5 6 THORAX 



the width of the left lung. (3) The anterior sharp margin 

 of the right lung is more or less straight ; the correspond- 

 ing margin of the left lung presents, in its lower part, a 

 marked angular deficiency (incisura cardiaca) for the reception 

 of the heart and the pericardium. (4) The right lung is sub- 

 divided into three lobes, and the left lung into two. 



Dissection. The cardiac branches of the vagus and the 

 sympathetic trunk which lie on the left surface of the arch of the 

 aorta have already been found (p. 35). Trace them now, from 

 the arch downwards into its concavity, to the right of the 

 ligamentum arteriosum, where they terminate in the super- 

 ficial cardiac plexus. Clean the superficial cardiac plexus, 

 as far as possible, and trace twigs from it (i) upwards and back- 

 wards below the arch of the aorta towards the deep cardiac 

 plexus, (2) downwards to the pulmonary artery and the heart, 

 (3) laterally to the anterior pulmonary plexus of the left side. 



The vagi nerves and branches from the thoracic sympathetic 

 ganglia have already been followed to the posterior pulmonary 

 plexuses on each side (p. 33). Now follow some of the branches 

 of the plexus to the walls of the bronchus. Trace towards the 

 cesoph agus other branches which connect the posterior pulmonary 

 plexuses of opposite sides together. They pass both in front of 

 and behind the oesophagus, and are of relatively large size. 



When the posterior pulmonary plexuses and their connections 

 have been examined, complete the cleaning of the bronchial 

 arteries which run along the posterior faces of the bronchial 

 tubes ; then proceed to a detailed study of the roots of the lungs, 

 using for the purpose the portions of the roots which are still 

 attached to the mediastinum. 



Eadix Pulmonis. The root of each lung is formed by a 

 number of structures which enter or leave the lung at the 

 hilum on its mediastinal surface. The main structures are : 

 (i) the bronchial tube, through which air passes to and 

 from the lung ; (2) a pulmonary artery which carries venous 

 or de-oxygenated blood from the right side of the heart to 

 the lung to be oxygenated ; (3) two pulmonary veins, upper 

 and lower, which convey oxygenated blood from the lungs to 

 the left side of the heart ; (4) lymph vessels and lymph glands 

 through which lymph passes on its way from the lung towards 

 the right lymph duct on the right side and the thoracic duct 

 on the left side ; (5) one bronchial artery on the right side, 

 and two on the left side, which carry oxygenated blood from 

 the aorta to the walls of the bronchial tubes ; (6) the anterior 

 and posterior pulmonary plexuses of nerves and their 

 branches. 



The structures which compose the root of the lung are 

 enclosed in a layer of visceral pleura, which has been 



