Sentence:  In this illustration, some license is taken, since the amnion is shown as still separate from the <WSD>chorion</WSD>; this is done to illustrate the process of apposition of the amniotic sac to the <WSD>chorion</WSD> and to accentuate the interposition of the yolk sac between the amnion and the <WSD>chorion</WSD>. 
Meaning of the word marked with <WSD> tags:  The protective and nutritive membrane in higher vertebrates that attaches the fetus to the uterus.