572 THE VASCULAR SYSTEMS 



The umbilical or hypogastric arteries are continued from the internal iliacs, 

 along the sides of the bladder to its apex; they pass out of the abdomen at the 

 umbilicus and are carried in the umbilical cord to the placenta. They convev 

 the blood which has circulated in the system of the fetus 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. 



CONUS 

 ARTERIOSUS 



VALVE OF 

 FORAMEN OVALE 



VALVE OF AURICULOVENTRICULAR 

 CORONARY SINUS OPENING 



PIG. 425. The right auricle of a fetal heart (eighth month). Enlarged. (Spalteholz.) 



Fetal Circulation (Fig. 426). The blood destined for the nutrition of the 

 fetus 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 suspensory ligament of the liver to the under surface of that organ, where it 

 gives off two or three branches to the left lobe, one of which is of large size, and 

 others to the quadrate and Spigelian lobes. At the transverse fissure it divides 

 into two branches; of these, the larger is joined by the portal vein and enters the 

 right lobe: the smaller branch continues outward, under the name of the ductus 

 venosus f and joins the left hepatic vein at the point of junction of that vessel with 

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

 reaches the inferior vena cava in three different ways; the greater quantity circu- 

 lates 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 also returned 

 to the inferior vena cava by the hepatic veins; the smaller quantity passes directly 

 into the inferior vena cava by the junction of the ductus venosus with the left hepatic 

 vein. 



In the inferior vena cava (postcava) the blood carried by the ductus venosus and 

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

 wall of the abdomen. It enters the right auricle, and, guided by the Eustachian 

 yalve, passes through the foramen ovale into the left auricle, where it becomes 

 mixed with a small quantity of blood returned from the lungs by the^pulmonary 

 veins. From the left auricle 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 



