FCETAL CIRCULATION. 767 



The umbilical, or hypogastric 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 umbili- 

 cus, 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 

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

 umbilical vein, and with the inferior vena cava by the ductus venosus. 



The arterial 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 upwards 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 on- 

 wards, 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 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 vis- 

 cera 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 pulmo- 

 nary 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 re- 

 turned 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 distributed to them, by the right and left pul- 

 monary arteries, which 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 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 reoxy- 

 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 cava ; hence the large size of this organ, especially 

 at an early period of foetal life. 



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

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

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



