THE TRACHEA. 



1109 



this subdivides into two branches for the middle and lower lobes of the right 

 lung. 



The Left Bronchus is smaller, longer, and more oblique than the right, being 

 nearly two inches in length. It enters the root of the left lung opposite the sixth 

 dorsal vertebra, about an inch lower than the right bronchus. It passes beneath 

 the arch of the aorta, crosses, in front of the oesophagus, the thoracic duct and 



Superior 

 Cornu. 



FIG. 705. Front view of cartilages of larynx; the trachea and bronchi. 



the descending aorta, and has the left pulmonary artery lying at first above and 

 then in front of it. It is entirely hyparterial, having no eparterial branch, and 

 divides into two branches for the upper and lower lobes of the left lung. If a 

 transverse section is made across the trachea a short distance above its point of 

 bifurcation, it is seen, in many cases, on looking down the tube that the right 

 bronchus appears to continue the direction of the trachea more directly than does 

 the left. 



Subdivisions of the Bronchi. According to Aeby, whose observations are based 

 on casts of the trachea and bronchi made with Roser's fusible alloy, the following 

 is the arrangement of the bronchi and larger bronchial tubes (Fig. 706) : The right 

 {'/-'itchus, after giving off the eparterial branch, becomes hyparterial, which the left 

 bronchus is from the beginning. Each bronchus then passes downward and back- 



