928 



CARE AND NOURISHMENT OF THE DEVELOPING YOUNG 



SUPERIOR VENA CAVA 

 RIGHT LUNG 



LEFT LUNG 



LIGAMENTUM 

 ARTERl 

 DUCTUS 

 ARTERl 



RIGHT AT 



RIGHT VENTRICLE 



AORTA 

 LIGAMENTUM TERES 

 PORTAL VEIN 



URACHUS 



INFERIOR VENA CAVA 



UMBILICAL A 



Fig. 379. Diagrams of probable fetal and postpartum circulations through the heart 

 in the mammal. (A) Fetal circulation. Oxygenated blood passes through umbilical vein, 

 to liver. Passing through the liver by means of the ductus venosus it gathers blood from 

 the liver veins and empties into the inferior vena cava through the hepatic vein. Within 

 the inferior vena cava it mixes with non-oxygenated blood from the posterior part of 

 the body. Reaching the right atrium it passes across the atrium through the foramen 

 ovale and into the left atrium and from thence into left ventricle. The blood from the 

 superior vena cava crosses to one side of the blood current from the inferior vena cava 

 in the right atrium on its way to right ventricle. Most of the blood from the right ventricle 

 courses through the ductus arteriosus into the descending aorta. A small amount goes to 

 the lungs via the pulmonary arteries. (B) Circulation after birth. Observe there is no 

 passage of blood from the right atrium into the left atrium. The blood in the left atrium 

 is returning oxygenated blood from the lungs. The ductus arteriosus has atrophied. (See 

 text.) (A redrawn and modified from Windle, 1940, Physiology of the Fetus, Saunders, 

 Philadelphia. B adapted from A.) 



and excretory regions before birth and hatching. The circulatory system 

 therefore must accommodate these areas in the fulfillment of the respiratory 

 and excretory functions. However, at the same time the developing heart and 

 immediate blood vessels in relation to the heart also must look forward, as 

 it were, to the requirements of the period after birth (mammals) or after 

 hatching (reptiles and birds). A diagram of the circulation of the blood 

 through the heart previous to birth in the mammalian heart is shown in figure 

 379A, and figure 379B delineates the pathway of the blood after birth. 

 Before birth the valve-like arrangement of the interatrial septa, I and II, per- 

 mits the oxygenated blood from the placenta to flow from the right atrium 



