352 



REPRODUCTION 



space becomes smaller and is obliterated by the end of the fifth 

 month. After this time both vera and reflexa undergo retro- 

 grade changes due to pressure and become closely attached to 



FIG. 109. Diagrammatic view of a vertical transverse section of the uterus 

 at the seventh or eighth week of pregnancy. 



c, c, c', cavity of uterus, which becomes the cavity of the decidua, opening at c, c, 

 the cornua, into the Fallopian tubes, and at ff into the cavity of the cervix, which is 

 closed by a plug of mucus; dv, decidua vera; dr, decidua reflexa, with the sparser villi 

 imbedded in its substance; ds, decidua serotina, involving the more developed 

 chorionic vili of the commencing placenta. The fetus is seen lying in the amniotic 

 sac; passing up from the umbilicus is seen the umbilical cord and its vessels passing 

 to their distribution in the villi of the chorion; also the pedicle of the yolk-sac, which 

 lies in the cavity between the amnion and chorion. (Kirkes after Allen Thomson.) 



the chorion. They are discharged with the membranes at birth. 

 Placenta. The placenta is the organ of nutrition for the 



