Experimental cardiac morphogenesis. I. Development of the ventricular septum in the chick

An experimental technique utilizing microfiber markers and radioautography was used to study the morphogenesis of the ventricular septum in the ckick embryo heart from stages 22 to 33 of Hamburger & Hamilton (1951). Fibers placed in the myocardium of the primitive ventricles of 4-day-old embryos within 250 mum to each side of the future site of the ventricular septum resulted in shortening of the distance between the two fibers until both were found within the myocardium of the septum at 7 days. The fibers coated with tritiated thymidine labeled the myocytes of the trabeculae immediately adjacent to where the fibers were placed and showed that when trabeculae were labled within the 400-500 mum width centered on the ventricular septum, they aggregated together. The labeled myocytes in the trabeculae were found from the smooth crest to the most apical portion of the septum. These findings suggest that the muscular ventricular septum is formed by aggregation and coaptation of trabeculae and is of a single developmental origin.