THE FCETAL MEMBRANES OF MAN. 



265 



According to the second diametrically opposite view, which finds its 

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

 others, the intervilkw&~ 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 



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. 



ERCOLANI, ROMITI, 

 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 



Pig. 149. Diagrammatic representation of the finer struc- 

 ture of the human placenta, after TURNER. 



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

 artery ; up, vein which conducts the blood away from 

 the intervillous maternal blood-sinus (d') ; 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 fcetal villi (Haftwurzeln) ; ds, decidua 

 serotina of the placenta. 



