A, Coronal section of orbits and cranial base anterior to the orbital apex. The floor of the orbit faces the maxillary sinus and the medial wall faces the ethmoid air cells. The inferior concha is a separate bone attached to the medial maxillary wall. The middle turbinate, an appendage of the ethmoid bone, attaches to the lateral nasal wall at the level of the roof of the maxillary sinus. B, Enlarged view of right side shown in A. The ophthalmic artery enters the orbit on the lateral side of the optic nerve and crosses medially above the nerve. The abducens nerve enters the medial surface of the lateral rectus muscle. The optic nerve is enclosed in the optic sheath. The nerve to the inferior oblique muscle courses along the lateral edge of the inferior rectus muscle. C, Anterosuperior view showing the relationship of the orbital apex to the optic strut, optic canal, and superior orbital fissure. The optic strut, which has been removed, separates the optic nerve in the optic canal from the superior orbital fissure. The optic nerve enters the orbit on the medial side of the optic strut and the oculomotor, trochlear, abducens, and ophthalmic nerves enter the orbit on the lateral side of the strut. The rectus muscles arise from the annular tendon, which encircles the optic canal and the central part of the superior orbital fissure. The anterior clinoid process has been removed to expose the clinoid segment of the internal carotid artery. The upper dural ring surrounds the carotid artery at the upper edge of the clinoid segment. D, Cross section of right orbit just in front of the apex. The ophthalmic artery enters the orbit on the lateral side of the optic nerve. The branch of the inferior division of the oculomotor nerve to the medial rectus muscle passes below the optic nerve. (Images courtesy of AL Rhoton, Jr.)