78 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 



.EnToderm of 



yuf 



Splanchnic meioderm 



Hind-gut 



-Somatic and 

 Splanchnic 

 mesodertn 



YoIK-sac 



Entod 



erm 



-Chorionic mesoderm 

 Chorionic ectoderm 

 Uterine I 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). 



