472 DISSECTION OF THE THORAX. 



large pos- The posterior branches are larger and much more numerous. 

 ter 'i r f rm Forming a plexiform arrangement (posterior pulmonary plexus) 

 behind the root of the lung by the flattening and splitting of the 

 trunk of the nerve, they are joined by filaments from the third and 

 fourth ganglia of the knotted cord of the sympathetic, and are 

 conveyed into the lung on the divisions of the airtube, 



(Esophageal d. CEsophageal branches are furnished to the gullet, but in 

 forma* 68 greatest abundance in the lower half. Below the root of the lung 

 plexus. the branches of the pneumo-gastric nerves surround the oesophagus 



with a network (plexus gulce). 



Sympathetic SYMPATHETIC NERVE. In the thorax the sympathetic nerve con- 

 sists of a knotted cord along each side of the spinal column, which 

 communicates with the spinal nerves ; and of a large prevertebral 

 or cardiac plexus, which distributes branches to the heart and the 

 luDgs. 



a gangiiated The gangliated cord will be seen in a future stage of the dissec- 

 cord, tion, after the heart and the lungs have been removed, 



and a cen- The CARDIAC PLEXUS lies over the lower end of the trachea, and 

 trai cardiac above the bifurcation of the pulmonary artery. A part of this 

 network, the superficial cardiac plexus, has been already described 

 on page 457. The remaining part, or the deep cardiac plexus, is 

 placed beneath the arch of the aorta. 



Dissection Directions. The cardiac plexus has been injured by the previous 

 examination of the heart, so that it should be dissected in a body 

 in which the heart and the large vessels are entire, but the student 

 should make them out in his part as well as he can. 



to expose Dissection. The ascending aorta is to be cut across near the 



part, lght heart, and is to be drawn over to the left side, after the manner of 

 fig. 163, p. 448 : next, the upper cava is to be divided above the 

 entrance of the azygos vein, and its lower part is to be thrown 

 down. By the removal of some fibrous and fatty tissues and 

 lymphatic glands, the right part of the plexus will be seen in front 

 of the trachea, above the right branch of the pulmonary artery. 

 The offsets to the heart should be followed downwards on the trunk 

 of the pulmonary artery ; and those to the lung should be traced 

 along the right branch of that vessel. 



To lay bare the part of the plexus into which the nerves of the 



and the left, left side enter, the aorta is to be cut through a second time, between 



the subclavian artery and the attachment of the ligament of the 



ductus arteriosus ; and the arch is to be turned upwards with the 



great vessels attached. The lymphatic glands and the areolar and 



fatty tissue being cleared away from the plexus as on the opposite 



side, the offsets to the left coronary plexus of the heart will be visible. 



Deep cardiac The deep cardiac plexus is situate between the trachea and the arch 



plexus. O f ^ aor fc aj an( j consists of right and left halves, which are joined 



by cross branches. In it are united the cardiac nerves of the 



sympathetic and vagus, with the exception of two branches of the 



left side ; and from it nerves are furnished to the heart and lungs. 



Right part, The right part of the plexus is placed above the right branch of 



ormed; ^ pulmonary artery, and receives the nerves of the right side, 



