350 



REPRODUCTION 



cord at birth, while that inside the body becomes the first part 

 of the male and the whole of the female urethra, the bladder 

 and the urachus. 



Chorion. The chorion is the outer surrounding membrane 

 of the embryo after the appearance of the amnion. It consists of 



FIG. 108. Diagrammatic sections of an embryo. 



Showing the destiny of the yolk-sac, ys. vt, vitelline membrane; pp, pleuroperit- 

 oneal cavity; ac, cavity of the amnion; a, amnion; a', alimentary canal; ys, yolk-sac. 



three layers. From without inward these are the original 

 vitelline membrane, the false amnion and the allantois. The 

 allantois has been seen to extend around between the two amni- 

 otic folds and to blend with the outer. From its formation from 

 these several membranes, the chorion evidently consists of the 

 outer ectodermic, inner entodermic and intervening mesodermic 

 strata. 



