The umbilical cord is formed from the extraembryonic or fetal membranes of the embryo during the fifth week of development. It contains two arteries and one vein. The arteries carry carbon dioxide and nitrogen wastes from the embryo to the placenta, and the vein carries oxygen and nutrients from the placenta to the embryo. The umbilical cord is usually 0.4 to 0.8 inches in diameter (1 to 2 centimeters) and 19 to 22 inches long (50 to 55 centimeters).