542 ANGIOLOGY 





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 estab- 

 lished, an increased amount of blood from the pulmonary artery passes through the 

 lungs, and the placental circulation is cut oft'. 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 estab- 

 lished, 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 Aortae, 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 Menschlicheii 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. 



