138 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



side through the atrio-ventricular foramen. Between these openings is the endocardial cushion, 

 which in part forms the anlages of the tricuspid and bicuspid valves. The atria are marked off 



Spinal gang. 



/Votochord j ^S - 1 



mmm 



_>Spinal cord 



R. clesc. Aorta. 

 Sinus venosus — 



fl. valve sinus — 

 Venosus n 



Upper limb bud 



Esophagus 



Lcom.ee/rdvein 



Pericardial cavity —& 



R.Ventncle 

 Jnterveifr. Septum 



i jam. 



R.Ventricle JLJfg \ 

 — 1 I BS> — &wi 





BL 



Endocardial 

 cushion 



WM 



Fig. 129. — Transverse section through the sinus venosus of the heart in a 10 mm. pig embryo. X 22.5. 

 L. com. card, vein, left common cardinal vein; R. desc. Aorta, right descending aorta. 



Foramen 

 ovale 



RJtriUm 



-L. Atrium 



fcst~-<*xmM7 Septum 1 



Endocardial 

 cushion 



1 ' . ' I i '"tea V i VilWcm jff\ — Latrio-vent 



wfpw 



tntervenh 

 Septuiri 



Fig. 130. — Transverse section through the foramen ovale of the heart in a 10 mm. pig embryo. 

 X 22.5. L. atrio-vent. foramen, R. atrio-vent. foramen, left and right atrio-ventricular foramen; 

 Intervenl. septum, interventricular septum. 



externally from the ventricles by the coronary sulcus. Between the two ventricles is the inter- 

 ventricular septum. The ventricular walls are thick and spongy, forming a network of muscular 



