Development of ribs and intercostal muscles in the chicken embryo.

In the thorax of higher vertebrates, ribs and intercostal muscles play a decisive role in stability and respiratory movements of the body wall. They are derivatives of the somites, the ribs originating in the sclerotome and the intercostal muscles originating in the myotome. During thorax development, ribs and intercostal muscles extend into the lateral plate mesoderm and eventually contact the sternum during ventral closure.