THE CARDIAC PLEXUS 1041 



hypogastric plexuses are situated in front of the lumbar vertebrae. Each plexus 

 receives not only sympathetic fibres which have passed from or through the 

 ganglia of the sympathetic trunks of either side, but also both afferent and efferent 

 cranio-spinal nerve-fibres derived directly from the cranio-spinal nerves. In 

 addition the cardiac and coeliac plexuses receive both efferent visceral and cranio- 

 spinal sensor}^ or afferent visceral fibres from both vagus nerves. It should be 

 clearly understood that the branches which run from the sympathetic gangliated 

 trunks to the prevertebral plexuses contain meduUated fibres which are passing, 

 like the fibres from the sacral nei-ves, directly from the spinal cord to terminate 

 about the cells of the plexuses. 



1. The Cardiac Plexus 



The cardiac plexus is formed by the cardiac branches from both vagus nerves 

 and from both sympathetic trunks. It lies beneath and dorsal to the arch of the 

 aorta, in front of the bifurcation of the trachea, and extends a short distance 

 upward on the sides of the trachea. It is composed of a superficial and a deep 

 part (fig. 789). 



The superficial part of the cardiac plexus is much smaller than the deep part, 

 and lies beneath the arch of the aorta in front of the right pulmonary artery. It 

 is formed chiefly by the cardiac branches of the left vagus and by the left superior 

 cardiac nerve, but sometimes receives filaments from the deep cardiac plexus. 

 The cardiac ganglion (ganglion of Wrisberg,) usually found connected with this 

 plexus, lies on the right side of the ligamentum arteriosum. 



Branches. — From this plexus some branches pass to the left half of the deep cardiac plexus, 

 and others accompany the left pulmonary artery to the left anterior pulmonary plexus. It also 

 sends branches to the right anterior coronary plexus. 



The deep portion of the cardiac plexus lies dorsal to the arch of the aorta at the 

 sides of the lower part of the trachea and in front of its bifurcation. It consists of 

 two lateral parts, more or less distinct, connected by numerous branches, which 

 pass around the lower part of the trachea. It is formed by the superior, middle, 

 and inferior cervical cardiac branches from the right sympathetic trunk, the mid- 

 dle and inferior cervical cardiac branches from the left trunk, and all the cervical 

 and thoracic cardiac branches of the vagus except the superior cervical cardiac 

 branch of the left vagus. It also receives branches from the superficial cardiac 

 plexus. 



The left part of the deep cardiac plexus gives branches to the left atrium (auricle) of the heart, 

 to the left anterior pulmonary plexus, to the left coronary plexus, and sometimes to the super- 

 ficial part of the cardiac plexus. 



The right part of the deep cardiac plexus gives branches to the right atrium, to the right an- 

 terior pulmonary plexus, and to the right and the left coronary plexuses (fig. 789) . The branches 

 to the left coronary plexus pass behind the pulmonary artery. Some of those to the right coro- 

 nary plexus pass anterior and some posterior to the right pulmonary artery. 



The coronary plexuses are formed by branches given off by the cardiac plexus. 

 They accompany the coronary arteries and are right and left. 



The right {anterior) coronary plexus receives filaments from the superficial part 

 of the cardiac plexus, but is formed chiefly by filaments from the right portion of 

 the deep cardiac plexus (fig. 789). Its distribution to the heart follows that of 

 the right coronary arter3^ 



The left (posterior) coronary plexus is larger than the right plexus, and is formed 

 for the most part by filaments from the left portion of the deep cardiac plexus, but 

 it receives some filaments from the right portion of the deep cardiac plexus 

 (fig. 789). Its distribution to the hoart follows that of the left coronary artery. 



The cardiac plexus and the network of nervous structures in the walls of the atria are the 

 remains of the primitive plexuses found in the embryo, which are called the bulbar^ the inter- 

 mediate, and the atrial plexuses, terms which sufficiently indicate their relative positions. The 

 bulbar plexus gives off the coronary nerves and is transformed into the superficial part of the 

 deep cardiac plexus; the remainder of the deep cardiac plexus is formed by the intermediate 

 plexus, and the atrial plexus becomes the network of the atrium. 



The fibres which pass to the cardiac plexus are medulla ted and non-medullated; the former 



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