Middle Scalene, Gross Anatomy

Description

Running deep in the lateral neck, the middle scalene (musculus scalenus medius) is shown arising from the posterior tubercles of the transverse processes of the mid cervical vertebrae (classically C2 to C7) and descending inferolaterally to its costal attachment on the superior surface of the first rib, posterior to the scalene tubercle. Anteriorly it lies behind the sternocleidomastoid and adjacent to the anterior scalene, while posteriorly it approaches the levator scapulae and the prevertebral fascia. Between the anterior and middle scalenes, the interscalene interval is implied, the corridor that transmits the roots and trunks of the brachial plexus and the subclavian artery as they pass toward the axilla. Small, but decisive. Clinically, the middle scalene matters because its bulk and tone define the posterior boundary of the scalene triangle, a common site of neurogenic thoracic outlet syndrome where brachial plexus elements are irritated by fibrous bands, hypertrophy, or postural narrowing. The costal insertion on rib 1 anchors this muscle as an accessory inspiratory elevator of the thoracic inlet, so spasm after whiplash or overuse can produce lateral neck pain that radiates into the shoulder girdle. Anesthesiologists also track this anatomy during interscalene brachial plexus block, where needle placement between anterior and middle scalenes must respect nearby vascular structures and the pleural dome at the thoracic inlet. Facial musculature, sternocleidomastoid contours, and the upper thorax with pectoralis major and adjacent mammary gland lobules place the scalene in a realistic female surface anatomy context for teaching and publishing. Suitable for head and neck anatomy courses, thoracic outlet syndrome lectures, anesthesia training materials, and operative atlases discussing supraclavicular approaches and neurovascular relationships. Anatomical accuracy verified by SciePro's Medical Advisory Board.