THE NOSE. 



The Olfactory Region. The highly specialized regio olfactoria is 

 quite limited in extent and embraces an area situated over the upper and 

 adjoining part of the middle turbinate and the corresponding part of the 

 septum. In fresh preparations the olfactory area usually, but not always, 

 can be approximately mapped out by the yellowish hue, lighter or darker, 

 that distinguishes it from the respiratory region in which the mucous 

 membrane exhibits a rosy tint. 



The epithelium contains two chief constituents the supporting and 

 the olfactory cells. The supporting cells are tall cylindrical elements, 

 about 60 fj. in height, that extend the entire thickness of the epithelium. 

 Their outer and broader ends are of uniform width and contain the oval 

 nuclei which, lying approximately at the same line and staining readily, 

 form a deeply colored and conspicuous nuclear stratum at some distance 

 beneath the free margin. Between the latter and the row of nuclei, the 



Outer zone 

 Nuclear layer of 

 supporting cells 



Olfactory cells 



Blood-vessel 

 Glands 



Bundle of 



olfactory nerves 



FIG. 426. Section of olfactory mucous membrane. X 300. 



epithelium presents a clear zone Devoid of nuclei. The inner part of 

 the supporting cells is thinner and irregular in contour and often terminates 

 by splitting into two or more basal processes that rest upon the tunica 

 propria. Between these ends lie smaller pyramidal elements, the basal 

 fells, that probably represent younger and supplementary forms of the 

 sustentacular cells. The granular protoplasm of the basal processes often 

 contains pigment particles. 



The olfactory cells, the perceptive elements receiving the smell- 

 stimuli, consist of a fusiform body, lodging a spherical nucleus enclosed by 

 a thin envelope of cytoplasm, and two attenuated processes, a peripheral 

 and a central. The olfactory cells are in fact sensory neurones that have 

 retained their primitive position within the surface epithelium, as in many 

 invertebrates, instead of receding, as is usual in the higher animals, to situa- 

 tions 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 



