Fig. 50. — Sagittal section of the embryo represented in 

 Fig. 47. (After Duval.) 



Am, head-fold of the amnion, /^i?, aorta. C/t^ notochord. CJif^ medullary 

 canal, ex, ectoderm. I'f/j entoderm. PA, pharynx or fore-gut. Pl^^ mesoblastic 

 somites, ks, posterior limit of ectoderm of head-fold. K^ and K^, fore- and 

 mid-brains. VOM, venous portion of heart. 



150 



