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 parietalis; dr, decidual capsularis; ds, decidua basalis; ch, chorion with villi; the villi 

 extending into the decidua basalis are from the chorion frondosum; am, amnion; u, umbilical 

 cord;_c/,_allantois; y,y', yolk sac and stalk. 



Mesoderm 



Syncytial 

 Irophoderm 



Core of villus 



- Canalized fibrin 

 Endolhelium 



Canalized fibrin Maternal capillary Intermllous space 



FIG. 242. Diagram illustrating the development 'of the chorionic villi and placenta (after 



Peters). 





