i'LATE 2 



EXPLANATION OF FIGURES 



7 Reconstruction of the heart of a 21.0 mm. embryo. The right atrium and 

 right ventricle have been opened from the right side, the cut passing through a 

 part of the coronary sinus (Sn.cor.). Magnified about 25 diameters. 



8 Same as figure 7 but in slightly different position. The right sinus valve 

 (V.v.d.) has been partly cut away, exposing the orifices of the coronary sinus 

 and inferior vena cava. Probes have been inserted in the superior and inferior 

 cavae and the coronary sinus. The probe in the coronary sinus passes across 

 the sinus septum {S.sn.) under the right valve. Magnified about 25 diameters. 



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