Transversus thoracis muscle
Encyclopedia
The transversus 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 and the innermost intercostal 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.
The muscle is supplied by the anterior rami of the Thoracic spinal nerves (intercostal nerves).
.
Contraction of this muscle aids in exertional expiration by decreasing the transverse diameter of the thoracic cage.
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
Xiphoid process
The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process of the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major...
, and from the sternal ends of the costal cartilages
Costal cartilages
The costal cartilages are bars of hyaline cartilage which serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the thorax.-Differences from 1-12:...
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
Intermediate fibers
Intermediate fibers, also known as fast oxidative-glycolytic fibers, are fast twitch muscle fibers which have been converted via endurance training. These fibers are slightly larger in diameter, have more mitochondria as well as a greater blood supply and more endurance than typical fast twitch...
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.
The muscle is supplied by the anterior rami of the Thoracic spinal nerves (intercostal nerves).
Function
It is almost completely without function, but it separates the thoracic cage from the parietal pleuraParietal pleura
The portion of the pleura external to the pulmonary pleura lines the inner surface of the chest wall, covers the diaphragm, and is reflected over the structures occupying the middle of the thorax; this portion is termed the parietal pleura....
.
Contraction of this muscle aids in exertional expiration by decreasing the transverse diameter of the thoracic cage.