THE UTERUS DURING MENSTRUATION AND PREGNANCY 



241 



outlined cubical cells, and an outer syncytial trophoderm layer (Fig. 235). The 

 epithelium also forms solid columns of cells which anchor the ends of certain villi 

 to the maternal tissue. Islands, or nodes of epithelial cells, are attached to the 



Border cleft 



Posterior 



lip of os 



uteri 



Border zone 



Apex of 

 dccidua 



Cervical 

 canal 



Fig. 233. — Section through a gravid uterus of twelve to fourteen days (Kollmann's Atlas). 



villi or lie free in the decidua basalis and represent portions of the primitive troph- 

 ectoderm. In the vessels of the chorionic villi the chorionic circulation of the 

 embryo is established. The blood-vessels of the uterus open into the intervillous 

 16 



