The middle scalene (scalenus medius) is another muscle of the scalene muscle group. As the name suggests, it is situated between the anterior and posterior scalenes in the lateral compartment of the neck.

The middle scalene is the largest and longest of the scalene muscles. Together with the anterior scalene, it forms an interscalene triangle through which the brachial plexus and subclavian artery pass.

The lower aspect of the muscle is crossed by the omohyoid muscle, while posterior to it is the posterior scalene muscle and levator scapulae. Also, the muscle is closely related to the long thoracic and dorsal scapular nerves.

Origin: posterior tubercles of the transverse processes of the second to seventh cervical vertebrae (C2 - C7). Some variants also include transverse process of the atlas (C1) as the origin site of the muscle.

Insertion: superior surface of the first rib posterior to the groove for subclavian artery.

Action: bilateral contractions - flexion of the neck; unilateral contractions - lateral flexion of the neck to the ipsilateral (same) side; as an accessory inspiration muscle, it elevates the first rib.

Innervation: anterior rami of the third to eighth cervical spinal nerves (C3 - C8).

Blood supply: ascending cervical branch of the inferior thyroid artery.

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Middle scalene (scalenus medius)