Common tendinous ring
Anulus tendineus communis
- Synonym: Common anular tendon
- Eponym: Anulus of Zinn
- Related terms: Common tendinous ring; Common anular tendon
Definition
The common tendinous ring, also known as the annulus of Zinn, is a fibrous ring located at the apex of the orbit, encircling the optic canal and the medial part of the superior orbital fissure.
It is formed by a thickening of the periorbita (the periosteum lining the orbital bones) in the posterior part of the orbital cavity. The ring surrounds the optic nerve (cranial nerve II) and the ophthalmic artery as they enter the orbit.
The oculomotor nerve (cranial nerve III) — both its superior and inferior divisions — the abducent nerve (cranial nerve VI), and the nasociliary branch of the ophthalmic nerve (V₁) also pass through the ring as they enter the orbital cavity via the superior orbital fissure.
Muscular Attachments
The common tendinous ring serves as the common origin for the four recti muscles of the eyeball, which together form a muscular cone surrounding the optic nerve:
Superior rectus: passes forward and upward.
Inferior rectus: passes forward and downward.
Medial rectus: passes directly forward along the medial wall.
Lateral rectus: passes forward along the lateral wall.
References
Gray, H. (2016) Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 41st edn. Edited by S. Standring. New York: Elsevier. Chapter 41: Orbit and Accessory Visual Apparatus, p. 670-672.
