 Good everybody. Dr. Sanjay Sahanyal, Professor Department Chair. This is going to be a demonstration of the interior of the anterior thoracic wall. So we have dissected out the anterior thoracic wall from this cadaver and we have turned it to show the inner side. So just to bring up to speed, this is the inner surface of the sternum and we can see that here, this is the inner surface of the manubrium sternum. This is the junction between the manubrium sternum and the body of the sternum. And lower down, this is the zephoid process. We are seeing all of them from the inner aspect and we are seeing the inner aspect of the ribs. Before I go any further, I would like to draw your attention to these muscles which are attached to the inner surface of the manubrium. These are the intrahydride strap muscles of the neck, most notably the sternum hyoid and the sternum thyroid. We shall not talk about them any further because they go up to the neck. I will draw your attention to these vessels here on either side of the sternum. This is the internal thoracic or the internal mammary artery and the accompanying vein. They are the branches from the subclavian artery on both the sides and they enter the thorax and they are coming down. This internal thoracic artery is accompanied by the internal thoracic vein. Normally the internal thoracic vein is on the medial side of the artery. But we noticed as we go lower down, it is not one but two. These are the venae cometantes of the internal thoracic artery. So from approximately the second or third rib onwards, it is not just a single vein but a venae cometantes. The next thing we notice is that the internal thoracic artery and the vein is disappearing inside this muscle, even on this side also. And we have split over part of the muscle on this side and this side to show it is disappearing. This is the transversus thoracis muscle which I shall come to just a little later. This internal thoracic artery is the one which supplies the first to the sixth intercostal spaces by means of two arteries, two anterior intercostal arteries. From the seventh space downwards, internal thoracic artery divides into a musculophrenic which supplies the diaphragm and a superior epigastric. The musculophrenic artery supplies the intercostal spaces from the seventh to the ninth anterior. Tenth and the eleventh intercostal space do not have any anterior intercostal arteries and the twelfth one is the subcostal artery which also does not have any anterior. I will turn this specimen to show you the superior epigastric one side just now. We have lifted up the rectus abdominis on the left side and we can see an artery emerging through. This is the superior epigastric on the left side. This superior epigastric is one of the two terminal branches of the internal thoracic artery which goes to the abdominal wall. Now again I am turning it back to come back to where we were. The internal thoracic artery on the left side is used for coronary artery bypass grafting also referred to as left internal mammary artery bypass, lima bypass. That brings me to the next point. This internal thoracic artery is also referred to as internal mammary artery because especially in the second, third and fourth intercostal space it gives us to perforating arteries which perforate through and come to the anterior chest hole. And from there it supplies the breast in the female from the medial side as the medial mammary branches. And they are very important arteries and they have to be carefully dissected and ligated during mastectomy and that is why this internal thoracic is also referred to as internal mammary artery. So that is about the internal thoracic artery. Now let me draw your attention to this muscle which I have mentioned just a little while back. Transversal thoracic muscle is present only on the anterior aspect of the chest wall and this is the muscle which becomes continuous with the transversal abdominis muscle. This actually belongs to layer number three of the chest wall. The outermost layer was the external intercostal muscle, the middle layer is the internal intercostal muscle and the innermost layer actually is composed of three indistinctly divided muscles. One is called the subcostal muscle which is present only on the posterior aspect near the angles of the ribs. We cannot see it here. Then we can have something called the innermost intercostal which also is very vaguely defined and only clearly well defined is this transversal thoracis. So this belongs to the third layer and we know that the neurovascular plane is between layers number two and three and that is the reason why the internal thoracic artery and the vein is disappearing deep to the transversal thoracis. That brings me to the next point here. We can see these structures that we have dissected out. This one here, this one here and my assistant has done a wonderful job of dissecting them out here and we can see the same thing on this side also and this side. These are the intercostal nerves and we can see these intercostal nerves, they are the ones which supply the muscles and they also supply the chest wall. The intercostal neurovascular bundle they run on in relation to the lower border of the rib above in a small shallow groove called the costal groove. And the relationship is very constant. From above downwards we have the vein artery nerve. The vein and artery are hidden deep inside but the nerve is visible here and here and here and we can see the nerves here. That brings me to the next point. We have removed two layers of structures from this inner surface. One layer was a shiny layer which little bit of it is visible here. This is the parietal pleura. And once we strip of the parietal pleura then we can have a little bit of areola tissue and fatty layer which is referred to as the endothoracic fascia. And running in the endothoracic fascia are the neurovascular bundle which then runs and enters into the neurovascular plane between layers 2 and 3. That also we have removed and only after removing them we can see all these structures so clearly and we can see the transversal thoracis. And once we have removed all those layers in this view we can clearly see this muscle here. This is the internal intercostal muscle. The internal intercostal muscle, the interocious part is responsible for depression of the ribs and the intercondar part is responsible for elevation of the ribs. The reason being the interocious part is at right angles to the slope of the ribs and the intercondar part is almost parallel to the slope of the ribs. Any muscle fiber which is parallel to the slope of the ribs will cause elevation. Any muscle fiber which is at right angles to the slope of the ribs will cause depression. So that is the standard rule to be followed here. We can use the intercostal space for any life saving procedures. Like for example a person gets tension hemothorax or tension hemo pneumothorax or pneumothorax. We have to put in a chest tube and we usually select the fifth intercostal space in the mid-axillary line. And for that I will turn this to show how we count the ribs. We count this as the second, second space, third space, fourth space, fifth space. This is the approximate location of the mid-axillary line. And through here after giving local anesthesia we put in a needle. We usually have to safeguard the main neurovascular bundle which is running in relation to the lower border of the rib above. And we have to safeguard the collateral branches which run in relation to the upper border of the rib below. So therefore we put the needle or the trocar somewhere here. And then we aspirate or connect to an underwater seal drainage. Since we are on the inner surface of the chest wall this is the right time to show you this additional structure which is attached taking origin from the ribs and we have turned it and we have partially cut it here. This as you would have guessed is the diaphragm. The coastal part of the diaphragm which takes attachment from the ribs and all these muscular fibres that we can see here on this side and this side they all converge towards the central tendon here. So this is the diaphragm. And on the upper surface of the diaphragm this is the location and the cut margin is visible here. This is the location where the pericardium fibres pericardium was sitting with the heart. And therefore this is a remnant of the pericardium phrenic ligament. That also we can see from the inner surface of the chest wall. These are some of the points which I want to mention to you about the inner surface of the chest wall. Thank you very much for watching Dr. Sanjay Sanyal signing out. David who is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day.