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fibres which arc passing, like the fibres from tin 1 sacral nerves, directly from the 

 spinal cord to the cells of the plexuses 



Tin: ('MIDI \< l'i 



The cardiac plexus is formed by tin- cardiac brandies from both vagu^ nerves and 

 from both sympathetic trunks. It lies beneath and behind the arch of the aorta, in 

 front of the bifurcation of the trachea, and extends a short distance upwards on the 

 sides of the t rachea. It is composed of a superficial and a deep part (fig. 720). 



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 arteriosurn. 



Branches. From this plexus some connecting branches pass to the left half 

 of the deep cardiac plexus, and others accompany the left pulmonary artery to the 

 le]l anterior pulmonary plexus. It also sends branches to the right anterior cororary 

 plexus. 



The deep portion of the cardiac plexus lies behind 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 infe- 

 rior cervical cardiac branches from the right sympathetic trunk, the middle and in- 

 ferior cervical cardiac branches from the left trunk, and all the cervical and thoracic 

 cardiac branches of the vagus nerves except the inferior 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 superficial part of the cardiac plexus. 



The right part oj the deep cardiac plexus gives branches to the right atrium, to the 

 right anterior pulmonary plexus, and to the right and the left coronary plexuses 

 (fig. 720). The branches to the left coronary plexus pass behind the pulmonary 

 artery. Some of those to the right coronary 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. 



Theantt r/or (right) 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. 720). Its distribution to the heart follows that of the 

 right coronary artery. 



The jioslrrior (left) coronary plexus is larger than the anterior 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. 720). 

 Its distribution to the heart follows that of the left coronary artery. 



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



reiiKiiiks of the primitive plexuses found in the embryo, which are called the bulbar, the inler- 

 iiKiliutf. and the nlrml plexuses, term- which siillicienlly indicate their relative positions. The 

 bulbar plexus (jives nil 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 medullated and non-medullated : 

 the former are inhibitor}', the latter motor. The inhibitory impulses leave the cen- 

 tral nervous system by the spinal accessory and vagus nerves. The motor fibres 

 leave the spinal cord by the ventral roots and white ratni communicantes of the 

 thoracic nerves and terminate about the cells of the intervening sympathetic 

 ganglia. Krom the cells of these ganglia arise the non-medullated (grey) fibres of 

 the plexus. 



THE CUCLIAC I'I.KXI - 



The co?liac (solar or epigastric) plexus is the largest of the prevertebral plexu-i-. 

 It is unpaired, and is continuous above with the aortic plexus of the thorax and below 



