Anterior abdominal wall from now an anterior view or anterior perspective. So here are those layers of the abdominal wall from skin down to the coelomic sac and everything in between. And so the last time we did this in the other tutorial we did it by a cross-section. This time we're going to do the same thing, go through these same layers from anterior views.
So here we have a step dissection of the front of the abdomen and so the skin is this outside pinkish type color and If we now take a look at the dermatome picture of the body and take a square and blow it up, we'll see that the abdominal wall is segmentally innervated by the intercostal nerves. We know they're intercostal nerves because the T7 represents the T7 spinal nerve or the thoracic 7 spinal nerve, which is associated with the T7 spinal cord, spinal vertebral level, and neurological level. And these are intercostals, and they just go out in the same belt-like pattern.
So segmentally innervated down to T9, T10 for belly button, T11, T12, and then L1 in that inguinal region. We now take a look at a cross-section through, say, the T10 level, and we see there is our ventral ramus, and it courses between the internal oblique and transverse abdominus muscles all the way to the front. And it gives rise laterally to a lateral cutaneous nerve.
And... Look at the picture of the dermatomes, and it gives that type of innervation. And then also an anterior cutaneous branch, which gives that innervation down to the central mid-sagittal line. The same thing happens on the other side or bilaterally, making a belt-like pattern. So there's the innervation of the skin.
Now, the second layer is the hypodermis, which is made up of fascia. Camper's fascia makes up the majority of this. This is an adipose tissue, and it's... the fat that makes the pannus or that beer belly on Uncle Phil. And then there we have also on the very deep surface of this camper's fascia, a more fibrotic layer of tissue called scarpus fascia.
It's only really found between the umbilicus and the inguinal region. And it's thicker and you can actually be stitched up. There's scarpus fascia.
Now the external muscle fascia is the one that covers, it's deep to the hypodermis. and it covers the outside layer of the whole somatic muscle plane. And whether you know this or not, to be honest, it doesn't so much concern me. Now, the muscle in the aponeurosis layer, this is the layer that comes from those somites, those hypoxial muscles.
And there is a subvertebral muscle, four-layered lateral wall muscle, and ventral strap muscle, like we've covered before. I mean, this... Just for the order in which I cover, I'm going to switch. So I'm going to cover the four-layered lateral wall first, and then I'm also going to cover the ventral strap.
I'm not going to talk about the subvertebral muscle right now. That's the psoas because that's going to be in a posterior abdominal wall lecture. So really I'm going to focus on that four-layered lateral wall and the ventral strap muscle.
And there's four layers, and I'm going to talk about layers one and two because it's really just one muscle, our external oblique muscle that we see coursing along. The word oblique means at an angle, and external is outside. And so at an angle, these muscle fibers course from the ribs all the way down, and then the muscle stops near the midclavicular line, and the external oblique aponeurosis is the anterior projection that goes to the very midline. and connects to this white line called the linea alba, which simply means white line, and knits both the external oblique on the right and the external oblique aponeurosis on the left, knits it right down that midline.
Let's take a look at some cadaver dissections for a minute. So there we have the external oblique muscle, the superficial layer, and there's the deep layer, the external oblique muscle. And so they're dissected, a really fine dissection by Sean Miller here that shows this nice two layers.
And then... there's that deep layer again. So the external oblique really has two layers to it. Layer 3 is the internal oblique muscle. And that muscle courses many parts at a right angle to the external oblique.
And then also, when the muscle stops, the internal oblique aponeurosis courses right to the midline and fuses in that linea alba, that white line in the middle. So the internal oblique aponeurosis on the right and the left fuse in that midline. at that linea alba.
Layer four is the transverse abdominis muscle. So this is now the deepest layer. This muscle, to help see it better, we're going to outline this area of the, we'll talk about rectus abdominis soon, and we're going to cut that out.
And so what we have now is the following. We can see this transverse abdominis muscle, but The aponeurosis courses to that linea alba, but you'll recognize it's coursing behind that rectus abdominis. So we're going to see that's going to be significant soon. And all of these abdominal muscles, they help for lateral flexion of the vertebral column, rotation of the vertebral column, and when they contract, they compress abdominal contents, like whenever you cough or urinate or defecate or give birth to a baby.
So, let's take a look at this ventral strap muscle now, and there's our rectus abdominis. Rectus for straight, abdominis for abdominal region, where the obliques are coming at angles. This one goes straight up and down.
Straight up and down from the bottom of the ribs, all the way in sternum, and all the way down to the inguinal ligament. And the linea alba separates the two bellies of this rectus abdominis. And notice these intersection tendons that are in between that give the six. It's actually an...
eight-pack, most people call it six-pack, appearance to the rectus abdominis. This helps with flexion of the vertebral column. Okay, so here we have now the rectus sheath. So the rectus sheath is this white structure that we see.
I'm going to dissect it down so we now see the back of this rectus sheath. This line represents a cross-section above the umbilicus, and it's got the layers we've discussed. So there's our external oblique and internal oblique, transverse abdominis, there's our rectus abdominis, and there's the liniate. Now this yellow arrow represents the external oblique and part of the internal oblique aponeurosis as it courses over the front of the rectus abdominis and fuses at that linea alba. The second arrow represents now the transverse abdominis aponeurosis and the posterior lamina of the interoblique aponeurosis, and it courses behind the rectus abdominis to fuse at the linea alba.
So recognize there's an anterior, there's an... and anterior and posterior lamina to that. Now, here we've got the cross-section below, lower down, and recognize what happens.
There's our external oblique, internal oblique, transverse abdominis, rectus abdominis, and linea alba, but recognize that all three of those aponeuroses course in front of the rectus abdominis, and there's no aponeuroses that course behind. So the only supportive tissue behind the rectus abdominis down this low is this transversalis fascia. And so this arcuate line is the anatomical name given where the transition where above the arcuate line, the aponeuroses course in front of and behind the rectus abdominis. Below the arcuate line, all the aponeurosis only course in front of that rectus abdominis muscle. Here we have now the internal muscle fascia or that transversalis fascia.
It's all this fascia that's outlined. where the purple arrow just went down. This is now deep, not to be confused with the transversalis aponeurosis. Transversalis fascia is this internal muscle fascial layer, that other part of the sandwich that on the inside of the somite muscles.
The preperitoneal fascia is this yellow fascia, and I'm showing it in cross-section because I don't have a good illustration from the front to show it. The main thing is this is the fascia that's going to anchor or attract the parietal peritoneum to the body wall. So to show the parietal peritoneum, here we've got a coronal section through the anterior abdominal wall, the coronal section, and it's a posterior view.
So the green arrow is showing the parietal peritoneum on the internal surface. And that parietal peritoneum, as that extraperitoneal fat attaches it to the body wall, covers some structures. And so we call this the lateral umbilical folds.
The lateral umbilical folds are simply an elevation in this parietal peritoneum for the inferior epigastric artery and vein or inferior epigastric vessels. And it's paired, so that's why it says lateral umbilical folds, one on either side. The left side of this illustration has parietal peritoneum, the right side does not. The medial umbilical folds course all the way up to the umbilicus. are the obliterated umbilical arteries, one on either side.
And this is what's bringing, and when this was a fetus, bringing blood away from the heart into the umbilicus, out into the umbilical cord, into the placenta. And they're obliterated because they're not functioning anymore. And then the median, unpaired, right down the midline, coming from the bladder. is this median umbilical fold and it's surrounding the obliterated uricus, which is the structure that was taking urine from the fetal bladder into the umbilicus out.
into the amniotic sac. So there's the uracus. And I believe that's it.
I lied. I thought I had one more. That's right. The falciform ligament.
This is also coming from the umbilicus, that little hole in the middle. And the falciform ligament is important because it ignored the bladder. That's a mistake in my thing.
So this falciform ligament is coursing from the umbilicus all the way up between the two lobes of the liver. it houses the round ligament of the liver, which is the fetal remnant of the umbilical vein coming in from mummy through the umbilical cord, through the umbilicus, and then into the fetal circulation. Now, I think I'm done.