 Dr. Sanjay Sanyal, Professor, Department Chair, so this is going to be a demonstration of the layers of the abdominal wall. This is a supine cadaver. This is the right side. I'm standing on the right side. The camera person is also the right side. As we know the first layer is the skin and this patient had a very thick skin and under that is the next layer that is the fatty layer of the superficial fascia. Fatty layer of the superficial fascia is called the camper's fascia and this is the layer which gets thicker as the person grows more and more fat and that is what we call facetiously as a spare tire. Then we have a third layer and that is called the membranous layer of superficial fascia and we have retained a little bit of that here. This is the membranous layer of the superficial fascia. As it stretches over the abdomen then as it goes to the thigh it gets attached to the fascia later the thigh. However in the midline the membranous layer it continues in the male as the dartos fascia over the scrotum and then it continues further into the perineum. Then it becomes known as the colis fascia where it gets attached to the perineal membrane and there it forms a superficial perineal pouch. They're all continuous with each other. That is the third layer. That is the scarpus layer. Then we have the muscular layers and that is what we are seeing right now. The first muscle that we see are the flat oblique muscles of the abdomen. This is the external oblique muscle. The oblique muscle and the internal oblique and the transverse the prominence muscle as I will show you just now they have all got their own individual layers of deep fascia and we have removed part of it here. The traditional fibers of the external oblique muscle is like this as we can see them clearly here. This is as if the hands are in the pocket and as it goes down and medially it becomes a flat aponeurotic sheet. So this is the aponeurosis of the external oblique and here it forms a rectus sheet and further medially it forms a linear alba. Inferiorly the external oblique aponeurosis forms this ligament here and that is the inguinal ligament which is the inferior free margin of the aponeurosis of the external oblique. Now we will reflect the external oblique muscle of the abdomen and that is what I'm doing here. We have split one leaf and this is the other leaf of the external oblique muscle of the abdomen and we can see clearly that the lateral fibers are fleshy. The medial fiber is aponeurotic. And once we reflect it, we see the next layer of the abdomen that is the internal oblique muscle of the abdomen. And as I mentioned earlier, the internal oblique muscle has also got its own deep fascia and that is what we are seeing here. In this area we have removed the deep fascia to show the actual muscle. We can see that the direction of fibers of the internal oblique are opposite to the direction of fibers of the external oblique and they do have been kept here for comparison purposes. The fascia fibers of the internal oblique are as if the hands are crossed to the opposite chest. The internal oblique it takes origin from the lateral half of the inguinal ligament which we mentioned was formed by the aponeurosis of the external oblique. And it goes further up and gets attached to the 10th, 11th and 12th ribs and it also helps to form the rectus sheath and further medially it forms a linear album. This is the internal oblique muscle of the abdomen. Now we have split the internal oblique muscle of the abdomen and I am going to reflect it now. And I am reflecting the upper leaf of the split portion, one leaf which we have lifted up and this is the other portion that I am lifting up right now. And once we do so we see the next layer of the abdominal muscles and that is this. This is the transversus abdominis muscle and as the term implies the direction of fibers of the transversus abdominis are all running transversely. And we can keep show this here for comparison. This also has got its own deep fascia which we can see here and this crosses over and it just like the previous two muscles it helps to form the posterior layer of the rectus sheath and further medially it helps to contribute to the linear album. Between the internal oblique and the transversus abdominis that is this layer where my finger is located right now. This is referred to as the neurovascular plane because all the blood vessels and the nerves run in this plane and we can see them here. We can see the thoracobdominal nerve running here, we can see another nerve running here and we can see some other nerves are also running in this plane. Incidentally here we can see the cutaneous branches of the thoracobdominal nerves here and we can see another branch here. So what are the functions of these flat muscles of the abdomen? They help to compress the abdomen, they help to contain the intraabdominal organs. They help to increase the intraabdominal pressure like for example coughing, sneezing and defecation. And they also help to produce contralateral torsion of the trunk. So these are the functions of the three flat muscles of the abdomen. Now let's lift up the transversus abdominis also and that is what we have done here and we can see a very thin membranous structure here. This is the fascia transversalis also called the endoabdominal fascia. Through the endoabdominal fascia we can see this fat here. This is the extraperitoneal or the preperitoneal fat which is outside the peritoneum. This endoabdominal fascia completely invests the entire interior of the abdomen and then we have the preperitoneal fat which is located in a space called the space of bog rows. And if we go further deeper inside we will have the parietal peritoneum. If we quickly to recap the layers of the abdomen are 12 in number. We have the skin, we have the amper fascia which is the fatty layer of the superficial fascia. Then we have the scarpus fascia which is the membranous layer of the superficial fascia. Then we have the three flat muscles of the abdomen each with its own deep fascia which constitutes another nine layers. Then we have the fascia transversalis 10th layer. Then we have the extraperitoneal fat or the preperitoneal fat in the space of bog rows which is the 11th layer. And then we have the parietal peritoneum and that is the 12th layer. So these are the 12 layers of the anterior abdominal wall. Now let's take a look at the formation of the rectus sheath. We have split the rectus sheath here and we can see I have lifted up both the layers of the rectus sheath. And inside we have yet another muscle. Rectus sheath has got two layers. This is the anterior layer of rectus sheath and behind this muscle is the posterior layer of rectus sheath. The anterior layer of rectus sheath is formed by fused aponeurosis of the external oblique muscle. This one and by the anterior half of the aponeurosis of the internal oblique. The posterior layer of rectus sheath is composed of the posterior half of the aponeurosis of the internal oblique and the entire aponeurosis of the transverse abdominis. This what I described just now constitutes the upper three fourths of the rectus sheath. Four one fourth of the rectus sheath. All the three layers, aponeurotic layers are in front. However, in this particular cadaver, a particular surgery had been done in the lower abdomen and we can see the results of that surgery here. He had undergone an implant for erectile dysfunction and therefore a lot of additions were present in this entire region and therefore we cannot see the layers very clearly in the lower part of the abdomen. Now let's take a look at the muscle which I was referring to and this is the muscle which I have lifted up here. This is the rectus abdominis muscle. Rectus abdominis muscle is the most powerful muscle and as the term implies it is a straight muscle which extends from the pubic symphysis and goes all the way up and it spreads out and it gets inserted onto the costal cartilages of the seventh ribs. This rectus abdominis muscle is the one which is enclosed between the two layers of the rectus sheath and this is the one which gives the strength to the abdominal wall and we can see how wide it is. The lateral margin of the rectus abdominis muscle is referred to as the lenia semilunaris and that's a groove that you can see on the anterior abdominal wall in a thin or muscular person. If you look carefully you will see that the rectus abdominis has got these tendinous intersections. One intersection we can see here where it was adherent to the rectus sheath then we can see another tendinous intersection here where again it was adherent and we can see yet another one very indistinctly here. The tendinous intersections help to break up the fibers of the muscle into components and each of these components can act independently and they receive the nerve supply from the same thoracobdominal nerves in a segmental fashion. It's T7 to T12. The rectus abdominis muscle, as I mentioned, it gives the strength to the abdominal wall. It is also responsible for fixing the lumbar spine. It also is an anti-lordodic muscle. Those people who do workouts, this is the one which people develop when they do the crunch abdominal crunch exercises. We have heard of the term six-pack abdominis. Six-pack or eight-pack or four-pack, these are all produced by these tendinous intersections. In the points of tendinous intersections, the skin is adherent while the muscle gets hypertrophied in between and produces the bulge which produces the so-called packs. The rule of thumb is the number of tendinous intersections multiplied by two constitutes the number of packs. So three tendinous intersections means six-pack abdominis and so on and so forth. Rarely eight-pack or ten-pack abdominis or even four-pack abdominis have been documented. So this is the rectus abdominis muscle. While we are on the topic of this rectus sheath and the rectus abdominis muscle, I would like to draw your attention to this tough fibrous structure right in the midline which I have lifted up with Maori force. This midline structure is called the linea alba. The linea alba, as the term implies, is a white line and it is formed by criss-crossing fibres of the external oblique superficial fibres on one side, merging with the deep fibres of the external oblique on the other side and the fibres of the external oblique merging with the internal oblique fibres of the opposite side and these are respectively referred to as the intramuscular and inter-muscular exchange of fibres. So these criss-crossing fibres occur in the linea alba and that's what makes the linea alba such a tough structure. And as I mentioned in this particular cadaver because the lower part had been obliterated by dense fibres tissue because of the surgery, we cannot see them very clearly here and we can see some remnants of the suture material here. This linea alba is a useful site where we can do incisions for laparotomy, either suprambilical or inframbilical. In this particular cadaver they had done an inframbilical incision and they have closed it and we can see the remnants of the suture material shown by these greenish structures here. This is the umbilicus here, the location of the umbilicus. Umbilicus is the place where the umbilical cord was attached in infancy and this is the cicatrix which is the potential area of weakness. In children this can be the source of what is known as an umbilical hernia. However, in adults we do not have an umbilical hernia, we get what is known as a parambilical hernia. These are all the muscles which I want to show to you and the layers of the abdominal wall. More dissections will follow as we continue. Thank you very much for watching. Dr. Sanjay Sanyal signing out. Mr. Kendall Kambabaj is the commander person. If you have any questions or comments, please put them in the comment section below. Have a nice day.