Scalenus anterior muscle

The anterior scalene muscle is one of the three scalene muscles (anterior, middle, and posterior) forming the floor of the posterior triangle of the neck.

Anatomical Details

1. Origin

Anterior tubercles of the transverse processes of cervical vertebrae C3–C6

2. Insertion

Scalene tubercle on the inner border of the first rib, and the ridge on the upper surface of the first rib anterior to the groove for the subclavian artery

Innervation

Ventral rami of C4–C7 spinal nerves

Blood supply

All scalene muscles receive their arterial blood supply from the ascending cervical branch of the inferior thyroid artery. The posterior scalene receives an additional supply from the superficial cervical artery.

Actions

• Bilaterally: Flexes the neck and assists in elevation of the first rib during inspiration (as an accessory muscle of respiration).

• Unilaterally: Produces lateral flexion of the neck to the same side.

Relations

• Phrenic nerve (C3–C5) runs obliquely across the anterior surface of the anterior scalene — a key surgical landmark.

• The brachial plexus and subclavian artery pass posterior to it (between anterior and middle scalene muscles).

• The subclavian vein passes anterior to it — hence, vein in front, artery behind.