Medial Rectus
Extraocular · Head & Neck
The medial rectus is the largest and strongest of the extraocular muscles and the simplest in action. It arises from the medial part of the common tendinous ring, the annulus of Zinn, at the orbital apex and runs straight forward along the medial wall of the orbit to insert into the medial sclera about 5.5 mm behind the corneal limbus, the closest of the recti to the cornea. Its line of pull lies directly in the horizontal plane, so it produces pure adduction, turning the eye toward the nose. It is supplied by the inferior division of the oculomotor nerve (CN III).
Origin, Insertion, Action & Nerve
Origin
Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
Insertion
Medial sclera, ~5.5 mm posterior to the corneal limbus
Action
Adducts the eyeball
Nerve
Inferior division of the oculomotor nerve (CN III)
Attachments explained
The Medial Rectus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
Insertion
Medial sclera, ~5.5 mm posterior to the corneal limbus
Action & function
When the Medial Rectus contracts, it produces the following movement: Adducts the eyeball.
As part of the Extraocular group of the Head & Neck, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Medial Rectus receives its nerve supply from the Inferior division of the oculomotor nerve (CN III).
Because a muscle can only contract when its nerve is intact, injury to the Inferior division of the oculomotor nerve can weaken or paralyse the Medial Rectus, impairing the movements it normally produces (adducts the eyeball). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Medial Rectus (the OIANS method)
Learn the medial rectus as the pure adductor, the cleanest of all the extraocular actions: because its fibres run straight forward along the medial orbital wall, contraction simply swings the pupil toward the midline with no elevation, depression, or torsion. This purity makes it a useful reference point when reasoning about the more complex, obliquely pulling muscles.
Pair the two medial recti when you think about convergence, since both contract together to fix the eyes on a near object. Fix its nerve as the inferior division of the oculomotor nerve, and note that failure of adduction is a hallmark of oculomotor palsy and of internuclear ophthalmoplegia, giving the muscle real clinical weight despite its simple action.
Frequently asked questions
Where is the Medial Rectus located?
The Medial Rectus is a muscle of the Extraocular group, located in the Head & Neck.
What is the origin of the Medial Rectus?
Medial part of the common tendinous ring (annulus of Zinn) at the orbital apex
What is the insertion of the Medial Rectus?
Medial sclera, ~5.5 mm posterior to the corneal limbus
What movements does the Medial Rectus produce?
Adducts the eyeball
What nerve supplies the Medial Rectus?
Inferior division of the oculomotor nerve (CN III)
Is the Medial Rectus free to study in OIANS?
The Medial Rectus is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Medial Rectus
Test yourself on Head & Neck muscles with interactive quizzes and flashcards in the free OIANS app.
Quiz yourself → Flashcards Open the OIANS app
Browsing is always free. A one-time Lifetime unlock adds every region's quizzes, flashcards, progress tracking and explore tools.