414 



ANATOMY FOR NURSES 



[Chap. XX 



odors, but also to distinguish individual odors in a mixed smell. 

 The sensation takes some time to develop after the contact of 

 the odorous stimulus, and may last a long time. When the stim- 

 ulus is repeated, the sensation very soon dies out, the sensory 

 terminal organs quickly becoming exhausted.^ 



Olfactory nerves. — The olfactory nerves are the special nerves 

 of the sense of smell, and are spread out in a fine network over 



the surface of the superior tur- 

 binated processes of the ethmoid 

 bone and on the upper third of 

 the septum. The nerves end in 

 special organs known as olfac- 

 tory cells, which lie under the 

 epithelium, but send prolonga- 

 tions between the mucous cells 

 to the surface. The central por- 

 tions of the olfactory cells are 

 prolonged as nerve-fibres into 

 a mass of gray matter, called 

 the olfactory bulb, which rests 

 upon the cribriform plate of the 



The nerves which ramifv over 



Fig. 192. — Vertic.vl Longitudinal 

 Section or Nas.^.l Cavity. 1, olfactory ethmoid bonC. 

 nerve ; v, branch of fifth nerve ; h, hard 

 palate. 



the lower part of the lining 

 membrane of the nasal cavity are branches of the fifth or tri- 

 geminal nerve. These nerves furnish the tactile sense and enable 

 us to perceive, by the nose, the sensations of cold, heat, tickling, 

 pain, and tension or pressure. It is this nerve which is affected 

 when strong irritants, such as ammonia or pepper, are appreciated 

 by the nose. 



HEARING 



The auditory apparatus consists of : (1) the external ear ; (2) the 

 middle car ; (3) the internal ear ; and (4) the auditory nerve. 



External ear. — The external ear consists of an expanded por- 

 tion named pinna, or auricle, and the auditory canal, or meatus. 



» This accounts for the fact that one may easily become accustomed to foul odors, 

 and is of special importance to nurses. Foul odors are quickly noticed by any 

 one coming into a sick room from out of doors, but a nurse who is in the sick room 

 constantly may become accustomed to such odors. Hence the importance of act- 

 ing on the first sensation of a disagreeable odor. 



