

CHAP, ii.] 



PEEGNAKCY AND BIRTH. 



1133 



and upper limbs by the superior vena cava is distinctly venous ; 

 and this passing from the right ventricle by the ductus arterio- 

 sus is driven along the descending aorta, and together with 

 some of the blood passing from the left ventricle round the 



U.A 



FIG. 195. DIAGRAM TO ILLUSTRATE THE FCETAL CIRCULATION. 



It will be understood that the figure is purely diagrammatic and constructed 

 simply to shew in a convenient manner the general course taken by the blood. 



The winged arrow indicates venous, the plain arrow arterial, or, in parts, 

 mixed blood. 



UV. The umbilical vein, passing in part to the liver (indicated in outline), 

 joined by blood from the alimentary canal along the mesenteric, becoming the 

 portal vein F.P., but chiefly flowing on by the ductus venosus D. V. (into which 

 fall the hepatic veins V.H.) into the inferior vena cava, /. V. C. 



This chiefly arterial but still mixed blood passes through the right auricle 

 R.A., the foramen ovale/.o. to the left auricle L.A., thence to the left ventricle 

 L. V. and so by the arch of the aorta Ao. to the arteries of the head and upper 

 limbs. 



The venous blood of the head and upper limbs passes from the superior vena 

 cava S. V. C. through the right auricle to the right ventricle E. V. and thence by 

 the pulmonary artery P.A. and ductus arteriosus D.A. to the descending aorta, 

 and so to the umbilical arteries U.A. 



aortic arch falls into the umbilical arteries and so reaches the 

 placenta. The foetal circulation then appears to be so arranged 

 that, while the most distinctly venous blood is driven by the 

 right ventricle back to the placenta to be arterialized, the most 



