262 EMBRYOLOGY. 



epithelium, must be abandoned. The chorionic epithelium, which is 

 derived from the serosa, is preserved ; it constitutes in any event the 

 deeper layer, composed of epithelial cells, which lies immediately on the 

 membrana chorii or the gelatinous tissue of the villi. Perhaps there 

 Jbelongs to it in addition the so-called protoplasmic layer and the 

 canalised fibrin. However, the source and significance of these 

 structures, especially the latter substance, appear to me to be less 

 satisfactorily explained, and to be in need of still further investiga- 

 tions, in which the question of its origin from the maternal mucosa is 

 not to be overlooked. For even if TURNER has erred in regard to 

 the degeneration of the chorionic epithelium, he is probably in the 

 right in the second point, that the whole surface of the chorion 

 frondosum is directly invested by a layer of maternal tissue. 



The connective-tissue framework of the chorion frondosum, then, 

 is provided, as I think must be assumed, with a double investment : 

 (1) with a foetal epithelium, derived from the serosa, and (2) with 

 a layer, however thin it may be, of maternal tissue. 



I shall endeavor to establish this view in now turning to the 

 discussion of the placenta uterina, the structure of which likewise 

 presents great difficulties, and is therefore interpreted in very dif- 

 ferent ways. 



The placenta uterina is developed out of the part of i,he uterine 

 mucosa designated as decidua serotina (fig. 148 Dse). At birth it 

 detaches itself, like the corresponding part of the decidua vera, from 

 the inner surface of the womb at the line of separation shown on 

 Plate II., by the breaking down of the thin connective-tissue septa of 

 the underlying spongy layer. It then forms a thin membrane of only 

 O5 to 1 mm. thickness, the basal plate of WINKLER (Plate II. BP}, 

 and forms a complete investment over the placenta foetalis, which 

 it covers up at the time of the detachment of the foetal membranes. 

 At the margin it is directly continuous with the vera and reflexa 

 (fig. H8). 



The surface turned toward the wall of the uterus is divided by 

 deep furrows into separate divisions. Larger and smaller par- 

 titions, the septa placentae (figs. 139 and 143), corresponding in 

 position to the furrows, arise from the opposite surface of the mem- 

 brane and penetrate in between the chorionic villi (fig. 143 z) ; they 

 always unite a small number of these into a tuft or a cotyledon. If 

 we imagine the cotyledons wholly removed, there would be formed 

 in the placenta uterina a corresponding number of irregular com- 

 partments. These are in turn subdivided into smaller and more 



