THE TRACHEA. 517 



CHAPTER XVII. 



OF THE TRACHEA AND THE LUNGS. 



ALTHOUGH the principal part of the windpipe is situated in 

 the neck above the cavity of the thorax, it is so intimately 

 connected with the lungs, that it is necessary to describe them 

 together. 



Of the Trachea. 



Trachea is the technical name for the windpipe, or the tube 

 which passes from the larynx to the lungs. 



This tube begins at the lower edge of the cricoid cartilage, 

 and passes down the neck in front of the oesophagus as low as 

 the third dorsal vertebrae, when it divides into two branches 

 called Bronchia, one of which goes to the right and the other 

 to the left lung, in which they ramify very minutely. 



The right bronchium is larger than the left, in proportion 

 to the greater size of the right lung. It is also shorter and is 

 placed more in front, and is more horizontal than the left, in 

 consequence of the right lung being shorter in its vertical 

 diameter, and longer in its antero-posterior than the lung of 

 the left side. It enters near the centre of the root of the lung, 

 opposite to the fourth dorsal vertebra. 



The left bronchium enters the root of the left lung, opposite 

 the fifth dorsal vertebrae. The right bronchium is embraced 

 at its upper part by the vena azygos, the left by the arch of 

 the aorta. 



There is in the structure of the trachea, a number of flat cartil- 

 aginous rings placed at small distances from each other, the edges of 

 which are connected by membrane, so that they compose a tube. 



These cartilaginous rings are not complete, for they do not 

 form more than three-fourths or four-fifths of a circle ; but their 

 ends are connected by a membrane which forms the posterior 

 part of the tube. 



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