<prompt> True about umbilical cord ?Cantains two umbilical veinsCantains one umbilical aeryRight umbilical vein disappearsLength is 25-30 cm.  <response>: Umbilical cordUmbilical cord develops from connecting stalk, which extends from the caudal end of the embryo to the chorion.Umbilical cord is covered by amniotic epithelium and contains a core of mesenchyme known as whaans jelly.Contents of umbilical cord are : i Whaons jelly, ii Two umbilical aeries, iii One left umbilical vein, ivRemnant of yolk sac, and v Remnant of allanto-enteric diveiculum.Initially 2 umbilical aeries and 2 umbilical veins develop in mesoderm, but right umbilical vein disappears. Left umbilical vein persists along with 2 umbilical aeries.At full term, the umbilical cord measures 1-2cm in diameter, and 50-55cm in length and generally attached to the center of fetal surface of placenta. 