HEARING. 



567 



organ of hearing, and answers to the macula lutea of the eye 

 in many respects. 



The function of the organ of Corti is unknown. 



The structure of the ampullae of the semicircular canals, 

 and other parts of the labyrinth besides those specially con- 



FiG. 413.— Bistribntion of cochlear nerve in Bpiral lamina of antero-interior part of 

 cochlea of right ear (after Sappey). 1, trank of cochlea nerve; 8, membranous 

 zone of spiral lamina; 8, terminal expansion of cochlear nerve exposed through- 

 out by removal of superior plate of lamina spiralis; 4, orifice of communication 

 between scala tympani and scala vestibuli. 



sidered, with their peculiar hair-cells, suggests an auditory 

 function ; but what that may be is as yet quite undetermined. 

 It has been thought that the parts, other than the cochlea, are 

 concerned with the appreciation of noise, or perhaps the in- 

 tensity of sounds ; but this is a matter of pure speculation. 



AUDITOR? SENSATIONS, PERCEPTIONS, AND 

 JUDGMENTS. 



We have thus far been concerned with the conduction of 

 the aerial vibrations that are the physical cause of hearing ; 

 but before we can claim to have " heard " a word in the highest 

 sense, certain processes, some of them physiological and some 

 psychical, take place, as in the case of vision ; hence we may 

 speak of the affection of the end-organ or of auditory impulses, 

 and of the processes by which these become, by the mediation 

 of the brain, auditory sensations, and when brought under the 

 cognizance of the mind as auditory perceptions and judg- 

 ments. 



