

DEVELOPMENT OF THE VASCULAR SYSTEM 



513 



exists above its ventral portion (Fig. 468), but this foramen is ultimately closed by 

 fusion of the aortic septum .with the ventricular septum. 



FIG. 469. Diagrams to illustrate the transformation of the bulbus cordis. (Keith.) Ao. Truncus arteriosus. 

 Au. Atrium. B. Bulbus cordis. RV. Right ventricle. LV. Left ventricle. P. Pulmonary artery. 



When the heart assumes its S-shaped form the bulbus cordis lies ventral to and 

 in front of the primitive ventricle. The adjacent walls of the bulbus cordis and 

 ventricle approximate, fuse, and finally disappear, and the bulbus cordis now 



Aortic septum 



Aortic septum 



Common atrio- 

 ventricular aperture 



Y 



Right 

 ventricle 



Pulmonary 

 artery 



Aorta 



Right atrio- 

 ventricular 

 orifice 



Septum 

 inferius 



Left 

 ventricle 



Left atrio- 

 ventricular 

 orifice 



Right 

 ventricle 



Septum inferius 



Left 

 ventricle 



FIG. 470. Diagrams to show the development of the septum of the aortic bulb and of the ventricles. (Born.) 



communicates freely with the right ventricle, while the junction of the bulbus with 

 the truncus arteriosus is brought directly ventral to and applied to the atrial canal. 

 By the upgrowth of the ventricular septum the bulbus cordis is in great measure 



Aorta 



Aorta 



Aorta 



Pulmo- 

 nary artery 



FIG. 471. Transverse sections through the aortic bulb to show the growth of the aortic septum. The lowest 

 section is on the left, the highest on the right of the figure. (After His.) 



separated from the left ventricle, but remains an integral part otthe right ventricle, 

 of which it forms the infundibulum (Fig. 469). 





