THE HEART. 471 



arteriosus, and the communication between the internal iliac arteries and the 

 placenta by means of the umbilical arteries. 



The ductus arteriosus is a short tube, about half an inch in length at birth, and 

 of the diameter of a goosequill. In the early condition it forms the continuation of 

 the pulmonary artery, and opens into the descending aorta just below the origin 

 of the left subclavian artery, and so conducts the chief part of the blood from the 

 right ventricle into this vessel. 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 ; and the fibrous cord, which is all that remains 

 of the ductus arteriosus in later life, will be found to be attached to the root of 

 that vessel. 



The umbilical or Jiypogastric arteries arise from the internal iliacs, in addition 

 to the branches given off from those vessels in the adult. Ascending along the 

 sides of the bladder to its apex, they pass out of the abdomen at the umbilicus 

 and are continued along the umbilical cord to the placenta, coiling round the 

 umbilical vein. They carry to the placenta the blood which has circulated in 

 the system of the foetus. 



The peculiarity in the venous system of the foetus is the communication 

 established between the placenta and the liver and portal vein through the 

 umbilical vein, and the inferior vena cava through the ductus venosus. 



FCETAL CIRCULATION. 



The blood destined for the nutrition of the foetus is returned from the placenta 

 to the foetus 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 lobus quadratus and 

 lobulus Spigelii. 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, 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 circulates 

 through the liver with the portal venous blood before entering the vena cava 

 by the hepatic veins ; some enters the liver directly, and is also returned to the 

 inferior 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 cava 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 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, 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 

 tributaries of the superior vena cava to the right auricle, where it becomes mixed 

 with a small portion of the blood from the inferior cava. From the right auricle 

 it descends over the Eustachian valve into the right ventricle, and from the right 

 ventricle passes into the pulmonary artery. The lungs of the foetus 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 is returned by the pulmonary 

 Veins to the left auricle ; the greater part passes through the ductus arteriosus 

 into the commencement of the descending aoi'ta, where it becomes mixed with a 

 small quantity of blood transmitted by the left ventricle into the aorta. Through 



