298 



THE RESPIEATOEY SYSTEM 



the membrane through a pore-like opening in the cuticular membrane 

 which is formed by the cuticle of adjacent sustentacular cells. The 

 central process of the olfactory cell penetrates to the tunica propria and 

 becomes a non-medullated nerve fiber of one of the many rami of the 

 olfactory nerve ; it passes to the olfactory bulb,, where its terminal arbori- 

 zation with the dendrites of the mitral cells forms the olfactory glom- 

 eruli. 



The BASAL CELLS are flattened cells which form the deepest nuclear 

 zone of the olfactory neuro-epithelial layers. Their cytoplasm is finely 



granular and their nu- 

 clei are ovoid or flat- 

 tened. Frequently they 

 send a short process be- 

 tween the branched ends 

 of the sustentacular cells. 

 Many small nerve 

 trunks occur in the 

 tunica propria. The 

 great majority of these 

 are non-medullated and 

 are formed by the cen- 

 tral processes of the ol- 

 factory cells, which proc- 

 esses are true axons. 

 Several of the smaller 

 superficial fiber bundles 

 unite in the deeper part 

 of the tunica propria to 

 form one of the small 

 olfactory nerves. Taken 



together, about twenty in number on each side, these form two olfac- 

 tory nerves, unique among cerebrospinal nerves in being collectively 

 non-medullated. A few medullated fibers, derived from the trigeminus, 

 are also found in the tunica propria ; they distribute their terminal vaso- 

 motor branches to the blood-vessels, and, by fine sensory filaments which 

 end between the epithelial cells, supply the neuro-epithelial layer. The 

 trigeminus fibers supply a similar innervation to the respiratory mucosa. 

 The blood vessels of the olfactory mucous membrane are abundant. 

 Their capillary plexiises form several layers in the tunica propria, and 

 their veins mostly empty, through the ethmoidal veins, into the superior 



FIG. 284. VERTICAL SECTION OF THE OLFACTORY 

 MUCOSA OF, A KITTEN. 



a, deep, and b, superficial border of the epithe- 

 lium; c, olfactory cells; d, sustentacular cells; g, ol- 

 factory nerve fibers in the corium of the mucosa. 

 Golgi stain. X 325. (After Kolliker.) 



