Perineum: Boundaries and the Perineal Membrane

by James Pickering, PhD

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    00:01 So let's look at the boundaries of the perineum. This is a inferior view of the bony pelvis.

    00:07 We have anterior up here and we have posterior here.

    00:11 We have the pubic symphysis. We have the inferior pubic ramus. We have the ischiopubic ramus.

    00:17 We have the ischial tuberosity here.

    00:21 We have running from the ischial tuberosity to the sacrum, the sacrotuberous ligament and here we have the coccyx.

    00:29 And we can see that creates this diamond shape.

    00:33 If we do that again, we can see this diamond space has been created.

    00:39 Anteriorly we have the pubic symphysis Laterally we have ischial tuberosities.

    00:44 Posteriorly we have the coccyx. If we connect these four dots up via the inferior pubic rami and via the sacrotuberous ligament. We can see we have this diamond shape. This diamond shape can be divided into two triangles via the transverse line at the level of the ischial tuberosities.

    01:12 So if we to draw a transverse line across the ischial tuberosities, we have split this diamond into two.

    01:21 We have split into a more anterior triangle.

    01:25 This is the anterior aspect, at more anterior triangle and we have split into a more posterior triangle. This is a posterior aspect.

    01:35 So we now have this diamond split into two.

    01:38 This anterior triangle is known as the urogenital triangle.

    01:42 And what passes through this triangle. In the male it's going to be urethra and in the female, the urethra plus the vagina the urogenital triangle. This triangle here.

    01:56 The triangle that's posterior to it, that just contains one aperture.

    02:00 Its known as the anal triangle and this anal triangle allows the anus to pass through it. So we are looking at this as if someone is lying on their back, this is the posterior aspect.

    02:13 Anteriorly is up in this direction and we are looking through into their peritoneum, with their external genital removed, we can see the pubic symphysis.

    02:23 We can see the coccyx and we can divide this diamond shape into two triangles urogenital triangle, anal triangle. Within these triangles, we will have those apertures for the urethra/vagina and the anal.

    02:42 So now I just want to concentrate on the perineal membrane.

    02:47 And the perineal membrane is just associated with the urogenital triangle.

    02:54 Just associated with the urogenital triangle and that's what we can see here.

    02:58 If we look at this view, this anterior view of the pubic bone within the pelvis. This is superior up here. This is inferior at now.

    03:07 We can see the ischial tuberosities. We can see the pubic symphysis and we can see the inferior pubic ramus.

    03:16 So here if we draw those transverse line again we can see we have created this triangle which is the urogenital triangle.

    03:25 And we can see that just filling this urogenital triangle, just occupying the urogenital trinangle is a shelf like structure. A shelf like thin membrane known as the perineal membrane.

    03:42 We can that in this perineal membrane, there is a couple of holes.

    03:48 And the female is a good one to use as an example; because, there is two holes.

    03:50 We can see we have a hole for the urethra.

    03:53 We can see we have a hole for the vagina.

    03:57 So these structures are passing through this perineal membrane at the level of the urogenital triangle.

    04:06 We can see surrounding the urethra is the external urethral sphincter and we will explore other muscles in this area as we go on.

    04:17 But this perineal membrane is just located within the urogenital triangle. If we were to explore some other muscles then if we can appreciate that we have got the perineal membrane here.

    04:31 And that is just the shelf that's been put in the urogenital triangle.

    04:39 So if we were to do a transverse section through we could see the perineal membrane here. And then we would have the urethra passing through it.

    04:49 So we would have the perineal membrane here attaching to the ischial tuberosities; attaching to the ischial tuberosities here.

    04:59 And then we have got this perineal membrane that is just running across from ischial tuberosity to ischial tuberosity. Here that we could imagine the sections have been taken along here.

    05:11 And here we can see the free edge of the perineal membrane where it stops.

    05:17 Now associated with this posterior border...

    05:22 Associated with this posterior border, there is going to be two muscles - deep and superficial transverse perineal muscles.

    05:36 Along this posterior border which we can imagine is here.

    05:40 This posterior border, there is going to be a deep and a superficial transverse perineal muscle layer.

    05:53 Here we can see the deep transverse perineal muscle and here we can see the superficial transverse perineal muscle.

    06:03 And these lie along the posterior border of the perineal membrane running from ischial tuberosity to ischial tuberosity.

    06:10 Now where they converge in the midline here we find we have this fibro muscular structure. This fibrous mass and that is known as the perineal body, the perineal body.

    06:26 And the perineal body lies directly posterior to the vagina along the posterior border of the perineal membrane.

    06:34 It's in the midline and our perineal muscles converge into it is known as the perineal body. More posteriorly, we then find the anus.

    06:49 Located posterior to the vagina or the bulb of the penis, if we are in the male, we then would find the anus and the anal canal. And the perineal body is positioned between them.

    About the Lecture

    The lecture Perineum: Boundaries and the Perineal Membrane by James Pickering, PhD is from the course Pelvis.

    Included Quiz Questions

    1. Superficial
    2. Deep
    3. Lateral
    4. Posterior
    5. Anterior
    1. Pubic symphysis
    2. Ischial tuberosity
    3. Ischial spine
    4. Coccyx
    5. Perineal body
    1. Inferior rectal
    2. Superior rectal
    3. Middle rectal
    4. Inferior mesenteric
    5. Posterior rectal

    Author of lecture Perineum: Boundaries and the Perineal Membrane

     James Pickering, PhD

    James Pickering, PhD

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