T 7 



ELEMENTS OF MAMMALIAN ANATOMY. 



The trachea, or windpipe, is the tube leading from the 

 larynx to the lungs (Fig. 54). Its walls are prevented 

 from collapsing by the presence of about forty-five carti- 

 laginous rings which are incomplete dorsally. Before 

 passing into the lungs the trachea bifurcates into a right 

 and a left bronchus. The trachea and bronchi are lined by 

 ciliated columnar epithelium. The cilia project freely 



/* 



Wft/,^ P C 



peck* 



FIG. 80. DIAGRAMMATIC TRANSVERSE SECTION OF THE CHEST. 



ao, Aorta ; br, bronchus ; crd, spinal cord ; esoph, esophagus ; hd, head of 

 rib; pa, parietal pleura; pc, cavity of the pleura; sp, spinous process; 

 st, sternum ; tb, tubercle of rib ; tr, transverse process ; vp, visceral 

 pleura; t, thoracic duct; n, sympathetic nerve cord; az, azygos vein; 

 trc, trachea; v, pulmonary veins. 



into the lumen from the columnar walls, and are always 

 waving in such a manner as to carry the secreted mucus 

 lodged thereon toward the mouth, thereby preventing 

 the lungs from becoming clogged with foreign material. 

 Ciliated cells with the cilia in action may be easily demon- 

 strated by scraping very lightly a little mucus from the 

 posterior part of the roof of the frog's mouth, and mount- 



