CHAP. IT.] PKEGNANCY AND BIRTH. 391 



into the inferior vena cava arid so into the right auricle. Thence 



S.v.o VVC-. 



I.V 



U.A 

 FIG. 194. 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 V.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 f.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 bead and upper limbs passes from the superior vena cava 

 S.V.C. through the right auricle to the right ventricle R.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. 



it appears to be directed by the valve of Eustachius through the 

 foramen ovale into the left auricle, passing from which into the left 

 ventricle it is driven into the aorta. Part of the umbilical blood, 

 however, instead of passing directly to the inferior cava, enters 

 with the blood carried by the portal vein into the hepatic cir- 

 culation, from which it returns to the inferior cava by the hepatic 

 veins. The inferior cava also contains blood coming from the 



