abnormal visceral yolk sac morphology MP:0001718 MPheno.ontology abnormal secondary yolk sac morphology abnormal umbilical vesicle morphology abnormal vitelline sac morphology abnormal yolk sac morphology any structural anomaly of the extraembryonic tissue membrane, formed from the visceral endoderm and the extraembryonic mesoderm, which is located ventral to the embryonic disc and is connected to the presumptive midgut of the embryo; the yolk that it contains is the site of embryonic hematopoiesis and vitelline circulation is involved in early embryonic circulation; it is the origin of the primordial germ cells abnormal extraembryonic tissue morphology