The origin of the trabeculated ventricular septum in the chick embryo as determined by radioautographic mapping



The origin of the presumptive ventricular septum (PVS) in the chick embryo was traced by radioautographic analysis of the movements of tritiated thymidine-labeled grafts excised from medium streak (MS) to three somite (3S) stage embryos and transplanted to the primitive streak and endoderm-mesoderm layer of similarly staged recipient embryos. The migration of the PVS was traced from the streak into the heart of the early limb bud (ELB) stage embryos by combining the pathways of at least three labeled grafts, since none of the 15 embryos reported here developed all the way from the MS to the ELB stage.

At the MS stage the PVS cells are in the primitive streak approximately halfway between the anterior and posterior ends of the streak. Beginning at the late medium streak (LMS) stage, they migrate into the mesoderm of the lateral plate, anterior and lateral to the streak; during the early somite stages they are folded to the midline as part of the splanchnic mesoderm, where they form part of the atrial and ventricular myocardium at the 13S stage; they move into their definitive position at the apex of the ventricle by the ELB stage.