456 



MAMMALIA. 



known as the ilecidua xi'i-iiiiiM (h), and that part of the uterine 

 ■wall not related directly to the vesicle, the decidua vera {c). 



The chorion is directly attached to the decidua retlexn and 

 xcrutina. TIkj vascular connection between the reflexa and the 

 chorion atrophies, whilst that between the serotina and the 



Ul/-. — 



Fig. 1^37.— Diagrammatic Skction ov Pregnant Human Uterus with 



CONTAINED FOlTUS. 



d, AllaTit.<jic .stallv ; vv, umbilicil vpsit-'le ; (tvi, aiimion ; r/i, chorion ; h, decidua ^ori<- 

 iina ; c, deciduii vci'a ; /, decidua reflexa ; /-V, Fallopian tube ; g, cervix utei i ; if, fretal 

 villi of placenta ; e, embryo. (From Huxley, after Longet.) 



chorion increases, the villi liecoming much branched and fonu- 

 ing the chorion frondcmun. This latter structure and the decidua 

 aerotina form the true placenta. This placenta is discoidal, but 

 it is ventral, whereas the placenta of the rabljit is dorsal. At 

 birth the placenta and the fused decidua rem and reflexa are 

 all shed, and the ruptured blood-\'essels of the uterine wall 

 closed by its rapid contraction. 



3. The zonari/ pluroita. — Here the placenta is in the form of 

 a broad band. The yolk-sac never fuses with the chorion. At 

 first the allantois fuses with the sub-zonal membrane, at one 



