Trapezius Middle (Transverse Part)
Back · Trunk
The transverse, or middle, part of the trapezius runs horizontally across the upper back. It arises from the spinous processes and supraspinous ligaments of C7 to T3 and passes laterally to insert onto the medial acromion and the superior crest of the spine of the scapula. Because its fibres run straight from the vertebral column to the scapula, their contraction retracts, or adducts, the scapula, pulling it toward the midline and bracing the shoulder blade against the thoracic wall. Its motor supply is the accessory nerve (CN XI), with proprioception from the anterior rami of C3-C4.
Origin, Insertion, Action & Nerve
Origin
Spinous processes and supraspinous ligaments of C7–T3
Insertion
Medial acromion and superior crest of the spine of the scapula
Action
Retracts (adducts) the scapula
Nerve
Motor: accessory nerve (CN XI); proprioception: anterior rami of C3–C4
Attachments explained
The Trapezius Middle (Transverse Part) 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
Spinous processes and supraspinous ligaments of C7–T3
Insertion
Medial acromion and superior crest of the spine of the scapula
Action & function
When the Trapezius Middle (Transverse Part) contracts, it produces the following movement: Retracts (adducts) the scapula.
As part of the Back group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Trapezius Middle (Transverse Part) receives its nerve supply from the Motor: accessory nerve (CN XI); proprioception: anterior rami of C3–C4. This nerve carries fibres from spinal segment(s) C3, C4.
Because a muscle can only contract when its nerve is intact, injury to the Motor: accessory nerve or to its spinal roots (C3, C4) can weaken or paralyse the Trapezius Middle (Transverse Part), impairing the movements it normally produces (retracts (adducts) the scapula). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Trapezius Middle (Transverse Part) (the OIANS method)
Fix the middle trapezius by the direction of its fibres: they run horizontally from the C7-T3 spines to the scapular spine and acromion, so a horizontal pull produces the obvious action, retraction of the scapula. Whenever you squeeze your shoulder blades together, this is the part doing most of the work, and that movement image makes its action unforgettable.
Keep it distinct from its neighbours by action rather than nerve: all three parts share the accessory nerve (CN XI) and C3-C4 proprioception, but only the middle fibres are pure retractors, whereas the upper part elevates and the lower part depresses. Sorting the three by their vertical position and resulting action prevents them from blurring together.
Frequently asked questions
Where is the Trapezius Middle (Transverse Part) located?
The Trapezius Middle (Transverse Part) is a muscle of the Back group, located in the Trunk.
What is the origin of the Trapezius Middle (Transverse Part)?
Spinous processes and supraspinous ligaments of C7–T3
What is the insertion of the Trapezius Middle (Transverse Part)?
Medial acromion and superior crest of the spine of the scapula
What movements does the Trapezius Middle (Transverse Part) produce?
Retracts (adducts) the scapula
What nerve supplies the Trapezius Middle (Transverse Part)?
Motor: accessory nerve (CN XI); proprioception: anterior rami of C3–C4
Is the Trapezius Middle (Transverse Part) free to study in OIANS?
The Trapezius Middle (Transverse Part) 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 Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Trapezius Middle (Transverse Part)
Test yourself on Trunk 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.