120 



THE HUMAN EMBRYO. 



villous chorion of the ovum, and find, as above stated, that only the tips of the 

 villi are united with the surface of the reflexa. In the finished stage the 

 decidua is reddish-gray, spongy or pulpy, soft, and moist. After the fourth 

 month it acquires, especially in the superficial layers, a duller brownish color, 

 which subsequently becomes more marked. This coloration is due to the deci- 

 dual cells. During the first two or three months the scattered openings of the 

 uterine glands can still be distinguished over the surface of the serotina and vera. 



Muse. 



.. X 



ov.. 



D.ref, 





\„^ 



-L.g. 



Fig. 56. — Human Uterus, about Forty Days Advanced in Pregnancy. 

 Muse, Muscularis. Dv, Decidua vera. D.ref, Decidua reflexa. Ov., Ovary. Ovd, Oviduct (Fallopian tube). 

 Lig, Round ligament. Vg, Vagina. The uterus has been opened by cutting through the anterior walls 

 and reflecting the sides. — [After Coste.) 



The surfaces themselves of the vera and reflexa, though somewhat irregular, re- 

 main more or less smooth. The inner surface of the reflexa is more irregular and 

 has protuberant parts united with the tips of the future chorionic villi. The 

 surface of the decidua serotina, on the contrary, becomes very irregular during 

 the progress of pregnancy, forming little mounds which may become so high as 

 to resemble columns, or so broad as to constitute septa. In later stages the septa 



