 Good day everybody. Dr. Sanjay Sanyal, Professor of Department Chair. So, we have completely dissected out the anti-atheracic wall from this cadaver. And we are going to demonstrate the outer surface as well as the inner surface. Before we start with describing the thoracic wall itself, I just would like to draw your attention to the muscles which are attached, which do not belong to the thorax, but they are attached to the chest wall. As you understand, the thoracic wall itself provides a lot of real estate. And so therefore nature has used this real estate for attaching various muscles. This muscle that we see here on both the sides, this is the rectus abdominis muscle, which continues onto the abdomen. And it is attached to the fifth to the seventh costal cartilages. That's one muscle. Then we can see yet another muscle here. We can see the fibres are going like this. This is part of the external oblique muscle. The external oblique muscle is attached to the fifth to the twelfth ribs. And under that we have yet another muscle. That is the internal oblique, which is inserted to the tenth to the twelfth ribs. And we have the transverse abdominis, which is also attached to the seventh to the twelfth ribs. Then we can see yet another muscle here on the lateral aspect. And we can see the external fibres are different from that of the external oblique. External oblique are like this and these are the other set of fibres. This is the serratus anterior. And it's called serratus anterior by virtue of its multiple digitations on the ribs. This takes origin from the first to the eighth or the ninth ribs and the fibres then converge up and we have cut it here. Similarly, posteriorly we have many muscles. We have the serratus posterior superior inferior and many other muscles, including the back muscles. So this is one point which I wanted to draw your attention and therefore we have retained these muscles on this side. However, we have removed them on this side. Then we can see some muscles on the top, which also do not belong to the chest wall. This is jugular notch of the manuprium. And these two facets are where the clavicle was attached. So just under the clavicle, we have the first rib here and the first rib here. And attached to the first rib, we can see this muscle here and a part of this muscle. This is the scalyness anterior and the scalyness medius. And in between this is the location of the scalyne triangle. And here is the groove for the subclavian artery. This is the place where we can help aid the subclavian artery in the supraclavicular fossa. Then we can see this muscle here, which is attached to the second rib. This is the scalyness posterior and we can see the scalyness posterior here also attached to the second rib. And incidentally we can also see some of the remnants of the sternocleomastoid. The sternal part of the sternocleomastoid attached to the manuprium sternum. So these are some of the extrinsic other muscles other than the chest wall that we wanted to draw your attention to. Now let's come to the chest wall itself. As I mentioned, this is the jugular notch, so therefore this is the manuprium sternum. This portion is the body of the sternum and it is composed of four sternic pre, which have fused in embryonic life to form the body of the sternum. And this portion is the zephy sternum or the zafoid process. So this is the place where the manuprium sternum articulates with the body of the sternum and this is referred to as the sternal angle of Louis or the manupriosternal angle. And this place is the location where the zafoid process articulates with the body of the sternum to form the zephy sternal joint. The jugular notch is at the level of T3 vertebra. The sternal angle of Louis is at the level of T5 and the zephy sternal joint is at the level of T9. At the level of the sternal angle of Louis, we have the second rib here attached. And at the level of the zephy sternal joint, we have seventh rib attached. And below that we have the eighth, ninth and tenth ribs. I want you to draw your attention to this margin here. This margin and I am going to reflect this muscle up to show you this margin. This is referred to as the costal margin. And this angle projected here and here, this is referred to as the sub-costal angle. This costal margin is composed of seventh rib and below that is the eighth, ninth and tenth ribs. These three ribs are referred to as false ribs because they do not articulate directly with the zephy sternal joint. They articulate with the seventh rib. However, rarely even the eighth rib may articulate with the zephy sternal joint. So this articulation between the cartilages, this is referred to as the inter-chondral articulation. While this articulation between the costal cartilage and the rib is referred to as the costo-chondral joints. These costo-chondral joints tend to get ossified in old age. And when we are giving external cardiac massage, they can snap and they can produce rib fractures in cases of cardiopulmonary resuscitation. Thoracic surgeons use this approach as the anterior approach to thoracotomy. They split the pericondrium of the rib here in the form of an edge. And they reflect one half here, one half here and they shell out the cartilage here, here and here. And they get exposure to the thorax in the anterior. And this is the root used for anterior thoracotomy. Now let's come to the intercostal spaces. Each intercostal space is counted just below the corresponding rib. So therefore, if this is the first rib, then this is the first intercostal space. Second rib, second intercostal space and so on and so forth. In clinical practice, we cannot palpate the first rib because it is deep to the clavicle. So therefore, we palpate only the sternal angle of Louis, which is easily palpable and we can see it clearly in this cadaver. And in person, when we palpate the sternal angle, we know that that corresponds to the second rib. So therefore, we start counting the spaces from below that. So therefore, this is the second space, third space, fourth space, fifth space and so on and so forth. So that's about the intercostal spaces. Now let's take a look at what other structures we can see here apart from the muscles. We can see this nerve coming out here from the second intercostal space as I mentioned just now. This is a very large branch which comes from the second intercostal nerve and this is called the intercostal brachial nerve. The intercostal brachial nerve is the lateral cutaneous branch of the second intercostal nerve. And this is a large one that's why it's got a separate name by itself. And as the term implies, it supplies the second intercostal space and also supplies adjacent part of the chest wall as well as the medial part of the arm. This intercostal brachial nerve is the one which is responsible for referred pain to the medial side of the arm in angina pectoris and myocardial infarction. Additionally, we can see some of the other cutaneous branches of the nerves coming out here and we can see another nerve here. These are the cutaneous branches of the intercostal nerves. Having mentioned that, now let's come to the intercostal muscles itself. I will stretch the ribs here and this is what I have done. And we can see the muscles which are immediately visible in front of us. This muscle is the external intercostal muscle. If you take a look at the direction of fibers, we can see two things about the direction of fibers. Number one, the direction of fibers are roughly parallel to the slope of the ribs, roughly, not exactly. And secondly, the direction of fibers are as if the person has got his hands in his pocket. Now this is a very important concept. When the direction of fibers of the muscle is almost parallel or closely matching the direction of the sloping of the ribs, then when this muscle contracts, it is responsible for elevation of the ribs during forced respiration. Now let's continue with the external intercostal muscle. And here we noticed that the external intercostal muscle as it comes closer to the costum cartilage, it becomes membranous. And we have reflected that membrane here and here. This is called external intercostal membrane. So therefore, the medial portion of the external intercostal muscle is not a muscle anymore, it is just a membrane. When we reflect this membrane, we see the next muscle underneath. This is the internal intercostal muscle. And I will show you the internal intercostal muscle in one more space. We have reflected a little bit of the external intercostal here and we can see the internal intercostal here, apart from here. And we can see a little bit of that here also under the external intercostal membrane. The internal intercostal muscle, the direction of fibers as you can clearly see here, is at right angles to the direction of fibers of the external intercostal muscle. And I'm holding it up here for your comparison. This is the external intercostal, this is the internal intercostal. Because the direction of fibers are opposite, this has been likened to as if the person has got his hands crossed to the opposite chest. These internal intercostal muscles, they have been divided into two parts. One portion is between the bony part of the ribs. That portion is referred to as the inter-ocious part. And there is yet another part which is shown here, which is between the cartilaginous part of the ribs. And that is referred to as the inter-condrel part. The two of them have different functions, even though it's part of the same muscle. The inter-ocious part of the internal intercostal muscle, when it contracts, it is responsible for depression of the ribs during forced respiration. However, when the inter-condrel part of the same muscle when it contracts, it is responsible for elevation of the ribs. And how does this work? As I mentioned, when the direction of fibers are at right angles to the long axis of the slope of the ribs, their contraction will cause depression of the ribs. But in this place, in the inter-condrel part, we can see that the direction of fibers are closely matching the long axis of the cartilages. So therefore, when they contract, they are responsible for elevation of the ribs. So that's the unique point I wanted to mention about the function of the internal intercostal. So these are the things that we can notice in the anterior aspect of the chest wall. 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.