Middle Scalene
Neck
The largest scalene — the brachial plexus passes between it and the anterior scalene, making this corridor a key anatomical landmark for nerve blocks.
Function
Laterally flexes neck; elevates first rib
Origin
Posterior tubercles of transverse processes C2-C7
Insertion
Superior surface of first rib posterior to subclavian groove
Innervation
Anterior rami C3-C8