HEARING OR AUDITION. 



Fig. 32.* 



117 



substances introduced into the circulation would excite the olfactory 

 nerve to the perception of the odour, has not been ascertained ex- 

 perimentally. 



The cavities that communicate with the nasal passages have no 

 connexion with the sense of smell. 



HEARING OR AUDITION. 



By the sense of hearing the mind takes cognizance of the condi- 

 tion of the auditory nerve produced by those oscillations of elastic 

 matter which give rise to the phenomena of sound. The communi- 

 cation of these oscillations to the ear may lake place through the 

 air, or through the intervention of some solid conductor, brought into 

 immediate connexion with the organ of hearing. The following 

 condensed account of the organ is from the eighteenth chapter of 

 Todd and Bowman's Physiological Anatomy. The essential part of 

 the organ of hearing is a sac, containing fluid, upon which the nerve 

 of hearing is freely distributed ; this sac being in connexion with the 

 cranial parietes. This is represented in the human subject by that 

 small cavity excavated in the petrous portion of the temporal bone 

 called the vestibule. This, and three semicircular canals, with a 

 spirally disposed canal, divided by a partition, constituting the coch- 

 lea, form the labyrinth. External to this, and situate between the 

 squamous and petrous portions of the temporal bone, is a cavity, 



* a. Olfactory process, h. Olfactory bulb. c. Fifth nerve within the cranium, d. Its 

 superior maxillary division, anastomosing with the olfactory filaments, and with s, branches 

 of the nasal division of the ophthalmic nerve, o. Posterior palatine twigs from Meckel's 

 ganglion, supplying the soft and hard palate. 



The cut represents the outer wall of the nasal fossa, with the three spongy bones and 

 meatus. 



