Prelab Images - Superior Mediastinum & Lungs

Prelab should consist of reading the lab manual and dissector answers and viewing the dissection video. To begin your study, you may find it useful to look over the Netter's or LWW Atlas images listed below.

Step 1. Define the boundaries of the superior mediastinum and peel away the mediastinal pleura. (Play movie)

Plate N231 or TG4-35,TG4-36 shows the superior mediastinum (the boundaries are the superior thoracic aperture superiorly, the plane through the sternal angle and T4/T5 inferiorly, the sternum anteriorly, the spinal column posteriorly, and the mediastinal pleura laterally). Remove the mediastinal pleura from any structures it may be covering in the superior mediastinum. Plate N193 or TG4-35, TG4-36 shows the course of the phrenic nerve and that this nerve is accompanied by the pericardiacophrenic atery and vein (which are cut in this plate). Plate N191 or TG4-18 shows the pericardiacophrenic artery branching from the internal thoracic artery.

Step 2. Strip the pericardium from the thoracic cavity and identify the parts of the aortic arch, ligamentum arteriosum, pulmonary trunk, trachea, and bronchi. (Play movie)

Next, remove the pericardium to expose the great vessels, bifurcation of the trachea, and the esophagus. Plates N206 or TG4-29 and N232 or TG4-37 show the structures that you need to identify and their relations to each other. Plate N199 or TG4-31 shows the hilum of the lung. It is important to note that the pulmonary veins emerge from the hilum of the lung anteriorly to the pulmonary arteries and bronchi. Plates N206 or TG4-29, N212 or TG4-19, and N199 or TG4-34 can also be used to trace the pulmonary arteries to the hilum of the lung. Plates N206 or TG4-29 and N212 or TG4-19 label the ligamentum arteriosum. Plate N209 or TG4-45 labels the anterior and posterior pulmonary plexuses, which will be on the pulmonary arteries at the hilum of the lung.

Step 3. Remove the lungs. (Play movie)

Plates N206 or TG4-35 and TG4-36 and N232 or TG4-38 show the tracheal bifurcation and the relation of the main bronchi to the arch of the aorta, the esophagus, the azygos vein, and the pulmonary arteries. Plate N209 or TG4-38 shows the right and left vagus nerves moving behind the main bronchi. Next, cut through the main bronchi, the pulmonary arteries, and the pulmonary veins at the hilum of the lung and remove the lung. You can now see where the pulmonary arteries and veins and the bronchi enter or exit at the hilum of the lung (like in plate N199 or TG4-31).

Step 4. Clean and dissect the structures of the superior mediastinum, including the great vessels and remnants of the thymus. (Play movie)

Plate N212 or TG4-19 shows the junction of the internal jugular and subclavian veins to form the right and left brachiocephalic veins. You should have elevated the sternocleidomastoid and strap muscles (sternohyoid and sternothyroid) in an earlier lab, but you may need to elevate them more to see the brachiocephalic veins (plates N31 or TG7-13 and N32 or TG7-14 for the mentioned neck muscles). Plate N212 or TG4-19 labels the right and left brachiocephalic veins. Plate N211 or TG4-18 shows the thymic fat, which will have veins embedded within it that drain into the left brachiocephalic vein. Plate N74 or TG7-13 and TG4-19 shows the inferior thyroid veins. Plates N212 or TG4-19 and N191 or TG4-09 label the internal thoracic vein. Plate N231 or TG4-36 shows the left superior intercostal vein as it passes between the phrenic and vagus nerves on the arch of the aorta. Plate N212 or TG4-19 labels the superior vena cava and its position beneath the manubrium can be appreciated in plate N196 or TG4-15. Plate N230 or TG4-35 shows the azygos vein entering the superior vena cava on the right side. Plate N238 or TG4-40 shows the azygos system, which will be dissected in step 8. Looking at plate N212 or TG4-19, cut through the midpoint of the left brachiocephalic vein so you can better see the underlying vagus nerve. Plates N209 or TG4-38 and N240 or TG4-45 follow the vagus nerve and show it giving off cardiac branches. Plates N232 or TG4-38 and N237 or TG4-39 identify the major branches off the arch of the aorta: the brachiocephalic trunk, the left common carotid, and the left subclavian arteries. The vertebral artery is usually a branch off the subclavian artery (plate N33 or TG7-15), but sometimes the left vertebral artery will branch from the aortic arch. Plate N239 or TG4-44 shows a couple lymph nodes laying on the left brachiocephalic vein. These would be considered anterior mediastinal lymph nodes, but they are not labeled. The boundaries of the posterior mediastinum can be seen in plate N231 or TG4-35 and TG4-36 and are written in objective 5. Plates N185 or TG4-04 and N196 or TG4-15 show the vertebrae and ribs forming the thoracic wall.

Step 5. Explore the tracheal bifurcation and the main (primary) bronchi. (Play movie)

Plates N202 or TG4-33 and TG4-34 and N232 or TG4-38 show the trachea. Plates N209 or TG4-38 and N240 or TG4-45 show the trachea receiving its innervation from the vagus nerve (parasympathetic) and the sympathetic trunk (sympathetic). Plate N207 or TG4-39 shows the right and left bronchial arteries coming from the aorta. The trachea also receives blood from the inferior thyroid arteries (shown in plate N33 or TG7-14). The inferior thyroid vein (N74 or TG7-13) drains the trachea. The inferior thyroid artery and vein will be seen more in later labs. Plate N202 or TG4-33 shows the trachea branching into left and right main bronchi. If you cut the trachea open you will find a small piece of cartilage known as the carina at the point of bifurcation. Plate N202 or TG4-33 shows the right and left main bronchi by themselves. Plates N206 or TG4-29, N230 or TG4-35, N231 or TG4-36, and N232 or TG4-37 show the relations of the bronchi to the other structures of the thoracic cavity. Plate N199 or TG4-31 shows the relation of the bronchi to the other structures at the root of the lung (Note: the pulmonary veins enter the anterior portion of each lung). Plates N209 or TG4-38 and N240 or TG4-45 show the cardiac and pulmonary plexuses.

Step 6. Examine the surfaces and hilum of the lung. Identify the lymph nodes involved in lymphatic drainage of the lungs. (Play movie)

Plate N199 or TG4-31 shows the apex, base, surfaces, borders, lobes, and fissure of each lung. This plate also labels the cardiac notch of the left lung. Plates N196 or TG4-15, N197 or TG4-16, and N196 or TG4-13A and TG4-13B show the surface projections of the lung to the rib cage. Plate N199 or TG4-31 shows the visceral pleura covering the lung reflecting at the hilum. This reflection forms the pulmonary ligament (N199 or TG4-31). After the reflection the pleura becomes parietal pleura and lines the thoracic cavity (N198 or TG4-17). Dissect the structures at the hilum and note their relationship to one another (N199 or TG4-31).

Step 7. Dissect the bronchi, defining the lobar branches. (Play movie)

Plate N203 or TG4-34 shows the lobar (secondary) bronchi. Plate N205 or TG4-34 shows that the pulmonary artery follows the lobar bronchi (it follows the pathway that air takes all the way to the alveolus). Plate N199 or TG4-30 and TG4-31 identifies the lingula, plates N202 or TG4-33 and N203 label the lingular bronchus, and plate N201 or TG4-32AB and TG4-32CD shows the area of the lung supplied with air by the lingular bronchus. The segmental (tertiary) bronchi and bronchopulmonary segments of each lung are shown in plates N203 or TG4-32AB and TG4-32CD. Dissect the superior segmental (tertiary) bronchi of the right inferior lobar bronchus (labeled B6 in plate N203 or TG4-33). Follow the intermediate bronchus downward by using a probe to remove the lung tissue. Near the point where it divides into middle and inferior lobar bronchi you will see the superior segmental bronchus branching off posteriorly. Plate N205 or TG4-34A and TG4-34B once again shows that the pulmonary artery will follow the bronchi, while the pulmonary vein is in an intersegmental plane.

Plate N208 or TG4-42 or TG4-44 shows the lymphatic drainage of the lung. You may also want to check out plate N204 for a schema of the intrapulmonary pathway because these topics may be important.

Updated: 14 Oct 2011