 So this is going to be a demonstration of the posterior chest wall seen from the front. We have completely opened up the thorax. We have removed the two lungs and we are seeing the chest wall from the anterior aspect. We are looking at the interior of the chest wall. So this is a supine cadaver. This is the left side. This is the right side. I am narrating from the right side and the camera person is also on the right side. Now I will draw your attention to the other aspects of the neurovascular structures. So we will start from here. Accompanying this nerve, we can see this vein here, which I have lifted up. And just under the vein, we can see this structure here. This is the artery. Let's come to one space below. Again, we can see a vein here. We can see an artery here and then we can see the nerve here. Let's come to one more space. This is the vein. This is the artery and this is the nerve. And the same thing is seen here also, a vein, an artery and a nerve. So running in each intercostal space, accompanying the nerve, we have posterior intercostal vein, the posterior intercostal artery and the intercostal nerve. And these three structures, vein, artery, nerve, they run in the costal groove in relation to the lower border of the rib above. And as they are running, they all give a collateral branch. And we can see the collateral branch, which runs in relation to the upper border of the rib below. So the vein gives the collateral branch, the artery gives a collateral branch and the nerve gives a collateral branch. We can see the collateral branches here also, vein, artery, nerve. We can see the collateral branches here also. We can see the vein, artery and nerve. The collateral branches have got opposite relationship. They run in relation to the upper border of the rib below and the relationship is vein artery nerve from below up and this artery comes out from the posterior intercostal artery veins. On the right side they drain into the aegis vein which we have not dissected out and on the left side they drain into the hemi aegis accessory hemi aegis veins except the first one which drains into the brachial cephalic vein. So that brings me to a very important clinical correlation pertaining to the arterial supply. In the condition known as quactation of aorta there is a narrowing, a congenital narrowing of the arch of the aorta which is shown by my finger here. As a result of which there is no blood supply to the distal part of the aorta and concomitantly there is no blood supply to the posterior intercostal arteries. In such a situation the blood flow is reversed in the intercostal spaces. I have brought back the arteries just while here. We notice this internal thoracic artery on both the sides running on either side of the sternum. The internal thoracic arteries give rise to the two anterior intercostal arteries in each space which run and they anastomous with the posterior intercostal artery and its collateral branch normally but in quactation of aorta most of the blood comes through the internal thoracic artery and the blood flows through the anterior intercostal arteries to the posterior intercostal arteries and back to the aorta. So therefore the blood flow in the intercostal arteries gets reversed up to the ninth space. Tenth, eleventh space do not have any anterior intercostal arteries. So therefore there is no reversal of flow in the tenth and eleventh space. This reversal of flow also results in two other conditions one the internal thoracic arteries get considerably dilated and the anterior and the posterior intercostal arteries also get considerably dilated as a result of which they produce notching of the inferior margin of the ribs. That is visible in X-ray and it is called notching of the ribs which is an important sign of coactation of the aorta. This is the X-ray from the Cleveland Clinic to show notching of the ribs and the number three sign of coactation. That is the clinical significance of these intercostal arteries. That is all for now. Thank you very much for watching Dr. Sanjay Sanyal signing out David Ho is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day.