480 FUNCTIONS OF DIFFERENT PARTS OF THE LABYRINTH. 



cochlea and the semicircular canals, to the foramen stylo- 

 mastoideum. 



In this course it soon receives the Vidian nerve already 

 mentioned; and it sends off the chorda tympani, immediately 

 before it passes out at the foramen stylo-mastoideum. It also 

 sends off small fibrils to the muscles of the bones of the ear. 



It has not been ascertained whether the portio dura, the Vi- 

 dian nerve, and the chorda tympani, have any effect upon the 

 function of hearing. 



The situation of those branches of the auditory nerve which are expanded in 

 the vestibule and the semicircular canals, is somewhat different from the sit-, 

 uation of those which are in the cochlea ; but it has not yet been ascertained 

 how far their functions are different. 



The information on this subject derived from comparative anatomy, is very 

 interesting ; but, for want of more acquaintance with the state of this func- 

 tion, in the different animals, no very decisive inferences have been drawn 

 from it. 



The vestibule and semicircular canals occur much more frequently than the 

 cochlea, which is to be found in few animals, if any, besides those of the 

 classes of mammalia and of birds. It is therefore supposed necessary to 

 that perfect state of hearing which the animals of these classes enjoy. But 

 there remains a considerable difficulty on this subject ; the cochlea is not, by 

 any means, so perfect in birds as in quadrupeds ; yet many birds appear to 

 have clear perceptions of musical sounds, and some birds imitate articulate 

 sounds with considerable accuracy. 



That the impression which produces hearing is made on the nervous expansions 

 in the Labyrinth, does not appear to be doubted by any one. The structure 

 of the whole organ, and the analogy between it and the eye induce a strong 

 belief that this is the case. 



This belief is confirmed by a dissection recorded by Mr. Haighton,* in which 

 Original Deafness was found to depend upon a quantity of cheese-like matter, 

 which filled the whole labyrinth, and was attended with a considerable 

 diminution of the size of the auditory nerve, while all the other parts of the 

 organ were in a perfectly natural state. 



* See Memoirs of the Medical Society of London, vol. 3. 



