706 



MANUAL OF PHYSIOLOGY. 



arterial, but the blood in the descending aorta is of a mixed 

 character, as it contains blood which has nourished the head and 

 neck, besides blood which has come from the placenta by the 

 inferior vena cava through the right auricle, foramen ovale, left 

 auricle and left ventricle. 



FIG. 291. 



Diagram illustrating the circulation through the heart and the principal vessels of a 

 foetus. (Cleland.) a. Umbilical vein. 6. Ductus venosus. /. Portal vein. e. Vessels to 

 the viscera, d. Hypogastric arteries, c. Ductus arteriosus. 



As the foetal lungs are not called into play until after birth, 

 but little blood passes to them in the fcetus ; this state of things 

 is, however, completely altered at birth, when the lungs of the 



