Mediastinum . 155 



muscular fibres of the bronchi, while the sensory consti- 

 tute the cough exciting nerves of the lung. The oeso- 

 pha-geal plexus gives motion to the muscles of the oeso- 

 phagus and sensation to the upper part of the tube, the 

 lower portion of the oesophagus being almost entirely de- 

 void of sensation, and, lastly, the gastric branches afford 

 motion to the walls of the stomach. 



7. The sympathetic system of the thorax consists of a 

 set of ganglia lying on either side of the spine, one gang- 

 lion for each vertebra, with branches joining them to- 

 gether. External branches connect these ganglia with the 

 intercostal nerves, while internal ones connect them 

 with nearly all the important viscera ; thus, the internal 

 branches from the upper three or four thoracic ganglia 

 go to the pericardium, the aorta and the lung, whereas 

 those from the lower eight form the splanchnic nerves 

 that go to the abdomen. The sympathetic lies, partly in 

 the superior, and, partly, in the posterior mediastinum. 

 It carries the cilio-spinal nerve, which, emerging from the 

 lower cervical and the upper dorsal segments of the cord, 

 passes into the thoracic sympathetic system to be distri- 

 buted to the head and neck. This thoracic portion of the 

 sympathetic supplies accelerating fibres to the heart and 

 vasomotor fibres to the thoracic and abdominal organs, as 

 well as to the walls of the thorax and the upper extremity. 

 The vasomotor for the lungs, etc., arise from the first thor- 

 acic ganglia, while those for the skin and walls of the tho- 

 rax are derived from the dorsal ganglia and communicate 

 with the dorsal intercostal nerves. Those for the upper 

 extremity pass from the middle dorsal ganglia up to the 

 first dorsal, whence they pass to the first dorsal nerve and 

 thence to the brachial plexus. The internal branches of 

 the eight lower ganglia pass down to the abdomen as the 

 splanchnics and convey vasomotor fibres to the abdom- 

 inal viscera. 



