Anatomy · Muscles

Serratus anterior

The boxer's muscle

Thorax · side of the chest wall, moves the shoulder blade

A broad, saw-toothed sheet on the side of the chest wall that runs from the upper eight or nine ribs round to the inner edge of the shoulder blade. It holds the scapula flat against the ribcage and drags it forwards and round, which is what lets you punch, push and raise the arm above shoulder height. Paralysis of its nerve makes the scapula stick out like a wing.

How to spot them

▸A row of finger-like slips fanning from the sides of the upper ribs, the lower ones interlocking with the external oblique
▸Passes deep to the scapula and attaches along the whole of its medial border, on the rib-facing surface
▸Supplied by the long thoracic nerve, which runs down the outside of the muscle
▸Its failure produces a winged scapula

What to know

A saw-toothed sheet on the side of the chest whose lower slips interdigitate with the external oblique

Serratus anterior — serratus means saw-shaped.

Attaches to the rib-facing surface of the medial border of the shoulder blade, tying it to the chest wall

Serratus anterior — it runs deep to the scapula from ribs 1 to 8 or 9.

Paralysis leaves the inner edge of the shoulder blade sticking out from the back when the arm is pushed forward against a wall

Serratus anterior — a winged scapula from damage to the long thoracic nerve.

Supplied by a nerve arising directly from the roots C5, C6 and C7, before the brachial plexus forms, and running down the lateral chest wall

Serratus anterior — the long thoracic nerve (of Bell).

Protracts and upwardly rotates the scapula, so that the arm can be lifted above the horizontal

Serratus anterior — it acts with the trapezius to raise the arm beyond 90 degrees.

Nicknamed for the fighter who uses it to drive the shoulder forward in a jab

Serratus anterior — the boxer's muscle.

Its nerve may be injured during removal of the axillary lymph nodes, as in breast cancer surgery

Serratus anterior — the long thoracic nerve lies superficially on the chest wall.

Key ideas

Its lower slips do most of the rotating: they pull the inferior angle of the scapula forwards round the chest, tilting the socket upwards, while the trapezius rotates the upper part of the bone the same way.
The upper slips mainly hold the scapula against the chest wall, which is why loss of the nerve shows as winging rather than as a loss of arm strength alone.

Quick-fire facts

•Name from the Latin serratus, saw-shaped, because of the serrated edge of its rib attachments
•Origin: outer surfaces of the upper eight or nine ribs (with their attachments as slips)
•Insertion: costal (deep) surface of the medial border of the scapula, from the superior to the inferior angle
•Action: protracts the scapula, holds it against the chest wall, and rotates it upwards so the arm can rise above 90 degrees
•Nerve supply: long thoracic nerve (C5 to C7), also called the nerve of Bell
•Blood supply: lateral thoracic, thoracodorsal and superior thoracic arteries
•Damage to the long thoracic nerve produces a winged scapula, most obvious when the arm is pushed forward against a wall
•Sometimes called the boxer's muscle, because it drives the shoulder blade forward in punching
•Its lower slips interdigitate with the origin of the external oblique to give the saw-toothed pattern seen in lean athletes along the side of the chest

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Sources

TeachMeAnatomy — Serratus anterior