If we now move on to the actual walls of the
pelvis then we have a lateral wall, a posterior
wall and then anterior wall, but actually,
look at the orientation. If you look at the
orientation of the pelvis, you can see that
it’s kind of running down in this direction.
A lot of the weight which is coming down here
is actually being borne on the pubic symphysis.
It’s not tilted square. It is actually tilted
quite inferiorly. So, the actual pelvis is
tilted. So, we have this passageway coming
down through here, allowing the... allowing
the baby when it’s being borne to pass through
the pelvis and it takes this kind of this direction.
If we look at the anterior wall of the pelvis,
we can see it’s made up of the pubic symphysis
and the various pubic rami, superior and inferior
pubic rami, because this is the anterior wall.
The lateral wall over here, we can see is
made up of some important muscles and membrane.
Importantly, we have this muscle... this muscle,
here, we can see is running all the way over
here. This is obturator internus muscle, obturator
internus. It lines the lateral wall of the
pelvis and is within the obturator foramen.
It is really important, you remember, that
the obturator muscle, obturator internus muscle
is on the lateral wall of the pelvis. Its
tendon passes out through here. Its tendon
actually goes to, in a way, goes to attach
on to the femur and it passes out to the pelvis
via the lesser sciatic foramen. So, remember
that the tendon of the obturator internus
actually leaves the pelvis. What we can see
lying on top of obturator internus muscle
is this thin sheet and this is obturator fascia.
So, we have the obturator foramen, filling
the obturator foramen is obturator internus
and then you have obturator fascia and again,
that’s important, we will come back to it.
This forms the lateral wall of the pelvis.
We can also see we have got this defect here
and that allows obturator artery, nerve and
vein to leave the pelvis and pass into the
medial compartment of the thigh. If we then
look posteriorly, we find we have the sacrum
most posteriorly and we have some muscles
radiating from the sacrum from the coccyx
down here that form this posterior boundary.
Posterolaterally, we can see we have got coccygeus
muscle, you can see that muscle here. And
then superior to the coccygeus, we find we
have piriformis. And piriformis is running
out of the pelvis. And this also goes to attach
to the femur. It attaches the greater trochanter
of the femur, it’s a lateral rotator of
the thigh. But, it originates from the anterior
surface of the sacrum and it passes out through
the greater sciatic foramen. Remember that
passing out of the greater sciatic foramen
superior to it was the superior gluteal blood
vessel and passing out to the pelvis inferior
to it was the inferior gluteal artery and
also the internal pudendal artery.
What we have here, inferior to the piriformis,
is coccygeus. Coccygeus is running from the
coccyx to the ischial spine. It runs on the
inside of the sacrospinous ligament. So, when
we look posteriorly at the ligaments of the
pelvis, we can see the sacrospinous ligaments.
But, lying on the inside of the sacrospinous
ligament, we find we have coccyx... coccygeus
muscle... we find we have the coccygeus muscle
here. Here, I have mentioned both piriformis
and obturator internus exit the pelvis via
the greater and lesser sciatic foramina, respectively
and that the obturator membrane has a thickening
that runs from the superior pubic ramus to
the ischial spine and this, as we move on
to the pelvic floor, is really important.
If we have running along here, we see we have
this thickening. This is an important thickening
of the obturator fascia, obturator membrane
that's lying like medial to obturator internus
muscle. This thickening runs from the superior
pubic ramus up here all the way to the ischial
spine. And it forms an important attachment
site for the pelvic floor muscles, which we
are now going to talk about.