Corpus: Annular tendon

The annular tendon is a reinforced tendinous ring which, lying at the tip of the orbital pyramid, serves as the insertion for the straight external eye muscles. The annular tendon surrounds the optic nerve immediately before it enters the optic canal.

Some sources divide the annular tendon into an upper and a lower ligament:

• The superior portion serves as the origin for the superior rectus muscle, the medial rectus muscle and the upper fibre tracts of the lateral rectus muscle
• The "lower" part forms the origin for the inferior rectus muscle and the lower fibre tracts of the lateral rectus muscle.

2.1. Passing structures

Passing through the annular tendon

• Abducens nerve
• Oculomotor nerve
• Optic nerve
• Nasociliary nerve from the ophthalmic nerve
• Ophthalmic artery

The only cranial nerve that innervates part of the external eye musculature and does not pass through the annular nerve is the trochlear nerve.