 So this is going to be a demonstration of the few muscles of the posterior abdominal wall. Let's take a look at the muscles that we can see on this supine cadaver on the left side. I'm standing on the left side and the camera person is also on the left side towards the head end. Straight away, we can see this muscle here. This is actually a thin long tendon. This is the suas minor. Suas minor strictly speaking is not a true muscle of the posterior abdominal wall, but just for the sake of continuity we are mentioning it. It takes attachment from T12L1, thin long tendon then continues down and it gets attached to the iliopubic eminence of the pubic bone where my finger has gone in and from there it gives a fibrous arch which is known as the iliopectinia arch which attaches to the inner surface of the inguinal ligament and in so doing it separates the sub-inguinal space into a lateral muscular compartment and a medial vascular compartment. So that is the only role of the suas minor. Just under that we have this big muscle here and we can see the muscle taking origin from T12L1234 and the fibers are then coming down and they are passing through the lateral muscular compartment where my finger has come in. As they come down they merge with the fibers of this muscle here. This is the iliacus muscle and then they form the combined iliosuas tendon and we can see the iliosuas tendon under the inguinal ligament in the lateral muscular compartment and if I were to trace my finger down we can see that the iliosuas tendon goes inside the thigh and it gets attached to the lesser trochanter of the femur. So this is the full course of the iliacus and the suas muscle. The combined action of the iliosuas is flexion of the hip. When the hip is already flexed then the suas major muscle is responsible for flexion of the trunk, lumbar vertebrae. When acting unilaterally the suas major is responsible for lateral flexion of the trunk and the suas major is also responsible for maintaining lumbar lordosis and indirectly maintaining the thoracic kyphosis. In this respect the suas major has got action opposite to that of the rectus abdominis. The rectus abdominis is considered as an anti-lordotic muscle while the suas major is a lordotic muscle. The lower supply of the suas minor and the suas major is the lumbar flexions. The lower supply of the iliacus is from the femoral nerve and we can see branches of the femoral nerve supplying. So these are the two muscles of the posterior abdominal wall. That brings me to the third muscle of the posterior abdominal wall and that is this one which I'm tracing out with my finger here. This is the quadratus lumborum. The quadratus lumborum proximal attachment is iliac wrist and the ilio lumbar ligament and from the other fibers go up and as they go up they give multiple slips to the transverse processes of the lumbar vertebrae and on the top it gets attached to the 12th rib as well as to the diaphragm. That is an insertion. What is the action of the quadratus lumborum? Unilaterally it is responsible for lateral flexion of the spine and when it acts bilaterally it is responsible for extension of the spine as opposed to the suas major when it acts bilaterally it is responsible for flexion of the spine. The quadratus lumborum by virtue of its attachment to the 12th rib it also acts as an accessory muscle of respiration and it is useful during forced exhalation and it also acts with the diaphragm during forced inspiration. The suas major and the quadratus lumborum both of them are covered by two sheath respectively referred to as the suas sheath and the quadratus lumborum sheath but they're derived from completely different sources. The quadratus lumborum sheath is derived from the anterior layer of the thoracolumbar fascia which is formed by the fused posterior poneurosis of the transversus abdominis muscle and the internal oblique muscle and these two fused aponeurosis they form the poracolumbar fascia and that anterior layer forms the quadratus lumborum sheath. The suas sheath is formed from the extension of the fascia transversalis. In this connection we can mention one important clinical correlation. When there is osteomulitis of the lumbar spine then the pus can track between the suas sheath and the suas major muscle and that form what is known as the suas absis which can be clearly seen in a CT scan and this suas absis then tracks down between the suas sheath and the suas major muscle. It goes under the inguinal ligament where my finger has gone in and it goes down and it stops at the esotropic actor where it is inserted. So this is the course of the suas absis. This is a CT scan of the abdomen to show a right suas absis. This is the right side suas major and we know that appendicitis appendix is present on the right side. In the cases of pelvic appendicitis it can irritate the suas major muscle on the right side and can lead to spasm of the suas major muscle and such a patient will be present with painful flexion of the hip and that is known as suas side or the co-op side and if we passively extend the hip patient will have pain and that is known as the suas test or the co-op's test. That is another clinical coordination pertaining to the suas major muscle but that is present only on the right side. So these are some of the muscles that are present on the posterior abdominal wall that we wanted to show you. This is a CT scan of the abdomen to show the suas major and the quadratus lumbarum on either side of the abdominal wall. Thank you very much for watching Dr. Sanjay Sanyal signing out. David who is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day.