EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 



77 



toderm has invaded the mesoderm of the body stalk. This embryo, 

 seen from the dorsal side with the amnion cut away, shows a marked neural 



Yolk sac - 



. 

 < ' 



Amni 



^ '". "^. 

 . 



Neural groovt- 





Neurenteric canal 



Primitive streak 



Body stalk 



B 



A mnion 

 Embryonic disc 



Anlage of heart 



Splanchnic mesoderm 



Villi of chorion 



norion 

 Somatic mesoderm 



Body stalk 

 Primitive streak 



Allantois 

 Yolk sac 

 Entoderm 



Blood vessel 



FIG. 77. Views of a human embryo of 1.54 mm. (von Spee). X 23. A, Dorsal surface; B, 



median sagittal section. 



groove and primitive streak. In front of the primitive knot a pore is 

 figured, leading from the neural groove into the primitive intestinal 



