8;M the nervous SYSTEM 



THE GPvEAT PREVERTEBRAL PLEXUSES 



Tho great prevertebral plexuses, as we have already noticed, are the cardiac, 

 solar, anil hv})()gastric. They are formed mainly by branches derived from the 

 gangliated cords, but also receive fibres from the cerebro-s])inal nerves; thus the 

 cardiac plexus and solar plexuses are joined by branches of the iineumo,2;astric, and 

 the hyjiogastric plexus is joined l)y branches of the third and fourth and sometimes 

 the second sacral nerves. 



CARDIAC PLEXUS 



As already noted, each pneumogastric nerve gives off two or three cervical 

 cardiac branches, a thoracic cardiac branch, and additional branches may s])ring 

 from the recurrent laryngeal nerve. There are also three cardiac nerves which 

 arise from the cervical sympathetic cord on each side. These nerves all proceed 

 to the cardiac plexus, but their course and arrangement is extremely varialilc. 

 It is very common to find the upper cervical cardiac branches of the vagus and 

 sympathetic uniting to form a common trunk; in other cases the nerves l)ranch 

 and communicate with one another in a plexiform manner. The cardiac plexus, 

 although forming a continuous network of nerves, is for convenience divided into 

 a superficial and a deep plexus. The superficial plexus is situated immediately 

 l)elow the arch of the aorta, internal to the ligamentum ductus arteriosus; it 

 receives the left superior cardiac nerve of the sympathetic and the left inferior 

 cervical cardiac branch of the pneumogastric. The deep cardiac plexus is placed 

 in front of the ])ifurcation of the trachea between tliat structure and the aortic 

 arch; it receives all the other cardiac nerves. 



Superficial cardiac plexus. — The superior cardiac branch of the sympathetic 

 and the inferior cervical cardiac branch of the vagus cross the aortic arch on its left 

 side, being placed between the artery and the left pleura. The nerves then enter 

 the interval between the aortic arch and the bifurcation of the pulmonary artery, 

 Avhere they communicate with the deep cardiac plexus. A small ganglion (the 

 carfliac ganglion of M^risberg) is usually developed at the point of communication. 

 Branches are furnished to the right coronary plexus and also to the left lung. The 

 latter Ijranches join the anterior pulmonary plexus. 



Deep cardiac plexus. — The deep cardiac plexus receives all the right cardiac 

 nerves, and also the cardiac nerves of the left side, with the excejition of the 

 superior cervical cardiac of the sympathetic and the inferior cervical cardiac of 

 the vagus. The plexus is placed in front of the l^ifurcation of the trachea, and 

 gives off the following branches: — (a) Branches to the anterior pulmonary plexuses 

 of both sides; (6) the left coronar}^ plexus; (c) branches to the right auricle; 

 (d ) communicating branches to the superficial cardiac plexus; and (e) branches to 

 the right coronary plexus. 



Right coronary plexus. — This plexus is formed by branches from both the 

 superficial and deep cardiac plexuses. It follows the branches of the right coronary 

 artery for a certain distance, beyond Avhich the nerves diverge from the arteries, and 

 run between the pericardium and the muscular sulistance of the heart. Finally 

 they enter the muscular substance. 



Left coronary plexus. — This plexus is larger than the riglit. It arises from 

 the deep cardiac plexus, passes forwards between the left auricular appendix and 

 the pulmonary artery, and accompanies the branches of the left coronary artery. 



The auricles are supplied by the lower, and the ventricles, pulmonary artery 

 and aorta l)y the upper cardiac nerves. 



The cardiac plexuses and the network of nervous structures in the walls of the 

 auricles are the remains of the i)rimitive jilexuses found in the endiryo whicli are 

 called the bulbar, the intermediate, and tlie atrial plexuses, terms which sufficiently 

 indicate their relative positions. The Indbar jilexus gives oft" the coronary nerves 

 and is transformed into the superficial and part of the deep cardiac ])lexus; the 

 remainder of the deep cardiac i)lexus is formed l^y the intermediate plexus and the 

 atrial plexus becomes the auricular network. 



