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A TEXTBOOK OF PHYSIOLOGY 



Smell. The Receptor Mechanism is formed by the olfactory cells 

 situated in the mucous membrane of the upper ineatus of the nose, 

 and covering the upper part of the superior turbinate bone and nasal 

 septum. The middle and inferior meatus constitute part of the 

 respiratory tract. 



The nasal mucous membrane, or Schneiderian membrane, is thick 

 and of a yellowish hue, in marked contrast to the reddish tint of the 

 respiratory portion of the nose. In section it is seen to consist of 

 an epithelial layer the olfactory epithelium which rests upon a 

 basement membrane, and separates it from the deeper mucous layer 

 or corium (Fig. 334). 



FIG. 334. SECTION OF OLFACTORY EPITHELIUM OF THE FOWL, SHOWING sup. c., SUP- 

 PORTING CELLS; sen. c., SENSORY CELLS; AND ba. c., BASAL CELLS. (Redrawn 

 from Dahlgren and Kepner.) 



The receptor olfactory cells lie in the epithelial layer. They 

 possess a central nucleus surrounded by a small quantity of protoplasm, 

 from which there passes towards the surface a narrow round filament 

 with a cilium attached. A smaller similar process, arising from the 

 base of the cells, arborizes with the terminal ramifications of the 

 olfactory nerve. Supporting these cells are other " sustentacular 

 cells." These have a knife-handle-like shape, the upper hah* being 

 cylindrical in shape, and often provided with stiff cilia attached to 

 the free border. The lower hah* is narrow, and ends in a long process 

 which joins with the neighbouring cells. At the boundary of the 



