WINDPIPE AND UJNGS. 



135 



and subdivides into smaller and smaller bronchial tubes, the 

 larger of which have crescentic cartilages arranged in their 

 walls, not, as in the trachea, one directly over another, but 

 in such a way as to maintain the cylindrical form of the 

 tube 011 every aspect, while in the smaller these cartilages 

 degenerate to irregular nodules, and disappear. 



Fig. 74. HUMAN WINDPIPE AND LUNGS, a, Hyoid bone; &, c, 

 thyroid and cricoid cartilages of larynx ; d, trachea dividing 

 inferiorly into right and left bronchus; e, root of left lung, the 

 pulmonary artery and vein cut across; /, /, the bases of the 

 lungs, which rest 011 the diaphragm; g, g, portions of the anterior 

 margins, which in the body reach to the middle line, and have 

 only folds of pleura between them. The right lung is seen to 

 have three lobes, the left two; the right is shorter than the left, 

 and the anterior part of the left is hollowed out opposite the 

 position of the apex of the heart. 



In all these tubes, except the smallest, there is a longi- 



