the perineal membrane.

Inferior to the pelvic diaphragm, you've got this membrane which is called the perineal

membrane. You can see this triangularly-shaped structure here, which I've outlined in green.

This is a thick fascial structure which attaches along the pubic arch. So you've got this attachment

along the pubic arch here. At the back, it's got this posterior border, which is free.

It's not attached to anything.

This membrane actually provides attachment for the roots of the external genitalia. I'll

come on to talk about this in another tutorial on the perineum. But importantly, it's got

these two holes to allow structures to pass from the pelvic floor into the perineum. This

is a model of a woman, so you've got these two holes here. Anteriorly, you've got the

urethral orifice and behind it, you've got the vaginal orifice. In males, obviously,

you don't have this orifice for the vagina. You've just got the anterior urethral orifice

in males.

So if you remember, I mentioned the urogenital hiatus of the pelvic diaphragm, that u-shaped

defect. Above the perineal membrane, you've got this urogenital hiatus. If I just rotate

the model anteriorly again, you can see that there's this little gap between the anterior

border of the perineal membrane and the pubic symphysis. So you've got a little gap here.

If I rotate back to superior view, you can see the urogenital hiatus here and the parts

of the perineal membrane with the two orifices for the vagina and the urethra.

I've just added the female reproductive system in and you can see the vagina entering into

the pelvic cavity through this vaginal orifice in the perineal membrane. With the urinary

system added, you can see the bladder and you can see the urethra here.

So the last part of pelvic floor to mention is the deep perineal pouch. The deep perineal

pouch is this fascial capsule which lies above the perineal membrane. This contains various

layers of skeletal muscle which differ between men and women. All the muscles in this compartment

are innervated by the perineal branches of the pudendal nerve.

So what I'm going to do is I'm going to switch to a cross-section to try and illustrate the

deep perineal pouch. What I've done here is taken a median sagittal section of this model.

If I just rotate inferiorly, you can see that I've sliced in half the perineal membrane.

If I just rotate around laterally, I'll show you what we're looking at.

So we've got the layer of levator ani muscles here, so the pelvic diaphragm above here superiorly.

And then just below it, we've got the perineal membrane.

So between the pelvic diaphragm muscles and the perineal membrane, you've got this deep

perineal pouch. So it lies like this. It's actually opened above. So there's no layer

separating the pelvic diaphragm muscles from the perineal pouch. So you've got this fascial

pouch, which I've drawn in green and it's opened superiorly.

So like I've said, you've got a few different structures within this pouch and they're innervated

by the perineal branches of the pudendal nerve and they're different in men and women.

So what I'm going to do is show you some of the structures that are within this perineal

pouch, this deep perineal pouch. Back to the superior view of the pelvic, which you're

familiar with, I'm just going to dissect away the pelvic diaphragm muscles, so I've got

rid of those muscles and we're looking superiorly at the perineal membrane. So the content of

the pouch sits on top of this in this fascial pouch.

So remember, we're looking at a model of a woman, so we've got the vaginal opening here

and we've got the urethral opening anteriorly.

So first, we'll look at the muscles in female because they've got two more muscles than

men. We've got this free border of the perineal membrane at the posterior aspect. In the midline,

we've got this little body called the perineal body, which is a fibromuscular connective

tissue node, which connects the structures of the perineum to the pelvic cavity above,

the pelvic floor above.

So the first muscle that we have is this deep transverse perineal muscle. It attaches laterally

on the ischiopubic ramus and it inserts onto this perineal body in the midline. So that's

the deep transverse perineal muscle.

And then over here, you can see this little muscle here. This is the external urethral

sphincter. This surrounds the proximal part of the urethra in women and the membranous

part of the urethra in males.

And then we've got two muscles which are unique to females. So we've got the compressor urethrae.

And then we've got the sphincter urethrovaginalis.

So the compressor urethrae originates from the sides of the ischiopubic ramus. And then

it loops in like this and meets anteriorly to the urethra. So you've got this compressor

urethrae muscle and it meets anterior to the urethra. This muscle aids the external urethral

sphincter in closing off the urethra.

And then you've got this muscle called the sphincter urethrovaginalis. As the name suggests,

it forms this sphincter around the opening of the vagina in the perineal membrane and

it also blends with these fibers here. So it surrounds the opening of the urethra as

well, so urethrovaginalis.

This originates on the perineal body at the back. I'm going to pass this forward surrounding

the opening with the vagina and then it blends anteriorly with the muscles surrounding the

urethral opening in the perineal membrane.

So in men, you've just got the deep transverse perineal muscle and the external urethral

sphincter. Something else to remember in males is that within this deep perineal pouch, you've

also got these glands called bulbourethral glands, which are also known as the glands

of Cowper. So they lie within the deep perineal pouch.