EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 



75 



allantoic diverticulum of the entoderm has invaded the mesoderm of the body 

 stalk. This embryo, seen from the dorsal side with the amnion cut away, shows 



All I II 



Neural groo i 



Neur enteric canal 



Primitive streal 



Body stalk 



Villi of chorion 



Rudiment of heart 



Mesoderm 



Embryonic disc —m 



Chorion 

 ^^Mesoderm 



Body stalk 

 Primitive streak 



Blood vessel 



Fig. 77. — Views of a human embryo 1.54 mm. long (Graf Spee). X 23. A, Dorsal surface; B, median 



sagittal section. 



a marked neural groove and primitive streak. In front of the primitive knot a 

 pore is figured leading from the neural groove into the primitive intestinal 



