BRONCHI. 



239 



BRONCHI AND BRONCHIOLES. 



The primary bronchi have the same structure as the trachea. In 

 their subdivisions changes occur, the C shaped cartilages being replaced 

 by irregular plates found on all sides of the tube (Fig. 270). These diminish 

 in size and thickness as the branches of the bronchi become smaller, and 

 disappear in those about i mm. in diameter. Branched tubulo-alveolar 



Tunica Circular 



Epithelium. propria. muscle fibers. ', 



, 



. ' ?; : '-. '-. 



";.''''.': ' :, :;'' 



%:' : 'ik.... $. .?^l.^' Alveoli. 



Fat .cells. 



Cartilage. 



Connective tissue. 

 Bronchial gland. 



Duct of gland. 



FIG. 270. CROSS SECTION OF A BRONCHUS 2 MM. IN DIAMETER, FROM A CHILD. 



glands occur as far as the cartilages extend. They are situated in a loose 

 connective tissue layer containing many nerves, blood and lymphatic ves- 

 sels, together with small lymph glands. The bodies of the bronchial glands 

 lie outside of a rather loose smooth muscle layer with fibers chiefly cir- 

 cular. The mucosa is -thrown into longitudinal folds. It consists of a 

 pseudo-stratified ciliated epithelium in the larger bronchi, changing grad- 

 ually to a simple epithelium in the small ones. The stroke of the cilia, 

 as .in the trachea, is toward the pharynx. The epithelium contains goblet 



