The optic nerve enters the orbit enclosed in a dural sheath continuous with the intracranial dura. The subarachnoid space around the nerve communicates with the intracranial space. The ophthalmic artery, the first branch of the intracranial internal carotid artery (see brain circulation), enters the orbit with the optic nerve through the optic foramen. It lies inferolateral to the nerve, bound to it by the dural sheath of the nerve. The levator palpebrae superioris, superior oblique and inferior oblique muscles have origins separate from the tendinous ring.
The origins of the orbital nerves are best visualized internally around the region of the bony sella turcica. The internal carotid arteries pass through the cavernous sinuses (see brain circulation) flanking the sella and give rise to the ophthalmic arteries at the sharp rearward turn medial to the anterior clinoid processes. These pass through the optic foramen with the optic nerve. The superior orbital fissure admits the motor nerves and sensory ophthalmic division of the trigeminal nerve. The foramen rotundum allows passage of the second or maxillary division of the trigeminal into the pterygopalatine fossa. From there the sensory infraorbital branch enters the orbit through the infraorbital fissure.
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