 Good day everybody. Dr. Sainjal Sanyal, Professor of Department Chair. So we are going to demonstrate the chest wall from the posterior aspect. This is the prone cadaver. I'm standing on the left side of the cadaver. The camera person is also on the left side. Before we go to the chest wall proper, let me give you a quick overview of the muscles that have reflected. So this is the larcimus dorsi. And we have reflected the larcimus dorsi. And on the under surface of the larcimus dorsi, we can see this remnant of this muscle here. This is the ceritus posterior inferior, which I shall mention again a little later. Coming up, we have this muscle here. This is the trapezius, which we have reflected from its origin to the spinous process. Under the trapezius, we have this muscle here. This is the levator scapulae. Then we have the rhomboidus minor. And this is the cut portion of the rhomboidus major. All of which we have cut and we are reflecting. Once we reflect it, we see this muscle here with this shiny aponeurosis, which we have cut. This is the ceritus posterior superior. And we can see that the lateral fibers are fleshy. Immediately it becomes shiny aponeurotic and it gets inserted. This is an accessory muscle of respiration, which is used during forced respiration. And this is responsible for assisting in elevation of the ribs. So this is the ceritus posterior superior. So therefore the counterpart of this is below here. This is the cut portion of the ceritus posterior inferior, which is located deep to the larcimus dorsi. And the other cut portion is here. And this is the ceritus posterior inferior. And if we put it back here, we can see that it will be oriented like this. This is responsible for depression of ribs during forced respiration. To continue further, we have reflected the ceritus posterior superior. We can see the erector spinae muscle here. The erector spinae muscle has got three components. The lateral component is the iliocostalis. As the term implies, it starts from the ilium by means of a very strong stout tendon, which is the erector spinae or the sacrospinalis tendon. And they get inserted by means of numerous slips to all the ribs here. And we have cut them at the ribs and we have reflected it. So this is the iliocostalis. And when we lift it up, we notice that these slips of the iliocostalis were attached to the ribs at these places. And these are the locations which constitute the angle of the ribs. And if you were to take a gross look at all the ribs in the posterior aspect, we find that they form an almost straight line here. And this is the angle of the rib. And this marks the lateral limit of attachment of the erector spinae or the iliocostalis to be more specific. The next muscle that we see here, medial to the iliocostalis, which also we have reflected, is the longismus. The longismus also takes origin from the same tendon. And it goes up, also gives slips to the ribs. And it goes all the way up to the cervical region and to the base of the skull. That's why it is called longismus. We have reflected that also. And the medial most muscle that we see, which does not take origin from this erector spinae tendon, but is attached right to the spinal's processes, is the medial most muscle. This is the spinalis muscle. But we shall not allude to the spinalis muscle anymore. Just to complete the picture, these three muscles together constitute the erector spinae, which are enclosed in the two layers of thoracolumbar fascia. Now, I would draw your attention to get one more muscle, which I have not mentioned till now. I have reflected all the superficial muscles of the back of the chest. And we can see yet one muscle here. And I'm tracing them outlined here. This is the muscle. And this is the spleenus, services and the spleenus capitis. This is the superficial most group of the intrinsic back muscles. In fact, this is superficial to the erector spinae. And this is what we can see here. So having mentioned these muscles, now we can see the full back of the chest in all its clarity. So these are the medial portions of the ribs. The medial portion of the rib has got the head, neck and a tubercle, all of which we cannot see. The head articulates with the body of the thoracic vertebrae. The same thoracic vertebra and a little bit of the body of the thoracic vertebra above, by means of demi-faces. The tubercle articulates with the transverse process of the same vertebra as the rib. Then we have the angle of the ribs, which I mentioned earlier. And this is the angle of the rib where the lateral limit of the erector spinae were attached. Then the rib makes a curve. And it goes anteriorly. And this region of the rib is referred to as the posterior lateral bend of the rib. The point to remember is that the posterior lateral bend of the rib is not the same as the angle of the rib. And then we have the shaft of the rib which continues and anteriorly it becomes the caustic cartilage which articulates with the sternum. So these are the salient points about the ribs. In between the ribs, we can see these muscles here. These are the intercostal muscles. We have three layers of muscles out of which the outer and the second layers are the most prominent and we have reflected them in certain places. We have cut the intercostal space here and we have lifted up this. This is the external intercostal muscle. The dash of fibers of the external intercostal muscle as we can see, they are as if the hands are in the pocket. They come from the rib above, obliquely down to the rib below. And in forced respiration, they are responsible for elevation of the ribs. They start from the medial most margin and anteriorly they stop and they become known as the external intercostal membrane. In this intercostal space, we can see it much more clearly and I have separated them with beams of artery forcibly and we can see the external intercostal muscle clearly here. Under the external intercostal muscle, we have the next, that is the internal intercostal muscle. And we can see that the dash of fibers of the internal intercostal muscle is exactly at right angles to the external intercostal muscle. The internal intercostal muscle, the action of fibers are as if the hands are crossed to the opposite chest. Here posteriorly, the internal intercostal muscle is deficient and it is replaced by a membrane which is referred to as the internal intercostal membrane. While anteriorly, it continues right up to the sternum. The internal intercostal is responsible for depressing the interocious part of the rib during forced respiration. Deep to that will be a very poorly defined muscle but we cannot see that here. That is called the subcostalist muscle which is in relation to the angle of the ribs but on the inner surface. That is part of the innermost intercostal. Having mentioned that, now I will draw your attention to two other structures. Take a look at these muscles here which I am separating with my artery forcibly with my instrument. These muscles, they are starting from one transverse process and going obliquely down and getting attached to the rib. This is the libatoris costorum muscle. So it is going from one transverse process above to the rib below. One transverse process above to the rib below. This libatoris costorum actually has got dual function. First of all, it is a muscle of the intrinsic deep back muscles. Therefore, it is supplied by the dorsal rami. But, however, as the term implies, it originates from the transverse process and goes to the rib below. Therefore, it elevates the ribs during forced respiration. So therefore, this is also an accessory muscle of respiration, just like the serratus posterior superior and the serratus posterior inferior. The next point which I would like to draw your attention to is a small triangular space. One boundary of which is bounded by the libatoris costorum. So let's take a look at this one here. We can see that this is one boundary of the triangle bounded by the libatoris costorum. The other boundary is this structure here. This is the inter-transverse ligament which goes from one transverse process to the next transverse process. And there is another structure which goes like this from the transverse process to the rib that is known as the lateral costor transverse ligament. So this triangular space gives passage to this nerve here. This is the dorsal ramus of the spinal nerve. We can see the same thing here also. I have lifted up this nerve here. We can see the libatoris costorum here. We can see the inter-transverse ligament and we can see the lateral costor transverse ligament and coming between this is this nerve. This is the dorsal ramus of spinal nerves. This dorsal ramus of spinal nerves are the ones which supply all the intrinsic back muscles. In fact, that is one of the criteria by which we distinguish an intrinsic back muscle. Namely, they are supplied by the dorsal ramus of spinal nerves. So this dorsal ramus of spinal nerves is the one which supplies not only the libatoris costorum but it also supplies the electric spinal muscles, namely the ideocostalis, longismus, spinalis and other intrinsic back muscles. In contrast, these other accessory muscles of respiration, namely the cirrhotus posterior superior and the cirrhotus posterior inferior, they are not supplied by the dorsal ramus of spinal nerves. They are supplied by the intercostal nerves which also supply the intercostal muscles, namely the external, internal and innermost intercostal. These intercostal nerves and the intercostal arteries and the veins, they are not visible in this dissection because they are very small and they are located deep. They run between the internal intercostal and the innermost intercostal. So therefore that is the neurovascular plane. Now let's mention a few clinical correlations pertaining to the ribs, especially insofar as they pertain to the posterior aspect. As we mentioned in the beginning, this region of the rib is referred to as the posterior lateral bend of the rib. It is not the same as the angle just to repeat. This is the place where the rib goes from the posterior lateral aspect and becomes anterior. This is the area where the ribs tend to get fractured when there is an anterior posterior compression of the chest, like for example in a steering wheel accident. And the ribs which are most commonly fractured are the fourth and the ninth ribs. The point to be remembered is that the rib fracture at the posterior lateral bend is not due to a direct blow, but it is an indirect compression. When the rib is compressed from front and back, the sides fracture. So therefore it is an indirect spring type of fracture. The first rib is very rarely fractured because it is located under the clavicle. However, there is a potential weak point on the first rib where it is crossed over by the subclavian artery in the veins. So if the first rib does fracture, it usually fractures at that location. The next point which I want to draw your attention to was a technique which is known as posterior lateral thoracotomy. That is an approach which we use for surgeries on the lung to remove a lung tumor or do a pneumonectomy. The approach to the posterior lateral thoracotomy is through the bed of the rib. And I have drawn it here and I've done it here. What we do is we make an incision on the periosteum of the rib and we reflect the periosteum up and down and we make the rib bare. And then the rib is elevated by means of special instrument and it is resected out under the periosteum. So that is referred to as the subperiosteal resection of the ribs. And then we enter the chest through the bed of the rib. By so doing, we get the benefit of the space above and the intercostal space below. So therefore it gives a wider exposure. And therefore that is referred to as posterior lateral thoracotomy by means of a subperiosteal rib resection. And after we close the chest, the rib can grow back because the periosteum has just been reflected, it has not been removed. So that is the approach which is done for posterior lateral thoracotomy. So these are some of the points which I want to mention to you about the chest wall as we see them from behind. Thank you very much for watching. Dr. Sanjay Sanyal signing out. David O is the camera person. If you have any questions or comments, please put them in the comment section below. Have a nice day.