PROBABLE ACTION OF THE COCHLEA. 1185 



4. NERVE FIBRES IN COCHLEAR DIVISION OF AUDITORY NERVE, 14,000. 

 Range of audition, 11 octaves. 



nerve fibres for each octave. 



Assuming that the number of auditory filaments is the same for each of the 

 eleven octaves 



1273 x 6 = 7638 for 6 octaves used in music. 



127S 



- - = 106 nerve fibres for each semitone. 



1 06 



less than 2 nerve fibres for fa of a semitone. 



64 



5. FIBRES IN MEMBRANA BASILARLS (RETZIUS) 

 basilar fibres for eaoh octave . 



2182 x 6 = 13,092 for 6 octaves used in music. 



2182 



- =180 basilar fibres for each semitone. 



180 



. less than 3 basilar fibres for each fa semitone. 

 64 



6. HAIR CELLS INNER, 3487 ; OUTER, 11,700 = 15,237 

 cells for each octave. 



1385 x 6 = 8310 hair cells for 6 octaves used in music. 

 = 115 cells for each semitone. 



=less than 2 for each -fa semitone. 

 64 



7. CORTI'S RODS. INNER, 5590 ; OUTER, 3848 = 9438. 

 ^i 3 ^ = 858 rods for each octave. 



858 x 6 = 5148 rods for 6 octaves. 



858 



= 71 for each semitone. 

 12 



at least one rod for each fa semitone. As each rod forms half of a 

 61 Corti's arch, there will be nearly one arch for each fa. 



There are thus in the cochlea a sufficient number of possible vibratile 

 masses to satisfy theory. 



Careful measurements of parts of the cochlea have also shown remark- 

 able differentiation, indicating that we have an organ which cannot be 

 supposed to act only as a whole. These measurements show, for 

 example, that the breadth of the basilar membrane increases towards 

 the apex ; that the osseous lamina spiralis diminishes in breadth as 

 the basilar membrane increases ; that from base to apex, both the 



VOL. it. 75 



