134 



ELEMENTARY PHYSIOLOGY 



an epithelium of ciliated cells, interspersed with 

 mucous cells ; these lie on a distinct basement mem- 

 brane and below this is a small amount of lymphoid and 

 elastic tissue. (See Lesson XII.) Between the mucous 

 membrane and the outer layer which carries the hoops of 

 cartilage, there is a certain amount of areolar connective 



Fio. 40. — Ciliated EpiTHKi.iUMCKt.i.s from the Trachea of the Rabbit, 



UlnHLY MAGNIFIED. (ScHAFER.) 



ml, to2j «t3, mucus-secreting cells lying between the ciliated cells and 

 seen in various stages of mucin-formation. 



tissue (p. 86), in which some small mucous glands are 

 imbedded ; this constitutes the submucous layer. The 

 ciliated cells are elongated columnar cells with a large and 

 distinct nucleus. During life the cilia vibrate incessantly 

 backwards and forwards, but work on the whole in such a 

 way as to sweep both liquid (mucus) and solid particles 

 outwards or towards the mouth. (See also Lesson VII.) 

 The mucous and ciliated cells extend from the trachea into 

 the smallest branches of the bronchi. 



are covered with a viscid secretion called mucus, whose characteristic 

 constituent, mucin, is secreted by speciiil mucous cells or by small 

 mucous glands, imbedded in or lying beneath the membrane. 



