7 8 



THE FETAL MEMBRANES AND EARLY HUMAN EMBRYOS 



chorionic cells (Fig. 69) . When the allantoic circulation is established, waste prod- 

 ucts given off from the blood of the embryo must pass through the epithelia of 



Spinal cord 



Mes.se/me/it 



Amniotic cavity 



Upper 

 limb bud 



fbstcmdinoJ 

 vein 



'Dorsal aorta. 

 Glomerulus 

 Rumb'ilical Vein 



WallofYolK-sac 



LumbilicaJ 

 Vein 



L'.vitellim 

 fein 



■Entoderm of 



gut 



Splanchnic mesoderm. 



Entoderm of 

 primitive gut 



3 .Amnio 



Ectoderm 



Hind-gut 



Fore-gut 



Somatic and 

 Splanchnic 

 mesoderm 



YolK-sac 



Entoderm 



-Chorionic mesoderm 



■ Chorionic ectoderm 



• Uterinex epithelium 



-Tunica propria of uterus 



Fig. 69. — A , Transverse section through the yolk-sac and stalk of a 5 mm. pig embryo showing 

 attachment of amnion. B, Diagram of the fetal membranes and allantoic placenta of a pig embryo in 

 median sagittal section (based on figures of Heisler and Minot). 



