Transversus Thoracis
Thorax · Trunk
The transversus thoracis is a thin, fan-shaped muscle on the internal surface of the anterior thoracic wall, hidden behind the sternum. It arises from the posterior surface of the lower body of the sternum and the xiphoid process, and its fibres radiate upward and laterally to insert onto the internal surfaces of the costal cartilages of the second to sixth ribs. By drawing these costal cartilages downward it depresses the ribs, providing weak assistance to expiration. The muscle is continuous below with the transversus abdominis and is supplied by the intercostal nerves of the second to sixth spaces.
Origin, Insertion, Action & Nerve
Origin
Posterior surface of the lower body of the sternum and xiphoid process
Insertion
Internal surfaces of the costal cartilages of ribs 2–6
Action
Depresses the costal cartilages, weakly aiding expiration
Nerve
Intercostal nerves (T2–T6)
Attachments explained
The Transversus Thoracis 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
Posterior surface of the lower body of the sternum and xiphoid process
Insertion
Internal surfaces of the costal cartilages of ribs 2–6
Action & function
When the Transversus Thoracis contracts, it produces the following movement: Depresses the costal cartilages, weakly aiding expiration.
As part of the Thorax 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 Transversus Thoracis receives its nerve supply from the Intercostal nerves (T2–T6). This nerve carries fibres from spinal segment(s) T2, T6.
Because a muscle can only contract when its nerve is intact, injury to the Intercostal nerves or to its spinal roots (T2, T6) can weaken or paralyse the Transversus Thoracis, impairing the movements it normally produces (depresses the costal cartilages, weakly aiding expiration). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Transversus Thoracis (the OIANS method)
Picture transversus thoracis as a fan opening from the back of the sternum out to the costal cartilages, which makes its weak rib-depressing action easy to reason out from the downward and outward pull of its fibres. Because it lies deep to the sternum on the inner chest wall, it is not palpable, so its position is best learned relative to the internal thoracic vessels that descend just lateral to its attachments.
Link it vertically to transversus abdominis, with which it is continuous across the costal margin, to remember that both are quiet expiratory or wall-tensing muscles rather than prime movers. Its segmental supply from the intercostal nerves of T2 to T6 matches the ribs it attaches to, so the nerve levels can be recovered directly from the insertion.
Frequently asked questions
Where is the Transversus Thoracis located?
The Transversus Thoracis is a muscle of the Thorax group, located in the Trunk.
What is the origin of the Transversus Thoracis?
Posterior surface of the lower body of the sternum and xiphoid process
What is the insertion of the Transversus Thoracis?
Internal surfaces of the costal cartilages of ribs 2–6
What movements does the Transversus Thoracis produce?
Depresses the costal cartilages, weakly aiding expiration
What nerve supplies the Transversus Thoracis?
Intercostal nerves (T2–T6)
Is the Transversus Thoracis free to study in OIANS?
The Transversus Thoracis 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
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