A patent opening called the primitive umbilical ring exists on the ventral surface of the developing embryo through which three structures pass: the yolk sac (vitelline duct), connecting stalk, and allantois. The allantois is not functional in humans and degenerates to form the median umbilical ligament in the adult. As the amnion expands, it pushes the vitelline duct, connecting stalk, and allantois together to form the primitive umbilical cord. The definitive umbilical cord at term is pearl-white, 1–2 cm in diameter, 50–60 cm long, eccentrically positioned, and contains the right and left umbilical arteries, left umbilical vein, and mucus connective tissue (Wharton’s jelly). The right and left umbilical arteries carry deoxygenated blood from the fetus to the placenta. The left umbilical vein carries oxygenated blood from the placenta to the fetus. Key Concept: Umblical cord contains the right and left umbilical arteries, left umbilical vein, and mucus connective tissue (Wharton’s jelly).
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