|Human rib cage|
|The human rib cage. (Source: Gray's Anatomy of the Human Body, 20th ed. 1918.)|
The human rib cage, also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic (chest) cavity and supports the pectoral (shoulder) girdle, forming a core portion of the human skeleton. A typical human rib cage consists of 24 ribs, the sternum, costal cartilages, and the 12 thoracic vertebrae. It, along with the skin and associated fascia and muscles, make up the thoracic wall, and provides attachments for the muscles of the neck, thorax, upper abdomen, and back.
The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while contraction of intercostal muscles lift the rib cage up and out. These actions produce an increase in volume, and a resulting partial vacuum, or negative pressure, in the thoracic cavity, resulting in atmospheric pressure pushing air into the lungs, inflating them. An exhalation results when the diaphragm and intercostal muscles relax, and elastic recoil of the rib cage and lungs expels the air.
All ribs are attached in the back to the thoracic vertebrae.
The upper seven true ribs (costae verae, vertebrosternal ribs, I-VII). are attached in the front to the sternum by means of costal cartilage. Due to their elasticity they allow movement when inhaling and exhaling.
The 8th, 9th, and 10th ribs are called false ribs (costae spuriae, vertebrochondral ribs, VIII-X), and join with the costal cartilages of the ribs above.
The 11th and 12th ribs are known as floating ribs (costae fluitantes, vertebral ribs, XI-XII), as they do not have any anterior connection to the sternum.
The human rib parts:
The atypical ribs are the 1st, 2nd, and 11th to 12th.
The number of ribs was noted by the Flemish anatomist Vesalius in his key work of anatomy De humani corporis fabrica in 1543, setting off a wave of controversy, as it was traditionally assumed from the Biblical story of Adam and Eve that men's ribs would number one fewer than women's. A small portion of people have one extra pair of ribs, or one fewer, but this is unrelated to gender.
Abnormalities of the rib cage include pectus excavatum ("sunken chest") and pectus carinatum ("pigeon chest"). Bifid or bifurcated ribs, in which the sternal end of the rib is cleaved in two, is a congenital abnormality occurring in about 1.2% of the population. The rib remnant of the 7th cervical vertebra on one or both sides is occasionally replaced by a free extra rib called a cervical rib, which can cause problems in the nerves going to the arm.
Rib removal is the surgical excision of ribs for therapeutic or cosmetic reasons.
The content of this section is licensed under the GNU Free Documentation License (local copy). It uses material from the Wikipedia article "Human rib cage" modified November 23, 2008 with previous authors listed in its history.