Middle Scalene, Lateral View

Description

Running along the lateral cervical spine, the left middle scalene (scalenus medius) is shown as a long, vertically oriented muscle belly descending from the posterior tubercles of the transverse processes of C2 to C7 to its insertion on the superior surface of the first rib, posterior to the subclavian groove. Anterior to it sits the anterior scalene, separated by the interscalene interval, while posteriorly the muscle borders the posterior cervical triangle deep to the superficial fascia. Superiorly, the muscle lies deep to the sternocleidomastoid region and adjacent to the mandibular angle and auricle in profile; inferiorly it approaches the clavicle, first rib, and the apex of the lung. Lateral exposure of scalenus medius matters because this is the dominant posterior boundary of the interscalene triangle, the passage for the roots and trunks of the brachial plexus and the subclavian artery as they course toward the axilla. This is the anatomy behind thoracic outlet syndrome, where hypertrophy, spasm, fibrous bands, or a cervical rib can narrow that corridor and provoke neurogenic symptoms in the ulnar distribution or vascular changes with arm elevation. It also frames regional anesthesia: during an interscalene brachial plexus block, the plexus is targeted in the groove between the anterior and middle scalenes, while the phrenic nerve typically runs on the anterior surface of the anterior scalene and can be inadvertently affected. A tight space. Common use cases include illustrating scalene attachments and neck compartments in gross anatomy and head and neck courses, clarifying needle trajectory and risk structures for anesthesiology teaching files, and supporting surgical or rehabilitation publications on thoracic outlet decompression and scalene myofascial pain. Anatomical accuracy verified by SciePro's Medical Advisory Board.