698 



MANUAL OF PHYSIOLOGY. 



This septum is, however, not at once complete at its upper part, a 

 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. 



