THE HEART. 1097 



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

 placenta by means of the umbilical arteries. 



The duetus 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 duetus arteriosus, the latter is chiefly connected 

 to the left pulmonary artery ; and the fibrous cord, which is all that remains 

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

 that vessel. 



The umbilical or hypogastrie 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 fundus. 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 return 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 estab- 

 lished between the placenta and the liver and portal vein through the umbilical 

 vein, and the inferior vena cava through the duetus venosus. 



FCETAL CIRCULATION. 



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

 to the foetus, along the umbilical cord, by the umbilical vein. The umbilical 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 onward, under the name of 

 the duetus 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 duetus venosus with the left 

 hepatic vein. 



In the inferior cava the blood carried by the duetus 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 branches 

 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 solid and almost 

 impervious, only a small quantity of the blood of the pulmonary artery is distrib- 

 uted 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 duetus 

 arteriosus into the commencement of the descending aorta, where it becomes mixed 

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



