A, Superior view of the right orbit. The levator, superior rectus, and superior oblique muscles have been reflected to expose the ophthalmic artery coursing above the optic nerve. The ophthalmic artery passes above the optic nerve and between the superior oblique and the medial rectus muscles, where it gives rise to the anterior and posterior ethmoidal arteries. The anterior and posterior ethmoidal arteries pass through the anterior and posterior ethmoidal canals with the anterior and posterior ethmoidal nerves to supply the dura in the region of the cribriform plate and send branches that descend to supply the upper part of the nasal cavity. B, A segment of the optic nerve and ophthalmic artery have been removed to expose the central retinal artery arising as one of the first branches of the ophthalmic artery and entering the lower surface of the optic nerve. C, Central retinal artery, inferior view. An ophthalmic artery, which courses below the optic nerve, has been retracted posteriorly to show the tortuous course of the central retinal artery before penetrating the optic nerve. The central retinal artery, which is the first or one of the earliest and smallest branches of the ophthalmic artery, pierces the lower surface of the nerve and courses a short distance inside the dural sheath of the nerve before passing to the center of the nerve, where it courses to the retina. D, Inferior view. The inferior rectus has been retracted to expose a tortuous central retinal artery. Inset: Anterior view of the right orbit after removal of the globe. The central retinal artery, after penetrating the optic nerve, passes forward in the center of the nerve. The central retinal artery is a terminal branch without anastomotic connections. The ciliary arteries, coursing around the nerve, are divided into long and short and anterior ciliary arteries. The long and short ciliary arteries pierce the sclera around the optic nerve and supply the choroidal coat and ciliary processes. The anterior ciliary arteries are derived from the muscular branches of the ophthalmic artery and run to the front of the globe with the tendons of the extraocular muscles, where they pierce the sclera and end in the greater arterial circle of the iris. The subarachnoid space extends forward between the nerve and sheath. (Images courtesy of AL Rhoton, Jr.)