470 



DISSECTION OF THE THORAX. 



Left veins. 



the upper and middle lobes of the lung ; and the inferior vein is 

 formed by branches from the lower lobe. 



The left veins cross in front of the descending aorta ; and one 

 springs from each lobe of the lung. 



Nerves of 

 the thorax. 



To trace 



vagus. 



Phrenic 

 nerve from 

 the cervical 

 plexus, 



passes to 

 diaphragm. 



Right nerve 

 above root 

 of lung. 



Left nerve 

 above root. 



Some off- 

 sets. 



Internal 



mammary 



artery 



gives 



phrenic 



branch. 



NERVES OF THE THORAX. 



The pneumo-gastric and the sympathetic nerves supply the viscera 

 of the thorax ; and the phrenic nerve courses through the cavity to 

 the diaphragm. 



Dissection. The phrenic nerves have already been fully 

 displayed ; but the pneumo-gastric nerves are now to be prepared. 



The vagus is to be followed, on each side, behind the root of the 

 lung, and its large plexus in that position is to be dissected out, 

 the lung being thrown well over to the opposite side : some fine 

 branches from the gangliated cord of the sympathetic coining for- 

 wards over the spinal column to the plexus, must also be looked for. 

 The vagus also supplies a few filaments to the front of the root. 

 Beyond the root, the nerve is to be pursued along the oesophagus 

 by raising the lung and removing the pleura. 



The PHRENIC NERVE is derived from the anterior division of the 

 cervical plexus ; from the fourth and fifth cervical nerves, mainly 

 from the fourth. In its course through the thorax it lies along the 

 side of the pericardium, and at a little distance in front of the root 

 of the lung, with a small companion artery. When near the dia- 

 phragm it divides into branches, which perforate the muscle, and 

 are distributed on the under service. The nerves of opposite sides 

 differ in length, and in their relations above the root of the lung. 



The right nerve is shorter and straighter than the left. On enter- 

 ing the chest it crosses behind the subclavian vein, but in front of 

 the internal mammary artery ; and it lies afterwards along the 

 right side of the innominate vein and superior cava till it reaches 

 the pericardium. 



The left nerve crosses the subclavian artery, and has the same 

 position as the right to the mammary vessels when entering the 

 cavity. In the thorax it is directed over the arch of the aorta to 

 the root of the lung, and makes a curve lower down around the 

 projecting heart. Before reaching the aorta the nerve is placed 

 external to the left common carotid artery ; and it inclines 

 gradually from without inwards, so as to be in front of the left 

 vagus over the aortic arch. 



Branches. Some small filaments are said to be furnished from 

 the nerve to the pleura and pericardium. 



INTERNAL MAMMARY ARTERY. A small part of this artery, 

 which lies beneath the first rib, and winds round the phrenic 

 nerve and the innominate vein to reach the side of the sternum, is 

 now to be seen. It gives the following offset : 



The superior phrenic branch (conies nervi phrenici) is a very 

 slender artery, which accompanies the phrenic nerve to the dia- 

 phragm, and is distributed to that muscle, anastomising therein 



