THE THORAX 967 



nerve is necessarily dra\v-n downwards, and the right nerve becomes recurrent 

 round the first part of the right subclavian artery (the original fourth right 

 arterial arch), whilst the left nerve becomes recurrent round the arch of the 

 aorta (the original fourth left arterial arch) at the place of attachment of the 

 ligamentum ductus arteriosi. 



The cardiac branches of the right pneumogastric are two or three 

 in number, and they descend upon the trachea to the deep cardiac 

 plexus. (The cardiac branches on the left side are derived, as 

 stated, from the left recurrent laryngeal nerse as it winds round the 

 arch of the aorta.) 



The pulmonary branches are arranged in two sets, anterior and 

 posterior. The anterior fidmonary branches are two or three in 

 number, and arise from the parent trunk before it disappears 

 behind the root of the lung. They pass to the anterior aspect of 

 the root, and, being joined by sympathetic twigs, they form the 

 anterior pulmonary plexus, which is reinforced by twigs from the 

 deep cardiac plexus, and, in the case of the left anterior pulmonary 

 plexus, by twigs from the superficial cardiac plexus. The branches 

 of the anterior pulmonary plexus enter the limg, and accompany 

 the ramifications of the bronchial tubes. 



The posterior pulmonary branches arise from the pneumogastric 

 nerve behind the root of the lung. They are larger and more 

 numerous than the anterior branches, and, being joined by twigs 

 from the second, third, and fourth thoracic sympathetic ganglia, 

 they form the posterior pulmonary plexus. The iDranches of this 

 plexus, like those of the anterior, enter the limg, and accompany 

 the ramifications of the bronchial tubes. 



The (esophageal branches arise chiefly from the plexus guise, below 

 the level of the roots of the lungs, and they are distributed to the 

 portion of the oesophagus which occupies the posterior mediastinum. 

 Other oesophageal branches, however, arise above the level of the 

 roots of the lungs, and are distributed to the portion of the oeso- 

 phagus which occupies the superior mediastinum. 



The pericardial branches arise from the plexus guise, and are dis- 

 tributed to the pericardium, which they enter from behind. 



Summary ol Branches. 



Right Pneumogastric Nerve. Left Pneumogastric Nerve. 



Cardiac. Recurrent Lar^-ngeal (which gives off 



Anterior Pulmonary. Cardiac branches). 



Posterior Pulmonary. Anterior Pulmonary. 



QEsophageal. Posterior Pulmonary'. 



Pericardial. (Esophageal. 



Pericardial. 



Cardiac Plexus. — ^The cardiac plexus is one of three large pre- 

 vertebral plexuses associated with the s^Tupathetic system, the 

 other two, namely, the epigastric or solar and the hypogastric, 

 being situated in the abdominal cavity. The plexus is situated 

 partly in the concavity of the arch of the aorta, and partly upon 



