A, The dura has been removed from the part of the frontal and sphenoid bones forming the orbital roof. The olfactory bulb rests on the cribriform plate. B, The orbit and optic canal have been unroofed, the anterior clinoid process removed, and the periorbita opened to expose the trochlear, frontal, and lacrimal nerves coursing in the orbital fat just beneath the periorbita. The optic strut, which has been partially removed, separates the optic canal and superior orbital fissure. C, The orbital fat has been removed. The ophthalmic nerve divides into the lacrimal, frontal, and nasociliary nerves. The frontal nerve passes through the superior orbital fissure and courses on the levator muscle where it divides into a supratrochlear nerve, which passes above the trochlea of the superior oblique muscle, and the supraorbital nerve, which passes through a foramen or notch in the supraorbital margin. The lacrimal nerve passes above the lateral rectus muscle to innervate the lacrimal gland and convey sensation to the area around the lateral part of the supraorbital margin. The trochlear nerve passes medially above the levator muscle to reach the superior oblique muscle. The nasociliary branch of the ophthalmic nerve passes between the superior rectus muscle and the optic nerve to reach the medial side of the orbit. The tendon of the superior oblique muscle passes through the trochlea and below the superior rectus muscle to insert on the globe between the attachment of the superior and lateral rectus muscles. D, The frontal nerve and the levator and superior rectus muscles have been divided and reflected. This exposes the superior ophthalmic vein, ophthalmic artery, and nasociliary nerve as they pass above the optic nerve. The dura lining the middle cranial fossa has been removed to expose the oculomotor, trochlear, and ophthalmic nerves as they course in the lateral wall of the cavernous sinus, and the maxillary and mandibular nerves in the middle fossa. The trochlear nerve passes forward in the wall of the cavernous sinus between the oculomotor and ophthalmic nerves and turns medially at the level of the superior orbital fissure to pass above the levator muscle. The optic nerve and ophthalmic artery pass through the optic canal and the medial part of the annular tendon. The trochlear, lacrimal, and frontal nerves and the superior ophthalmic vein pass through the narrow lateral part of the superior orbital fissure above and outside the annular tendon. The superior and inferior divisions of the oculomotor nerve, and the nasociliary and abducens nerves pass through the larger medial part of the superior orbital fissure and the annular tendon. (Images courtesy of AL Rhoton, Jr.)