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 artery, 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 
erura 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 cells. 
The visceral branches comprise aortic, cardiac, pulmonary, and cesophageal 
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 pulmonary branches join with 
corresponding branches of the vagus and filaments from the cardiac plexus in 
forming the pulmonary 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. The cesophageal branches join with those of the vagus in the forma- 
tion of the cesophageal plexus (P. cesophageus). 
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. 
