30 IRVING HARDESTY 



peculiarly adapted for undulatory motion. The vibrations are 

 imparted by the base of the stapes by way of the fenestra vestib- 

 uli (ovalis), first to the fluid in the scala vestibuli, which scala 

 is on the apical side of the spiral organ. The tectorial mem- 

 brane projects over the apical side of the spiral organ and there- 

 fore is in the logical position for being most readily disturbed 

 by the motion imparted. Finally, among other advantages, 

 the tectorial membrane varies far more in its proportions than 

 does the membranous spiral lamina and especially more than 

 the basilar membrane. In width, its vibratory or outspanning 

 zone is about 7 times wider in the apical than in the basal end 

 while the width of the apical end of the supposedly vibrating part 

 of the spiral lamina is only about 1 .4 times its width in the basal 

 end. The differences })etween the volume of the two ends of 

 the tectorial membrane very evidently exceed those of the 

 lamina to a much greater extent than do the differences in width, 

 and variations in volume are the most important for the func- 

 tions ascribed to the membranes in the telephone theory. 



It has been computed that the actual force of the vibrations 

 of the tympanic membrane, produced by sound waves, is in- 

 creased about 30 times as repeated in the vibrations of the base of 

 the stapes, and that the amplitude of certain waves as im- 

 parted to the tympanic membrane may be reduced as much as 

 76 times in their transference to the base of the stapes. Both 

 force and amplitude are decreased in overcoming resistance 

 in the cochlea. It is quite possible that very strong sound 

 stimuli may throw into vibrations both the tectorial membrane 

 and the membranous spiral lamina while the less strong and more 

 ordinary stimuli affect the more adapted tectorial membrane 

 alone. If the two were equally affected by the given strong 

 stimuli, their resultant movements would be parallel and the 

 required stimulation of the hair cells in the way usually supposed 

 would not occur. If, however, the position and greater flexibility 

 of the tectorial membrane should result in greater excursion or 

 amplitude of vibration in it than in the lamina, then the hair 

 cells could be stimulated in the way supposed and in accord 

 with the vibration frequency of the wave motion applied. It 



