EARLY DEVELOPMENT OF THE HEART AND PAIRED BLOOD-VESSELS 



265 



ventricular foramen. Corresponding to the internal attachment of the septum 



there is formed externally the interventricular sulcus which marks the external 



line of separation between the large left ventricle and the smaller right ventricle. 



Origin of Aorta and Pulmonary Artery from Bulbus. — Coincident with the 



Pulmonary artery 

 Dorsal swelling 



Ventral endocardial 

 cushion- 



Aorta 



Dorsal endocardial 

 cushion 



A trio-ventricular 

 foramen 



Interventricular 

 septum 



Interventricular 

 sulcus 



Aorta 



Arrow in pulmonary 

 artery 



Prox. bulbar septum 



Interventricular 

 foramen 



R. atrio-ventricular 

 foramen 



R. ventricle 



Pulmonary artery 

 Base of aorta 



Arrow in aorta 



L. atrio-ventricular 

 foramen 



Interventricular 

 septum 



Fig. 259. — Two stages in the development of the heart to show the differentiation of the bulbus 

 cordis into the aorta and pulmonary trunk: A, heart of a 5 mm. embryo; B, of a 7.5 mm. embryo 

 (Kollmann's Handatlas). 



