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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
vena cava being guided by the valve of this vessel into the left atrium, while that in the superior vena cava descends into the right ventricle. At an early period of fetal life it is highly probable that the two streams are quite distinct; for the inferior vena cava opens almost directly into the left atrium, and the valve of the inferior vena cava would exclude the current from the right ventricle. At a later period, as the separation between the two atria becomes more distinct, it seems probable that some mixture of the two streams must take place. (4) The pure blood carried from the placenta to the fetus by the umbilical vein, mixed with the blood from the portal vein and inferior vena cava, passes almost directly to the arch of the aorta, and is distributed by the branches of that vessel to the head and upper extremities. (5) The blood contained in the descending aorta, chiefly derived from that which has already circulated through the head and limbs, together with a small quantity from the left ventricle, is distributed to the abdomen and lower extremities.

Changes in the Vascular System at Birth.—At birth, when respiration is established, an increased amount of blood from the pulmonary artery passes through the lungs, and the placental circulation is cut off. The foramen ovale is closed by about the tenth day after birth: the valvular fold above mentioned adheres to the margin of the foramen for the greater part of its circumference, but a slit-like opening is left between the two atria above, and this sometimes persists.
  The ductus arteriosus begins to contract immediately after respiration is established, and is completely closed from the fourth to the tenth day; it ultimately degenerates into an impervious cord, the ligamentum arteriosum, which connects the left pulmonary artery to the arch of the aorta.
  Of the hypogastric arteries, the parts extending from the sides of the bladder to the umbilicus become obliterated between the second and fifth days after birth, and project as fibrous cords, the lateral umbilical ligaments, toward the abdominal cavity, carrying on them folds of peritoneum.
  The umbilical vein and ductus venosus are completely obliterated between the second and fifth days after birth; the former becomes the ligamentum teres, the latter the ligamentum venosum, of the liver.
 
Bibliography
 
  BREMER, J. L.: The Earliest Bloodvessels in Man, Am. Jour. Anat., 1914, xvi.
  EVANS, H. M.: On the Development of the Aortæ, Cardinal and Umbilical Veins and Other Bloodvessels of the Vertebrate Embryos from Capillaries, Anat. Rec., 1909, iii.
  EVANS, H. M.: The Development of the Vascular System, Keibel and Mall, Manual of Human Embryology.
  HIS, W.: Anatomie Menschlichen Embryonen, Leipzig, 1880–85.
  MACCALLUM, J. B.: On the Muscular Architecture and Growth of the Ventricles of the Heart, Johns Hop. Hosp. Rep., 1900, ix.
  MALL, F. P.: A Study of the Structural Unit of the Liver, Am. Jour. Anat., 1906, v.
  MALL, F. P.: On the Muscular Architecture of the Ventricles of the Human Heart, Am. Jour. Anat., 1911, xi.
  MALL, F. P.: The Development of the Internal Mammary and Deep Epigastric Arteries in Man, Johns Hop. Hosp. Bulletin, 1898.
  STOCKARD, C. R.: A Study of Wandering Mesenchymal Cells on the Living Yolk Sac and Their Developmental Products: Chromatophores, Vascular Endothelium and Blood Cells, Am. Jour. Anat., 1915, xviii.
  STREETER, G. L.: The Development of the Venous Sinuses of the Dura Mater in the Human Embryo, Am. Jour. Anat., 1915, xviii.
  THOMA, R.: Text-book of General Pathology and Pathological Anatomy, Translated by Bruce, London, 1896.

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