FIG. 50. SAGITTAL SECTION OF THE EMBRYO REPRESENTED IN 

 FIG. 47. (After Duval.) 



Am, head-fold of the amnion. Ao, aorta. Ch, notochord. CM, medullary 

 canal, ex, ectoderm, in, entoderm. Ph, pharynx or fore-gut. PV^ mesoblastic 

 somites. RE, posterior limit of ectoderm of head-fold, y 1 and V^^ fore- and 

 mid-brains. VOM^ venous portion of heart. 



150 



