FCETAL CIRCULATION. 701 



free margin of the suspensory ligament of the liver, to the under surface of this 

 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 lobus 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 onwards, 

 under the name of the ductus venosus, and joins the left hepatic vein at the 

 point of junction of this vessel with the inferior vena cava. The blood, there- 

 fore, 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 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 viscera 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, from whence 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. 

 into the pulmonary artery. The lungs of the foetus being solid, and almost 

 impervious, only a small quantity of blood is distributed to them, by the right 

 and left pulmonary arteries, which is returned by the pulmonary veins to the left 

 auricle ; the greater part passes through the ductus arteriosus into the commence- 

 ment of the descending aorta, where it becomes mixed with a small quantity of 

 blood transmitted by the left ventricle into the aorta. Along this vessel it 

 descends to supply the lower extremities and viscera of the abdomen and pelvis, 

 the chief portion being, however, conveyed by the umbilical arteries to the 

 placenta. 



From the preceding account of the circulation of the blood in the foetus, it will 

 be seen: 



1. That the placenta serves the double purpose of a respiratory and nutritive 

 organ, receiving the venous blood from the foetus, and returning it again re-oxy- 

 genated, and charged with additional nutritive material. 



2. That nearly the whole of the blood of the umbilical vein traverses the liver 

 before entering the inferior vena cava ; hence the large size of this organ, especially 

 at an early period of fcetal life. 



3. That the right auricle is the point of meeting of a double current, the 

 blood in the inferior vena cava being guided by the Eustachian valve into the left 

 auricle, whilst that in the superior vena cava descends into the right ventricle. At 

 an early period of fcetal life, it is highly probable that the two streams are quite 

 distinct ; for the inferior vena cava opens almost directly into the left auricle, and the 

 Eustachian valve would exclude the current along the tube from entering the 

 right ventricle. At a later period, as the separation between the two auricles 

 becomes more distinct, it seems probable that some slight mixture of the two 

 streams must take place. 



4. The blood carried from the placenta to the foetus by the umbilical vein, 

 mixed with the blood from the inferior vena cava, passes almost directly to the arch 

 of the aorta, and is distributed by the branches of this vessel to the head and upper 

 extremities ; hence the large size and perfect development of these parts at birth. 



5. The blood contained in the descending aorta, chiefly derived from that 

 which has already circulated through the head and limbs, together with a small 



