THORACIC CAVITY 43 



attached to the mediastinum should be used for this 

 purpose. 



Dissection. Commence with the vagus nerve and follow it downwards 

 from a point just above the vena azygos on the right side, and from the arch 

 of the aorta on the left, looking carefully for small branches which spring 

 from its anterior border and pass to the anterior surface of the root, where 

 they communicate with the twigs from the sympathetic ganglia, and from 

 the deep cardiac plexus, to form the anterior pulmonary plexus, from 

 which branches are distributed to the walls of the air tube and the blood 

 vessels. On the left side a few twigs may be found passing from the super- 

 ficial cardiac plexus to the anterior pulmonary plexus. After the branches 

 of the vagus to the anterior pulmonary plexus have been identified, the 

 trunk of the vagus, on each side, must be followed down to the posterior 

 surface of the root of the lung, where it breaks up into branches which 

 unite with twigs from the corresponding sympathetic trunk to form the 

 posterior pulmonary plexus (see p. 28). The posterior pulmonary plexuses 

 of opposite sides are connected together by strong branches, which pass 

 both anterior and posterior to the oesophagus, and each gives branches to the 

 walls of the bronchial tube and the blood vessels of the root of its own side. 

 These various branches must be found and identified. After the posterior 

 pulmonary plexuses 'are satisfactorily displayed the bronchial blood vessels 

 should be found and cleaned. 



Arteriae Bronchiales. As a rule, two bronchial arteries are 

 distributed to the left lung and one to the right lung. The 

 two left bronchial arteries spring from the descending aorta. 

 The right bronchial artery is a branch either of the first right 

 aortic intercostal artery or of the upper left bronchial artery. 

 The bronchial arteries and their branches run along the 

 posterior surfaces of the bronchi and their branches, and 

 are the proper nutrient vessels of the lungs. Part of the 

 blood which they convey to the lungs is returned by the pul- 

 monary veins to the left atrium of the heart, but the remainder 

 is returned by bronchial veins, which open on the right side 

 into the vena azygos, and on the left side into the vena 

 hemiazygos accessoria, or into the left superior intercostal 

 vein. 



Dissection. After the bronchial vessels have been traced, the dissector 

 should separate the great vessels and the air tube from each other. Whilst 

 attempting this, he will find that his work is greatly impeded by the 

 hardened and pigmentecl bronchial glands. The relative positions of the 

 constituent parts of the roots of the lung have been noted already (p. 22). 



The Relations of the Roots of the Lungs. Anterior to the 

 root of each lung are the phrenic nerve, with its accompanying 

 vessels, and the anterior pulmonary plexus ; behind it, the 

 posterior pulmonary plexus, and below it, the ligamentum 

 pulmonis. In addition, in front of the root of the right lung 



