FIG. 50. SAGITTAL SECTION OF THE EMBRYO REPRESENTED IN 

 FlG. 47. (After Duval.) 



Am, head-fold of the amnion. A 0, aorta. Ch, notochord. CM, medullary 

 canal, ex, ectoderm, i 2 entoderm. Ph, pharynx or fore-gut. PV, mesoblastic 

 somites. RE, posterior limit of ectoderm of head-fold. IS 1 and K 2 , fore- and 

 mid-brains. VOM, venous portion of heart. 



150 



