474 IRVING HARDESTY 



ing according to the vibration frequencies of all the sounds the 

 organ is capable of appreciating, that mixtures of sounds are 

 analysed in the cochlea by the resonant vibration of the fibers 

 in different parts of it corresponding to the different tones con- 

 tained in the mixture. 



Aside from the many physiological difficulties met in applying 

 it, the Helmholtz theory is not supported by the later found 

 anatomy of the cochlea: (1) The basilar membrane is not 

 composed of independent fibers. The structure given the name 

 is composed of three layers of white fibrous tissue, one of which 

 courses at right angles to the others. That part of it which is 

 radially arranged is nothing more than a flat tendon, the fas- 

 ciculi of which are abundantly connected with each other by 

 collateral branches. (2) Were the basilar membrane composed 

 of radial fibers capable of vibrating independently, it is blanketed 

 on both its sides by continuous and thick layers prohibitive of 

 any such action. On its apical or vestibular side is spread the 

 spiral organ (of Corti) and the membrana propria of its epithe- 

 lium; on its basal or tympanic side extends the continuous layer 

 of epithelioidal syncytium with its blood vessels and the continu- 

 ous endothelium lining the scala tympani. (3) Were the mem- 

 brane as the theory assumes, the cells of the spiral organ are so 

 closel}^ associated and cemented together that individual hair 

 cells or groups of hair cells overlying the fibers concerned with 

 a given note could not be made to impinge separately against 

 the tectorial membrane by the resonant vibration of the fibers. 

 (4) It is questionable whether the fibers, were they independent 

 and free, are long enough for the resonant vibration assigned 

 them by the theory, especially for the sound waves of the lower 

 notes appreciated. Liberal measurements in the human cochlea 

 give the supposedly vibrating part of the membranous spiral 

 lamina a width of only fV mm. (304^4) at its apical end where 

 it is broadest and f\ mm. (168At) at its basal end. Measure- 

 ments of the same for the adult hog gave 258At as the average 

 width at the apical end and 185^ as the average width at the 

 basal end. Helmholtz himself appreciated the doubt whether 

 fibers so short as the width of the basilar membrane can be 



