240 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



trachea measures from four to four and one- half 

 inches in length, and three-fourths to one inch in 

 width. It is smallest at its commencement, and, 

 although quite uniform in its dimensions, is usually a 

 little wider midway between its two ends. 



At the lower end the trachea bifurcates to form 

 the right and left bronchi, which pass each to the root 



of the corresponding 

 lung. The right bron- 

 chus is larger than 

 the left and more 

 nearly vertical, so that 

 in looking down the 

 trachea more of the 

 right than of the left 

 bronchus can be seen. 

 The right bronchus di- 

 vides into branches, 

 one to each root of 

 the three lobes of the 

 right lung, while the 

 left gives off two 

 branches, one to each 

 lobe of the left lung. 



Structure. In the 

 wall of the trachea 



there are from sixteen to twenty C-shaped cartilage 

 rings that make a little more than two-thirds of a cir- 

 cle. The outer surface of these cartilages is flat, but 

 the inner surface is convex from above downward, so 

 as to give greater thickness in the middle than at the 

 edges. The cartilage is of the hyaline variety and is 



Ciliated epi- 

 thelium. 



Longitudinal 

 elastic fbers. 



^Mucous 

 glands. 



Fat cells. 



Cartilage. 



Fig. 185. From longitudinal sections 

 of trachea. 



