Development of the Ribs:
The ribs are developed from sclerotome cells in the paraxial cells. This cells growth out from the mesenchymal costal processes of the thoracic vertebrate. These ribs become cartilaginous during the embryonic period while they become ossify during the fetal period. The costal cartilages are developed by sclerotome cells that migrate across the lateral somatic frontier into the bordering lateral plate mesoderm (figure 11).
The ribs divide into three types, true, false, and floating. The true ribs are (1-7), and they attach directly to the sternum by their own cartilages while the false ribs (8-10) are attaché indirectly to the sternum by the cartilage of the rib above. The floating ribs (11-12) do not attach to the sternum.
The ribs divide into three types, true, false, and floating. The true ribs are (1-7), and they attach directly to the sternum by their own cartilages while the false ribs (8-10) are attaché indirectly to the sternum by the cartilage of the rib above. The floating ribs (11-12) do not attach to the sternum.
Development of the Sternum:
The sternum is developed independently. A pair of sternal bands is formed in the somatic layer of lateral plate mesoderm (ventrolateral). By 10 week of development, they fuse in the midline and form cartilaginous models of the manubrium, sternebrae, and xiphoid process (figure 11). Centers of ossification appear in the sternum before birth with exception of the xiphoid process which appears during childhood.