214 ELEMENTARY PHYSIOLOGY. [XX. 



h. Stretching between the ends of the cartilage, 

 a transverse band of unstriped muscular 

 fibres; there may also be visible outside 

 this the cut ends of muscular fibres running 

 longitudinally. 



c. The submucous coat continuous with the 

 fibrous coat, but of finer fibres. 



d- The small mucous and serous glands, the 

 alveoli of which form a nearly continuous 

 layer in the submucous tissue ; the ducts 

 will be less evident, but they may be seen 

 running towards the surface, and occasionally 

 opening on it. 



e. The cut ends of elastic fibres, which form a 

 distinct longitudinal layer, on the inner side 

 of the submucous tissue. It will be seen 

 that this is most marked in the membra- 

 nous part of the trachea ; here, too, the 

 fibres are frequently collected into bundles. 



/. The mucous coat. In this may be seen 



a. A number of fine elastic fibres with a 

 variable Quantity of adenoid tissue. 



/3. The distinct basement membrane. 



7. The epithelium, consisting of long colum- 

 nar ciliated cells, and of two, three, or 

 more layers of small cells lying between 

 the basal processes of the ciliated cells. 

 If the trachea has not been carefully 

 hardened and prepared, the cilia may 



