Editing Rib (section)

==Development==
Early in [[human embryogenesis|the developing embryo]], [[somite]]s form and soon subdivide into three [[mesoderm]]al components – the [[myotome]], [[Somite|dermatome]], and the [[sclerotome]]. The vertebrae and ribs develop from the sclerotomes.<ref name="Larsen">{{cite book |last1=Larsen |first1=William |title=Human embryology |date=2001 |publisher=Churchill Livingstone |isbn=0443065837 |pages=80–85 |edition=3rd}}</ref>

During the fourth week ([[Human fertilisation|fertilization age]]) ''costal processes'' have formed on the vertebral bodies. These processes are small, lateral protrusions of [[mesenchyme]] that develop in association with the vertebral arches. During the fifth week the costal processes on the thoracic vertebrae become longer to form the ribs. In the sixth week, the costovertebral joints begin to develop and separate the ribs from the vertebrae. The first seven pairs of ribs, the true ribs join at the front to the [[sternum|sternal]] bars. By the [[fetus|fetal]] stage the sternal bars have completely fused.<ref name="Larsen"/>

The ribs begin as cartilage that later [[ossification|ossifies]] – a process called [[endochondral ossification]]. Primary ossification centers are located near the angle of each rib, and ossification continues in the direction away from the head and neck. During [[adolescence]] secondary ossification centers are formed in the tubercles and heads of the ribs.<ref name="Larsen"/>