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Thoracic cage Anatomy
Thoracic cage Anatomy
The thoracic cage is an osseocartilaginous structure made up of 12 pairs of ribs, their costal cartilages, and the sternum. The ribs are attached posteriorly to the 12 thoracic vertebrae (T1–T12). This structure protects the heart and lungs. The thoracic cage is conical in shape, narrow at the top and wider at the bottom, flattened from front to back, and longer posteriorly than anteriorly.
Ribs
The ribs are curved, flattened bones that form most of the thoracic cage. There are 12 pairs, numbered according to the thoracic vertebrae they attach to. Each rib connects posteriorly to the vertebrae and usually connects anteriorly to the sternum through costal cartilage.
Rib length increases from the first to the seventh and then decreases toward the twelfth.
Ribs are classified based on how they connect to the sternum.
Ribs 1-7 are called true ribs because their costal cartilages attach directly to the sternum.
Ribs 8-12 are called false ribs because they do not attach directly.
Ribs 8-10 connect indirectly by attaching to the cartilage of the rib above.
Ribs 11 and 12 are called floating ribs because they do not connect to the sternum at all and instead end in the muscles of the abdominal wall.
A typical rib has a posterior end, an anterior end, and a shaft (body). The posterior end includes the head, neck, and tubercle.
The head articulates with the bodies of two adjacent vertebrae. The neck is a narrowed region next to the head. The tubercle is a small projection that connects with the transverse process of the corresponding vertebra.
The shaft, or body, is thin and curved. The point of greatest curvature is called the angle of the rib, which forms the most posterior part of the rib cage. Along the lower edge of the rib is a costal groove, which allows passage for blood vessels and a nerve.
The ribs vary in direction and shape. The upper ribs are less slanted, while the lower ribs are more oblique, with the greatest angle around the ninth rib.
Sternum
The sternum is a long, flat bone that forms the central part of the front of the chest. It consists of three parts: the manubrium, the body, and the xiphoid process.
The manubrium is the upper and wider part. At its top is a shallow, U-shaped depression called the jugular (suprasternal) notch, which can be felt at the base of the neck. On either side are clavicular notches, where the clavicles attach to form the sternoclavicular joints. The first ribs also attach to the manubrium.
The body is the long, central portion of the sternum. It joins the manubrium at the sternal angle, which forms a slight bend. The second rib attaches at this level, making it an important landmark for counting ribs, since the first rib is not easily felt. Ribs 3 to 7 attach along the body. The body shows transverse ridges that mark its developmental segments and provides attachment for muscles.
The xiphoid process is the small, lower part of the sternum. It is made of cartilage early in life and becomes partly ossified in adulthood. It varies in shape and provides attachment for ligaments, abdominal muscles, and part of the diaphragm.
Cartilage
Each rib ends anteriorly in a costal cartilage made of hyaline cartilage. These cartilages extend the ribs forward and add flexibility to the thoracic cage. The first seven connect directly to the sternum, ribs 8-10 connect to the cartilage above, and ribs 11-12 have free ends.
The cartilages vary in length, increasing from the first to the seventh and then decreasing. They are broader where they attach to the ribs and become narrower toward the front. They also differ in direction, with some descending, some horizontal, and others ascending toward the sternum.
Special Ribs
Some ribs have unique features. The first rib is the shortest, most curved, and flattened from above downward. It has grooves for blood vessels and a tubercle for muscle attachment. The second rib is longer and has a rough area for muscle attachment. The tenth rib has a single articular facet on its head. The eleventh and twelfth ribs are short, lack necks and tubercles, and have free anterior ends.
Need a recap? Take a look at the thoracic cage anatomy notes here.
Need a recap? Take a look at the thoracic cage anatomy notes here.
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References
References
Gray, H. (1918). Anatomy of the human body (W. H. Lewis, Ed.; 20th ed.). Lea & Febiger.
J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix. (2013, April 25). Anatomy and Physiology. OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/7-4-the-thoracic-cage.
Based on OpenStax, Anatomy and Physiology (2013), licensed under CC BY 4.0.
Access for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction.
Content paraphrased; adaptations were made.
Sobotta, J. (1914). Atlas and text-book of human anatomy (J. P. McMurrich, Ed.; W. H. Thomas, Trans.). W.B. Saunders Company.
Image Credis
Image Credis
Images used in this guide and games are from the following source:
Sobotta, J. (1914). Atlas and text-book of human anatomy (J. P. McMurrich, Ed.; W. H. Thomas, Trans.). W.B. Saunders Company.
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