DEVELOPMENT OF THE HEART. 



695 



communication between the right and left sides of the heart re- 

 maining for some time above this partition. With the growth 

 of the inter-ventricular septum, the external notch becomes less 

 prominent, but it is less permanently recognizable as the inter- 

 ventricular groove. 



In the auricles a fold develops from the anterior wall, which 

 ultimately unites with a process of later development from the 



FIG. 283. 



Diagrammatic views of the under surface of an embryo rabbit of nine days and three 

 hours old, showing the development of the heart. (Allen Thomson.) A. View of entire 

 embryo. B. An enlarged outline of the heart of A. C. A later stage of the development 

 of B. h h. Ununited heart, a a. Aorta. V V. Vitelline veins. 



posterior wall. This septum is not complete during foetal life, 

 but is interrupted by an opening leading from one auricle to the 

 other, called the foramen ovale. 



Simultaneously with the appearance of the posterior process 

 of the septum another fold arises, which is placed at the mouth 

 of the inferior vena cava, and forms the Eustachian valve. 



