THE SYMPATHETIC NERVOUS SYSTEM 831 



The cardiac nerves (Nn. cardiaci) are formed by branches from the posterior 

 cervical and first thoracic ganglia, together with twigs from the sympathetic trunks 

 and the vagi. They form the cardiac plexus (P. cardiacus) on the ventral face of the 

 trachea with each other and with branches of the vagus and recurrent nerves. 

 They are subject to considerable variation, but their general arrangement may be 

 stated as follows: 



(a) On the right side there are usually two cardiac nerves. Of these one 

 passes back with the vagus in the angle between the right brachial artery and the 

 bicarotid trunk, pierces the pericardium, crosses the aortic arch, and divides into 

 branches which are mingled with those of the left nerves. The second crosses 

 obliquely over the right face of the trachea and joins the vagus, where the latter 

 gives off the right recurrent nerve; a small plexus is formed here, from which two 

 or three cardiac branches are detached. These pass back beneath the trachea and 

 ramify on the atria and ventricles. 



(b) On the left side there are commonly three cardiac nerves. One of these is 

 distributed to the great vessels in the anterior mediastinum. The largest passes 

 back at first with the vagus beneath the arch of the left brachial arterj^, inclines 

 downward, perforates the pericardium, and divides into two branches. One 

 branch passes beneath the bifurcation of the pulmonary artery and is distributed 

 to the left atrium. The larger branch dips in between the aorta and the pulmonary 

 artery, gives twigs to these vessels, and ramifies on the ventricles, especially along 

 the course of the right coronary artery. The third nerve crosses the deep face of 

 the left brachial artery, passes back below the trachea, and unites with filaments 

 of a right cardiac nerve. It passes around the aorta and ramifies chiefly along the 

 course of the left coronary artery on the left face of the ventricles. 



3. The thoracic part (Pars thoracalis systematis sympathici) extends back- 

 ward ventral to the costo-vertebral joints from the posterior cervical ganglion to the 

 crura of the diaphragm, and passes between the latter and the psoas minor to be con- 

 tinued by the abdominal part. 



The trunk is concealed in the first part of its course by the subcostal vessels 

 and the lateral border of the longus colli, but further back it is visible under the 

 pleura. 



The ganglia are arranged segmentally at each intercostal space and partly on 

 the heads of the ribs. They are flattened and are small and fusiform, with the 

 exception of the first. This (G. thoracale primum) is extensive, irregularly quadri- 

 lateral in outline, and is united with the posterior cervical ganglion, as previously 

 mentioned. The ganglia are connected with the thoracic nerves by white and gray 

 rami communicantes. Distinct ganglia may be absent at two or three spaces 

 succeeding the first, and here the trunk is thickened and contains ganglion ceUs. 



The visceral branches comprise aortic, cardiac, pulmonary, and oesophageal 

 branches, and the splanchnic nerves. The aortic branches ramify on the thoracic 

 aorta, forming around that vessel the thoracic aortic plexus (P. aorticus thoracalis). 

 The cardiac branches concur with those of the vagus in forming the cardiac plexus 

 (P. cardiacus). From this branches go to form the coronary plexuses (P. coronarii) 

 along the course of the vessels of like name. The puhnonary branches join with 

 corresponding branches of the vagus and filaments from the cardiac plexus in 

 forming the puhnonary plexus (P. pulmonalis) at the root of the lung. Branches 

 of the plexus, on which are minute ganglia, ramify with the bronchi in the substance 

 of the lung.i The oesophageal branches join with those of the vagus in the forma- 

 tion of the oesophageal plexus (P. oesophageus). 



The great splanchnic nerve (N. splanchnicus major) arises by a series of roots 

 derived from the sixth or seventh to the fourteenth or fifteenth thoracic ganglia 



1 The right and left plexuses communicate with each other, so that both lungs receive fibers 

 from both vagi. 



