NUTRITION OF THE FCETUS 27 



ing trunk forms one vessel with the portal vein. At this spot, 

 then, the first mixture of the arterial blood of the umbilical 

 veins with the hepatic venous blood takes place. The trunk 

 of the umbilical veins divides in the liver into numerous 

 capillaries, from which finally the hepatic veins arise and 

 empty into the posterior vena cava. The arterial blood of 

 the umbilical veins, which, on account ot its mixing with 

 the vena portse, has been modified in its composition, now 

 undergoes a second mixing, namely, with the blood of the 

 posterior vena cava. 



Only a part of the blood of the umbilical veins circulates 

 through the liver, while another part, as already related, 

 empties into the posterior vena cava, via the ductus Arantii. 

 Hepatic veins and ductus Arantii finally carry the umbilical 

 veins' blood into the posterior vena cava, and the latter takes 

 it to the left auricle of the heart. When the blood arrives 

 in the right auricle, it runs through the oval foramen (situated 

 in the septum between right and left auricle) into the left 

 auricle, the blood current being guided by an eminence, the 

 tuberculum Lower i. 



During foetal life an oval orifice {foramen ovale) is found 

 replaced in the adult by the fossa ovalis. It has a diameter of 

 1 cm., has an infundibuliform opening into the right auricle, 

 and guides the blood carried by the posterior vena cava 

 directly into the left auricle. On that side of the septum 

 turned toward the left auricle lies the funnel-shaped valve of 

 the oval foramen {valvula foraminis ovalis), formed by a fold of 

 the endocardium. It is attached to the edge of the oval 

 foramen, and its perforated infundibulum projects into the 

 left auricle. This valve prevents a return flow of the blood 

 from the left into the right auricle. In the left auricle the 

 blood coming from the right auricle mixes with the venous 

 blood of the pulmonary veins. This mixture is of little 

 moment, as the amount of blood flowing through the lungs 

 during intrauterine life is a small quantity. From the left 

 auricle the foetal blood goes through the auriculo-ventricular 

 opening into the left auricle and on through the aorta to 



