FCETAL CIRCULATION. 



105 



gradually with the ventricle, the bifurcation is depressed 

 also; and when one of the two branches separates itself 

 entirely from the other, by completing the formation of the 

 opposite portions of their circumference, the pulmonary 

 appears, forming a distinct p JG> 12. 



trunk. But as the cavities of 

 the heart communicate, the 

 pulmonary continues not only 

 at first,, but during the whole 

 of foetal existence, with the 

 aorta of which it constitutes 

 the second root." 



The lymphatic circulation 

 will be noticed under the head 

 of the glandular tissue. 



We will conclude the vas- 

 cular tissue by briefly point- 

 ing out the difference between 

 the circulation in the foetus 

 and the adult. 



This difference is seen first 

 (Fig. 12) in the heart. Here, 

 in the foetus, the auricles com- 

 municate by the foramen ovale, 

 which after birth is closed. At 

 the mouth of the inferior cava 

 there is a valve in the foetus, 

 which disappears in the adult. 

 The pulmonary artery in the foetus communicates with the 

 aorta by the ductus arteriosus, which in the adult is closed. 



2d. The internal iliac arteries of the foetus carry venous 



FIG. 12 represents the foatal circulation, o Umbilical cord. 6 Placenta. 

 e Umbilical vein dividing into three branches, dd Two of which go to the 

 Liver, e The third is the ductus venous, which goes to the inferior cava. fg Por- 

 tal vein, h Right auricle. Left auricle, j Left ventricle, k Arch of 

 aorta. I m Show the return of blood by the jugular and subclavian veins, n 

 Superior cava. o Right ventricle, p Pulmonary artery, q Ductus arteriosus. 

 r Descending aorta, s Hypogastric'or internal iliacs. t External iliacs. 



