340 



RESPIRATION. 



[CH. XXIV. 



lymphoid tissue, separated from the ciliated epithelium which 

 lines it by a homogeneous basement membrane. The epithelium 

 is formed of several layers of cells, of which the most superficial 

 layer is ciliated ; while between these cells are smaller elongated 

 cells prolonged up towards the surface and down to the basement 



Fig. 310. Section of the trachea, a, columnar ciliated epithelium; 6 and c, corium of 

 the mucous membrane, containing elastic fibres cut across transversely ; d, submucous 

 tissue containing mucous glands, e, separated from the hyaline cartilage, g, by fine 

 fibrous tissue, /; h, external investment of fine fibrous tissue. (S. K. Alcock.) 



membrane. Beneath these are one or more layers of more 

 irregularly shaped cells (fig. 313). Many of the superficial cells 

 are of the goblet variety. In the deeper part of the corium of 

 the mucous membrane are many elastic fibres between which lie 

 connective-tissxie corpuscles and capillary blood-vessels. 



Numerous mucous glands are situated in the substance of the 

 mucous membrane of the trachea ; their ducts perforate the 



