264 



PHYSIOLOGY 



CHAP. 



In order to form a clear conception of the second circulation, 

 which is set up after the development of the allantois and the 

 complete formation of the placenta, and is therefore called cardio- 

 placental circulation, we must first consider the anatomical 



- 7 



FIG. 116. Filling of the foetal heart in diastole. Enlarged section of the heart of a new-born 

 child. (The white arrows show the direction in which the blood flows.) 1, opening of the 

 inferior vena cava in the right auricle ; 2, Eustachian valve ; 3, superior vena cava ; 4, right 

 auricle ; 5, right ventricle ; 6, inferior vena cava ; 7, left ventricle ; 8, left auricle ; 9, pul- 

 monary veins ; 10, limbus of the foramen ovale. 



peculiarities of the cardio-vascular system of the foetus. Whereas 

 in the adult the right heart is entirely separated from the left by 

 the inter-auricular and the inter-ventricular septum, in the foetus 

 the right auricle communicates with the left by means of the 

 foramen, known to Galen but called the foramen ovale Botalli, 



