[1] Initially it lies caudally to the trilaminar germ disc, but, with subsequent embryonic folding, the body stalk assume a more ventral position.

[2] Progressive expansion of the amnion from the umbilical ring (surrounding the roots of the vitelline duct and connecting stalk) creates a tube with a covering of amniotic membrane with allantois and umbilical vessels as its content and mesoderm of the connecting stalk as the ground substance.

[2] The amniotic membrane and its contents form the umbilical cord that connects the embryo and the placenta.

[3][4] The root of the connecting stalk contains the allantois as a diverticulum of hindgut endoderm along with umbilical vessels.

[6] They are due to defects in the formation of the cephalic, caudal, and lateral embryonic body folds,[7] that result in a reduced or absent umbilical cord.