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Clean the external intercostal muscle and note that its fibers are directed downward and forward from the inferior border of the rib above to the superior border of the rib below. Follow the muscle anteriorly to where it is continuous with an aponeurosis called the anterior intercostal membrance.
Remove the anterior intercostal membrance to expose the underlying portion of the internal intercostal muscle between the costochondral junction and sternum. Note that the fibers of the internal intercostal muscle are directed at right angles to the external intercostal fibers and pass downward and backwardfromthe superior border of the rib below.
The muscle extends backward from the sternum to the angles of the ribs posteriorly, where the muscle is replaced by an aponeurosis, the posterior intercostal membrance.
Identify the lateral cutaneous branch of the fifth intercostal nerve and follow it under the lower margin of the fifth rib to the fifth intercostal nerve. Carefully cut the internal intercostal muscle from the sixth rib and turn it upward. Identify again the fifth intercostal nerve and follow it anteriorly andposteriorly, noting its relationship to the rib and corresponding artery and vein.
The transversus thoracis muscle forms the deepest layer of the intercostal muscles; it is vestigial and corresponds to the transversus abdominis muscle in the anterior abdominal wall. The transversus thoracis muscle will be dissected later on the inside of the thorax.
Repeat the above dissection in the eighth intercostal space and note how the eighth intercostal nerve leaves the thoracic wall to enter the anterior abdominal wall by passing deep to the ninth costal cartilage.
Cut through the parietal pleura in the fourth and eighth intercostal spaces and note that you have entered the pleural cavity. Observe the underlying collapsed lung covered with visceral pleura.
Take a sharp, pointed probe and pierce an adjacent intercostal space. Picture in your mind the various layers of tissue that the probe passes through before it enters the pleural cavity. This exercise is of great clinical value.
Enter the thoracic cavity by cutting through on both sides the costal cartilages from the xiphisternal joint to the midaxillary line two figers breadth above and curving parallel with the costal margin. Be careful not to enter the abdomen by cutting through the diaphragm.
Continue the incision through the ribs with bone gorceps or bone cutting saw, superiorly along the midaxillary line. In the case of the second and third ribs, cut them as far posteriorly as possible without damaging the contents of the axilla. Cut across the first rib lateral to the origin of the subclavius muscle and the clavicle near its center.
Divide the sternum at or near the xiphisternal joint. Gently elevate the inferior end of the body of the sternum with the costal cartilages and the anterior parts of the ribs. Identify the costal parietal pleura and note how it is reflected from the back of the sternum onto themediastinumon both sides.
Divide the parietal pleura where it leaves the sternum and lift the anterior wall of the thorax upward, leaving it hinged at the root of the neck by the cervical fascia and attached neck muscles. Note the smoothparietal pleura on the posterior surface of the anterior thoracic wall.
Now strip the pleura from the back of the sternum and costalcartilages and expose the transversus thoracis muscle and the internal thoracic vessels and their branches. Clean the internal thoracic vessels and note the terminal division of the internal thoracic artery in the sixth intercostal space into the superior epigastric and musculophrenic arteries.
The trasversus thoracismuscle forms the deepest layer of the intercostal muscles and corresponds to the transversus abdominis muscle in the anterior abdominal wall. It may be divides into three portions, which are more or less separate fromone another: (1) the subcostalis, (2) the intercostalis intimus, and (3) the sternocostalis.
The internal thoracic artery is a branch of the first part of the subclavian artery in the neck. It descends vertically on the pleura posterior to the costal cartilages, a fingerbranch lateral to the sternum, and ends in the sixth intercostal space by dividing into the superior epigastric and musculophrenic arteries.
Now that the pleural cavity has been opened, it is possible to pass the hand around the collapsed lung, except where the visceral pleura becomes continuous with the mediastinal parietal pleura at the lung root. Carefully explore the extent of the pleural cavity andrealize that in the living, with the lung expanded, the visceral and parietal layers of pleura are in apposition, separated by only a thin film of pleural fluid.
Identifythe various parts of the parietal pleura, costal, diaphragmatic, mediastinal, and cervical. Place your fingers in the rightand left costodiaphragmatic recesses. Identify the root of the lung and the pulmonary ligament.
Identify the cardiac notch of the left lung. Retract the lungs laterally to expose the mediastinal pleura over the fibrous pericardium.
Study the root of the lung but do not cut into it yet. Verify that at the lung root the visceral pleura covering the lung becomes continuous with the mediastinal parietal pleura.
Push the lung laterally and stretch the root of the lung. Now divide the root with a scalpel and remove the lung. Repeat the process on the opposite side.
Study the surfaces and borders of each lung. The surfaces are costal, medial, and basal, and the borders are thin and are anterior and inferior. The apex of the lung projects superiorly into the root of the neck. Compare the right and left lungs.
Identify the structures in the lung root and follow them into the substance of the lung for a short distance. Examine the bronchus, pulmonary artery, and pulmonary vein,The bronchus is situated posteriorly, the pulmonary artery superiorly, and the pulmonary veins inferiorly. The right upper bronchus is different in that it lies superior to the pulmonary artery.