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Ischioanal Fossa – Perineum and External Genitalia

by James Pickering, PhD
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      Slides 18 Abdominal and Pelvic Anatomy Pickering.pdf
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    00:01 So now let's go on to looking at the anal triangle.

    00:04 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.

    00:26 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.

    00:36 This is obturator internus muscle and what we have lying over obturator internus muscle obturator membrane.

    00:45 What we have a thickening of obturator membrane here and a thickening of obturator membrane here we have the tendinous arch.

    00:55 We have the tendinous arch of obturator membrane.

    00:59 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.

    01:14 What we have done is we have cut this transversely in line with the rectum.

    01:21 We have cut it coronally down through the rectum.

    01:27 Now, because the rectum and the anus, which we can see down here, is positioned within the anal triangle.

    01:34 And because the anal triangle doesn't contain the perineal membrane we can see there is no structure traversing between the ischial tuberosities.

    01:48 We see there is no structures traversing between the ischial tuberosities.

    01:54 That means we have created this space here.

    01:59 Laterally we have got obturator internus muscle.

    02:03 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.

    02:22 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.

    02:39 A wedge shape space which we can see again here..

    02:43 That is lateral to the rectum and the anal canal.

    02:49 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.

    03:07 Therefore there is no separation into deep or superficial compartments which we will see when we look at the urogenital triangle in more detail.

    03:17 Let's have a look at the boundaries. Laterally we have the ischium which we can see here.

    03:22 We have obturator internus muscle and obturator internus fascia which we can see here.

    03:29 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.

    03:38 Posteriorly we can't see this. But we know the posterior boundary of the anal triangle is going to be the sacrotuberous ligaments.

    03:47 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.

    04:09 So we find we have the muscles associated with those external urethral sphincter, the deep and superficial transverse perineal muscles.

    04:17 And what we also have is the fat within the ischioanal fossa passing into the deep perineal pouch.

    04:28 The deep perineal pouch being located at the level of the urogenital triangle which is positioned above the perineal membrane.

    04:37 And this extension of the ischioanal fossa anteriorly into the deep perineal pouch is known as the anterior recess.

    04:48 We will explore that in future slides.


    About the Lecture

    The lecture Ischioanal Fossa – Perineum and External Genitalia by James Pickering, PhD is from the course Pelvis.


    Included Quiz Questions

    1. Sacrotuberous ligaments
    2. Levator ani
    3. Ischium
    4. Obturator internus
    5. External urethral sphincter
    1. The deep perineal pouch lies superior to the membrane
    2. The deep perineal pouch lies inferior to the membrane
    3. The deep perineal pouch lies anterior to the membrane
    4. The deep perineal pouch lies posterior to the membrane
    5. The deep perineal pouch lies lateral to the membrane

    Author of lecture Ischioanal Fossa – Perineum and External Genitalia

     James Pickering, PhD

    James Pickering, PhD


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