Fig. 2 Structures at the orbital apex. The anulus of Zinn is composed of the tendon of Zinn (TZ), tendon of Lockwood (TL), and the insertions of the rectus muscles. Structures exiting the superior orbital fissure outside the anulus of Zinn include the lacrimal nerve (LN), superior ophthalmic vein (SOV), the frontal nerve (FN), the trochlear nerve (IV). and the anastomotic branch between the middle meningeal artery and lacrimal artery (not shown). Structures passing through the anulus of Zinn include the superior (SUP III) and the inferior (INF III) branch of the oculomotor nerve, the nasociliary nerve (NCN), the abducens (VI), and the optic nerve (II) with its associated ophthalmic artery and sympathetic nerves. Structures exiting through the inferior orbital fissure include the infraorbital nerve (V2), the inferior ophthalmic vein (IOV), and the zygomatic branch of the infraorbital nerve (ZN). (Courtesy of Deborah D. Sherman, MD, Nashville, TN)