TRACHEA AND BRONCHI. 383 



right luilf of the deep plexus : they communicate with the branches of the 

 recurrent laryngeal nerve of the vagus. 



On the left side the highest cardiac nerve lies over the arch of the 

 aorta, and ends in the superficial cardiac plexus; it may give a branch 

 beneath the arch to the deep plexus. Only one other nerve, the lower 

 cardiac, may be seen entering the left side of the deep plexus, as the mid- 

 dle one throws itself oftentimes into it. 



THE TRACHEA AND THE LUNG. 



Dissection. To see the pieces of the air tube in the root of the lung, it 

 will be necessary to remove the pu'monary artery with its branches, and 

 the pulmonary veins. And when the transverse part of the arch of the 

 aorta, which has been already cut through, is turned to one side, the dis- 

 sector will be able to clear away the bronchial glands, the nerves, and the 

 fibrous tissue from the part of the trachea in the thorax, and from the 

 branches into which it bifurcates. 



The TRACHEA, or the air tube, reaches from the larynx to the lungs, 

 and lies on the front of the spinal column. The tube begins opposite the 

 fifth cervical vertebra ; and it ends commonly at the fourth dorsal vertebra 

 by dividing into two pieces (bronchi), one for each lung. Its point of 

 splitting may be a vertebra lower. 



Its connections in the neck are described in p. 121, and its structure in 

 p. 162. The part in the thorax remains to be studied. 



In the thorax the trachea is situate with the great vessels in the space 

 between the pleura! bags. Here it is covered by the arch of the aorta, by 

 the innominate and left carotid arteries, arid by the cardiac plexus of 

 nerves. Behind the air tube is the oesophagus, which is slightly inclined 

 to the left near the arch of the aorta. On the right side are the vagus, 

 and the innominate artery, for a short distance, alter this has passed over 

 the trachea ; and on the left side lie the left subclaviari artery, and the 

 vagus with its recurrent branch. 



The bronchi, or the branches of the air tube, are contained in the roots 

 of the lungs, and are surrounded by vessels, glands, and nerves. Near the 

 lung each is divided into as many primary pieces as there are lobes. In 

 their structure and form the bronchi resemble the windpipe, for they are 

 round and cartilaginous in front, but flat and muscular and membranous 

 behind. Their position behind the other pulmonary vessels has been de- 

 scribed at p. 310 ; but the characters of each are now to be noticed. 



The right branch is about an inch in length, and is larger than the left ; 

 it passes outwards, on a level with the fourth dorsal vertebra, beneath the 

 arch of the aorta and the upper cava, and above the right pulmonary 

 artery : the vena axygos arches above it. 



The left branch, about two inches long, is directed obliquely downwards 

 through the arch of the aorta, and joins the root of the left lung a vertebra 

 lower than on the opposite side. The tube lies on the rcsophagus and 

 thoracic duct, and on the aorta ; it is at first below the level of the corre- 

 sponding pulmonary artery. 



Dissection. The lungs are to be removed now from the body by cutting 

 through the vessels of the root. 



The remains of the heart and pericardium are to be taken away after- 

 wards. For their removal the interior cava is to be divided, and the peri- 

 cardium to be detached from the surface of the diaphragm ; in removing 



