804 THE NERVOUS SYSTEM. 



process of the last cervical vertebra and the neck of the first rib on the inner side 

 of the superior intercostal artery. Its form is irregular; it is larger in size than 

 the preceding, and frequently joined with the first thoracic ganglion. It is proba- 

 bly formed by the coalescence of two ganglia which correspond to the two last 

 cervical nerves. 



Its superior branches communicate with the middle cervical ganglion. 



Its inferior branches descend, some in front of, others behind, the subclavian 

 artery, to join the first thoracic ganglion. 



Its internal branch is the inferior cardiac nerve. 



The inferior cardiac nerve (nervus cardiacus nfinor] arises from the inferior 

 cervical or first thoracic ganglion. It passes down behind the subclavian artery 

 and along the front of the trachea to join the deep cardiac plexus. It communi- 

 cates freely behind the subclavian artery with the recurrent laryngeal and middle 

 cardiac nerves. 



The external branches consist of several filaments, some of which communi- 

 cate with the seventh and eighth spinal nerves ; others accompany the vertebral 

 artery along the vertebral canal, forming a plexus round the vessel, supplying it 

 with filaments, which are continued up the vertebral and basilar to the cerebral 

 arteries. The branches communicate with the cervical spinal nerves. 



The Thoracic Portion of the Gangliated Cord. 



The thoracic portion of the gangliated cord consists of a series of ganglia 

 which usually correspond in number to that of the vertebrae, but, from the occa- 

 sional coalescence of two, their number is uncertain. These ganglia are placed 

 on each side of the spine, resting against the heads of the ribs and covered by the 

 pleura costalis ; the last two are, however, anterior to the rest, being placed on the 

 side of the bodies of the eleventh and twelfth dorsal vertebrae. The ganglia are 

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

 elongated form and frequently blended with the last cervical. They are connected 

 together by cord-like prolongations from their substance. 



The external branches from each ganglion, usually two in number, communi- 

 cate with each of the dorsal spinal nerves. 



The internal branches from the five or six upper ganglia are very small ; they 

 supply filaments to the thoracic aorta and its branches, besides small branches to 

 the bodies of the vertebrae and their ligaments. Branches from the third and 

 fourth, and sometimes also from the first and second ganglia, form part of the 

 posterior pulmonary plexus. 



The internal branches from the six or seven lower ganglia are large and white 

 in color; they distribute filaments to the aorta, and unite to form the three 

 splanchnic nerves. These are named the great, the lesser, and the smallest or 

 renal splanchnic. 



The great splanchnic nerve is of a white color, firm in texture, and bears a 

 marked contrast to the ganglionic nerves. It is formed by branches from the 

 thoracic ganglia between the fifth or sixth and the ninth or tenth, but the fibres in 

 the higher roots may be traced upward in the sympathetic cord as far as the first 

 or second thoracic ganglia. These roots unite to form a large round cord of 

 considerable size. It descends obliquely inward in front of the bodies of the 

 vertebrae along the posterior mediastinum, perforates the crus of the Diaphragm, 

 and terminates in the semilunar ganglion of the solar plexus, distributing filaments 

 to the renal and suprarenal plexus. 



The lesser splanchnic nerve is formed by filaments from the tenth and eleventh 

 ganglia, and from the cord between them. It pierces the Diaphragm with the 

 preceding nerve, and joins the solar plexus. It communicates in the chest 

 with the great splanchnic nerve, and occasionally sends filaments to the renal 

 plexus. 



The smallest or renal splanchnic nerve arises from the last ganglion, and, 



