138 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



side through the atria-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. 

 /Votocnord 



R desc. Aorta. 

 Sinus venosus 



/?. valve sinus 

 Venosus 



Pericardia! cavity 



R. Ventricle 

 Intervent 3epTum 



cord 



Upper limb bud 

 Esophagus 

 Learn, card vein 



Trachea 



L Afriuia 



Endocardial 

 cushion 



Boc/y wa// 



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 



R,Atri urn 



L. Atriu 



Septum 1 



Endocardial 

 cushion 



L.atrio-vent 

 foramen 



LVenfride 



FIG. 130. Transverse section through the foramen ovale of the heart in a 10 mm. pig 

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

 Intervent. 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 



