REPRODUCTION. 85 
a maternal part, the decidua serotina, the two becoming blended 
so that the removal of one involves that of more or less of the 
others. The connection of parts is far closer than that described 
for the rabbit; and, even with the preparation that Nature makes 
for the final separation of the placenta from both foetus and 
Fie. 94.—Diagram illustrating the decidua, placenta, etc. (after Liégeois). e, embryo ; 
i, intestine ; p, pedicle of the umbilical vesicle ; u. v, umbilical vesicle ; a, amnion ; ch, 
chorion; v. ¢, vascular tufts of the chorion, constituting the foetal portion of the placenta; 
my 2, maternal portion of the placenta ; d. v, decidua vera; d. r, decidua reflexa; al, 
al is, 
mother, this event does not take place without some rupture of 
vessels and consequent hemorrhage. 
It is difficult to conceive of the great vascularity of the 
human placenta without an actual examination of this structure 
itself, which can be done after being cast off to great advan- 
tage when floating in water; by which simple method also the 
thinness and other characteristics of the membranes can be 
well made out. 
The great vessels conveying the foetal blood to and from the 
placenta are reduced to three, two arteries and one vein. The 
villi of the placenta (chorion) are usually said to hang freely 
