THE THORAX 1049 



removed, and the parts thoroughly cleansed. The Imes of the sternal and 

 costo-diaphragmatic reflections of the pleura are to be carefully studied. 

 In examining the antero-posterior reflections of the membrane the ligamentum 

 latum pulmonis, below the root of the lung, is to be noted, and the medias- 

 tinum thoracis, with its divisions, is to receive ver>' careful attention, these 

 divisions being anterior, superior, middle, and posterior. The two pleural 

 sacs which form the lateral boundaries of the anterior mediastinum are to 

 be separated, when the middle mediastinum \^-ill be exposed, with the peri- 

 cardium, enclosing the heart, l\"ing in it. 



The lungs are next to be studied. They have been already examined in 

 their inflated and collapsed conditions, but attention is now to be directed 

 to their form, component parts, fissure or fissures, and lobes. The difierences 

 between the t\vo lungs are also to be noted, which impress corresponding 

 differences upon the pleural sacs. The roots of the lungs are not to be dis- 

 sected at this stage. 



The superior mediastinum should now be examined, without disturbing 

 the pericardium, and the remains of the thymus body, together with the 

 superior mediastinal glands, are to be dissected. 



The right and left innominate veins are next to receive attention, and their 

 inferior thjToid and internal mammarj' tributaries, with, in some cases, the 

 first intercostal vein, are to be noted. The left superior intercostal vein is 

 to be displayed as an additional tributary of the left innominate vein, which 

 it joins not far from its commencement, after having crossed the back part 

 of the arch of the aorta. 



The superior vena cav^a, formed by the junction of the two innominate 

 veins, is to be showTi and followed down to where it pierces the pericardium, 

 but no farther in the meantime. The right azygos vein is to be displayed 

 arching over the root of the right lung, and opening into the superior vena 

 cava just before that vessel pierces the pericardium. 



The pericardium is now to be studied from the exterior. Connected with 

 its anterior wall parts of the superior and inferior stemo-pericardial ligaments 

 of Luschka are to be looked for. The relation of the fibrous portion of the 

 pericardium to the diaphragm is to be looked to, and its disposition upon 

 the great vessels at the base of the heart, for which it forms sheaths, is to 

 receive attention. 



The intimate relation of the phrenic nerves to the pericardium has been 

 already noted. The pericardium is now to be laid open by means of a vertical 

 median incision, extending over its entire length, and a transverse incision 

 opposite the roots of the lungs. The serous portion of the pericardium is 

 then to receive careful attention. It is to be observed that, being a serous 

 membrane, it is composed of parietal and viscercil portions, which enclose 

 between them a shut sac. The close relation of the parietal portion to the 

 fibrous part is to be noted, and the disposition of the visceral portion upon 

 tha ascending aorta and trunk of the pulmonary artery is to be carefully 

 studied. It will be seen to form a single sheath for them, and to rise upon 

 the ascending aorta for from i to i^ inches. The tiansverse sinus of the 

 pericardium should be explored with the finger. It will be found lying 

 behind the ascending aorta and trunk of the pulmonary arter5% and in front 

 of the auricular portion of the heart. In connection with the serous portion 

 of the pericardium the triangular fold, called the vestigial fold of Marshall, 

 is to be looked for in front of the root of the left lung, between the left pul- 

 monary artery and the subjacent pulmonary vein. XMien this fold is care- 

 fully dissected it will be found to contain a delicate fibrous cord, \s'iiich is a 

 vestige of the left duct of Cuvier of embryonic life. 



The pericardium is now to be removed, which will show the lower part 

 of the superior vena cava. The heart, being now exposed, should receive 

 the most careful attention. Its external form and component parts are to 

 be observed, and the relations of these parts to the thoracic wall must be 

 thoroughly mastered. More especially the relation of the valvular orifices 

 of the heart to the thoracic wall calls for the closest observation. The trunk 

 of the pulmonary arterj' is to be studied, as it springs from the conus arteriosus 



