THE EAR AND HEARING. 573 



the effective outer arm of this lever is about half as long again 

 as the inner, and so the movements transmitted by the drum- 

 membrane to the handle of the malleus are communicated 

 with diminished range, but increased power, to the base of 

 the stapes. 



Ordinarily, sound-waves reach the labyrinth through the 

 tympanum, but they may also be transmitted through the 

 bones of the head; if the handle of a vibrating tuning-fork 

 be placed on the vertex, the sounds heard by the person ex- 

 perimented upon seem to have their origin inside his own, 

 cranium. Similarly, when a vibrating body is held between 

 the teeth, sound reaches the end organs of the auditory nerve 

 through the skull-boDes; and persons who are deaf from dis- 

 ease or injury of the tympanum can thus be made to hear, as 

 with the audiplione. Of course if deafness be due to disease 

 of the proper nervous auditory apparatus no device can make 

 the person hear. 



Function of the Cochlea. We have already seen reason 

 to believe that in the ear there is an apparatus adapted for 

 sympathetic resonance, by which we recognize different musi- 

 cal tone-colors; the minute structure of the membranous 

 cochlea is such as to lead us to look for it there. An old view 

 was that the rods of Corti, which vary in length, were like so 

 many piano-strings, each tending to vibrate at a given rate 

 and picking out and responding to pendular aerial vibrations 

 of its own period, and exciting a nerve which gave rise to a 

 particular tone sensation. When the labyrinthic fluids were 

 set in non-pendular vibrations, the rods of Corti were thought 

 to analyze these into their pendular components, all rods of 

 the vibrational rate of these being set in sympathetic move- 

 ment, but that rod most whose period was that of the primary 

 partial tone; this rod would determine the pitch of the note, 

 and the less-marked sensation due to the others affected would 

 give the timbre. The rods, however, do not differ in size 

 sufficiently to account for the range of notes which we hear; 

 they are absent in birds, which undoubtedly distinguish differ- 

 ent musical notes; and the nerve-fibres of the cochlea are not 

 connected with them but with the hair-cells. 



On the whole it seems probable that the basilar membrane 

 is to be looked upon as the primary arrangement for sympa- 

 thetic resonance in the ear. It increases in breadth twelve 

 times from the base of the cochlea to its tip (the less width of: 



