THE NASAL MUCOUS MEMBRANE. 



1415 



the higher animals, to situations more remote from the exterior. The slender 

 peripheral process of the olfactory cell, which corresponds to the dendrite of the 

 neurone, is of uniform thickness and ends at the surface in a small hemispherical 

 knob that projects slightly beyond the general level of the epithelium and bears from 

 6-8 minute stif^ cilia, the olfactory liairs. The length of the peripheral processes, 

 being dependent upon the position of the nuclei, varies, since the latter occupy 

 difTerent levels within the epithelium in order to accommodate their greater number — 

 about 60 per cent, in excess of those of the supporting cells (Brunn). The central 



Fig. I 180. 



Fig. I 179. 



of^^i^SOl 



Section of human olfactory mucous 

 membrane, silver preparation ; two 

 olfactory cells are seen, one of which 

 sends nerve-fibre towards brain. X 335- 

 {Br linn.) 



Isolated elements of epithelium of olfactory 

 mucous membrane; a, olfactory cells; b, sup- 

 porting cells. X 1000. (Brunn.) 



processes of the olfactory cells, much more delicate than the peripheral, are directly 

 continued, as the axis-cylinders, into the subjacent nonmedullated nerve-fibres within 

 the tunica propria, from which they pass through the cribriform plate to enter the 

 brain and end in the arborizations within the olfactory glomeruli of the bulbus 

 olfactorius ( page 1 1 5 2 ) . • 



The tunica propria is differentiated into a superficial and a deep layer by 

 the adenoid character of the stratum immediately beneath the epithelium. The 

 superficial layer, from .015 -.020 mm. thick, consists of closely packed irregularly 

 round cells, resembling lymphocytes, and meagre bundles of delicate connective 

 tissue. The deep layer, on the other hand, contains robust bundles of fibro-elastic 

 tissue and relatively few cells. A distinct membrana propria is wanting within the 

 olfactory region. 



The glands of Bowman fglandulae olfactoriae) are characteristic of the olfactory 

 region and probably elaborate a specific secretion (Brunn). They open onto the 

 free surface by very narrow ducts that lead into saccular fusiform dilatations, into 

 which the tubular alveoli open. The ducts possess an independent lining of flattened 

 cells that extend as far as the surface and lie between the surrounding epithelial ele- 

 ments. The dilatations are clothed with flattened or low cuboidal cells, which are 

 replaced by those of irregular columnar or pyramidal form within the tubular 

 alveolar. From the character of their secretion the glands of Bowman are probably 

 to be reckoned as serous and not mucous (Brunn, Dogiel). 



The Respiratory Region. — The mucous membrane lining of the respiratory 

 region differs greatly in thickness in various parts of the nasal fossa. In situations 

 where the contained cavernous tissue is well represented, as over the inferior turbinate, 

 it may reach a thickness of several millimeters, while when such tissue is wanting, as 

 on the lateral wall, it is reduced to less than a millimeter. 



