NERVOUS SV8TE1M. 359 



sympathetic. At the bottom of the neck, the nerve hes within 

 the angle formed between the carotid and vertebral arteries ; it 

 then runs outward above the vertebral artery, over which we find 

 a bulbous enlargement of it, which takes the name of the pos- 

 terior cervical ganglion. The only branches given off by the cer- 

 vical portion of the sympathetic, are several threads of communi- 

 cation with the par vagum, as they proceed backward together. 



The posterior cervical ganglion., smaller than the anterior, is 

 seated under the first dorsal vertebra. From it pass — 1. A large 

 branch, and sometimes a smaller one along with it, to the sixth 

 cervical nerve, by which it has a mediate communication with 

 the five anterior cervical nerves. 2. A branch to the seventh 

 cervical nerve. 3. A filament to the first dorsal nerve. 4. An- 

 other to the second dorsal nerve. 5. Branches to the tracheal 

 plexus, 6. Filaments to the recurrent nerve. 7. To the cardiac 

 plexus. 



The tracheal plexus is an assemblage and intercommu- 

 nication of nerves, derived from the par vagum and recurrent as 

 well as the sympathetic, ramifying upon the under surface of 

 the trachea, as it passes between the two first ribs, from which 

 filaments are transmitted to the cardiac plexus. It supplies this 

 part of the air-tube, and also the contiguous portion of the 

 esophagus. 



The cardiac plexus, constituted of larger branches from 

 the same nervous trunks, and also of filaments from the tracheal 

 plexus, which are readily traceable to the roots of the large 

 bloodvessels, is formed for the supply of the heart. 



From the posterior cervical ganglion, the sympathetic con- 

 tinues its course backward, under the articulations of the ribs 

 with the spine, to the diaphragm, which it pierces in con)pany 

 with the posterior aorta. Between the heads of the ribs it pre- 

 sents little knots — dorsal ganglia — which correspond in number 

 to the intercostal spaces. These ganglia are of very small size 

 when compared with the cervical, and give off, each of them, two 

 filaments to every intercostal nerve. — As the sympathetic nerve 

 pursues its route along the spine, it grows flat, spreads out its 

 fibres, and at length separates into two branches, one of which, 

 by means of frequent remforcements from the ganglia as it passes 

 by them, ultimately attains a larger size than the original parent 

 nerve: this, from being destined to supply the abdominal viscera, 

 is named the greater splanchnic nerve. Before it leaves the 

 chest, while running along the crus of the diaphragm, the 

 sympatheticdetaches another branch : thisturns backward upon the 

 crus, describing an arch in escaping from the cavity, and is de- 

 nominated the lesser, secondari/, or accessory splanchnic nerve, 

 whose destination is nearly similar to that of the former. 



