosal sinus passes above the porus of Meckel’s cave to join the posterior part of the cavernous sinus. The superior orbital fissure is filled on its posterior side by the cavernous sinus and on its anterior margin by the fat in the orbital apex. B, The anterior clinoid, lateral orbital wall, and roof have been removed. The optic strut separates the optic nerve in the optic canal from the nerves passing through the superior orbital fissure. The superior ophthalmic vein can be seen through the periorbita as it exits the muscle cone to pass along the lateral margin of the superior orbital fissure and below the ophthalmic nerve to enter the anterior part of the cavernous sinus. C, The orbital fat has been removed to expose the nerve passing through the superior orbital fissure and the annular tendon from which the rectus muscles arise. The trochlear nerve passes medially above the oculomotor and ophthalmic nerves to reach the superior oblique muscles. The frontal, lacrimal, and trochlear nerves pass outside the annular tendon, and the nasociliary, oculomotor, and abducens nerves pass through the tendon. D, The frontal and lacrimal nerves have been depressed to show the nasociliary nerve arising from the medial side of the ophthalmic nerve. The oculomotor foramen is the portion of the opening in the annular tendon lateral to the optic foramen through which the superior and inferior divisions of the oculomotor nerve and the nasociliary nerve and abducens nerve pass. The oculomotor nerve divides into superior and inferior divisions just behind the superior orbital fissure. The abducens nerve courses on the medial side of the ophthalmic nerve in the cavernous sinus, but in the fissure, it turns laterally below the nerve to enter the medial side of the lateral rectus muscle. E, Enlarged view of the oculomotor foramen. F, The annular tendon has been divided between the origin of the superior and lateral rectus muscles. The abducens nerve enters the medial aspect of the lateral rectus muscle. The superior division of the oculomotor nerve passes upward to innervate the levator and superior rectus muscles. The inferior division innervates the inferior oblique, inferior rectus, and medial rectus muscles and gives rise to the motor parasympathetic pupilloconstrictor fibers to the ciliary ganglion. (Images courtesy of AL Rhoton, Jr.)