Scalenus medius
The largest and longest of the three scalenes, forming the back wall of the gap the arm's nerves pass through.
- Type
- Muscle
- Region
- Neck
- Standard name
- m. scalenus medius
- Origin
- Posterior tubercles of the transverse processes of the cervical vertebrae
- Insertion
- Upper surface of the first rib, behind the groove for the subclavian artery
- Actions
- neck sidebendingrib elevation
- Verify
- TA2 2153 TA98 A04.2.01.005
What it is
The biggest of the three scalene muscles, running from a broad origin along the cervical transverse processes down to the first rib, behind scalenus anterior.
Together with scalenus anterior it forms the interscalene triangle — this muscle is the back wall, scalenus anterior the front, and the first rib the base. The brachial plexus and subclavian artery pass through that gap on their way to the arm.
What it does
Side-bends the neck towards its own side, and lifts the first rib during forceful breathing in.
What loads it
The same as the other scalenes: resisted side-bending and laboured breathing.
What is commonly got wrong about it
That the scalenes are three versions of the same muscle. They attach to different ribs and tubercles and form the walls of a clinically important space between them.
Interscalene anatomy as something to self-assess. The region contains the nerve supply to the entire arm. Symptoms there belong with a clinician.