1932] PoUak: Afferent Fiber Systems, Primate Cerebral Cortex 97 



distinction between two simple stimuli will increase with the interval 

 between two stimulated groups of hair cells. In such a way the dis- 

 crimination, that is, the subjective distinction between two or more 

 simple, elementary acoustic sensations, is achieved. In this respect 

 the outer rows of hair cells together with their correlated groups of 

 orthoneura {A system in our scheme) are comparable to the fovea and 

 macula of the retina and to the macular portion of the visual path, 

 although, because of partial overlapping of teledendra, the discriminat- 

 ing ability appears to be less in the auditory system than in the visual 

 (since there does not exist an overlapping in the fovea centralis, com- 

 pare : Visual System in the present treatise, and Ramon y Cajal, 1909- 

 11, vol. 2, p. 347). This orthoneural apparatus of the inner ear must 

 be looked upon as a highly discriminative acoustic receptor-conductor 

 mechanism composed of a multitude of separate, minute receptor- 

 conductor gTOups (since in each simple excitation only the correspond- 

 ing receptor-conductor group is stimulated). This apparatus is, how- 

 ever, continuous throughout the entire cochlea and is, therefore, 

 adapted for the reception of every primitive, simple acoustic stimulus 

 or any combination of these, so far as these lie in the range of the 

 octaves perceived by the human ear. The distinction and naming of 

 the definite tones is, accordingly, a matter of conventional agreement. 

 For, whatever the pitch of the initial or basic tone to which other 

 subsequent tones in a series are referred, there always will be the same 

 relation between the primary and secondary tones in a given formula. 



So far as the perception and discrimination of simple tones and 

 some of the more complex acoustic phenomena and so far as influence 

 on pitch by intensity of stimulus is concerned, we have a rela- 

 tively simple morphological explanation in the continuous and yet 

 "spatially" organized orthoneural receptor and conductor system of 

 the cochlea. More difficult to explain morphologically are the mutual 

 relationships of several simple tones simultaneously perceived. These 

 phenomena appear at present as conditioned by an unknown central, 

 associative, or integrative cortical process. Can it be that certain inter- 

 relationships of several simple acoustic sensations called consonance, 

 similarity of octaves, and so forth, can perhaps be brought into connec- 

 tion with certain morphological features of the nervous apparatus of 

 the inner ear and be thus dispossessed of their mystical tinge ? 



It seems as if the external "spiral" fibers or spironeura, these also 

 being "individual" neurons, with their regular arrangement and 

 parallel turning in one direction, might help to explain the above phe- 



