165 



Iu the placental regiem on the mesooietric side, two 'coty- 

 ledons' are formed, as local thickenings of two longitudinal ridges. 

 There is here an intense proliferation of interglandular sub-epi- 

 thelial tissue; numerous glands open on the surface of the coty- 

 ledons. 



To these cotyledons the ectoplacenta becomes attached. The 

 ectoplacenta is a horse-shoe-shaped thickening of trophoblast 

 ('fer-a-cheval placentaire' of van Beneden) surrounding the posterior 

 end of the embryo. It consists of a lower 'couche cellulaire' and 

 an upper 'couche plasniodiale'. The epitheliura of the uterus 

 degenerates where the ectoplacenta is in contact with it, and 

 degeneration gradually proceeds into the deeper portions of the 

 glands. The subepithelial capillaries are thus brought into the 

 closest proximity with the ectoplacenta, becoming in fact em- 

 bedded in it; their endothelium disappears, and a circulation of 

 maternal blood is set up in lacunae bounded by a plasmodium 

 of trophoblastic origin. In the deeper parts of the uterine tissue 

 the capillaries are dilated, and beconie surrouuded by sheaths 

 (gaines périvasculaires) of vesicular (glycogenic) connective tissue 

 cells. This closes the first period of the formation of the ecto- 

 placenta. 



In the next period (that of remaniement) the ectoplacenta is 

 penetrated by the capillaries of the allantois and successively 

 subdivided into lobes, lobules and canaliculi. 



Foetal and maternal blood are thus brought into the closest 

 relation with one another. It is worthy of notice that the main 

 afferent maternal channels pass straight through the placenta on 

 to the foetal side, whence the blood ascends by the capillariform 

 lacunae to open into the veins on the maternal surface. 



In the maternal tissues Duval distinguishes three regions; 

 (1) a layer of vesicular cells next the muscularis ('couche vési- 

 culeuse protectrice') ; (2) a region of dilated blood vessels sur- 

 rounded by perivascular sheaths of vesicular uni-nucleated cells; 

 these sheaths have increased so much as to have fused into a 

 continuous mass ; (3) au intermediate layer of multinucleate vesi- 



