The scalenus medius, also known as the middle scalene muscle, is a neck muscle that spreads from the posterior tubercles of transverse processes of the six cervical (C2 to C7) vertebrae and then inserts into the upper part of the first rib (via a broad attachment) at the back of the artery under the collarbone. The nerves passing through it are the dorsal scapular and thoracic nerves. The position of the middle scalene muscle, like the anterior scalene muscle, allows it to lift or elevate the first rib upward and to bend the neck sideways during the inhalation of gas into the lungs. Brachial plexus, cervical nerves C7 to C8, put this scalene muscle into action. The scalenus medius, the scalenus anticus, and the scalenus posticus muscles are all accessories to inspiration. However, instead of acting on the first rib, the scalenus posticus or the posterior scalene muscle (the longest of the scalene muscles) lifts the second rib when air is being drawn into the lungs.
Written and medically reviewed by the Healthline Editorial Team
In Depth: Scalenus medius