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THE THORACIC PORTION OF THE SYMPATHETIC SYSTEM 981 



cervical ganglion by two or more cords, one of which forms a loop around the sub- 

 clavian artery and supplies offsets to it. This loop is named the ansa subclavia 

 (Vieussenii) . 



The ganglion sends gray rami communicantes to the seventh and eighth cervical 

 nerves. 



It gives off the inferior cardiac nerve, and offsets to bloodvessels. 



The inferior cardiac nerve (n. cardiacus inferior} arises from either the inferior 

 cervical or the first thoracic ganglion. It descends behind the subclavian artery 

 and along the front of the trachea, to join the deep part of the cardiac plexus. It 

 communicates freely behind the subclavian artery with the recurrent nerve and 

 the middle cardiac nerve. 



The offsets to bloodvessels form plexuses on the subclavian artery and its branches. 

 The plexus on the vertebral artery is continued on to the basilar, posterior cerebral, 

 and cerebellar arteries. The plexus on the inferior thyroid artery accompanies 

 the artery to the thyroid gland, and communicates with the recurrent and external 

 laryngeal nerves, with the superior cardiac nerve, and with the plexus on the 

 common carotid artery. 



THE THORACIC PORTION OF THE SYMPATHETIC SYSTEM (PARS 

 THORACALIS S. SMYPATHICI) (Fig. 846). 



The thoracic portion of the sympathetic trunk consists of a series of ganglia, 

 which usually correspond in number to that of the vertebrae; but, on account 

 of the occasional coalescence of two ganglia, their number is uncertain. The 

 thoracic ganglia rest against the heads of the ribs, and are covered by the costal 

 pleura; the last two, however, are more anterior than the rest, and are placed on 

 the sides of the bodies of the eleventh and twelfth thoracic vertebrae. The ganglia 

 are small in size, and of a grayish color. The first, larger than the others, is of 

 an elongated form, and frequently blended with the inferior cervical ganglion. 

 They are connected together by the intervening portions of the trunk. 



Two rami communicantes, a white and a gray, connect each ganglion with its 

 corresponding spinal nerve. 



The branches from the upper five ganglia are very small; they supply filaments 

 to the thoracic aorta and its branches. Twigs from the second, third, and fourth 

 ganglia enter the posterior pulmonary plexus. 



The branches from the lower seven ganglia are large, and white in color; they 

 distribute filaments to the aorta, and unite to form the greater, the lesser, and the 

 lowest splanchnic nerves. 



The greater splanchnic nerve (n. splanchnicus major; great splanchnic nerve} is 

 white in color, firm in texture, and of a considerable size; it is formed by branches 

 from the fifth to the ninth or tenth thoracic ganglia, but the fibers in the higher 

 roots may be traced upward in the sympathetic trunk as far as the first or second 

 thoracic ganglion. It descends obliquely on the bodies of the vertebrae, perforates 

 the crus of the diaphragm, and ends in the celiac ganglion. A ganglion (ganglion 

 splanchnicum) exists on this nerve opposite the eleventh or twelfth thoracic vertebra. 



The lesser splanchnic nerve (n. splanchnicus minor} is formed by filaments from 

 the ninth and tenth, and sometimes the eleventh thoracic ganglia, and from the 

 cord between them. It pierces the diaphragm with the preceding nerve, and 

 joins the aorticorenal ganglion. 



The lowest splanchnic nerve (n. splanchnicus imus; least splanchnic nerve) arises 

 from the last thoracic ganglion, and, piercing the diaphragm, ends in the renal 

 plexus. 



A striking analogy exists between the splanchnic and the cardiac nerves. The 

 cardiac nerves are three in number; they arise from all three cervical ganglia, 



