 This structure, which I've lifted up here, which is right at the posterior part of the posterior medial stenum. This is the azegus vein. Azegus vein is formed by the union of the ascending number veins, which unites L1234 veins. And as it climbs up, it unites with the subcostal vein and that forms the azegus vein. And this is the formation of the azegus vein that I've lifted up here. This azegus vein then enters into the thorax through the aortic hiatus. And my instrument has gone through the aortic hiatus and has come to the plumen to the thorax. On this side also, it has come to the thorax here. And we can see that that is the route the azegus vein takes to enter into the thorax. In the aortic hiatus, azegus vein is also accompanied by the thoracic duct and the aorta. From right to left, we have the azegus vein, the thoracic duct, and we have the aorta, A-D-A. Azegus vein then travels to the right of the east of Vegas in the posterior medial stenum. It is closely adhering to the acic vertebrae. Then, it passes behind the right principal bronchus. And we can see that clearly here. This is the cut portion of the right principal bronchus. It passes behind and it forms a hook-like arch. First here, it comes anteriorly and it opens into the superior vinaigrette which is here. This arch of the azegus vein, it forms a groove on the right lung and that is known as the impression for the arch of the azegus vein. Sometimes this azegus vein can actually form a groove on the right lung itself and can take the pleura with it and then it can produce what is known as azegus lobe of the right lung. But that is not very common. Now, I will draw your attention to these neurovascular structures on the right side. These are the posterior intercostal veins. These blue ones are the posterior intercostal veins. The right side of the posterior intercostal veins, except the first posterior intercostal vein, they all drain into the azegus vein and we can see that. We can see the azegus vein is receiving the posterior intercostal veins on the right side. What about the left side? On the left side, we do not have an azegus vein. Instead, we have something called hemi-azegus vein which is also formed the same way on the left side as the azegus vein is formed on the right side. Ascending lumbar vein unites with the left subcostal vein and forms a hemi-azegus vein. And the hemi- azegus vein receives a lower 4 posterior intercostal veins to the left side. And after that, it moves to the right and opens into the azegus vein on the right side. And this is that hemi-azegus vein which I have lifted up here. What about the middle 4 posterior intercostal veins on the left side? They all unite to form an accessory hemi-azegus vein and that also crosses to the right side and it opens into the azegus vein on the right side and that is what I have lifted up here. This is the accessory hemi-azegus vein. So, hemi-azegus vein, accessory hemi-azegus vein. They occur approximately to the level of T8, a little below and a little above that. This azegus vein and the hemi-azegus and the accessory hemi-azegus are collectively called the azegus, hemi-azegus system. They form an important route of communication between the inferior vena keva, permanent of that is seen here, and the superior vena keva which is seen here. So, therefore, when there is a compression or obstruction of the inferior vena keva like for example, in liver pathology, then these communications by virtue of the azegus vein and the hemi-azegus veins, they become prominent and they bypass the blood to the superior vena keva. So, this is a communication between the inferior vena keva system and the superior vena keva system. Now, let me draw your attention to the next structure here which is just to the left of the azegus vein and that is this one here. This is the thoracic duct. The thoracic duct starts in the abdomen as the cisternal chile. Cisternal chile is a small dilution which we cannot see very clearly here because it is located deep in the epicastrium of the abdomen. This is the cisternal chile receives lymph from the lump or lymphatic trunks, from the intestinal lymphatic trunks, the descending thoracic trunks and the posterior intercostal nodal trunks and then the cisternal chile gives off a major lymphatic channel which is known as the thoracic duct which enters through the diaphragm through the same hiatus as the aortic hiatus and here it is accompanied by not only the aorta but also by the azegus vein. Then it enters into the thorax. Thoracic duct happens to be the main lymphatic channel which carries lymphatics from the abdomen and the thorax. In the thorax initially it runs in the posterior intestine and it is located just to the left of the azegus vein. At the level of T5 approximately, we can see that it makes a curve to the left and it goes behind the isofagus. It goes to the left side and then it enters into the neck and it opens into the left venous angle. What are the tributaries of the thoracic duct? In the thorax it receives a posterior intercostal nodal lymph. It also receives lymph from the posterior medistinal lymph nodes. In the neck it receives lymphatics from the jugular lymphatic trunks, subclavian lymphatic trunks and the left bronchometestinal trunks all from the left side. On the right side there is no thoracic duct however we do have these three trunks, right bronchometestinal trunks, right subclavian trunks and a right jugular trunks and these three trunks unite to form what is known as the right lymphatic duct which opens into the right venous angle. Venous angle is this. It is the union between the internal jugular vein and the subclavian vein so this is the venous angle. So this is the site of drainage of the lymphatics. When there's an injury, stabbing injury or penetrating injury to the left side of the neck where the thoracic duct opens into the left venous angle. It can produce persistent drainage of milky white lymph and that is known as chyloria or lymphuria and the patient can lose anything from 1.5 to 3 liters of lymph in 24 hour period and that is a very difficult condition to treat and the only way to treat is to like it the thoracic duct here.