Thorax or chest is an irregularly shaped cylinder with a narrow opening (superior thoracic aperture) superiorly and a relatively large opening (inferior thoracic aperture) inferiorly.
The superior thoracic aperture is open, allowing continuity with the neck; the inferior thoracic aperture is closed by the diaphragm.
The thoracic wall consists of follwing skeletal elements and muscles (See Figure):
- posteriorly, it is made up of twelve thoracic vertebrae and their intervening intervertebral discs;
- laterally, the wall is formed by ribs (twelve on each side) and three layers of flat muscles, which span the intercostal spaces between adjacent ribs, move the ribs and provide support for the intercostal spaces;
- anteriorly, the wall is made up of the sternum, which consists of the manubrium of sternum, body of sternum, and xiphoid process.