 Dr. Sanjay Sanyal, Professor Department Chair. This is going to be a demonstration of the muscles of the posterior abdominal wall. I'm standing on the right side of the cadaver. This is a supine cadaver. Camera person is on the left side. This muscle that we can see in front of us. This is the Suas Major and the Suas Minor. This tendinous portion is the Suas Minor. It takes origin from T12 and goes all the way down and forms the ileopectenial arch and gets attached to the ileopubic eminence. And it divides the sub-inguinal space into a lateral muscular compartment and a medial vascular compartment. Through the muscular compartment passes the ileo-suas tendon and through the vascular compartment passes the external iliac vessels. So this is the Suas Minor. Under that, this major muscle that we see here, this is the Suas Major. This whole thing. It takes origin from T12, L1, 2, 3, 4, 5 and as it descends down, it forms a tendon which merges with the tendon of this muscle here. This is the iliacus muscle and the combined ileo-suas tendon then goes through the muscular compartment of the sub-inguinal space into the thigh and it gets inserted onto the lesser trochanter of the femur. At the place where it crosses the hip joint, there may be an ileo-suas persa to prevent friction. Unilaterally, when this muscle is acting, it produces lateral flexion of the lumbar spline. When it acts bilaterally, it produces flexion of the lumbar spline, especially when the person is sitting. When the person is standing, the ileo-suas together cause flexion of the hip. The Suas Major is referred to as the lortotic muscle. It is responsible for maintaining the lumbar lortosis and indirectly it helps to maintain the thoracic kyphosis. The next muscle as I've already mentioned is the iliacus muscle. This acts in conjunction with the Suas muscle as the ileo-suas tendon and its main action is flexion of the hip. The next muscle that I wanted to show you is this one here. This is the quadratus lumborum. It is shaped like a quadrangle and in the lumbar region, hence the name. It takes origin from the upper border of the iliac crest posteriorly and from this ligament, the ileolumbar ligament. And as the fibers ascend up, they give multiple slips to the transverse process of the lumbar vertebrae and the muscle then gets inserted onto the 12th rib. The action of this muscle again is unilaterally it produces lateral flexion of the lumbar spine. When it acts bilaterally, it produces extension of the lumbar spine. By virtue of the fact that it is attached to the 12th rib, it is useful as an accessory muscle of respiration during forced exhalation. And it also helps the diaphragm during forced inspiration. Coming to the nerve supply of all these muscles of the posterior abdominal wall, the Suas major and the Suas minor are supplied by the lumbar plexus. The iliacus is supplied by the femoral nerve. This is this one here, L234, posterior division of the lumbar plexus. Quadratus lumborum is also supplied by the lumbar plexus. Coming to the fascia of these muscles, the quadratus lumborum fascia or the sheath is derived from the posterior eponeurosis of the transverse abdominis and the internal oblique muscle. And that eponeurosis is called the thoracolumbar fascia. And the anterior layer of the thoracolumbar fascia forms the quadratus lumborum sheath. If we trace the quadratus lumborum sheath above, we find that it forms an upper free margin, which is traced by my instrument here. This is the lateral archivate ligament, which gives attachment to the diaphragm. The Suas sheath is derived from the transversal spacia. And just like the quadratus lumborum, it also has an upper free margin. This one I picked up here. This is known as the medial archivate ligament, which also gives attachment to the diaphragm. Let's mention a few clinical correlations. As it goes down, the ilio-suas tendon, it can get irritated by means of pelvic appendicitis. And then it produces spasm of the Suas major and the iliacus muscle and the flexion of the hip. The patient walks with the hip flex position. And that is known as the Suas sign or the Cope sign. And if we passively extend the hip in such a situation, it produces pain. And that is known as Suas test or the Cope's test. In infection of the lumbar vertebrae, that is known as KD spine, pus can track laterally and it can collect under the Suas sheath. It can be visible in a CT scan as a swelling on the lumbar region. And this pus can then track down like this. And it will go under the inguinal ligament and it will stop in the region of the lecetro canter. That is known as Suas absis. This is the transverse CT scan of the abdomen to show a right sided Suas absis under the Suas sheath. When the quadratus lumbarum gets attached to the 12th rib here, between the lateral border of the quadratus lumbarum and the 12th rib above this place where my finger is located, this is the potential site of a lumbar hernia. And this region is referred to as the superior lumbar angle of Greenfield Leshaff, which is really a site of hernia. There can be another site of hernia just above the iliac crest, but that is not visible from the inner surface. It is more on the outside. That is known as the inferior lumbar triangle of Pethi, which can also be a site of lumbar hernia. Just by way of encapsulation, now we are showing the same muscles on the left side of the abdomen. I'm still narrating from the right side, the camera person is on the left side. In this particular specimen, we cannot see the Suas minor, but this muscle that we can see here is the Suas major. Suas sheath has been removed. The next muscle that we see here, this is the iliacus muscle, which takes origin from the iliac fossa. Third muscle of the posterior abdominal wall is this one here. This is the quadratus lumbarum, which I have already described on the right side. All these were covered by the respective sheath, the quadratus lumbarum sheath, the Suas sheath and the iliacus fascia. To continue, the posterior muscles of the posterior abdominal wall, they constitute the bed for the kidneys. So therefore, these muscles, the quadratus lumbarum, the Suas major, they are the posterior relations of the kidney. And when we are doing a nephrectomy by means of the posterior approach, we have to go through these muscles. And in between these muscles and the kidney are these nerves, which are the nerves of the lumbar plexus, which have to be safeguarded. And this hollow that is produced on either side of the abdomen, by virtue of the projection of the lumbar vertebrae in the middle and the hollow of the posterior abdominal wall, these hollows are referred to as the para vertebral cutter. The kidneys are located here. So these are all the points which I want to mention about the posterior abdominal wall muscles. Thank you very much for watching. Dr. Sanjay Sanyal, signing out. Mr. Kendal Kambarbhaj is the camera person. If you have any questions or comments, please put them in the comment section below. Have a nice day.