PRE-CHORDAL 



.PLATE\ NEURAL PLATE ECTODERM 



iL ECTODERM 



YOLK SAC 



P R I M I T I V E 



NODE 



■PRIMITIVE 



P IT 



L A S T PORE) 



PRIM I T IV E 

 STREAK 



CHORION 



CHORIONIC VILLI 



PRIMITIVE "STREAK 



ALL A NT OE NTER I C DIVERTICULUM* 



BLOOD VESSEL 



Fig. 207. Three-germ-layer late gastrula of human embryo (pre-somite stage, after 

 Heuser: Contrib. to Embryo). Carnegie Inst., Washington, Publ. 138, 23: 1932). (A) 

 Dorsal view of embryonic disc, amnion removed. (B) Sagittal section through median 

 area of (A). Observe elongated notochordal canal. (C-G) Transverse sections as 

 mdicated. 



432 



