EARLY DEVELOPMENT OF THE HEART AND PAIRED BLOOD-VESSELS 



201 



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 



3epl.II 



.Sept. 1 



L.atr. Aorta 



Septl 

 Jnthr 



up.v.c. 



L ye.n1. 



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; /. v. c, inferior vena cava; 

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

 artery; Pnl. v., pulmonary vein; Sept. I, Sept. II, septum primum, septum secundum; Sup. v. c, 

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



torarnen oval' 



n. valve of sinus fenosus 

 Inf. Vena cav a. 



\ 



O up. Vena. Cava. 

 ■tSeptunt H 



Aorta 



Semilunar valve 

 of pulmonary 

 artery 



ifricle 



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



