Description
The thoracic cage (rib cage) is the osteocartilaginous structure found in the thoracic region of the axial skeleton. It provides the framework for the thoracic wall and protection to organs of the thoracic and upper abdominal regions.
The thoracic cage is birdcage-like in appearance and consists of twelve pairs of ribs and the sternum. The first to tenth ribs being connected to the sternum via costal cartilages. The thoracic cage is widest, transversely, at the level of the eighth or ninth ribs.
To allow for communication between the thorax and the body regions situated superior and inferior to it, the thoracic cage has superiorly and inferiorly located openings. The superior opening is the superior thoracic aperture (anatomical thoracic inlet). It is kidney-shaped, smaller than the inferior thoracic aperture, and its outline is defined:
- posteromedially, by the anterior aspect of the vertebral body of first thoracic vertebra;
- laterally, by the internal borders of both the right and left first ribs and their corresponding costal cartilages;
- anteromedially, by the superior border of the manubrium of sternum.
The inferior opening of the thorax is the inferior thoracic aperture (anatomical thoracic outlet). It is larger than the superior thoracic aperture, and its outline is defined:
- posteromedially, by the anterior aspect of the vertebral body of twelfth thoracic vertebra;
- posterolaterally, by the inferior borders of both the right and left twelfth ribs;
- laterally, by the costal cartilages of both the right and left eleventh ribs and the anterior end of the right and left tenth ribs;
- anterolaterally, by both the right and left costal margins;
- anteromedially, by the xiphisternal joint.
These structures not only outline the inferior thoracic aperture, but also provide attachment sites for the diaphragm.
Variations
The bones of the thorax also display sexual dimorphism. The thoracic inlet is more oblique in females. Additionally, the sternum is longer in males and its suprasternal notch is located at the level of the second thoracic vertebra. The suprasternal notch in females is at the level of the third thoracic vertebra. Thoracic capacity is also greater in males than females (Standring, 2020).
References
Standring, S. (2020) Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd edn.: Elsevier Health Sciences.
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Chest
The thorax is the upper part of the trunk between the neck and the abdomen, containing the chief organs of the circulatory and respiratory systems, such as the lungs and heart.
