Prelab Images - Thoracic Wall, Pleura, & Pericardium

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. Review the osteology. (Play movie)

Plate N178 or TG4-04 shows the sternum and its parts (manubrium, body, xiphoid process, and the sternal angle). Plates N 153, N154 or TG1-05, and N185 or TG4-04 show the thoracic vertebrae and their relation to the thoracic cavity. The typical rib is shown in plates N185 or TG4-04 and N186 or TG4-05. The head, neck, tubercle, angle, and costal groove of the rib are labeled in plate N186 or TG4-05. Plate N191 or TG4-09 shows how the neurovasculature runs in the costal groove. Plate N186 or TG4-05 shows the features of the first rib and plate N185 or TG4-04 shows that ribs eleven and twelve are floating ribs. Plate N153 or TG1-06 and N187 or TG4-06 show how the ribs attach to the vertebral bodies. Plates N185 or TG4-04 and N186 show how the ribs attach to the sternum. The costal margin is seen (unlabeled) in plate N185 or TG4-04 as the lower border of the cartilage of ribs 7-10 that forms the inferior border of the rib cage. Plate N186 shows the sternochondral junction (right where the radiate sternocostal ligaments are labeled). Plate N185 or TG4-04 shows the sternal angle and the suprasternal (jugular) notch.

Step 2. Reflect the serratus anterior muscle. (Play movie)

Plate N189 or TG4-08 (right side) shows what the anterior thoracic wall should look like after you reflected pectoralis minor in a previous lab. Next, cut serratus anterior from its origin on the ribs and reflect the muscle laterally.

Step 3. Reflect the skin from the root of the neck upward as shown in Figure 3. (Play movie)

Next, you want to pull some of the skin of the neck upward to give you more room for the dissection of the thorax. You can make a vertical midline incision (make sure not to cut too deep) near the suprasternal notch and extend this incision superiorly until you get about halfway to the mandible (jaw). Then you can pull the free edge of the skin that was overlying the clavicle superiorly (see figure 3 in the lab manual). Plate N26 or TG7-16 shows the paper-thin platysma muscle, which you will study later (try not to reflect it with the skin flap, but this may be unavoidable). Plate N28 or TG7-12 shows the sternocleidomastoid muscle underlying the platysma. Try not to damage the sternocleidomastoid or the strap muscles deep to it because they will be studied in a later lab.

Step 4. Cut the sternocleidomastoid and detach the strap muscles from the manubrium. (Play movie)

Plate N27 or TG7-16 and N28 or TG7-12 shows the sternocleidomastoid attaching to the manubrium and the clavicle. You need to cut through these attachments. Plates N29 or TG7-12 and N31 or TG7-13 show the strap muscles (the sternohyoid is deep to the sternocleidomastoid and the sternothyroid is deep to the sternohyoid). Using your fingers remove the sternohyoid and sternothyroid muscles from their attachment to the manubrium.

Step 5. Cut the clavicles and first ribs. (Play movie)

Remove the clavicle if you have not already done so. Plate N189 or TG4-07 shows the clavicle (make sure not to cut through any of the structures deep to it when you remove it). To remove the clavicle saw through it near where the trapezius attaches to it and cut through where it attaches to the sternum. You will also need to cut the subclavius muscle and costoclavicular ligament (see plates N186 or TG2-12 and N419) before removing the clavicle because these structures attach the clavicle to the first rib. Next use a chisel to break apart the attachment between the first rib and the sternum on each side (careful not to damage the vessels deep to this junction on plates N189 or TG4-07 and N190 or TG4-08).

Step 6. Cut intercostal muscles under rib 1. (Play movie) and Step 7. Reflect the anterior chest wall as shown in Figures 4 & 5. (Play movie)

The goal for this step is to remove the anterior thoracic wall (see plate N189 or TG4-08 or TG4-09 while doing this). On each side of the body starting at the sternum underneath rib one make a cut through the intercostal muscle moving laterally to the angle of the rib (do not cut too deep, only through the intercostal muscle). Then, using bone cutters cut inferiorly through ribs 2, 3, 4, 5, and 6 and the intercostal muscles between these ribs as you move inferiorly. Then cut through the intercostal muscle underneath rib 6 on both sides moving from lateral to medial (back towards the sternum). The internal thoracic arteries are branches off the subclavian artery (plate N33 or TG4-09). Looking at plate N190 or TG4-09, cut through the internal throracic arteries and veins as they pass deep to rib one. Do not cut the phrenic nerves (seen in plates N190 or TG4-09 and N193) as they pass near these vessels. Now you should be able to lift up on the manubrium and pull the sternum (with parts of ribs 2-6 attached to it) up off the body. The hinge point is right by the xiphoid process of the sternum (see figure 5 of the lab manual and plate N189 or TG4-08). You should be now able to fold the anterior chest wall downward toward the abdomen and expose the viscera inside the thoracic cavity. The inside of the chest plate will look like plate N190 or TG4-09 except it will have the parietal pleura attached to it. The parietal pleura serous membrane is anchored to the interior part of the thoracic wall by a fibrous endothoracic fascia.

Step 8. Identify and remove the external intercostal muscles from two intercostal spaces and expose internal intercostal muscle. (Play movie)

Plates N189 or TG4-08 and N191 (bottom) label the external intercostal muscle layer and the external intercostal membrane medial to the muscles. Plates N190 or TG4-09, N193 or TG4-11 and N254 show the intercostal nerves (with lateral and anterior cutaneous branches), which are accompanied by a vein and artery. Plate N190 or TG4-09 shows the internal intercostal muscle from the inside of the thoracic wall. Plate N193 or TG4-11 shows these muscles are deep to the external intercostal muscles. Note the fibers of the external intercostal muscles run down and medial and the fibers of the internal intercostal muscles run the opposite way. Plate N193 or TG4-10 and N254 show the internal intercostal membrane, which will not be seen in this lab. Plate N190 or TG4-09 or TG4-10 shows the intercostal veins, arteries, and nerves. Plates N190 or TG4-09 and N193 or TG4-10 show the innermost intercostal layer and its relationship to the neurovasculature. Plate N190 or TG4-09 shows the transversus thoracis muscle and plate N254 or TG4-10 shows the subcostal muscles (these will be seen later).

Plate N193 or TG4-09 and TG4-10 shows the posterior intercostal artery wrapping around to meet the anterior intercostal artery. The anterior intercostal artery is labeled in plate N190 or TG4-09. The intercostal nerve and its branches can be seen in plate N193 or TG4-11 and N254. The internal thoracic artery is shown in plates N33 and N190 or TG4-09. Plate N190 or TG4-09 identifies the tranversus thoracis muscle. You will need to cut this muscle to trace the internal thoracic artery. Plate N184 or TG2-11 shows the parasternal lymph nodes, which you may be able to find. The bifurcation of the internal thoracic artery into the superior epigastric artery and musculophrenic artery is in plate N190 or TG4-08 and TG4-09. Plates N190 or TG4-09 and N193 or TG4-10 together pretty much sum up the blood supply to an intercostal space. Plate N211 or TG4-18 shows the thymus gland (or fatty remnant of the thymus gland). Try to find lymph nodes and vessels within the thymic fat. Then, remove the fat (gland), but leave any lymph nodes and vessels that you were able to find intact.

Step 9. Explore the pleura and its recesses. (Play movie)

Plate N196 or TG4-15 identifies the cupula or cervical parietal pleura (the superior most extension of the parietal pleura). Plate N241 or TG4-29 shows the visceral pleura (covering the lung) to be continuous with the parietal pleura (lining the thoracic cavity) via a reflection at the hilum (place where the vessels enter) of the lung. Plates N199 or TG4-20 and N206 or TG4-29 (unlabeled in this plate) show the hilum of the lung. The pulmonary ligament is in plates N199 or TG4-31, N230 or TG4-35, and N231 or TG4-36. The costal, diaphragmatic, and mediastinal parts of the parietal pleura are labeled in plate N211 or TG4-18. Plates N230 or TG4-35, N231 or TG4-36, and N232 or TG4-37 show additional pictures of the pleural cavity that may be helpful. Plates N230 or TG4-35 and N231 or TG4-15, TG4-16 and TG4-17 label the costodiaphragmatic recess. Plate N194 or TG4-15 labels the costomediastinal recess. Plates N196 or TG4-15 and N197 or TG4-16 show how the lungs and pleura project to the rib cage (see surface projections of objective 4). The midclavicular, mid-axillary, and scapular lines of pleural reflection are explained in objective 4 (basically the pleura extends down two more rib spaces than the lung, which can be useful clinically).

Step 10. Open the pericardial sac and identify its features. (Play movie)

Plate N211 or TG4-18 shows the fibrous pericardial sac, the phrenic nerves, and the pericardiophrenic vessels. Looking at plate N231 or TG4-36 and objective 5 of the dissector answers you should be able to define the boundaries of the superior, anterior, middle, and posterior mediastinum (it may help to draw them into plate N231 or TG4-35, TG4-36, and TG4-37 ). Looking at plates N211 or TG4-18 and N212 or TG4-19, cut through the parietal pericardium (fibrous and serous layers) with a midline incision from the inferior (diaphragm) to superior (towards the arch of the aorta). Then make a cut through the pericardium from the diaphragm laterally towards the apex of the heart (N208 or TG4-19). Detach the pericardium from the superior vena cava, aorta, and pulmonary trunk (all seen in N212 or TG4-19). The inferior vena cava and right and left pulmonary arteries and veins are shown in plate N206 or TG4-29 (they are difficult to see with the heart in place). The inferior vena cava is also shown in plate N265 or TG5-34 below the diaphragm. Plate N212 or TG4-19 and N206 or TG4-29 shows the ligamentum arteriosum. Plate N231 or TG4-36 shows the left superior intercostal vein. Plates N231 or TG4-36 and N232 or TG4-37 show the left vagus nerve and its recurrent laryngeal branch. Plates N209 or TG4-38 and N226 or TG4-45 show cardiac nerves and the vagus nerve descending.

Step 11. Examine the great vessels and gross features of the heart. (Play movie)

Plates N206 or TG4-29 and N212 or TG4-19 show the great vessels in relation to the trachea. Plate N241 or TG4-19 shows that the serous layer of pericardium has parietal and visceral part (not labeled in the picture). Plate N212 or TG4-19 shows (not labeled) that the visceral pericardium reflects at the great vessels to become the parietal pericardium. Plates N212 or TG4-20 and N215 label the transverse pericardial sinus and plate N215 or TG4-20 labels the oblique pericardial sinus. By looking at plates N196 or TG4-15 and N212 or TG4-19, TG4-35, and TG4-36 you should have an idea of where the heart is in relation to the sternum and the rib cage (sternocostal projection). The apex of the heart is labeled in plate N212 or TG4-19, but the base of the heart (where the vessels emerge) is not labeled. Plate N214 or TG4-22 shows the base and diaphragmatic surfaces of the heart. Plate N212 or TG4-15 shows the apex and the right and left margins (not labeled, but self-explanatory). Plate N212 or TG4-19 shows the atrioventricular (coronary) sulcus, anterior interventricular sulcus, right atrium, and auricle of the right atrium. Plate N214 or TG4-22 shows the left atrium and auricle of the left atrium. Plates N212 or TG4-19 and N231 or TG4-36 show the relationship of the heart to the diaphragm, pleural cavities, and posterior mediastinum.