Maternal blood 



Extra-embryonic 

 ectoderm 



Posterior amniotic 

 fold 



Ectoplacental cone 



Yolk cavity 



Distal entoderm 



Proximal entoderm 



Exocoelom 



Mesoderm 



Anterior amniotic 

 fold 



Primitive streak 



Squamous entoderm 



Head process 



Fig. 12. — Sagittal section of embryo of 7 days i hour showing the amniotic folds and 

 the head process. Reichert's membrane omitted. Projection drawing (X300). 



17 



