234 



THE UROGENITAL SYSTEM 



Fig. 241. — Diagrammatic section through a pregnant uterus at the seventh or eighth week (after 

 Allen Thomson). c,c, Openings of uterine tubes; c', cervix with mucous plug; dv, decidua vera or pari- 

 etalis; dr, decidual capsularis; ds, decidua basilis (serotina); ch, chorion with villi; the villi extending 

 into the decidua basalis are from the chorion trondosum; am, amnion; u, umbilical cord; al, allantois; 



y,y', yolk sac and stalk. 



M esoderm 



Syncytial . 



trophodernv 



Core of villus 



-^e^ — Canalized fibrin 

 Endothelium 



Canalized fibrin Maternal capillary Intervillous space 

 Fig. 242. — Diagram illustrating the second phase in the development of the chorionic villi and 



placenta (after Peters) 



embryo is established. The blood vessels of the uterus open into the intervillous 

 blood spaces and here the maternal blood circulates. The syncytial trophoderm 



