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Tendinous ring

contributed by Dr Frank Gaillard on May 2, 2008

System: Central Nervous System
Section: Anatomy

The tendinous ring (also known as the Annulus of Zinn) is the common origin of the four rectus muscles (extraocular muscles).

The tendinous ring straddles the superior orbital fissure and through it (from superior to inferior) pass:

  1. superior division of the oculomotor nerve (CN III)
  2. nasociliary nerve (a branch of the ophthalmic nerve)
  3. inferior division of the oculomotor nerve (CN III)
  4. abducens nerve (CN VI)

The medial portion of the ring also encompasses the optic foramen through which the optic nerve and ophthalmic artery pass.