 Good day everybody. This is Dr. Sanjay Sanyal, Professor, Department Chair. So this is going to be a demonstration of the anti-authoristic world that we have already removed from the cadaver. So first we will show it from outside and then we will show it from inside. So let's take a look at the salient parts first. This is the manubrium sternum. This is the body of the sternum and this is the Zephoid process. This is the manubrium sternum joint which forms the sternum angle of Louie and we can see it is projecting forward and we can feel it in our own selves. And attached to either side of the sternum angle of Louie, we have the second rib, second costal cartilage to be more precise. At the Zephi sternum joint, we have the seventh costal cartilage inserting here. Now let's take a look at each rib and the costal cartilage itself. This is the place where the first rib is attached to the manubrium sternum and above that is the Articular facet for the clavicles which have been removed. These had formed the sternoclavicular joints. This is the second rib as I already mentioned and this is the third, fourth, fifth, sixth, seventh. We notice that the costal cartilage is the terminal part of the rib, the medial portion. Before that is the bony portion and at the costal cartilage it makes an angle and it goes towards the sternum. This is going to play a significant role when I mention the muscles. The next thing I draw your attention to are the muscles themselves that we can see here. If you take a look, these muscles that we see here, these are the external intercostal muscles. These muscles are used only during forced respiration in what is called the thoracobdominal respiration. External intercostal muscles, they go from the rib above down to the rib below and they go in the direction as if like hands are in the pocket. The purpose of these are to elevate the ribs during forced inspiration. The external intercostal muscle as it comes towards the sternum. It becomes a membranous structure and I should show that membrane structure on the other side here. If you take a look, closer to the sternum it does not form muscle anymore. Now it's called a membrane. This is called external intercostal membrane. I have lifted it up here. I'm going to lift up the other side also. You can see it here. This is the external intercostal membrane. So therefore, closer to the sternum there is no muscle, external intercostal muscle. There is only external intercostal membrane. Now let's take a look at the next muscle under that and for that we will come to a lower portion here. We have removed the external intercostal muscle and we can see another muscle underneath and we can notice that the direction of fibers are different. The direction of fibers are going from the rib below to the rib above and they are at right angles to the previous muscle. This is the internal intercostal muscle. This internal intercostal muscle has got two portions. One portion is between the bony part of the ribs and that is called the interocious part and there's another portion which is between the cartilaginous part of the ribs and that is called the intercontral part. The two of them have got different types of action. The interocious part is responsible for depressing the ribs. Therefore it is used in forced respiration for exhalation while the intercontral part is responsible for the same action as the external intercostal. It is responsible for elevation of the ribs. Now why is it so? It is a simple law of mechanics. When the direction of muscle fibers are almost parallel to the direction of the ribs then they will produce elevation and when they are at right angles to the direction of the ribs they will produce depression. In the region of the costal cartilages the intercontral part of the internal intercostal direction of fibers are parallel to the direction of the ribs and therefore they produce elevation just like external intercostal. But in the interocious part the direction of fibers are at right angles to the direction of ribs and therefore they produce depression. So that is based on a simple law of mechanics. Seventh rib is attached to the zephyrstinal joint as I already mentioned. The eighth, ninth and tenth ribs are attached to the seventh cartilage. Therefore they form what is known as the intercontral articulation. The first rib articulation is a synchonrosis. Other articulations are synovial joints where there is a little bit of movement possible but with advancing age they become ossified. This angle that you see, this is the costal margin and this is called the infraternal angle or the subcostal angle. Incidentally this structure that we see attached to the zephyr process, this is a remnant of the linea alba which is a part of the abdomen. We shall not talk about this anymore. Now I am going to turn this and we shall take a look at the interior of the chest wall. In a living person the interior is entirely covered by two structures first. First we will have the parietal pleura and under that will be the endothoracic fascia. In certain parts of this dissection we can see a shiny white structure here that is the parietal pleura. But we have removed most of it along with the endothoracic fascia and we can see some of it in certain parts of it. The next thing that we see are the under leg muscles which we have already described. The main thing which I would like to show you in this side is these vessels that we can see on either side of the sternum. Just to orient you this is again the inner surface of the manabrium sternum. This is the juggler notch. These are the facets for articulation with the clavicle. This is the first rib here. This is the articulation with the body of the sternum. This is the body of the sternum itself and this is the zephyde process. Let's now focus on these neurovascular structures here. We can see one artery running down from the neck all the way on either side of the sternum. This is the internal thoracic artery also known as the internal mammary artery because this is an important artery which provides the medial mammary branches to the female breast. That's why some books also refer to it as the internal mammary artery. This internal thoracic artery it comes from the first part of the subclimane artery and it descends down. And as it descends down in each intercostal space it gives two anterior intercostal arteries which are quite small and we cannot see them in this particular dissection. And these anterior intercostal arteries, the anastomus with the posterior intercostal artery and its collateral branch. This happens up to the sixth intercostal space. From the seventh intercostal space downwards, this divides into a musculophrenic artery and a superior epigastric artery. The superior epigastric artery runs like this towards the abdomen. The musculophrenic runs obliquely and supplies the chest wall adjacent part of the diaphragm and the adjacent part of the abdominal wall. In the seventh and eighth and ninth spaces the musculophrenic artery gives the anterior intercostal arteries. This internal thoracic artery on the left side is used for coronary artery bypass grafting, the so-called left internal mammary artery bypass, lima bypass. And in very small percentage of cases in females, LIMA has been used for bypass and they have documented an area of breast necrosis because as I told you this internal mammary artery provides important circulation to the breast. But this incidence of breast necrosis is very, very rare. It is something in the order of 0.003%. Now let's take a look at the next structure next to the internal mammary artery, this bluish black structure that we see here on this side and on this side. This is the internal thoracic vein. The internal thoracic vein below the second rib is in the form of a vinae comitantes and we can see it here. Vinae comitantes means accompanying veins. One on this side, one on this side. Above the level of the second rib, the two of them unite to form a distinct single internal thoracic vein. Similarly we can here see, we can see this, a very small one on this side and a very small one on this side, but above it becomes a single one. This internal thoracic veins, they drain into the brachiocephalic vein respectively on either side. Both these are trees and veins. As they descend down, they enter under the transversus thoracus muscle. Now we have removed most of the transversus thoracus muscle just to show you the vessels, but we have kept a few remnants of that. We can see one muscle fiber here. We can see a little bit of muscle fiber here. Similarly we can see some remnants of muscle fibers here and here. These are the remnants of the transversus thoracus, which is actually a part of the innermost intercostal muscle. The transversus thoracus muscle fibers, they go like this, like this, like this and like this on either side and these two vessels, they go under the transversus thoracus. So this is what I wanted to show you in this particular view, the internal thoracic artery and its significance. Now let's mention a few quick clinical correlations pertaining to the chest wall itself. So for that I'm going to turn this again. So now again we have come back to the external surface of the chest wall. We use the intercostal spaces for various procedures, like for example putting in a chest tube. Before that we have to give anesthesia to the intercostal space. We must remember that the intercostal vessels and nerves, the main intercostal vessels and nerves are running in relation to the lower border of the rib above in this groove called the costal groove. But all of them give a collateral branch which runs in relation to the upper border of the rib below. So therefore when we give local anesthesia, we have to anesthetize both the branches, the main branch of the intercostal nerve and the collateral branch. The next point is when we are doing any intercostal procedure, we have to put in the trocar of the needle far from the lower border of the rib above and not very close to the upper border of the rib below, so somewhere here. And the usual site is the mid-axillary line in the fifth intercostal space. Now let's mention a few quick words about how to approach the chest itself through the chest wall, so-called thoracotomy. We can do a midline anesthesia which is usually done for CABG and that is called a midline sternotomy. We open the sternum and after the procedure we close it with steel sutures. We can do anterior thoracotomy where the pericondrium of the cartilage is removed by making an H-shaped incision and the cartilages are shelled out. And then we can open that is anterior thoracotomy. Another more common procedure which cannot be shown here but I will demonstrate it here, it is done from the posterior lateral aspect and that is called posterior lateral thoracotomy. That is done not through the intercostal spaces but it is done through a rib. The periosteum of the rib is incised, that portion of the rib is shelled out and we approach the thorax through the bed of the rib. That way we give the advantage of both the space above and below. When we suture the periosteum back the rib can grow back. So that is called posterior lateral thoracotomy through the bed of the rib. So these are some approaches through the chest wall, sternotomy, anterior thoracotomy, posterior lateral thoracotomy and other procedures. So these are the few salient points that I wanted to show you in this particular dissection. Thank you very much for watching. Dr. Sanjay Sanyal signing out. SIP is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day. Please like and subscribe.