 So, this is a demonstration of the muscles of the posterior abdominal wall. What we see in front of us is the right side of the cadaver, that is the head end and this is the lower end. This is the right side. We have removed all the structures including the kidney and we can see the remnant of the transversal espacea with its covering baritonium here. So, let's reflect that. Once we reflect, we can clearly see the three important muscles of the posterior abdominal wall. One that we see here is this one. This is the suas major which comes from T12 all the way down to L5 and on top of the suas major is this muscle which we have lifted up, the slip of a muscle. This is the suas minor which starts from T12. Let's take a quick look at the suas major. As it comes down, it gets multiple attachments to the lumbar vertebra and it continues down and it goes under the inguinal ligament where my finger has gone in, the tendon and as it goes down, it merges with the tendon of this muscle here. This is the iliacus muscle which is arising from the iliac fossa. This is the iliac fossa and as it goes, this also goes under the inguinal ligament where my finger has come and now the two tendons have become one and now they form what is known as the iliosuas tendon. We can see the continuity from here. This is the iliosuas tendon and the iliosuas tendon then goes down and it gets inserted on to the lecetrocantin. So this is the iliosuas muscle. The suas major muscle is supplied by branches, the lumbar plexus and I will show you the lumbar plexus in another video and this is L12, L3. The iliacus is supplied by branches on the femoral nerve and femoral nerve is this one here. The function of the suas major, when it is acting from one side, it is responsible for lateral flexion of the lumbar spine. When it acts on both the sides, it is responsible for when the patient is sitting, it flexes the lumbar spine. When the patient is standing, it is responsible for hip flexion in which case both the iliacus and the suas they together act. It also helps to maintain the lumbar lordosis and indirectly maintain the thoracic kyphosis. So that is the important function of the suas major. The suas minor does not have any of these actions because it gets inserted on to the iliopubic evinence and it forms an iliopubic arch which divides the subanguinal space into a lateral muscular compartment and a medial vascular compartment. So therefore it does not participate in this activity. The next muscle that we see here is this muscle here in front of me. This is the quadratus lumborum muscle, it is shaped like a quadrangle. It starts from the iliacrest and it goes all the way up and gets attached to the twelfth rib and we can see this is the twelfth rib here, this is the twelfth rib and it is getting attached and as it goes up it gives multiple slips to the transverse process of the lumbar vertebra. This is also supplied by the lumbar plexus T12L1234. Action of this again when it is acting unilaterally, it is responsible lateral flexion of the lumbar and when it acts bilaterally, this extends the lumbar spine and because it is attached to the twelfth rib, it also acts an accessory muscle of respiration during forced exhalation and it also accesses the diaphragm in inhalation. When both the sides act together, they extend the lumbar spine. This is about the quadratus. Now let me mention quickly about the fascia. The suas major and the minor is enclosed in the suas sheath. The suas sheath is a continuation of the fascia transversalis which I showed in the beginning. It forms a real fascia which has been removed and then it continues to form the suas sheath. The quadratus lumbarum has got its own sheath which is formed by the anterior layer of the thoracolumbar fascia which is derived from the posterior aponeurosis of the internal oblique and the transverse abdominis. The upper limit of the suas sheath is here and this curved line that we see here, this is what is known as the medial archivate ligament which gives it has been to the diaphragm. And the upper limit of the quadratus lumbarum sheath is here and this forms what is known as the lateral archivate ligament which also gives attachment to the diaphragm. And this is the diaphragm that we have lifted up here. So this is about the sheath. Now let us come to a few important clinical correlations pertaining to the suas major. Rupture of the suas muscle, heliosuas tendon or tendonitis will produce severe pain in the upper part of the thigh and the patient will not be able to flex his hip in the sitting position. And that is known as Ludlov sign that is number one. There is a bursa between the heliosuas tendon and the hip joint and that is known as the heliosuas bursa which can also get inflamed. The next important clinical correlation is in ostomalitis of the lumbar vertebrae. Puss can form under the suas sheath and it can track down and as it tracks down it comes under the inguinal ligament and it stops here where my finger is gone in because the heliosuas tendon is inserted from the lesser trochanter that is called a suas abscess. So that is the second important clinical correlation. This is an axial CT scan of the abdomen and the lumbar vertebrae to show a suas abscess. The third important clinical correlation is as we can see the suas muscle is in relation to very close to the pelvis. Some patients have what is called a pelvic appendicitis and that can irritate the suas major muscle and can produce suas spasm in which case the patient will maintain a hip flexion on the right side and the patient will prefer to lie in a fetal position and that is known as the suas sign or the cork sign and when we passively try to extend the hip the patient will have pain and that is known as the suas test or the zacric cork test. So this is about the suas major. The quadratus lumbarum also forms one of the boundaries of this angle. This is the twelfth rib and this is the lateral margin of the quadratus lumbarum. So this angle where my finger is located this is known as the superior lumbar triangle or the angle of greenfield less shaft. This is one of the lumbar triangles from where there can be a potential site of herniation. So that is about the quadratus lumbarum and the suas. So that is all for now about the muscles of the posterior abdominal wall. If you have any questions or comments please put them in the comment section below. Dr. Sanjay Sanyal.