Scalenus Medius
Neck · Head & Neck
The scalenus medius is the largest and longest of the three scalene muscles, lying on the lateral neck behind the scalenus anterior. It arises from the transverse processes of the C2 to C7 vertebrae and descends to insert on the superior surface of the first rib, posterior to the groove for the subclavian artery. Like the other scalenes, it elevates the first rib to aid inspiration and laterally flexes the neck. It is supplied by the anterior rami of the cervical nerves (C3 to C8). Together with the scalenus anterior it forms the boundaries of the interscalene space through which the brachial plexus and subclavian artery pass.
Origin, Insertion, Action & Nerve
Origin
Transverse processes of C2–C7
Insertion
Superior surface of 1st rib, posterior to subclavian groove
Action
Elevates 1st rib in inspiration; laterally flexes neck
Nerve
Anterior rami of cervical nerves (C3–C8)
Attachments explained
The Scalenus Medius is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Transverse processes of C2–C7
Insertion
Superior surface of 1st rib, posterior to subclavian groove
Action & function
When the Scalenus Medius contracts, it produces the following movements: Elevates 1st rib in inspiration; laterally flexes neck.
As part of the Neck group of the Head & Neck, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Scalenus Medius receives its nerve supply from the Anterior rami of cervical nerves (C3–C8). This nerve carries fibres from spinal segment(s) C3, C8.
Because a muscle can only contract when its nerve is intact, injury to the Anterior rami of cervical nerves or to its spinal roots (C3, C8) can weaken or paralyse the Scalenus Medius, impairing the movements it normally produces (elevates 1st rib in inspiration). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Scalenus Medius (the OIANS method)
Locate the scalenus medius as the broad muscle just behind the anterior scalene, and let the gap between them define the interscalene triangle through which the brachial plexus and subclavian artery travel. Remembering that its first-rib attachment lies behind the subclavian groove, in contrast to the anterior scalene in front, cements the relationship of the great vessels to the scalene muscles.
For its function, note that its wide origin from nearly all the cervical transverse processes gives it the same dual role as its neighbours: elevating the first rib in inspiration and laterally flexing the neck. Keep it in the scalene trio supplied by anterior cervical rami, distinguishing it from the posterior scalene, which reaches the second rib rather than the first.
Frequently asked questions
Where is the Scalenus Medius located?
The Scalenus Medius is a muscle of the Neck group, located in the Head & Neck.
What is the origin of the Scalenus Medius?
Transverse processes of C2–C7
What is the insertion of the Scalenus Medius?
Superior surface of 1st rib, posterior to subclavian groove
What movements does the Scalenus Medius produce?
Elevates 1st rib in inspiration; laterally flexes neck
What nerve supplies the Scalenus Medius?
Anterior rami of cervical nerves (C3–C8)
Is the Scalenus Medius free to study in OIANS?
The Scalenus Medius is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Head & Neck is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Scalenus Medius
Test yourself on Head & Neck muscles with interactive quizzes and flashcards in the free OIANS app.
Quiz yourself → Flashcards Open the OIANS app
Browsing is always free. A one-time Lifetime unlock adds every region's quizzes, flashcards, progress tracking and explore tools.