Serratus anterior: origin, insertion, action and innervation
The serratus anterior arises from the outer surfaces of the upper eight ribs and inserts on the medial border of the scapula. It protracts and upwardly rotates the scapula and is supplied by the long thoracic nerve.
Quick answer
- Latin name
- Musculus serratus anterior
- Origin
- Outer surfaces of ribs 1–8 (sometimes 9), by finger-like slips
- Insertion
- Costal (front) surface of the medial border of the scapula, from the superior to the inferior angle
- Action
- Protracts the scapula and rotates it upward; holds it against the chest wall
- Innervation
- Long thoracic nerve (C5–C7)
- Blood supply
- Lateral thoracic and thoracodorsal arteries
The serratus anterior gets its name from its saw-toothed (serrated) edge on the side of the chest. It's often called the "boxer's muscle" because it drives the shoulder forward in a punch.
Where it is
It lies on the side of the thorax, under the armpit. From the front of the upper ribs, its slips wrap backwards around the chest wall and pass under the scapula, between the scapula and the ribs, to reach its inner border.
Origin and insertion
- Origin: the outer surfaces of the first eight (sometimes nine) ribs, by fleshy slips that interlock with the external oblique lower down.
- Insertion: the front (costal) surface of the medial border of the scapula, with the strongest part at the inferior angle.
What it does
- Protraction: pulls the scapula forward around the chest, as in punching or pushing.
- Upward rotation: with the trapezius, it rotates the scapula so the arm can rise above the head.
- Holds the scapula against the ribs. When it's weak, the medial border lifts off the back, which is called a winged scapula.
Innervation and blood supply
The long thoracic nerve (C5–C7) runs down the outer surface of the muscle. Blood comes from the lateral thoracic and thoracodorsal arteries.
How to remember it
- "Serrated" = saw-tooth slips on the ribs.
- "C5, 6, 7 raise your wings to heaven": the long thoracic nerve (C5–C7) supplies serratus, and damage to it causes a winged scapula.
Frequently asked questions
What does the serratus anterior do?
It protracts the scapula, rotates it upward and holds it against the chest wall.
Which nerve supplies the serratus anterior?
The long thoracic nerve, from roots C5 to C7.
What is a winged scapula?
When the serratus anterior is weak or its nerve is injured, the medial border of the scapula lifts away from the back, especially when pushing against a wall.