37 



HISTOLOGY 



through the persistent body stalk. The amniotic cavity greatly enlarges 

 to accommodate the growing embryo, and the mesoderm of the amnion 

 comes in contact with that of the chorion, to which it adheres more or less 

 firmly. The embryo is bathed in the amniotic fluid (liquor amnii) of 

 uncertain derivation, once thought to be sweat from the embryo, and later 

 considered to contain the products of the Wolffian body, and urine from 

 the permanent kidneys. Occasionally toward birth the meconium from 



PIG. 370. A NORMAL HUMAN EMBRYO OF 10.0 MM., REMOVED SURGICALLY WITH THE UTERUS. Six, WEEKS 



AFTER THE LAST MENSTRUATION. 



the intestine mingles with it and discolors it. It is now generally believed 

 to be secreted by the amniotic epithelium. 



Relation between the Embryonic Membranes and the Uterus. When the 

 embryo within its chorionic vesicle passes from the tube into the uterus, 

 it is probably in a stage comparable with that shown in Fig. 368 (B or C). 

 By the activity of the proliferating trophoderm, the uterine mucosa is 

 partially destroyed and the chorionic vesicle becomes imbedded in its 

 substance. This process is known as the implantation of the ovum. The 

 walls of the vessels in the tunica propria of the uterus are broken down, 

 and the maternal blood flows over and around the chorionic villi, in con- 



