94 GLANDS. 



of these, the deeper layers of cells are many-sided, and 

 present nothing worthy of note ; but those upon the 

 surface are conical, with their bases directed towards 

 the axis of the canal, and furnished with vibratile 

 cilia (PL I. fig. VII.). In the most minute bronchial 

 tubes the deeper strata of epithelial cells disappear 

 entirely the ciliated layer alone remaining. 



Underlying the epithelial layer we have the mu- 

 cous membrane, consisting of a delicate web of inter- 

 mingled connective and elastic fibres. These latter 

 have a longitudinal direction, and occupy the outer 

 aspect of the membrane. In bronchise of some size 

 they form small whitish longitudinal fasciculi, per- 

 fectly visible to the naked eye. Outside of the mu- 

 cous membrane we have a layer of unstriped mus- 

 cular fibres, circular in their direction. In the tra- 

 chea, and its larger subdivisions, these fibres are found 

 only in their posterior aspect, or in the membranous 

 portion of the canal, and their connexion with the 

 extremities of the cartilaginous rings has been demon- 

 strated (Kolliker). Here, also, longitudinal muscular 

 fasciculi have been recognised, occupying the outer 

 aspect of the circular layer. 



Fibrous coat. Finally, the external or fibrous coat of the bron- 

 chial tubes is formed by a dense interlacement of 

 connective and elastic fibres. It contains also carti- 

 laginous plates of variable shape, which are found 

 only upon the anterior and lateral regions of the tra- 

 chea and large bronchi, whilst they are distributed 

 upon the whole circumference of the smaller canals. 

 It is to be noticed that these cartilaginous lamellae 

 become smaller and less frequent in proportion as the 



