6 IRVING HARDESTY 



organ. Observations of others were cited both as agreeing and dis- 

 puting that this outer part of the membrane is free, and it was ad- 

 vanced that all the disputing claims are Imsed either upon studies of 

 mammalian cochleae in stages of development before the production 

 of the membrane is completed or upon studies of sections of dehydrated 

 and embedded cochleae in which, due to shrinkage and distortion pro- 

 duced by the treatment, the membrane was shrunken and pressed upon 

 and thus apparently attached upon the surface of the spiral organ. 



It was finally urged in the paper that the tectorial membrane and not 

 the basilar membrane (membranous part of the spiral lamina) is the 

 chief vibratory structure in the mechanics of hearing. The principal 

 of the considerations upon which this suggestion was based are the fol- 

 lowing: (1) The general acceptation that the cochlea is the peripheral 

 organ of the auditory apparatus, that auditory impulses are aroused 

 in the hair cells of the spiral organ, about which cells the telodendria 

 of the auditory (cochlear) nerve fibers terminate, and that these im- 

 pulses are initiated by the impingement of the hairs of the hair cells 

 against the basal surface of the tectorial membrane. (2) That the 

 tectorial membrane is far more flexible and by structure far more ca- 

 pable and quahfied to serve as a vibratory mechanism than is the 

 basilar membrane. (3) That the tectorial membrane varies in its 

 proportions considerably more than the basilar, its thick and broad 

 apical end gradually tapering to its narrow basal end, thus allowing 

 greater possibilities of resonant activities and in wider range. (4) 

 That in development and structure, the basilar membrane is not com- 

 posed of individual nor independent fibers but is nothing more than a 

 flat tendon whose component fasciculi are intimately connected with 

 each other; and further that even if it were composed of independent 

 fibers, being blanketed on its either side by continuous layers of tissue 

 far thicker than itself, one of which layers is a syncytium, its fibers 

 could not be thrown into vibration either individually or in groups. 

 (5) That the tectoral membrane is always entirely coextensive with 

 the spiral organ while the basilar membrane is not always so. (6) 

 That the position of the tectorial membrane in the cochlea is more 

 logical for the function than is that of the basilar membrane. The 

 tectorial membrane may impart stimuli to the peripheral ends of the 

 auditory cells and it also lies nearest the scala vestibuli, that is, to the 

 fluid to which the foot of the stapes transfers directly the energy im- 

 parted by sound waves. 



The theories in which the basilar membrane is considered the vibrat- 

 ing mechanism of the cochlea were, therefore, deemed untenable and 

 an application of the 'telephone theory' to the tectorial membrane 

 was suggested. 



Since the publication of the above paper by the writer, three other 

 papers dealing chiefly with the tectorial membrane have appeared. 



The very instructive paper by Held ('09) deals with the develop- 

 ment in the cochleae of the rabbit, chick and pigeon. He used embryos 

 and various fetal stages of the rabbit before and after birth and used 



