#vena_cava  either of two large veins that return oxygen-depleted blood to the right atrium of the heart
  supertype:  #vein__vena  a blood vessel that carries blood from the capillaries toward the heart; all veins except the pulmonary carry unaerated blood
  subtype:  #inferior_vena_cava__postcava  receives blood from lower limbs and abdominal organs and empties into the posterior part of the right atrium of the heart; formed from the union of the two iliac veins
  subtype:  #superior_vena_cava__precava  receives blood from the head and arms and chest and empties into the right atrium of the heart; formed from the azygos and both brachiocephalic veins

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