258 EMBRYOLOGY. 



chorion frondosum to form a nutritive organ for the embryo, 

 the after-birth, or placenta. 



According to the statements of KUNDRAT and LEOPOLD it under- 

 goes changes similar to those of the decidua vera. Here also the 

 uterine glands grow rapidly in its deeper portions (fig. 148) and are 

 converted into irregular spaces (dh), which are from the beginning, 

 however, most extended in breadth. Subsequently they are crowded 

 together still more by the pressure and the growth of the placenta 

 until they become narrow fissures which lie parallel to the surface 

 of the uterus. 



The glandular epithelia disintegrate to a still greater extent than 

 in the vera, and by disintegrating and swelling up become detached 

 from the connective-tissue walls ; only those regions of the glands 

 which are adjacent to the muscular layer (M) retain their cylindrical 

 cells. 



In this presentation KUNDRAT and LEOPOLD disagree with KOLLIKER 

 and with TURNER, who likewise, it is true, find great spaces in the 

 deeper layer of the serotina, but interpret them for the most part 

 as greatly enlarged blood-vessels, an assumption according to which 

 there would exist an important difference between the serotina and 

 the vera. 



In the superficial layer the outlets of the glands must disappear 

 early, since they become pressed together. Besides, more active cell- 

 proliferation takes place in the inter-glandular tissue. 



Therefore the decidua serotina (fig. 148 Dse) is also converted 

 into two readily distinguishable layers : 



(1) A deeper spongy layer (Sp), in which the detachment of 



the placenta subsequently takes place, and 



(2) A superficial, more compact layer ( C). The latter alone shares 



in the formation of the placenta, and is accordingly called 

 the placenta uterina (or materna). It undergoes from the 

 second month forward more profound alterations. 

 We shall become acquainted with these in the description of the 

 placenta, to which we now pass. 



5. The Placenta. 



The placenta is a very vase alar, and when filled a spongy or doughy, 

 disc-shaped structure, which at the height of its developxient mea- 

 sures 15 to 20 cm. in diameter and is 3 to 4 cm. thick. Its weight, 

 reaches somewhat more than a pound (500 grammes). Hie surface 



