FCETAL NUTRITION: THE PLACENTA 



453 



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



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



placental lol^es 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 trophulilast 



proliferates in concentric 



areas on either side of 



the embryonic rudiment, 



which is placed oiDposite 



the groove lietween the 



placental cushions. Here 



the ovum is generally 



said to gain its first 



attachment, the oli- 

 placental loljes having by 

 this time disappeared.^ 



Where the maternal 

 and fi.etal tissues are in 

 contact, the surface 

 epithelium shows a form 

 of degeneration similar 

 to the epithelial sym- 

 plasma of the zonary 

 liilacenta — fusion of cells 

 and fragmentation of 

 nuclei. It is attacked 

 liy the thickened, horse- 

 shoe-shaped trophoblast, 

 the cdo'iilavi-nta of Duval, 

 and its edge presents 

 microscopically a " 1 litten 

 or corroded appearance." 

 This pliagocytic or 

 chemical action leads 

 later to the comjilete disappearance of the epithelium, so tliat 

 the trophoblast conies in contact with tlie connective tissue of 



1 Assheton {Quar. Jour. Mirr. Svienre, 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. 



Sv 



^ V 



Fig. 128. — Section through uterine mucosa of 

 rabbit pregnant about eighteen clays. The 

 section shows decidual tissue and, near the 

 surface, giant-cells which are supposed to 

 be detached ti'ophoblast cells, and therefore 

 of fietal oi'igin. (From Hamiuond.) 



