THE EARLY EMBRYOLOGY OF THE MOUSE 



49 



Somatic mesoderm Neural groove 



Amnion 



Exocoelom 



Epi-myocardium 

 (Splanchnic mesoderm) 



Endocardium 



Entoderm 



Coelom 



Fig. 29. — Slightly diagonal transverse section through median endocardial pri- 

 mordium (see Fig. 30), just cephalad to fore-gut. Embryo of 8 days 6 hours, 5 somites. 

 Projection drawing (X150). 



Forebrain 



Cut edge of entoderm 



Median endocardial 

 primordium 



Aortic arch I 



Atrium 



Anterior intestinal portal 



Fig. 30. — Diagram of the fore-gut region viewed from the ventral surface, showing 

 distribution of the endocardium. Endocardial tissue is represented by horizontal 

 lines. Rat embryo of 9 days 16 hours, 3 somites. {Modified after Goss.) 



