592 SCIENCE PROGRESS 



more and more into the general body of the scala tympani, till 

 at last the connexions with the brain cavity (canalis perilymph- 

 aticus) and the exterior (foramen rotundum) become sessile upon 

 the wall of the scala tympani itself. 1 



So from the very simplest beginnings, by gradual elabora- 

 tion of the sense organ and simplification of the path by which 

 vibrations may reach it, our ear has reached its present form. 

 It is, however, one thing to pick a complex piece of mechanism 

 to pieces, quite another to explain its working. And that is 

 just the present position. The structure of the ear is fairly 

 well known, its action is still very obscure. At present there 

 are two classes of theory by which it is sought to explain the 

 mechanism of hearing : by one (the telephone theory) the 

 vibrations transmitted to the cochlea are supposed to act upon 

 the sense organ as a whole and the resolution of complex sound 

 is referred to the brain, by the other (the resonance theory) 

 the preliminary sorting is done by the ear. By the various 

 resonance theories, amongst which that of Helmholtz still holds 

 the field, the analysis of complex sounds is supposed to depend 

 on the sympathetic vibration of some part of the cochlea to each 

 particular note and the selective stimulation of corresponding 

 sensory cells of the organ of Corti. 



Such theories rest upon the ordered distribution and 

 regular increase in length, size and number of the various 

 elements of the cochlea to which reference was recently made, 

 which is such a striking and remarkable feature in the anatomy 

 of this organ. 



The parts most frequently regarded as the resonators are 

 the parallel cords lying in the basilar membrane upon which 

 the sense organ (the organ of Corti) rests, like piano-wires 

 stretched between the lamina spiralis and ligamentum spirale 

 (fig. i, Membr. bas.). Those cords that by their length and 

 degree of tension are in tune with any particular note vibrate in 

 unison with that note and tap the sensory hairs of the sense 

 cells resting upon them against the lower surface of the tectorial 

 membrane that floats like a hood above them. 



This is the theory. 



Recently it has been questioned seriously whether the 

 basilar membrane and organ of Corti are by their structure 

 capable of acting as they should do upon this theory and 



1 Gray, Proc. R. Soc. 1908, p. 521. 



