The ribcage is composed of twelve pairs of |ribs| which articulate with the |vertebrae| of the spinal column and the |sternum| (with some exceptions) to create the thoracic cavity. The |ribs| themselves are flat, curved bones, all of which articulate posteriorly with the |vertebrae| at ~costal~ ~facets~. The upper seven pairs of |ribs| also articulate anteriorly with the |sternum|, while the lower five pairs do not. The eighth, ninth, and tenth pairs are attached by |costal cartilage| to the seventh pair, while the eleventh and twelfth pairs are not attached anteriorly at all. The ribcage provides a sturdy support for the thorax, protecting the |heart|, |lungs|, and other important internal organs. The arrangement of the |ribs|, however, allows the expansion of the ribcage, as during breathing. A large number of muscles and ~ligaments~ attach to the |ribs| which, with the flexibility of the ribcage, allow the thorax to be both supple and strong.
