Superior views of right and left orbits and frontal, ethmoid, and sphenoid sinuses. The orbital plates 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). A superficial strata of extraocular muscles can be seen in each orbit: superior oblique muscles follow the medial wall, lateral rectus muscles follow the lateral wall, and the levator palpebrae superioris muscles course forward between these to the upper eyelid. The superior rectus muscles lie deep to the levator, and the medial rectus muscles lie deep to the superior oblique. The recti muscles attach in common to the annulus of Zinn or tendinous ring 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 artery, a branch of the internal carotid artery, enters the orbit with the optic nerve and gives rise to the lacrimal artery before crossing the optic nerve, in company with the nasociliary nerve, toward the medial side of the orbit. It gives rise to the 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 ophthalmic nerve typically gives rise to its "NFL" branches (nasociliary, frontal, lacrimal), which then enter the orbit through the superior orbital fissure. The lacrimal nerve courses along the lateral wall of the orbit (near the superior border of the lateral rectus) to the lacrimal gland. 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. The floor (greater wing of sphenoid bone) of the middle fossa is intact on the left side of the image and shows the ophthalmic, maxillary, and mandibular branches of the trigeminal nerve leaving the trigeminal ganglion. This bone has been removed on the right side to reveal the lateral pterygoid muscle and mandibular nerve in the infratemporal fossa. (Image courtesy of AL Rhoton, Jr.)