XI.] 



THE CHORION. 

 Fig. 115. 



^_^^^^j^^_pc 



349 



Diagram of the Fcetal Membranes op a Mammal. (From 

 Turner.) 



Structures which either are or have been at an earlier period 

 of development continuous with each other are represented by 

 the same character of shading. 



pc. zona with viUi ; S0. subzonal membrane ; B. epiblast of 

 embryo; am. amnion; AC. amniotic cavity; if. mesoblast 

 of embryo ; H. hypoblast of embryo ; UV. umbilical vesicle ; 

 al. allantois; ALO. allantoic cavity. 



cation of the dorsal aorta, and returned to the body 

 by one, or rarely two, allantoic veins, v^hich join the 

 vitelline veins from the yolk-sac. From the outer sur- 

 face of the true chorion (Fig. 114!,S,ch.z,llQ) villi grow 

 out and fit into crypts or depressions which have in the 



