140 ANATOMY AND PHYSIOLOGY FOR NURSES 



of junction of this vessel with the inferior vena cava. 

 The blood, therefore, that traverses the umbilical vein 

 reaches the inferior vena cava in three different ways: 

 The greater quantity circulates through the liver with the 

 portal venous blood before entering the vena cava by the 

 hepatic veins; some blood enters the liver directly, and is 

 also returned to the inferior vena cava by the hepatic 

 veins; the smaller quantity passes directly into the vena 

 cava by the junction of the ductus venosus with the left 

 hepatic vein. 



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 viscera 

 of the abdomen. It enters the right auricle, and, guided 

 by the Bustachian valve, 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, whence it is distributed almost entirely to the 

 head and upper extremities, a small quantity being carried 

 into the descending aorta. From the head and upper 

 extremities the blood is returned by the branches of the 

 superior vena cava to the right auricle, where it becomes 

 mixed with a small portion of the blood from the inferior 

 vena cava. 



From the right auricle it descends over the Eustachian 

 valve into the right ventricle, and from the right ventricle 

 it passes into the pulmonary artery. The lungs of the 

 fetus are solid and almost impervious, hence only a small 

 quantity of blood is distributed to them by the right 

 and left pulmonary arteries, and this is returned by the 

 pulmonary veins to the left auricle ; the greater part passes 

 through the ductus arteriosus into the commencement of 

 the descending aorta, where it becomes mixed with a small 



