XL] 



THE CHORION, 

 Fig. 117. 



357 



Diagrammatic Section of Pregnant Human Uterus with 

 CONTAINED FcETUS. (From Huxley after Longet.) 



al. allantoic stalk ; nh. umbilical vesicle ; am. amnion ; ch. cho- 

 rion ; ds. decidua serotina ; o?m. decidua vera ; dr. decidua 

 reflexa ; I. fallopian tube ; c. cervix uteri ; u. uterus ; z. foetal 

 villi of true placenta; ^. villi of non-placental part of 

 chorion. 



The placenta has a somewhat discoidal form, with a slightly 

 convex uterine surface and a concave embryonic surface. At its 

 edge it is continuous both with the decidua reflexa and decidua 

 vera. Near the centre of the embryonic surface is implanted the 

 umbilical cord. As has already been mentioned, the placenta is 

 formed of the decidua serotina and the foetal villi of the chorion 

 frondosum. The foetal and maternal tissues are far more closely 

 united than in the placenta of the rabbit. The villi of the 

 chorion, which were originally comparatively simple, become 

 more and more complicated, and assume an extremely arborescent 

 form. At birth the whole placenta, together with the fused de- 



