ANGIOLOGY 



septum in which the foramen ovale is situated; shortly after birth it fuses with 

 the primary septum and the foramen ovale is obliterated. 



The valve of the inferior vena cava serves to direct the blood from that vessel 

 through the foramen ovale into the left atrium. 



The peculiarities in the arterial system of the fetus are the communication 

 between the pulmonary artery and the aorta by means of the ductus arteriosus, 

 and the continuation of the hypogastric arteries as the umbilical arteries to the 

 placenta. 



The ductus arteriosus is a short tube, about 1.25 cm. in length at birth, and 

 of the diameter of a goose-quill. In the early condition it forms the continuation 

 of the pulmonary artery, and opens into the aorta, just beyond the origin of the 

 left subclavian artery; and so conducts the greater amount of the blood from the 

 right ventricle into the aorta. When the branches of the pulmonary artery have 

 become larger relatively to the ductus arteriosus, the latter is chiefly connected 

 to the left pulmonary artery. 



The hypogastric arteries run along the sides of the bladder and thence upward 

 on the back of the anterior abdominal wall to the umbilicus; here they pass out 

 of the abdomen and are continued as the umbilical arteries in the umbilical cord 

 to the placenta. They convey the fetal blood to the placenta. 



The peculiarities in the venous system of the fetus are the communications 

 established between the placenta and the liver and portal vein, through the umbil- 

 ical vein ; and between the umbilical vein and the inferior vena cava through the 

 ductus venosus. 



Fetal Circulation (Fig. 502). The fetal blood is returned from the placenta to 

 the fetus by the umbilical vein. This vein enters the abdomen at the umbilicus, 

 and passes upward along the free margin of the falciform ligament of the liver to 

 the under surface of that organ, where it gives off two or three branches, one of 

 large size to the left lobe, and others to the lobus quadratus and lobus caudatus. 

 At the porta hepatis (transverse fissure of the liver) it divides into two branches : 

 of these, the larger is joined by the portal vein, and enters the right lobe; the 

 smaller is continued upward, under the name of the ductus venosus, and joins 

 the inferior vena cava. The blood, therefore, which traverses the umbilical vein, 

 passes to the inferior vena cava in three different ways. A considerable quantity 

 circulates through the liver with the portal venous blood, before entering the 

 inferior vena cava by the hepatic veins; some enters the liver directly, and is 

 carried to the inferior cava by the hepatic veins; the remainder passes directly 

 into the inferior vena cava through the ductus venosus. 



In the inferior vena cava, the blood carried by the ductus venosus and hepatic 

 veins becomes mixed with that returning from the lower extremities and abdominal 

 wall. It enters the right atrium, and, guided by the valve of the inferior vena 

 cava, passes through the foramen ovale into the left atrium, where it mixes with 

 a small quantity of blood returned from the lungs by the pulmonary veins. From 

 the left atrium it passes into the left ventricle; and from the left ventricle into the 

 aorta, by means of which it is distributed almost entirely to the head and upper 

 extremities, a small quantity being probably carried into the descending aorta. 

 From the head and upper extremities the blood is returned by the superior vena 

 cava to the right atrium, where it mixes with a small portion of the blood from the 

 inferior vena cava. From the right atrium it descends into the right ventricle, 

 and thence passes into the pulmonary artery. The lungs of the fetus being inactive, 

 only a small quantity of the blood of the pulmonary artery is distributed to them 

 by the right and left pulmonary arteries, and returned by the pulmonary veins 

 to the left atrium: the greater part passes through the ductus arteriosus into the 

 aorta, where it mixes with a small quantity of the blood transmitted by the left 

 ventricle into the aorta. Through this vessel it descends, and is in part distributed 





