The chest has two main types of bones: the sternum and the ribs. A large amount of cartilage connects ribs to one another as well as to the sternum. The collar bones (although more properly located in the shoulders) and the spine (behind the chest cavity) are directly connected to the bones of the chest.
Sternal Bones
The sternum is a large, flat bone in the center of the chest directly over the heart and mediastinum (middle chest). It is composed of three parts: the manubrium, the body of the sternum (the gladiolus) and the xyphoid process. The three portions of the sternum are joined by fibrous joints and have little movement, though they do move with the breath. The manubrium forms a joint with the clavicles (collar bones) and the cartilages of the first two ribs. The body of the sternum articulates with the costal cartilages (cartilages of the ribs) of the second through seventh ribs. The xyphoid process is a small, tail-like bone that forms at the lower end of the sternum and articulates with the costal cartilage of the seventh rib.
Ribs
The ribs form a cage around the chest cavity or thoracic cavity. The first seven ribs are known as "true ribs" because they have their own individual connections to the sternum (see Section 3). The eighth through 10th ribs are known as "false ribs" because they connect to the sternum through the costal cartilages of other ribs. The final two ribs are known as floating ribs because they do not connect to the sternum at all.
Some natural variation exists among bodies and, although rare, some people have extra ribs at either the upper or lower end of the rib cage (cervical ribs are an example). Some people's lower ribs can also vary in how they connect to the sternum. This variation is considered normal physiologically and doesn't compromise a person's health.
Costal Cartilage
The cartilages of the ribs (the costal cartilage) connects these bones to the sternum. The first five ribs have short cartilages that connect directly to the sternum. The next two ribs form more complex cartilages that connect the ribs to the sternum and to the eighth through 10th ribs. The remaining two ribs, as mentioned previously, are usually not connected to the sternum.
Again, variation can occur. The fifth rib can have cartilaginous connection to other ribs; the 10th rib may be floating; and the 11th rib may be attached. This does not normally affect a person's health, but it can be of consequence during emergency or surgical situations.
The costal cartilages are prone to inflammation because they are partially flexible and can be damaged during trauma to the chest that does not cause broken ribs. This situation, along with other conditions, will often lead to an inflammation of the costal cartilage called costochondritis. Costochondritis is a painful condition with symptoms mimicking a broken rib, damage to the lungs or even a heart attack. A doctor should be consulted whenever chest pain occurs to ensure nothing major is happening.
References
- "Gray's Anatomy: The Anatomical Basis of Clinical Practice"; Susan Standring, 2008
- "Trail Guide to the Body: How to Locate Muscles, Bones and More"; Andrew Biel, 2005
