Transversus thoracis muscle

At a glance

English

Transversus thoracis muscle

Latin (TA2)

Musculus transversus thoracis

System

Muscle

Region

Trunk

Side

Paired, left and right

Arises from

The xiphoid process

About the transversus thoracis muscle

Transversus thoracis, also called sternocostalis or triangularis sterni, lines the thorax from inside, behind its front wall. It lies behind the sternum and costal cartilages, in the deepest layer of the chest wall together with the innermost intercostals and the subcostal muscles. It is usually a delicate, partly tendinous sheet, though in some people it is quite substantial, and it varies widely between people and even between the two sides.

It arises from the back of the lower third of the sternal body, from the xiphoid process behind, and from the lower true ribs' cartilages where they meet the sternum. From this base its slips fan upward and outward to the inner surfaces and lower borders of the cartilages of the second to sixth ribs. The lowest slips run almost horizontally and are continuous with the upper fibres of transversus abdominis, so the two muscles form a continuous inner layer of the trunk wall. The middle slips are oblique and the highest almost vertical. The internal thoracic artery and vein run down between the muscle and the costal cartilages in front of it, while the pleura and the endothoracic fascia lie behind.

By pulling the costal cartilages down towards the sternum, transversus thoracis lowers the ribs and narrows the chest, assisting forced breathing out, for example during speech, coughing or hard exercise. In quiet breathing its role is very small.

Its nerve supply comes from the intercostal nerves of the second to sixth spaces, and it receives blood from the internal thoracic artery and its anterior intercostal branches. Its close relationship with the internal thoracic vessels matters in heart surgery, where these vessels are often harvested as bypass grafts and the muscle is part of the tissue lifted with them.

Attachments, action and supply

Origin

Posterior surface of the lower sternal body, the xiphoid process and the sternal ends of the lower true ribs' cartilages.

Insertion

Inner surfaces and lower borders of the second to sixth costal cartilages.

Action

Depresses the costal cartilages and ribs, assisting forced expiration.

Nerve supply

Intercostal nerves (T2-T6).

Blood supply

Internal thoracic artery and its anterior intercostal branches.