ACTION OF THE TECTORIAL MEMBRANE 473 



ances known as sound waves; (3) that sensations of sounds of 

 the highest pitches of which the apparatus is capable are medi- 

 ated by the basal end of the coil of the cochlea. For example, 

 Munk destroyed the basal end of the spiral organ in dogs, oper- 

 ating through the fenestra cochleae (rotunda), and found deaf- 

 ness to high notes to result, and Baginski destroyed the cochlea 

 of one side entirely and then operated to destroy parts of the 

 cochlea of the other side, obtaining results confirming those of 

 Munk. 



The most commonly accepted theories of hearing may be 

 divided into two: that elaborated by Helmholtz, comprising ideas 

 involving phenomena of resonance purely, and the Telephone 

 Theory, comprising ideas involving little or no resonance. 



One of the earliest advanced ideas was that the hairs of the 

 hair cells are themselves agitated selectively, or in resonance, 

 by the different sound vibrations imparted to the cochlea. This 

 was quickly abandoned as untenable on the ground that the hairs 

 are neither suitably constructed, long enough, nor vary sufficiently 

 in length to be effectively acted upon by the vibrations as trans- 

 ferred to the endolymph in the cochlear duct. The Helmholtz 

 theory is a resonance theory wholly and was applied solely to the 

 basilar membrane, that narrow, thinnest span of the membran- 

 ous spiral lamina. Practically all who have tried to apply it 

 to given phenomena have had to modify it. Based upon errone- 

 ous descriptions by others (Nuel, 1872, for example) of the 

 basilar membrane as composed of independent, radially dis- 

 posed fibers and upon the fact that the membrane increases in 

 width (in length of the fibers) in passing from the basal to the 

 apical end of the cochlea, the theory requires the sympathetic 

 or selective vibration of these fibers in resonance with the various 

 vibration frequencies imparted to the endolymph. The hairs 

 of those hair cells resting over fibers of the basilar membrane 

 with a length, or natural vibration frequency, corresponding to 

 the vibration frequency of a given note, were thought to be 

 thrown against the basal surface of the tectorial membrane by 

 the selective vibration of such fibers. Thus the theory assumed 

 that the basilar membrane is composed of fibers of lengths vary- 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 18, NO. 3 



