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Transversus thoracis muscle

Transversus thoracis muscle (Musculus transversus thoracis)
Transversus thoracis muscle (Musculus transversus thoracis)

Transversus thoracis (triangularis sternae, sternocostalis) is a muscle found on the inner surface of the anterior chest wall. It belongs to the intrinsic muscles of the chest wall, along with the intercostals, subcostal, levatores costarum and serratus posterior muscles. Transversus thoracis is organized into several slips that radiate from the body and xiphoid process of sternum towards the costal cartilages of ribs 2-6.

Just like all the intrinsic chest muscles (except for levatores costarum), transversus thoracis is innervated by the adjacent intercostal nerves. Like all these muscles, transversus thoracis helps to move the ribs during forced breathing and support the thoracic cage during the breathing process.

This article will discuss the anatomy and function of the transversus thoracis muscle.

Key facts about the transversus thoracis muscle
Origin Inferoposterior surface of body of sternum and xiphoid process; sternal ends of costal cartilages of ribs 4-7
Insertion Internal surface of costal cartilages of ribs 2-6
Action Depresses ribs during forced expiration; Supports intercostal spaces and thoracic cage
Innervation Intercostal nerves
Blood supply Sternal branches of internal thoracic artery
  1. Origin and insertion
  2. Relations
  3. Innervation
  4. Blood supply
  5. Functions
  6. Clinical notes
  7. Sources
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Origin and insertion

The transversus thoracis muscle originates from three points; inferior third of the posterior surface of the body of sternum, posterior surface of the xiphoid process and sternal ends of the costal cartilages of ribs 4-7. Its fibers diverge and course superolaterally, forming 4-5 slips on each side of the sternum. The muscle slips serially insert into the inner surfaces of the costal cartilages of ribs 2-6, respectively.

The inferiormost fibers of transversus thoracis lie in the horizontal plane and are continuous with the transversus abdominis muscle. The intermediate fibers run obliquely in a superolateral direction, whilst the superiormost fibers lie nearly vertically.

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Transversus thoracis lies deep to the central part of the thoracic cage, forming the anterior wall of the anterior mediastinum. It separates the pleura from the intercostal nerves. The upper border of transversus abdominis is in direct contact with the inferior border of transversus thoracis. The superior epigastric artery and vein pass anterior to both muscles.


Transversus thoracis is innervated by the second to fifth thoracic intercostal nerves. These nerves are the anterior rami of spinal nerves T2-T6.

Blood supply

The blood supply to transversus thoracis comes from the sternal branches of internal thoracic artery, a branch of the subclavian artery.


Transversus thoracis is an accessory respiratory muscle that is active during forced expiration. It pulls ribs 2-6 towards the sternum during forced expiration, which results in depression of those ribs. This action consequently decreases the anteroposterior diameter of the thoracic cavity.

Besides this, transversus thoracis stiffens the thoracic wall during inspiration, thus preventing paradoxical movements of the chest wall.

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