 Okay, so this is going to be a demonstration of the thoracic cage from the posterior aspect. This is a prone cadaver. This is the right side of the cadaver. I'm standing on the right side and the camera person is on the left side. This muscle, which I have lifted up here, we can see that the medial portion is bone neurotic and shiny, and the lateral portion is muscular. This is the cirrhosis posterior superior muscle. This was located under the rhomboidus major, minor, and above that the trapezius, all of which we have reflected. This cirrhosis posterior superior is an accessory muscle of respiration, and it is supplied by the intercostal nerves. And this is responsible for elevation of the upper ribs. When it pulls, it elevates the upper ribs. And we can see that the distal attachment is to the ribs. Now let's come to this muscle here. Again, we can see a similar muscle. The medial portion is a bone neurotic and shiny. The lateral portion is fleshy. And again, we can see that the distal portion is attached to the lower ribs. This is the cirrhosis posterior inferior. This was located under the latsomus dorsi muscle, most of which we have removed. We have retained just a little bit of the latsomus dorsi to show that it is located under that. And this is also supplied by the intercostal nerves, and it is responsible for depression of the lower ribs. It's also an accessory muscle of respiration. Now I will reflect this to show the intercostal muscles. So these are the intercostal muscles from the posterior aspect. This is the posterior part of the internal intercostal muscle. We notice that this is the membranous structure here. Internal intercostal muscle, as it moves posteriorly towards the vertebral column, it becomes membranous. And that is known as the internal intercostal membrane. This is in contrast to the external intercostal muscle, where it becomes membranous near the sternum, where it is known as the external intercostal membrane. The neurovascular structures run between layers 2 and 3, namely between internal intercostal and the innermost intercostal. The next structure, which I would like to draw your attention to, the thoracic cage itself. So we are looking at the posterior aspect of the ribs. We notice these elevations on the ribs, and we can see that they're almost in a straight line. This is the angle of the rib, and you can see remnants of this aponeurotic facial structure attached to it. This marks the lateral most limit of the attachment of the erector spinae muscle. We can see the tendon of the erector spinae muscle, which includes the iliocostalis, longismus, and the spinalis. Iliocostalis muscle fibres get attached to the ribs. They were attached here, and that's what constitutes the angle of the ribs. The head, neck, and the tubercle of the ribs, we cannot see because the head is articulating with the vertebral body. Neck is just after that, and the tubercle articulates with the transverse processes of the thoracic vertebra. This is the angle, and the rest of the rib is the shaft of the rib. And we know that anteriorly it becomes cartilaginous. At this juncture, I can tell you ribs are most likely to be fractured at the postrolateral bend in this region by compression injury from front to back. Like for example, when there's a car crash and the steering wheel touches against the chest wall. And the fourth and the ninth ribs are the ones which are most likely fractured. Now let's take a look at the next set of muscles. We see these muscles running from one transverse process to the rib below. One transverse process to the rib below. Next, next, next. These are known as the libatoris or sterum. They, as the term implies, when they contract, they elevate the rib. So they are also accessory muscles of respiration, but they're also the intrinsic deep back muscles. They are also supplied by the posterior ramia of the spinal nerves. At this juncture, I would like to draw your attention to something very special. Focus on these neurovascular bundle which I'm lifting up and each space. These are the posterior ramia of the spinal nerves. And we notice that these posterior ramia of the spinal nerves, they are emerging through a triangular space bounded on one side by the libatoris or sterum muscle. Immediately, it is bounded by this ligament structure here, which is the inter-transverse ligament and below it is bounded by this ligament here which extends from the transverse process to the rib, that is known as the lateral osteotransverse ligament. So it is through this triangular process that the posterior ramia of the spinal nerve is emerging and this is the one which supplies all the intrinsic back muscles. So let's see the triangle again in this place here. We can see that one boundary is the libatoris or sterum. The other boundary is the inter-transverse ligament and the inferior boundary is the lateral costotransverse ligament. So this triangular space is the one which gives passage to the posterior ramia of the spinal nerves. Next thing, we notice these muscles here in the groove that is being traced by my finger. This groove is the groove between the spinous process of the thoracic vertebrae here and the transverse process of the thoracic vertebrae here. So these muscles which are located in that groove, they are referred to as the transversal spinalis muscles. These are deep intrinsic back muscles and they are distributed in three layers. Going from superficial to deep, we have the semi-spinalis, multifidus and rotators. These intrinsic deep back muscles can only be seen after we have completely removed the erector spinae muscle, which I mentioned earlier, namely the heliocostalis, longismus and spinalis. And while we are at this topic, I would like to draw your attention to yet one more muscle. This is that muscle here. We notice that it is deep to the sinus posterior superior and it is attached to the spinous process of the thoracic vertebrae here and it is thin, flat and a small muscle. This is the splenius services and there is a similar muscle which goes higher up, that is known as the splenius capitis. This is the superficial most groove of the intrinsic back muscles, the splenius services and the splenius capitis. The word splenius in Greek means bandage-like. Before I conclude, I want to mention one important surgical correlation pertaining to the posterior aspect of the chest wall. There is a procedure called postural lateral thoracotomy. The patient is in a semi-prone lateral position and when we want to enter the chest wall, we enter the chest wall by making an incision on the periosteum of the rib as being traced by my instrument. Once we split open the periosteum, we reflect it above and below and we do a sub-periosteal resection of the rib so that it can grow back later on. Then we enter the chest wall through the bed of the rib and that gives us the advantage of the space below and the space above. That procedure is referred to as postural lateral thoracotomy. These are some of the points which I want to mention about the chest wall from the posterior aspect. Thank you very much for watching. Dr. Sanjay Sanyal signing out. Mr. Kendal Kumbhach is the camera person. If you have any questions or comments, please put them in the comment section below. Have a nice day.