at one side of the external structure.
Now, let’s step back another layer and we’ll
look at it in the context of the uterus. Here,
we’re looking at a view, a section through
the mother from the side looking at the uterus,
and you can see how the whole developing structure
is beginning to project into the uterine cavity.
And as the amniotic cavity gets larger and
larger, obliterates all the other spaces,
gradually, it will come to almost completely
fill the uterus. So at later stages,
the amniotic cavity is
almost completely occupying all of that space
projecting into the uterine cavity, until
finally, it’s almost completely excluded,
all the other species are excluded by this
amniotic cavity developing on the yolk side.
The structures we should derive from the mother
remain as called the “chorion”. So these
are described as the chorion. So the amnion
is meeting the chorion and forming a fused
membrane once all the space is eliminated.
The area where the villi is concentrated
is called the “chorion frondosum”, and
the remaining smooth part is called the “chorion
laeve”. You can see in this late picture,
five months into the pregnancy, all of the
space is taken up by the amniotic cavity,
the amniotic fluid, and the baby within that.
So for the baby to get out, it exits down
through the cervix, then what’s going to
happen is it has to rupture those membranes
that lie between it and the outside world.
Of course, these chorionic villi, you can
sample them. The ones which are going to disappear
are obviously not important for our survival.
So you can insert a needle and take a sample
of the chorionic villi, and then analyze them
for genetic defects. And that’s called “chorionic
villus sampling”. It is in itself a slightly
risky procedure, and therefore, slightly safer
to take a little piece of the amniotic fluid.
So again, you can insert a needle in, draw
off some amniotic fluid, not only analyze
the biochemical composition of the amniotic
fluid, but you can also look for embryo cells
that have been shed into the amniotic fluid.
These can be cultured, and again, examined
for genetic defects. Now, the things that
we were looking at are