One of the most important needs of any embryo throughout the pregnancy is regular supply of nutrition and blood without which the fetus cannot grow. This blood is initially transported to the sac wall by primitive aortae and after travelling through wide-meshed capillary plexus, it returns back via vitelline veins into the embryo’s tubular heart. This is called as the vitelline circulation and during this process, nutrition from the yolk sac is sent to the embryo.