50 



386. The Windpipe, Trachea. 



The trachea extends from the lower part of the larynx, on a level 

 with the fifth cervical vertebra, to opposite the third dorsal, where it divides 

 into the two bronchi; in front and at the sides are a series of imperfect carti- 

 laginous rings, Cartilagines tracheales, 16 20 in number, held together by a 

 strong fibrous membrane; the posterior portion is membranous, and presents trans- 

 verse muscular fibres of the unstriped variety. The right bronchus, Bronchus 

 dexter, is more horizontal, x shortcr and wider than the left bronchus, Bronchus 

 sinister; the former has 6 8, the latter 9 12 cartilages, similar to those of the 

 trachea. The bronchi, upon entering the substance of the lungs, divide, the right 

 into three, the left into two branches, these again into smaller branches, and so on; 

 each of the smaller subdivisions enters a pulmonary lobule, and, again sub- 

 dividing, ultimately terminates in the intercellular passages and air cells of 

 which the lobule is composed. 



