236 



THE UROGENITAL SYSTEM 



241). Through the umbilical vein and arteries in the cord the placental 

 circulation of the embryo takes place. 



The Decidua Vera. During the first phase of menstruation the 

 uterine mucosa begins to differentiate into a broad, superficial compact 

 layer and into a narrower, deep spongy layer in which are found the dilated 

 ends of the uterine glands. After pregnancy these two layers are still 

 further differentiated in the wall of the decidua vera and decidua basalis. 

 The compact layer is much thicker than the spongy layer and in it are 

 found numerous stroma cells, enlarged blood vessels, and decidual cells 

 (Fig. 244). The decidual cells, frequently niultinucleate, are derived 



Amnion 



Chorion 



Compact layer 



Spongy layer i?. 



Vein 



--Gland 



Vein 



Muscular: s> ' 

 fe 



FIG. 244. Vertical section through the wall of the uterus about seven months pregnant, with 

 the membranes in situ (Schaper in Lewis and Stohr). X 30. 



from the stroma cells of the mucosa. They are large, being 50 n in 

 diameter, with clear cytoplasm and vesicular nuclei. Their function 

 is in doubt. Glycogen has been found in them, but during the later 

 months of pregnancy many of them degenerate. 



In the spongy layer of the mucosa occur the enlarged and tortuous 

 uterine glands of pregnancy (Fig. 244). During the first two months of 

 pregnancy the long axes of the glands are perpendicular to the surface 

 of the mucosa. Later, as the decidua is stretched and compressed owing 

 to the growth of the fetus, the glands are broadened and shortened and 

 the cavities of the glands become elongated clefts parallel to each other 

 and to the surface of the decidua. The gland cells become stretched 



