1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 95 



induced me to search for a more detailed explanation of the func- 

 tion of the striictures of the entire auditory system, an explanation 

 which might serve at least as a working hypothesis for future investi- 

 gations. (It is not my intention to enter here into the discussion of the 

 purely psycho-physiological aspect of audition in so far as this cannot 

 be brought into direct connection with the anatomical structures.) 



The sensory cells of the mammalian cochlea, the so-called hair cells 

 of the papilla basilaris, are arranged in several outer rows of some- 

 what smaller, and one single inner row of somewhat larger elements 

 (see Kolmer, 1924, 1927; Held, 1926). In the present consideration, 

 unfortunately, these latter must be omitted since their innervation is 

 insufficiently known. The outer rows of the hair cells representing 

 the majority of the sensory acoustic elements form, in reality, a con- 

 tinuous receptor organ which is nothing else than a flat narrow spiral 

 receptor surface stretching along the entire cochlea. This receptor 

 organ, although it appears continuous, is not "diffusely" innervated. 

 The nerve fibers which ramify with their teledendra around the outer 

 hair cells, are of two kinds: "direct fibers" (orthoneura) and "spiral 

 fibers" (spironeura) of Ebner. Both kinds of fibers unmistakably 

 bear the character of ' * individual ' ' neurons. That is, each single fiber 

 ramifies around a limited number of sensory hair cells which form a 

 well defined, close cell group, and does not come into contact with two 

 or more such cell groups. Thus, each of either the "direct" or the 

 "spiral fibers" receives impulses from a small number of closely 

 neighboring hair cells and only from them. Some nerve fibers, how- 

 ever, touch one single hair cell only. But it can be assumed that the 

 majority of cochlear nerve fibers actually terminate by small teledendra 

 around a group of hair cells. Since in every simple, elementary audi- 

 tory process (simple tone) not a single string or chord but several 

 of these constituting the basilar membrane and forming a close iso- 

 dynamic group of chords are put into vibration, not a single hair cell 

 but a group of these mounted upon the vibrating group of basilar 

 chords will be stimulated. It is, therefore, self-evident that not a 

 single fiber but a group of closely neighboring cochlear nerve fibers 

 will be used for the transmission centralward of impulses caused by 

 every simple or elementary acoustic stimulus. Just as in the somato- 

 sensory and in the visual systems, so also in the acoustic system, 

 local sig-ns or signatures are created since each hair-cell-orthoneural 

 group is always stimulated by the same stimulus. Because the 

 majority of fibers ramifying around the outer hair cells are "direct" 



