Fig. 9. MyoD expression in the developing somites of a 15-somite embryo. Expression can be seen the posteriormost seven somites, and in a single band in the presomitic mesoderm at the site of imminent somite formation. The anteriormost somites are by this time unstained for MyoD. Arrowhead, most recent somite furrow. nm, notochord/mesoderm boundary; Ad, unstained adaxial cells. Scale bar, 100 µm.