FCETAL NUTRITION: THE PLACENTA 



453 



As the blastodermic vesicle grows, it presses against the folds and 

 levels them. Hence at the time of attachment the surfaces of the 

 placental lobes are nearly regular. The covering epithelium again 

 returns to normal, but 

 the active proliferation 

 of the connective tissue 

 cells is continued to 

 form the placental coty- 

 ledons. At the same 

 time the trophoblast 

 proliferates in concentric 

 areas ' on either side of 

 the embryonic rudiment, 

 which is placed opposite 

 the groove between the 

 placental cushions. Here 

 the ovum is generally 

 said to gain its first 

 attachment, the ob- 

 placental lobes having by 

 this time disappeared. 1 



Where the maternal 

 and foetal tissues are in 

 contact, the surface 

 epithelium shows a form 

 of degeneration similar 

 to the epithelial sym- 

 plasma of the zonary 

 placenta fusion of cells 

 and fragmentation of 

 nuclei. It is attacked 

 by the thickened, horse- 

 shoe-shaped trophoblast, 

 the ectopltirnifti of Duval, 

 and its edge presents 

 microscopically a "bitten 

 or corroded appearance." 

 This phagocytic or 

 chemical action leads 

 later to the complete disappearance of tin- epithelium, so that 

 the trophoblast comes in contact with the connective tissue of 



1 Assheton (Qti,: Jour. ,\[icr. Science, vol. xxxvii., 1895) states that the tropho- 

 blast shows papillary thickenings over the ob-placental and peri-placental 

 lobes, and that by them the ovum obtains the first attachment over its lower 

 pole. 





FIG. 128. Section through uterine mucosa of 

 rabbit pregnant about eighteen days. The 

 section shows decidual tissue and, near the 

 surface, giant-cells which are supposed to 

 be detached trophoblast cells, and therefore 

 of fo?tal origin. (From Hammond.) 



