So now let's go on to looking
at the anal triangle.
The anal triangle is now at the
posterior level of the perineum.
So we have moved now behind
the perineal membrane. And what we
have done is we have made a section
a coronal section through the
pelvis and now we need to remember
the lateral boundaries of the pelvis.
We need to remind ourselves that if
this is going to be the ischium over here
and then lining on the ischium we
have the obturator internus muscle.
This is obturator internus muscle and what we
have lying over obturator internus muscle
What we have a thickening of
obturator membrane here
and a thickening of obturator membrane
here we have the tendinous arch.
We have the tendinous arch
of obturator membrane.
And what comes away from the tendinous
arch to merge in the midline?
The pelvic floor muscles,
specifically levator ani
and this is what we can see
here - running towards the midline.
What we have done is we have cut this
transversely in line with the rectum.
We have cut it coronally
down through the rectum.
Now, because the rectum and the
anus, which we can see down here,
is positioned within the anal triangle.
And because the anal triangle doesn't
contain the perineal membrane
we can see there is no
between the ischial tuberosities.
We see there is no structures traversing
between the ischial tuberosities.
That means we have
created this space here.
Laterally we have got
obturator internus muscle.
Medially we have got
our levator ani muscle
and inferiorly we just got the skin here.
The skin here, this perianal skin,
that surrounds the anal opening
which means we have got this nice space
either side of the retum.
We have cut it down coronally.
What this space is called
is the ischioanal fossa
and this is a fat filled space that
sits either side of the
rectum and the anal canal.
It's a wedge shaped space.
A wedge shape space which
we can see again here..
That is lateral to
the rectum and the anal canal.
Remember, that we have cut coronally
down through the anal triangle
and at this level the
perineal membrane does not
exist. Really important that at
the level of the anal triangle
the perineal membrane does not exist.
Therefore there is no separation into
deep or superficial compartments
which we will see when we look at the
urogenital triangle in more detail.
Let's have a look at the boundaries. Laterally
we have the ischium which we can see here.
We have obturator internus muscle and obturator
internus fascia which we can see here.
Medially we can see we have
the anal canal with levator ani
and external anal sphincters. We can see
these external anal sphincter down here.
Posteriorly we can't see this.
But we know the posterior boundary
of the anal triangle is going to
be the sacrotuberous ligaments.
Remember that from the diamond
shaped arrangement that we saw
and also we could have part of coccyx
in there as well. And anteriorly
what we are going to have anteriorly...
Well what would we find anterior
to the rectum?
We find we have the vagina or
we find we have the urethra.
So we find we have the muscles associated
with those external urethral sphincter,
the deep and superficial
transverse perineal muscles.
And what we also have is the fat
within the ischioanal fossa
passing into the deep perineal pouch.
The deep perineal pouch being located at
the level of the urogenital triangle
which is positioned above
the perineal membrane.
And this extension of the
ischioanal fossa anteriorly
into the deep perineal pouch
is known as the anterior recess.
We will explore that in future slides.