THORACIC CAVITY 33 



After this stage of the dissection is completed, the dissectors 

 should examine the triangular interval between the left phrenic 

 and left vagus nerves in the upper part of the thorax. Com- 

 mencing above, they should follow the vagus nerve down- 

 wards ; just before it reaches the lower border of the aortic 

 arch, it gives off a very distinct branch which turns round 

 the lower border of the arch. This is the important recurrent 

 nerve which supplies the majority of the intrinsic muscles of 

 the larynx of the same side. Immediately anterior and 

 medial to the point where the recurrent nerve turns beneath 

 the arch, a very distinct fibrous cord must be defined. It 

 connects the arch with the upper border of the left pulmonary 

 artery close to its origin. This is the ligamentum arteriosum^ 

 and it is the remains of the ductus arteriosus, through which 

 blood passed from the pulmonary artery to the aorta during 

 foetal life. When this has been secured the areolar tissue 

 between the phrenic and vagus nerves must be carefully 

 removed. In this tissue two small nerves will be found 

 which run downwards, parallel with the vagus, across the arch 

 of the aorta. The one next the vagus is the superior cervical 

 cardiac branch of the left sympathetic, and the one next the 

 phrenic is the inferior cervical cardiac branch of the left 

 vagus. When these nerves are followed downwards they 

 will be found to end in the superficial cardiac plexus, which 

 lies in the areolar tissue below the aortic arch and to the right 

 of the ligamentum arteriosum. 



Dissection. After the pericardium has been cleaned, incisions should 

 be made through it on each side, and the flaps formed should be turned 

 aside so that the dissectors may make themselves familiar with the relation- 

 ships of the heart to the mediastinal portions of the pleural sacs. Two 

 longitudinal incisions must be made on each side, one anterior and one 

 posterior to the longitudinal strip of pleura left on the lateral surface of the 

 phrenic nerve (see Figs. 12 and 13). On the right side the incisions should 

 commence at the level of the upper pulmonary vein. On the left side 

 the anterior incision should begin at the lower border of the aortic arch 

 and the posterior at the level of the left pulmonary artery (see Fig. 13). 

 On both sides the longitudinal incisions must descend to the lower border 

 of the pericardium. On both sides incisions should be carried anteriorly 

 from the upper and lower ends of the anterior longitudinal incision to the 

 line along which the mediastinal pleura was left attached to the anterior 

 surface of the pericardium (see Figs. 12 and 13). From the upper end of 

 the posterior longitudinal incision on the right side a cut should be made 

 downwards and posteriorly along the anterior aspect of the root of the lung 

 to the upper end of the inferior vena cava (see Fig. 12). 



From the upper end of the posterior longitudinal incision on the left side 

 an oblique cut must be made downwards and posteriorly, along the line of 

 VOL. II 3 



