Superior views of orbital apex and adjacent structures. The orbital plates of the frontal bone and underlying periorbita have been removed and the apicies of the orbits are in view. The ophthalmic nerve gives rise to three "NFL" branches (nasociliary, frontal, lacrimal) just prior to the superior orbital fissure. Of these, the frontal and lacrimal nerves do not pass through the common tendinous ring. The frontal nerve courses superficial to the levator palpebrae superioris muscles from the orbital apex toward the orbital base. Deep to the levator palpebrae muscles are the superior rectus muscles. Both are supplied by the oculomotor nerve as are the medial and inferior rectus and inferior oblique muscles. The superior oblique muscles course along the superior medial orbital wall and receive their motor supply from the trochlear nerve, which enters the orbit just medial to the frontal nerve. These, too, lie outside the common tendinous ring and enter the superior border of these muscles. Near the apex, the posterior ethmoidal nerve, a branch of the nasociliary nerve, passes through its foramen to supply posterior ethmoid cells and the sphenoid sinus. The lateral rectus muscles follow the lateral walls of the orbit to the eyeball and are innervated by the abducens nerve, which enter the muscle on its medial border. This nerve passes through the common tendinous ring. The superior ophthalmic vein originates near the upper medial aspect of the orbit and generally parallels the course of the ophthalmic artery crossing the optic nerve from medial to lateral. It passes through the superior orbital fissure to drain much of the orbit to the cavernous sinus. These sinuses communicate across the midline via anterior and posterior intercavernous sinuses located within the diaphragma sellae (removed to show the pituitary gland and infundibulum). The ophthalmic arteries and optic nerves enter the orbits via the optic canals. The optic nerve, embryologically a tract of the brain, is enclosed by meningeal coverings as the optic nerve sheath. Immediately medial to the medial walls of the orbits are the honey-combed arrangement of ethmoid air cells. Posterior to these are the sphenoid sinuses within the body of the sphenoid. Adjacent to the sphenoid body are the cavernous segments of the internal carotid arteries within the cavernous sinus. This sinus also communicates with the pterygoid venous plexus located in the infratemporal fossa via the foramen ovale, which transmits the mandibular branch of the trigeminal nerve. In the midline is the cribriform plate of the ethmoid bone upon which lay the olfactory bulbs and tracts conveying sensory information of smell from the olfactory epithelium and nerves. (Image courtesy of AL Rhoton, Jr.)