THE NASAL MUCOUS MEMBRANE. 403 



walls and on the lower part of the nasal septum they are present in 

 large numbers. As already mentioned, the veins of the mucosa are 

 so wide and plentiful that the layer in which they lie appears like 

 cavernous tissue. 



The mucous membrane lining the accessory spaces of the nasal 

 fossae the sphenoidal, the frontal, and the maxillary sinuses 

 and the ethmoidal cells closely resembles that of the respiratory 

 region, being covered by a stratified ciliated epithelium, which 

 rests upon a thin tunica propria closely united with the periosteum. 

 These tracts are chiefly distinguished from the respiratory surface by 

 the marked reduction in the thickness of the mucous membrane, 

 which within these spaces is seldom more than .02 mm. The meagre 

 supply of glands is another point of difference, the glandular struct- 

 ures within these spaces being represented by small and sparingly 

 distributed groups often exhibiting peculiar modifications of the 

 racemose type. 



The olfactory region is distinguished macroscopically from the 

 respiratory portions of the nasal fossae by the yellowish-brown 

 tinge of its mucous membrane as contrasted with the rosy hue of 

 that covering the adjacent region ; the more deeply colored tract 

 indicates in only a general way the boundaries of the olfactory 

 region, since the limits of the two do not closely correspond, the 

 brownish area in man being usually somewhat less extensive than 

 the entire surface 

 possessing the 

 structure of the ol- 

 factory mucous 

 membrane. The 

 latter is also dis- 

 tinguished by its 

 greater thickness 

 and by the absence 

 of ciliated cells. 



The olfactory 

 mucosa consists of 

 the epithelium and 

 the tunica propria, 

 the characteristic 

 appearances of the 

 tissue depending 

 upon the peculiari- 

 ties of the former, another example of neuro-epithelium. This epi- 

 thelium consists of two kinds of cells, the sustentacular and the 

 olfactory elements. The sustentacular or support cells present 



Section through olfactory mucous membrane from child's nose : a t 

 zone of oval nuclei belonging to sustentacular cells ; b, zone of 

 spherical nuclei of olfactory elements ; c, basilar cells ; d, subepi- 

 thelial tissue ; e, glands of Bowman. 



