Rectus Sheath II – Anterolateral Abdominal Wall

00:01 This view is slightly different. This view is as if we have cut down sagittally through the abdomen to have a look at these layers. So, in this diagram, we have got anterior here and we have got posterior. And here, we have got a reminder of those layers above and below the umbilicus. So, here we see above the umbilicus and here we see below the umbilicus.

00:24 So, here on the diagram, this arrow is pointing to umbilicus. So, the umbilicus will be about here. And then we can see above it and we can see below it. Above the umbilicus, we had external oblique, okay? So, we had external oblique. So, we can draw in external oblique.

00:42 And that's going to be indicated here in blue. This blue line here is external oblique.

00:46 In orange, we can see the skin of the body. So, external oblique is anterior to rectus abdominis. Here, we can see rectus abdominis muscle. If we look below the umbilicus, external oblique is still there. So, now, we are below the umbilicus, external oblique is still present.

01:07 It just always lies anteriorly. If we go deep to external oblique, pick it up in green here, we can see that we have got internal oblique's anterior layer because, also in green, above the umbilicus, we can see internal oblique's posterior layer. So, here, we have internal oblique... internal oblique, its anterior and posterior layers where remember, above the umbilicus, its divided. What we can also see, if we keep going posterior, is transversus abdominis. In purple here, we can see transversus abdominis and this is above the umbilicus and then most posteriorly again, we can see transversalis fascia here in black which is then the peritoneum. So, importantly, above the umbilicus, we can see we have got external oblique, anterior layer of internal oblique, rectus abdominis. We have got the posterior layer of internal oblique and then we have got the transversus abdominis and then transversalis fascia.

02:18 Just below the umbilicus, we can see the rectus abdominis muscle penetrates these layers. So, we can see rectus abdominis is penetrating these layers so that it actually pierces them and lies posterior to these layers. So, now, that we are below the umbilicus, you can see we have external oblique, internal oblique, the anterior and posterior lamina have merged and we can see we have transversalis fascia. If we were to look, if we were to stand in the abdomen and look at the anterior abdominal wall from the inside, we could see this transition. We could see this transition and it's known as the arcuate line.

03:14 Here, we can see this arrow is indicating what's known as the arcuate line and that's where you have this covering posterior rectus abdominis which then disappears. And hopefully, you are gonna appreciate that when we look at posterior view of the anterolateral abdominal wall.