FETAL CIRCULATION 



285 



through the liver sinusoids and hepatic vein, and is again mixed with the 

 venous blood. Entering the right atrium it mingles more or less with the 

 venous blood which enters the atrium through the superior vena cava. From 

 the right atrium the blood may take 

 two paths. That from the inferior vena 

 cava is said to be directed by the valve 

 of this vein through the foramen ovale 

 into the left atrium, which, before birth, 

 receives little venous blood from the 

 lungs. The venous blood of the supe- 

 rior vena cava, somewhat mixed, is sup- 

 posed to pass from the right atrium into 

 the right ventricle. 



The purer blood of the left atrium 

 enters the left ventricle, whence it is 

 driven out through the aorta and dis- 

 tributed chiefly to the head and upper 

 extremities. The mixed blood of the right 

 ventricle passes out by the pulmonary 

 artery. A small amount of this blood is 

 conveyed to the lungs by the pulmonary 

 arteries, but, as the fetal lungs do not 

 function, most of it passes to the dorsal 

 aorta by way of the ductus arteriosus and 

 is distributed to the trunk, viscera and 

 lower extremities. The placental circuit 



is completed by the hypogastric or um- FIG. 27 8.-Diagrammatic outline of the 



organs of circulation in the fetus of six months 

 (Allen Thomson). 1 RA, right atrium of the 

 heart; RV, right ventricle; LA, left atrium; 



Ev, valve of inf. vena cava ; LV, left ventricle; L, liver; K, left kidney; /, portion of small intestine; a, 

 arch of the aorta; a', its dorsal part; a", lower end; vcs, superior vena cava; vci, inferior vena where it 

 joins the right atrium; vci', its lower end; s, subclavian vessels; j, right jugular vein; c, common ca- 

 rotid arteries; four curved dotted arrow lines are carried through the aortic and pulmonary opening and 

 the atrioventricular orifices; da, opposite to the one passing through the pulmonary artery, marks the 

 place of the ductus arteriosus; a similar arrow line is shown passing from the vena cava inferior 

 through the fossa ovalis of the right atrium and the foramen ovale into the left atrium; hv, the he- 

 patic veins; vp, vena portae; x to vci, the ductus venosus; uv, umbilical vein; ua, umbilical arteries; 

 uc, umbilical cord cut short; i, i', iliac vessels. 



1 In this diagram the arteries are conventionally colored red and the veins blue, but these colors are 

 not intended to indicate the nature of the blood conveyed by the respective vessels. 



