FCETAL NUTRITION: THE PLACENTA 423 



cells proliferate and fill up the superficial culs-de-sac of the 

 mucous membrane. The glands are as yet unchanged, and 

 the increased blood supply leads to a free secretion which is 

 usually considered to be added to the albumen-layer, and then 

 to be absorbed by the trophoblast. There is no appreciable 

 transudation of lymph such as occurs in Ruminants. 



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 

 cotyledons. 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 dis- 

 appeared. 1 



Where the maternal and foetal tissues are in contact, the 

 surface epithelium shows a form of degeneration similar to the 

 epithelial symplasma of the zonary placenta fusion of cells and 

 fragmentation of nuclei. It is attacked by the thickened, 

 horseshoe-shaped trophoblast, the ectoplacenta of Duval, and 

 its edge presents microscopically a " bitten or corroded ap- 

 pearance." 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 the 

 uterus. The glands are dilated, and their proliferated endo- 

 thelium forms a symplasma which blocks the lumina. At 

 these places the trophoblast advances more quickly, as if the 

 resistance was weaker, and the line of attachment is undulating 

 (Fig. 102). The dips thus correspond to the gland orifices and 

 represent the beginnings of the future villi. The blood-vessels 

 are large and numerous and have no adventitia, i.e. they are 

 wholly capillaries. But the more deeply placed of them 

 acquire an adventitia, the perivascular sheath (Masquelin and 



1 Assheton (Quar. Jour. Micr. Sci., vol. xxxvii., 1895) states that the 

 trophoblast 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. 



