transversus thoracis

The tranversus thoracis lies internal to the thoracic cage, anteriorly. It is a thin plane of muscular and tendinous fibers, situated upon the inner surface of the front wall of the chest. It is in the same layer as the subcostal muscles. It arises on either side from the lower third of the posterior surface of the body of the sternum, from the posterior surface of the xiphoid process, and from the sternal ends of the costal cartilages of the lower three or four true ribs. Its fibers diverge upward and lateralward, to be inserted by slips into the lower borders and inner surfaces of the costal cartilages of the second, third, fourth, fifth, and sixth ribs. The lowest fibers of this muscle are horizontal in their direction, and are continuous with those of the Transversus abdominis; the intermediate fibers are oblique, while the highest are almost vertical. This muscle varies in its attachments, not only in different subjects, but on opposite sides of the same subject. [WP,unvetted].

Type Bone
FMA ID 9760

Frequently Asked Questions

What is the transversus thoracis muscle?
The transversus thoracis (also called the triangularis sterni or sternocostalis) is a thin, flat muscle on the inner (posterior) surface of the anterior chest wall. It lies in the same plane as the subcostal muscles and innermost intercostals.
What are the origins and insertions of the transversus thoracis?
The transversus thoracis originates from the lower third of the posterior surface of the sternum and the xiphoid process. It inserts into the inner surfaces of costal cartilages 2 through 6.
What is the function of the transversus thoracis?
The transversus thoracis assists in forced expiration by depressing the anterior ends of the ribs and costal cartilages, thereby reducing the anteroposterior diameter of the chest. It is not active during quiet breathing.
What nerve innervates the transversus thoracis?
The transversus thoracis is innervated by the anterior rami of the intercostal nerves (T2–T6), corresponding to the levels at which it inserts into the costal cartilages.
What structures are related to the transversus thoracis?
The internal thoracic (mammary) artery and vein run vertically on the inner chest wall, sandwiched between the transversus thoracis and the costal cartilages. These vessels are important in cardiac bypass surgery (LIMA graft) and must be respected during harvest.

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Educational Disclaimer

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Data sources: Terminologia Anatomica, Foundational Model of Anatomy, Wikidata.