EARLY DEVELOPMENT OF THE HEART AND PAIRED BLOOD-VESSELS 



261 



tant, as it later fuses with the left valve of the sinus venosus and with it forms a 

 great part of the atrial septum of the late fetal and adult heart. 



Sinus Venosus and its Valves. The opening of the sinus venosus into the 



SepT.H , 



Aorta 



/tort. 



A B C 



FIG. 254. Lateral dissections of the heart from the left side. A, 6 mm.; B, 9 mm.; C, 12 mm. 

 (A and B are based on reconstructions by Tandler). Cor. sin., coronary sinus; D. end. c., dorsal 

 endocardial cushion; For. ov., foramen ovale; Int. for., interatrial foramen; 7. v. c., inferior vena cava; 

 L. atr., left atrium; L. va. s. v., left valve of sinus venosus; L. vent., left ventricle; Pul. a., pulmonary 

 artery; Pul. v., pulmonary vein; Sept. I, Sept. If, septum primum, septum secundum; Sup. v. c., 

 superior vena cava; V. end. c., ventral endocardial cushion. 



foramen ovale 



n.va.Lve of sinus 

 Inf. Vena cava. 



\ 



Septum / 



uup.Veaa- CCLVO, 

 tSeptum H 



Aorta. 



Semdunar valve 

 of pulmonary 

 artery 



. Ventricle 



FIG. 255. Dissection of the heart of a 65 mm. embryo from the right side. X 12. 



