618 



OF REPRODUCTION. 



Aorta. The lowest pair arises from the Pulmonary trunk, and forms the Pul- 

 monary artery on each side ; that on the left side, however, goes on to join the 

 descending Aorta as before, and thus constitutes the Ductus Arteriosus. ~-The 

 following is the course of the circulation of the blood in the Foetus. The fluid 

 brought from the Placenta by the Umbilical Vein is partly conveyed at once 

 to the Vena Cava ascendens, by means of the Ductus Venosus, and partly 

 flows through the Vena portae into the Liver, whence it reaches the ascending 

 Cava by the Hepatic Vein. Having thus been transmitted through the two 



U 



The Foetal Circulation; 1, the umbilical cord, consisting of the umbilical vein and two umbilical arteries ; 

 proceeding from the placenta (2) ; 3, the umbilical vein dividing into three branches ; two (4, 4) to be distri- 

 buted to the liver; and one (5), the ductus venosus, which enters the inferior vena cava (6) ; 7, the portal 

 vein, returning the blood from the intestines, and uniting with the right hepatic branch; 8, the right auricle; 

 the course of the blood is denoted by the arrow, proceeding from 8 to 9, the left auricle ; 10, the left ventricle : 

 the blood following the arrow to the arch of the aorta (11), to be distributed through the branches given off 

 by the arch to the head and upper extremities. The arrows, 12 and 13, represent the return of the blood 

 from the head and upper extremities through the jugular and subclavian veins, to the superior vena cava 

 (14), to the right auricle (8), and in the course of the arrow through the right ventricle (15), to the pulmonary 

 artery (16) ; 17, the ductus arteriosus, which appears to be a proper continuation of the pulmonary artery 

 the offsets at each side are the right and left pulmonary artery cut off; these are of extremely small size as 

 compared with the ductus arteriosus. The ductus arteriosus joins the descending aorta (18, 18). which 

 divides into the common iliacs, and these into the internal iliacs, which become the umbilical arteries (19), 

 find return the blood along the umbilical cord to the placenta; while the other divisions, the external iliacs 

 (20), are continued intp the lower extremities. The arrows at the termination of these vessels mark the 

 return- of the venous bloo(f by the "veins to the inferior cava. 



