Superior view of medial wall of right orbit and frontal, ethmoid, and sphenoid sinuses. The orbital plate of the frontal bone and bone roofing the ethmoid and sphenoid sinuses have been removed to expose the sinuses along the medial wall of the orbit. The eyeball or globe occupies the anterior half of the orbit while the extraocular muscles, fat, and neurovascular elements populate the posterior half. The latter structures enter the apex of the orbit through the optic canal (for the optic nerve and ophthalmic artery) and the superior orbital fissure (for the oculomotor, trochlear, ophthalmic, and abducens nerves, and the superior ophthalmic vein). The optic nerve, developmentally a tract of the brain, is enclosed by meninges as the optic nerve sheath. The levator palpebrae superioris and superior rectus muscles were reflected laterally to better visualize the optic nerve and the lateral-to-medial course of the ophthalmic artery and nasociliary nerve, a branch of the ophthalmic nerve. The ophthalmic artery can be seen here giving rise to its supraorbital and posterior and anterior ethmoidal branches. The latter pass through foramina on the medial wall of the orbit to supply ethmoid and sphenoid sinuses before entering the nasal cavity. The olfactory bulbs lie in the olfactory grooves of the cribriform plate of the ethmoid bone. These continue posteriorly as the olfactory tracts to the olfactory cortex. The crista galli, a vertical projection of bone in the cribriform plate, is a site of attachment of the falx cerebri. The annulus of Zinn or tendinous ring is the whitish connective tissue that the recti muscles attach to at the orbital apex. The optic, oculomotor, abducens, and nasociliary nerves and the ophthalmic artery pass through this ring to enter the orbit. The ophthalmic nerve typically gives rise to its "NFL" branches (nasociliary, frontal, lacrimal), which then enter the orbit through the superior orbital fissure. The proximal portion of the lacrimal nerve can be seen coursing toward the lateral wall of the orbit. The frontal nerve courses forward in the orbit superficial to the levator palpebrae superioris and superior rectus muscles before dividing into the supraorbital and supratrochlear branches. The supraorbital artery, a branch of the ophthalmic artery, follows the supraorbital nerve. The medial wall of the orbit borders the lateral walls of the ethmoid and sphenoid sinuses. The latter is located beneath the planum sphenoidale. At the apex of the orbit, the trochlear nerve bends medially (medial to the frontal nerve) to enter the superior border of the superior oblique muscle. (Image courtesy of AL Rhoton, Jr.)