 My name is Dr. Sajjai Sanyal, I'm the professor and department chair of anatomical sciences and the camera person is Ms. Selvi Krishnan. So what I'm holding in front of you is a dissected specimen of the anterior chest wall from a cadaver. So let's quickly identify the parts and then I shall mention a few salient points about each of them. What we see here is the sternum or the breastbone. So henceforth we shall use the word sternum. The best way to see the sternum is from the inner surface. We see that it's got three parts. This upper part, this is the manobrium sternum. This is the manobrium. We are seeing it from the inner surface now. The larger portion is the sternum proper, the body of the sternum and this has got four components which have fuse together. Each individual component is known as a sternibra. So therefore the body of the sternum is composed of four sternibray and the last part here that you see here is the zephysternum or the zephyde process which you can feel in your epigastrium. So therefore this junction between the manobrium and the body of the sternum is called the manobrio sternal angle of Louie and that you can see on the anterior surface here. I should tell a few more points a little later. Likewise the junction between the body of the sternum and the zephyde process this is the zephysternal joint. Okay so having mentioned these now let's come back to the anterior surface. We see that the manobrium sternum articulates with these two bones here. These are the clavicles. So therefore this is the sternoclavicular joint that you see here. Just under the sternoclavicular joint we see the first strip which is articulating with the manobrium sternum. This articulation is a synchondrosis. The synchondrosis of the first rib and this does not allow any movement. In contrast the other articulations, other sternocostal articulations are synovial joints and they allow a limited movement. But anyway let's come back to this. So the first rib articulates with the manobrium sternum. Now let's come to the second rib. The second rib is the one which articulates exactly at the manobrium sternum angle of Louie. So therefore half of the second rib articulates with the manobrium and the other half of the second rib articulates with the body of the sternum. This is the third rib, fourth rib, fifth rib, sixth rib, seventh rib. As we all know first two seven ribs are called the true ribs. At this juncture I need to tell you something more. If you look carefully you find that the ribs which are attached to the sternum have two parts and outer the lateral portion and the medial portion. The lateral portion the medial portion. So what's the difference? The lateral portion of the ribs are bony and the medial portion are cartilaginous. So it's actually the cartilaginous portion of the ribs which articulate with the sternum. So this is the cartilage of the second rib, the cartilage of the third rib, fourth rib and so on and so forth. So from the second, third, fourth, fifth, sixth, seventh. Up to the seventh rib articulates with the sternum and the safety sternum joint, the seventh rib articulates at the safety sternum joint just like the second rib articulated at the manobrium sternum joint. So this is the cartilage of these are referred to as the costal cartilaginous. At this juncture I would like you to notice something. You notice that the axis of the bony part of the rib is in this axis and the cartilaginous part of the rib has an angle which is different from the angle of the bony part and this will play a significant role for us when I come to the muscles. So this junction between the rib and the bone and the sternum is called the sternocostal joint. You can come in if you want and the junction between the bone and the cartilage is known as the costoconeral joint. Seventh rib as I told you articulates directly with the zippie sternal joint and the eighth, ninth and tenth ribs their costal cartilages articulate directly with the costal cartilage of the seventh rib and therefore they refer to as the false ribs. And the junction the articulation is refers to as the interconral articulation. This is the costoconeral articulation. Okay just to bring up to speed you can have a look at the same thing from the inner surface. This is the inner surface of the chest wall. You can see the cartilaginous part. Now that we mentioned the salient points about the the skeleton of the chest wall now let's come to the next aspect namely the muscles. This is going to be a little significant for us. Basically there are three constant layers of muscle on the chest wall and we can see them here. And going from outer to inner the first layer is referred to as the external intercostal muscle. External intercostal muscle. The layer just next to the deep to the external intercostal muscle and a little bit of it is visible here under the external intercostal muscle where my probe has gone in these muscles which you can see a little bit here. This is the internal intercostal muscle. And finally deepest we have another layer which you can see from this side. They are the innermost intercostal muscle. There are a few other muscles which I shall tell you a little later but let me tell a few salient points about each of these muscles first especially the direction of the fibers and their actions. The external intercostal muscle if you take a close look you notice that the direction of fibers go from the rib above to the rib below and they are directed anterior inferiorly. It's like as if you put your hands in your pocket. So therefore the direction is the hands in the pocket direction. That's point number one. That's about the external intercostal muscles. The external intercostal muscle they do not go right up to the sternum. As you can see here they stop short of the sternum. So what is there the rest of the place they are covered by a membrane and that membrane is known as the anterior intercostal or the external intercostal membrane. So then we come to the internal intercostal. If you take a look at the little bit that is visible here the direction of fibers of the internal intercostal is exactly at right angles to the internal fibers of the external intercostal and therefore the the direction of fibers is described as as if you have crossed your hand in front of your chest and your hand goes to the opposite chest. So this is the direction of fibers of the internal intercostal. This is the direction of fibers of the external intercostal. Okay so having mentioned that the next point that I need to tell you about is just like we had the external intercostal muscles stopping short of the sternum here and being replaced by the external intercostal membrane. Similarly the internal intercostal muscles also do not go right up to the sternum inside. They stop short before the sternum on the inside and here they are replaced by a membrane which is known as the internal intercostal membrane or the posterior intercostal membrane. Sorry please correction not up to the sternum because this is only the anterior chest wall the ribs are going all the way around like this they go to the vertebra. So the internal intercostal muscles they stop short of the vertebra vertebral column and the rest of it is replaced by the internal intercostal membrane or the posterior intercostal membrane. There was a mistake on my part I showed the sternum I should have mentioned the vertebra. Okay have you mentioned the direction of fibers I need to tell you one more important point about the internal intercostal muscle. Since the internal intercostal muscles are present right up to the sternum they are deficient only in the vertebral region. There are two components of the internal intercostal muscle. One component of the internal intercostal muscle as you can see a little bit here is between the bony parts of the ribs. So therefore that component of the internal intercostal muscle is referred to as the interocious part and that portion of the internal intercostal muscle which is between the cartilaginous portion that is referred to as the intercontral part. Now why are we differentiating between the two because their mode of actions are different. So let's come that that brings me to the next point what are the actions of these muscles. Let's start with the external intercostal. The direction of fibers as I said earlier are from above going obliquely downwards like hands the pocket. The direction of fibers of the external intercostal are roughly corresponding parallel to the direction of axis curvature of the rib. Now this is a fundamental law of mechanics. When the direction of the fibers are roughly parallel to the direction of the curvature of the ribs the action of the external intercostal is to elevate the ribs. Contrary wise the direction of fibers of the internal intercostal the interocious part is at right angles to the direction of the curvature of the ribs. Therefore the action of the interocious part of the internal intercostal muscle is to depress the ribs. But wait the story is not over yet. We mentioned that the internal intercostal has also got an intercontral part. The intercontral part the direction of fibers are almost at right angles to the direction of the interocious part and they roughly correspond to the axis of the cartilage. So therefore the intercontral part of the internal intercostal muscle also help to elevate the ribs. And what about the innermost intercostal? Their actions are similar to the internal intercostal. At this juncture before I proceed to the next topic external intercostal being the layer number one internal intercostal being the layer number two and innermost intercostal being the layer number three. Layer number two and three between the layers two and three is the neurobascular plane where all the nerves vessels and the arteries and veins they run the intercostal nerves arteries and veins okay. What are the other muscles? For the other muscles we should come back to the internal surface again of the anterior chest wall. If you look closely you'll see a few slips of muscle fibers going from the sternum obliquely up like this. These are the transversus thoracis muscles. They are present on the anterior chest wall on the inner surface close to the sternum. What is not shown in this what is not visible in this specimen because this only the anterior chest wall but as I told you the ribs curve like this and they go to the vertebral column near the angles of the ribs again on the inner surface we have got another group of muscles and few slips of muscle fibers which are referred to as the subcostal muscle. And finally we have some other muscles which are also not visible in this specimen namely the serotis posterior superior serotis posterior inferior and levator costaural. So what are the functions of these? The subcostal muscle the transversus thoracis muscle they help to depress the rib. Serotis posterior superior elevates the rib. Serotis posterior inferior suppresses the rib. Levator costaural elevates the ribs. One more point but I'll tell you that later okay. Since we are on the inner surface of the chest wall at this juncture I can show you look at the direction of the fibers of the innermost intercostal. They are roughly parallel to the internal intercostal and if you look on the external surface you will find that they are at right angles to the direction of fibers of the external intercostal. Their direction of fibers are at right angles to the external intercostal. What we are seeing here is another layer of membrane which I have not mentioned earlier and that is the endothoracic fascia which is going to be our subsequent topic of discussion but not in this specimen. So the inner surface of the chest wall is lined by a layer of deep fascia which is referred to as the endothoracic fascia and after that will come the parietal clura and all the rest of it covering the lungs. Okay now let's come to another important point here. Now that we have mentioned the muscles and their actions I will draw your attention to this vessels here which are seen on the inner surface just next to the sternum. So can you see this main vessel here and just next to that another vessel similarly on this side also we can see a vessel here and a vessel here. These are the internal thoracic or the internal mammary vessels. So the medial one is the internal thoracic vein. The lateral one is the internal thoracic artery. The internal thoracic vein is the medial one, the darker one, the lateral one is the internal thoracic artery. The internal thoracic artery is a branch of the first part of the subclavian artery which arises from here and where does the internal thoracic vein drain? It drains into the br cemetery vein, the respective brachiosophalic vein. So therefore the left side will will drain into the left bricocephalic, the right side will drain into the right bricocephalic. Where in which plane do these vessels run? The internal thoracic or the internal mammary vessels, they run between the innermost intercostal and the transversal thoracic muscle. They run in this plane. At this point, one point of clinical significance. All of you would have heard about coronary artery bypass grafting. One of the vessels which is used for coronary artery bypass grafting is the internal thoracic artery, internal mammary artery. The surgeons call it internal mammary artery. Okay. This I did not mention to you in the class. I'm mentioning it to you right now. Okay. So, before I conclude, one final point remains. This curvature that is seen on the upper surface of the manabrium, this is known as the juggler notch because there's a space here called the suprasternal space of burns. And there is a vessel, a vein here, which is known as the anterior juggler arch. And therefore, juggler venous arch, sorry. And therefore, this is known as the juggler notch, but that comes under the topic in the neck. So, this in a nutshell tells us a few scenic points about the anterior chest wall. What we cannot see here are the intercostal vessels because as I told you, the intercostal vessels, they run between layers two and three. So, I'll have to strip off layer three here in order to show you the intercostal vessels. What I can tell you is that the majority, the main intercostal vessel, they run in a coastal groove in relation to the lower border of the rib above. So, therefore, if this is the first rib, this is the second rib, this is the first intercostal space. If this is the second rib, this is the third rib, this is the second intercostal space. So, the second intercostal vessels, they will run in relation to the coastal groove that is the lower border of the rib above. But while they are running, they will give of a collateral branch which will run in relation to the upper border of the rib below. The anterior intercostal vessels are branches of the internal thoracic artery. Likewise, what is not visible here, the posterior intercostal vessels are mostly branches of the descending thoracic aorta. And it is the posterior intercostal vessels. There are two anterior intercostal vessels for each space, but there is only one posterior intercostal artery. And that is why each posterior intercostal artery gives rise to a collateral branch which I mentioned just now, and they all anastomers with each other. And they also give rise to posterior branch, cutaneous branch, lateral cutaneous branch and anterior cutaneous branch. And the anterior cutaneous branches, especially in the space second, third and fourth, they are called the perforating arteries. And they constitute a very important blood supply to the female breast. Okay, so this more or less concludes a few salient points about the chest wall. Thank you for watching. If there are any questions or comments, put them in the comment section below. Have a nice day. Dr. Sanjay Sanyal signing off.