The umbilical cord runs between the placenta and the abdomen of the developing fetus. It is the organ which supplies the fetus with all of its nourishment and oxygen. Although formed from an egg, human embryos do not depend on egg yolk for nourishment. The human egg does include an egg sac, but it degenerates early in pregnancy. Instead, the embryo forms a connection to the cells that will become themycontentbreak placenta through a body stalk, which later becomes the umbilical cord.