Author: Dr Peter de Souza
Last modified: 17 December 2020


Okay, so this is a tutorial on the different layers of the abdominal wall.   Firstly, I'm just going to show you the various muscles very briefly and then we'll run through the different layers that make up the abdominal wall.


Right in the middle, we've got this muscle here, which is called the rectus abdominis. And then on the side, laterally, we've got three different muscles.   Superficially, we've got this muscle with its fibers oriented infero-medially. This is the external oblique muscle. I'll just remove that.

Underneath the external oblique, we've got the internal oblique. This has the majority of its fibers oriented superomedially. And then underneath this, we've got the transversus abdominis with its horizontally oriented fibers.


Let’s just take a look at a cross-section.   We’re going to slice the abdomen in half and we're going to look at a cross-section and the different layers that we pass through.


We’re looking at a cross-section now. I'll just orientate you. Anterior is this side, so you can see the rectus abdominis muscles. And then laterally, you can see the three muscles I've just showed you – so the external oblique, the internal oblique and the transversus abdominis.


We’re going to just imagine passing a needle through the lateral side of the abdomen. We're going to take a look at the layers that the needle would pass through if we stuck it through this side of the person.


The first thing we'd pass through is obviously the skin. I'll just draw that on here. And then next, we'd pass through the superficial fascia.   The superficial fasciae consists of two layers. You've got the superficial fatty layer, which is called Camper's fascia. And you've got the deeper membranous layer, which is called Scarpa's fascia.


The way I remember which way around these two guys, the letter C is the before the letter S, so Camper's is more superficial than Scarpa's fascia.   I'll just draw that on here. Let me scribble that on. This is the superficial fascia. This is the fatty Camper's fascia. And we've got the membranous layer, so the Scarpa's fascia. This is the superficial fascia and that lies under the skin.


And then after the superficial fascia, it depends where you're really putting the knife or the needle or whatever. If we're putting it through the lateral part of the abdomen, so through here, we're next going to pass through the muscles that I showed you, so the external and internal obliques and the transversus abdominis muscle.


If we're chopping through here, then we'll pass through the aponeuroses of these muscles.  And obviously, if we put it through here, we'll pass through the rectus sheath and the rectus abdominis muscle.


Let’s just say we're passing the knife through this part here.   We’ve gone through skin and then the superficial fascia, which consists of the Camper's and Scarpa's fascia. And now we're going to go through these three muscles.   This is the external oblique, then the internal oblique and then finally, the transversus abdominis.


After the transversus abdominis, there's this thin layer of fascia, which is called the transversalis fascia. This lines the transversus abdominis and it also lines the abdominal cavity.   It lies right underneath the transversus abdominis and it runs just underneath. It lines the abdominal cavity. I'm drawing this on in green. This is the transversalis fascia.


Underneath the transversalis fascia, we've got the extraperitoneal fascia.   I'll draw this on in purple. This is a thin layer of connective tissue and this lies between the transversalis fascia and the next layer, which is the parietal peritoneum.   That’s why it gets the name extra + peritoneal fascia because it lies outside the parietal peritoneum. I'll just draw the parietal peritoneum in here in red. This is the final layer of fascia that your needle will pass through (or your knife or whatever you're using).


The parietal peritoneum lines the walls of the abdomen. And it's a thin serous membrane.   The peritoneum, you've got the parietal peritoneum, which lines the walls of the abdomen, then you've got the visceral peritoneum, which covers the viscera and then you've got mesenteries, which is kind of doubling up of the peritoneum to wrap around the organs and suspend it from the abdominal walls. I'll do another tutorial on the peritoneal cavity and the peritoneum.


Those are the layers of the abdominal wall.   You’ve got the skin, the superficial fascia consisting of Camper's and Scarpa's fascia (so fatty and membranous fascia). And then you've got the three muscles, the external and internal obliques and the transversus abdominis muscle.


And then you've got the transversalis fascia, which lie immediately below these muscles. And then you've got the extraperitoneal fascia. And then below that, you've got the parietal peritoneum.