

EARLY HUMAN EMBRYOS AND THEIR MEMBRANES 



8l 



to Unguiculates and Primates. It connects the mesoderm of the embryo with 

 the mesoderm of the chorion. Into it there has grown from the gut of the em- 

 bryo the entodermal diver ticulum of the allantois. 



The Chorion. The human chorion is derived directly from the outer troph- 

 ectoderm layer of the blastodermic vesicle and from the extra-embryonic somatic 

 mesoderm. Its early structure resembles that of the pig's chorion. The troph- 



Ecfaderm 



Amniotic cavity 



Coe/om 



Trophecto derm 

 Archenteron 



Entoderm 

 Mesoderm 



Ectoderm oPamttion 

 Ectoderm of embryo 



ophecfoderm 

 YolK-sac 



Ectoderm ofembry 

 Cavity of ammo 

 Mesoderm ofamn 



D 



Allantois . BodysUlK 



Ectoderm ofcfio 



Cavity of yolk 

 sac 

 Entoderm of. 



Entoderm Cavity ofyolK 

 sac 



Splanchnic 

 mesoderm 



Mesoderm of 



Exlra-embiyonie. 

 Coelom 



Extraembryon 

 coelom 



Chorionic 



mcsoderm Mesoderm of Ch 

 Trophoderm 



Chorionic villi 



FIG. 70. Four diagrams showing hypothetical stages of early human embryos (based on figures of 



Robinson and Minot). 





ectoderm of the human embryo early gives rise to a thickened outer layer, the 

 trophoderm (syncytial and nutrient layer) . When the developing embryo comes 

 into contact with the uterine wall the trophoderm destroys the maternal tissues. 

 The destruction of the uterine mucosa serves two purposes: (i) the embedding 

 and attachment of the embryo, it being grafted, so to speak, to the uterine wall; 

 and (2) it supplies the embryo with a new source of nutrition. To obtain nutri- 



