THE FCETAL MEMBRANES OF MAN. 263 



shallow compartments by finer connective-tissue outgrowths from 

 the membrane and the septa. 



The edges of the septa do not reach to the roots of the villi in 

 the middle of the placenta, but only in a narrow peripheral region, 

 where they come into immediate contact with the membrana chorii 

 (Plate II. m), and are joined together underneath it into a thin, 

 closely applied membrane, which is pierced by the roots of the villi. 

 This has been called by WINKLEE closing plate (Schlussplatte, SP), 

 by KOLLIKEK decidua placentalis subchorialis. Still more appro- 

 priate is the term employed by WALDEYER, subchorial terminal ring 

 (Schlussring), because it is thereby stated that the membrane in 

 question is present only at the margin of the placenta, leaving the 

 middle area of the chorion free. 



The connective-tissue framework of the placenta uterina possesses 

 in general the properties of the compact, abundantly cellular layer 

 of the decidua vera and reflexa, but exhibits one peculiarity in the 

 presence of a very special form of cells, the so-called giant cells. 

 These are large masses of protoplasm appearing yellowish grey, and 

 with from ten to forty nuclei ; they begin to develop in the fifth month, 

 and are found in the after-birth in great numbers ; they lie partly 

 in the basal plate, partly in the septa, ordinarily in the immediate 

 vicinity of large blood-vessels ; but they are also found isolated in 

 the spongy layer of the decidua serotina and even between the 

 adjacent muscle-bundles of the uterus. 



The greatest difficulties in the investigation of the placenta uterina 

 are caused by its blood-courses. Numerous spirally twisted arterial 

 stems (Plate II. a) penetrate through the muscular layer of the womb, 

 and, passing through the spongy layer, reach the basal plate of the 

 placenta uterina, where their structure undergoes important changes. 

 For they here lose their muscular layer, and now appear as large 

 tubes, lined with endothelium only. From the basal plate they 

 penetrate in part into the septa placentae. From here they are 

 not to be followed further as closed vessels ; a transition to capillaries 

 does not take place anywhere. On the contrary, it can be proved that 

 through openings in the basal plate and the septa they^pojir-their 

 blood into a system of cavities between the chorionic villi, i.e., into 

 tlae^intervittous' urvilfi'Sjilacental spaces (c). The latter are bounded 

 on the one side by the membrana chorii (m) with its villi (z), on the 

 the other side by the basal plate (BP) with its septa. 



The blood is collected from this system of cavernous spaces into 

 large veins, which are likewise simply tubes lined with endothelium. 



