154 Anatomy Applied to Medicine and Surgery. 



spends to : ( 1 ) The point where the aorta reaches the ver- 

 tebral column; (2) the lower level of the superior media- 

 stinum; (3) to where the oesophagus passes behind the 

 left end of the arch of the aorta; (4) to about where the 

 oesophagus reaches the middle line; (5) to the bifurcation 

 of the trachea; (6) to the origin of the left recurrent 

 laryngeal nerve; (7) to where the thoracic duct is nar- 

 rowest, and (8) to where it deviates to the left; (9) to 

 the upper limit of the pericardium, and (10) to the third 

 dorsal spine. 



6. Pneumogastric Nerves. On entering the 

 thorax, the right nerve takes a different course from the 

 left, since it passes downwards, on the outsideiof the innom- 

 inate artery, and, on reaching the side of the trachea, 

 spreads out into a plexus behind the root of the right 

 lung. It then passes to the posterior surface of the oeso- 

 phagus, on which it forms a plexus, and terminates in the 

 abdomen, by supplying the posterior surface of the stom- 

 ach, and sending numerous filaments to the cceliac, splenic 

 and the renal plexuses. The left pneumogastric enters 

 the chest between the left common carotid and the left 

 subclavian arteries, passes down in front of the arch of 

 the aorta, and, then, behind the root of the left lung and 

 along the anterior surface of the oesophagus to the stom- 

 ach, which it supplies, and from which filaments are con- 

 tinued onwards to the hepatic plexus. The branches of 

 the pneumogastric nerve to the larynx, viz., the recurrent 

 laryngeal, convey motor fibres to all the muscles of the 

 larynx, with the exception of the crico-thyroid ; the 

 branches to the cardiac plexus contain inhibitory fibres 

 for the heart and, in addition, a few sensory fibres, which 

 form a plexus under the synovial layer of the pericardium 

 that covers the surface of this organ. The pulmonary 

 branches supply sensation and motion to the lungs ; the 

 motor fibres of these branches influence the involuntary 



