THORACIC CAVITY 99 



branches : (i) ventral, which run towards the anterior border of the lung, 

 and (2) dorsal, which pass posteriorly to the thick posterior border. As 

 these branches are given off below the point where the pulmonary artery 

 crosses anterior to the bronchus they are called hyparlerial branches. The 

 hyparterial branches arise alternately, first a ventral and then a dorsal 

 branch, and, in addition, a number of small accessory branches are given 

 off from the stem bronchus in some of the intervals between the dorsal and 

 ventral branches. On the right side, the eparterial bronchus, which is given 

 off from the extra-pulmonary part of the right stem bronchus, supplies the 

 upper lobe of the right lung. The first ventral hyparterial branch supplies 

 the middle lobe, and all the remaining branches are distributed to the lower 

 lobe. On the left side, the first ventral branch goes to the upper lobe of the 

 left lung, and all the other branches go to the lower lobe. 



The intra-pulmonary part of each pulmonary artery descends along the 

 postero-lateral aspect of the intra-pulmonary part of the stem bronchus, 

 between the ventral branches anteriorly and the dorsal branches posteriorly, 

 and it gives off branches which correspond with the branches of the main 

 bronchus. 



The vein from the upper lobe, on the right side, runs along the antero- 

 medial aspect of the eparterial bronchus to the hilus, where it joins the 

 vein of the middle lobe, which lies along the antero-medial border of the 

 first ventral hyparterial bronchus, to form the upper right pulmonary vein. 

 The vein from the lower lobe ascends along the antero-medial border of 

 the intra-pulmonary part of the stem bronchus. On the left side, the upper 

 left pulmonary vein accompanies the first ventral bronchus, and the lower 

 accompanies the intra-pulmonary part of the stem bronchus ; each vein 

 lies along the ventro-medial aspect of the bronchus which it accompanies. 



The Thoracic Portions of the Vagi Nerves. The thoracic 

 parts of the vagi nerves, which are still in position, should 

 now be examined. Both vagi enter the thorax at the upper 

 aperture. The right vagus descends, through the superior 

 mediastinum, posterior to the right innominate vein and the 

 superior vena cava, passing obliquely downwards and pos- 

 teriorly (Fig. 12) along the side of the trachea, and between 

 the trachea medially, and the right pleura laterally, to the 

 arch of the azygos vein. Next it passes between the trachea 

 medially, and the arch of the azygos vein laterally, and reaches 

 the posterior aspect of the root of the right lung, where it breaks 

 up into a number of branches which unite with branches of 

 the sympathetic trunk to form the posterior pulmonary plexus. 

 It emerges from the plexus as a single trunk which runs 

 downwards and medially, in the posterior mediastinum, to the 

 front of the oesophagus. On the oesophagus it breaks up into 

 branches which unite with branches of the left vagus to form 

 the (Ksophageal plexus (Fig. 47). At the lower end of the 

 thorax the right vagus again becomes distinct ; it passes to the 

 posterior aspect of the oesophagus and enters the abdomen 

 through the cesophageal orifice of the diaphragm. 



