THE F(ETAL MEMBRANES OF MAN. 



265 



According to the second diametrically opposite view, which finds its 

 defenders in VIRCHOW, TURNER, ERCOLANI, LEOPOLD, WALDEYER, and 

 others, the intervillous spaces are nothing else than the enormously 

 enlarged capillary blood-vessels of the maternal mucosa. Chorion and 

 decidua serotina early unite very intimately by means of their sur- 

 faces, so that no fissures are left between them. The villi grow into 

 the mucous tissue, the 

 superficial capillaries of 

 which enlarge to capa- 

 cious spaces. 



If this view is cor- 

 rect, the chorionic villi 

 will necessarily be sur- 

 rounded on all sides by 

 thin coverings of ma- 

 ternal tissue, or, since 

 a partial degeneration 

 of the covering would 

 certainly be possible, 

 there will of necessity 

 be at least a stage in the 

 development in which 

 such a covering will be 

 demonstrable. 



Fig-. 149. Diagrammatic representation of the finer struc- 

 ture of the human placenta, after TURNER. 



F, Placenta foetalis ; M, placenta uterina ; cot, tortuous 

 artery ; up, vein which conducts the blood away from 

 the intervillous maternal blood-sinus (<f ) ; x, a con- 

 tinuation of the maternal tissue over the villi : this 

 lies outside the layer e' (the metamorphosed epithelium 

 of the uterine mucosa), and is probably a connective- 

 tissue membrane with vascular endothelium ; t, cords 

 of the placenta uterina, which unite with the tips of 

 some of the foetal villi (Haftwurzeln) ; ds, decidua 

 serotina of the placenta. 



and TURNER have in 

 fact, as has been pre- 

 viously stated, expressed 

 themselves to the effect 

 that probably the epi- 

 thelial layer resting 

 upon the connective- 

 tissue axis of the villi 



is not the original chori- 

 onic epithelium derived from the serosa, but a covering which arises 

 from the decidua placentalis a view the untenableness of which has 

 already been shown. 



In the diagram which TURNER has sketched to illustrate his view 

 of the structure of the human placenta (fig. 149) the real original 

 villous epithelium is degenerated. 



The cell-layer e' is the epithelium of the uterine mucosa, into which 



