82 



THE FETAL MEMBRANES AND EARLY HUMAN EMBRYOS 



ment to better advantage, there grow out from the chorion into the uterine 

 mucosa branched processes or villi. The villi are bathed in maternal blood, and 

 in them blood-vessels are developed, the trunks of which pass to and from the 

 embryo as the umbilical vessels. The embryo receives its nutriment and oxygen, 



Inner cell-mass 



Entodei 



Irophoblast 



Inner eel l-mass Trophoblast 



Embryonic ectoderm Entoderm 



Maternal bloodvessels 



Syncytiotrcphoblast 



Cytotropboblasf 



Embryonic ectoderm Entoderm 



Fig. 71. — Section showing three stages in the formation of the amnion of bat embryo (after Van Beneden). 



and gets rid of waste products through the walls of the villi. The region where 

 the attachment of the chorionic villi to the uterine wall persists during fetal life 

 is known as the placenta. It will be described later with the decidual membranes 

 of the uterus. We saw how the allantois of Ungulates had assumed the nutritive 



