Final answer:
The ribs are formed from the mesoderm, which is responsible for developing various connective tissues including the ribs, through a process known as endochondral ossification.
Step-by-step explanation:
The ribs form from the mesoderm. The mesoderm is one of the three germ layers that emerge during embryonic development. This particular layer is responsible for the development of various connective tissues within the body, including structures like the ribs, lungs, and segmental muscles. The process by which the ribs and sternum form is known as endochondral ossification. During this process, mesenchymal cells accumulate around the notochord to produce hyaline cartilage models of the vertebrae and, in the thorax region, a portion of the vertebral cartilage model splits off to form the ribs.
The ribs then become attached to the developing cartilage model of the sternum, eventually undergoing ossification and converting into bone.The ribs form from the mesoderm, which develops into various connective tissues such as the ribs, lungs, segmental muscle, and the notochord. The mesoderm is located at the border of the neural plate and the non-neural ectoderm. It is reorganized into groups of cells called somites, which further develop into the ribs, lungs, and segmental muscle.