FCETAL NUTRITION: THE PLACENTA 



453 



*"* 



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



levels them. Hence at the tune 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 "X 



form the placental coty- 

 ledons. At the same 



time the trophoblast 



proliferates in concentric r . 



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 fretal 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 ectoplacenta of Duval, 

 and its edge presents 

 microscopically a " bitten 

 or corroded appearance." 

 This phagocytic or 

 chemical action leads 

 later to the complete disappearance of the epithelium, so that 

 the trophoblast comes in contact with the connective tissue of 



1 Assheton (Quar. Jour. Micr. Science, vol. xxxvii., 1895) states that the tropho- 

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

 obes, 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 foetal origin. (From Hammond.) 



