328 NORMAI, HISTOLOGY AND ORGANOGRAPHY. 



tuous mucous glands. Blood-vessels also form a 

 plexus in the spongy layer. 



The decidua reflexa disappears during the first 

 months of pregnancy, while the decidua serotina 

 enters into the formation of the placenta. 



Placenta. The placenta is a vascular organ for 

 the nourishment of the fetus, and serves the purpose 

 of bringing the fetal and maternal blood into closest 

 proximity without actually blending. The organ 



Villi. 



.:- ' ^' ~'2J^4- *"*';-*-* ^* ^> ^s^ Compact layer of de- 

 -* + ffx*r- "^r^ ' .~~ -Vt T'. cidua with decidual 



i~- ~ ^ .*~ ^~ ^ r7 ^- "* '."'^^L^-- ' 



Spongy layer of de- 

 cidua -with gland 

 spaces. 



Fig. 235. Section of the decidua serotina at the margin of the placenta. 



may be divided into an embryonic part, the placenta 

 jcetalis, and a maternal part, the placenta materna. 

 The latter is the modified uterine mucosa or decidua 

 serotina. 



The fertilized ovum usually finds lodgment in the 

 fundus of the uterus. Very early it becomes en- 

 closed in an envelope of its own production called 

 the chorion. This chorion has an outer epithelial 



