DISTRIBUTION OF PIBEES AND ORGANS 



449 



E-' 



walls of this cavity are formed by the inferior maxillary 

 palate, the nasal and ethmoid bones, and is lined through- 

 out ^\'ith mucous membrane. In this membrane are dis- 

 tributed the fibers of the first pair of cranial nerves (the 



olfactories), and through 

 these fibers impulses of 

 smell are carried to the 

 olfactory lobes. These 

 fibers end in the upper 

 part of the membrane of 

 this cavity in special end 

 organs of smell. The lin- 

 ing of the nose is, there- 

 fore, divided into a lower 

 or respiratorj' membrane 

 composed mainly of cili- 

 ated epithelial cells, and an 

 upper or olfactory mem- 

 brane, rich in nerve fibers, 

 and devoid of ciliated cells. 

 The end organs themselves 

 consist of the ends of the 

 fibers developed into long, 

 oKactory cells, and these 

 cells are protected on all 

 sides by surrounding nucleated, epithelial cells. The 

 olfactory cells show a long, nucleated cell body some- 

 what like a taste cell, and, like that, ending in tiny hair- 

 like projections at one end, while the other is continuous 

 with the nerve fiber. The hairlike processes are first 

 stimulated, and transmit this stimulus to the fiber which 

 conveys the impulses to the brain. 



EDDT. PHV3. — 29 



Fig. 211 — Olfactory cells from lining of 

 nose; O, O, olfactory cells terminating 

 nerve fibers; E, E, ordinary epithelial 

 cells of the mucous membrane; H^ 

 sensitive cilia affected by odor. 



