Middle Scalene Muscle Beneath the Skin

Description

Running deep to the sternocleidomastoid and beneath the subcutaneous tissue, the middle scalene (scalenus medius) occupies the lateral cervical region as a thick vertical muscle belly descending from the posterior tubercles of the cervical transverse processes to the superior surface of the first rib, posterior to the subclavian groove. Anterior to it, the anterior scalene forms the other border of the interscalene interval, while the sternocleidomastoid lies more superficial and anterior, spanning from the manubrium and medial clavicle to the mastoid process. Posteriorly and laterally, fibers of trapezius and the contour of the deltoid frame the cervicothoracic junction, and the platysma may appear as a thin superficial sheet overlying the neck. Depth relationships matter here. Clinically, the middle scalene is a key landmark because the brachial plexus trunks and subclavian artery pass between the anterior and middle scalenes in the interscalene triangle, a confined space that becomes symptomatic in neurogenic thoracic outlet syndrome when scalene hypertrophy, spasm, or fibrous bands narrow the interval. Anesthetists track this anatomy for an interscalene brachial plexus block, where needle placement just lateral to the carotid sheath and posterior to the sternocleidomastoid targets the plexus at the level of C5 to C7, and unintended spread can reach the phrenic nerve along the anterior scalene. Surgeons also watch the relationship to the first rib when working near the subclavian vessels. Small errors have consequences. Neck anatomy teaching benefits from this view when you need a clear, layered explanation of why the scalenes sit deep to the sternocleidomastoid and how they relate to the first rib, clavicle, and shoulder girdle. It also fits well in anesthesia manuals, thoracic outlet syndrome patient education, and operative planning references for supraclavicular approaches. Anatomical accuracy verified by SciePro's Medical Advisory Board.