104 University of California Publications in Anatomy [^ol. 2 



impulses must be settled by further investig^ations. At any rate, the 

 assumption that a large portion of the temporal lobe, or perhaps that 

 entire lobe, receives direct auditory impulses from the subcortical 

 regions has little anatomical evidence to support it. (In the present 

 studies the hippocampal and cingnlar convolutions and their possible 

 afferent paths were not considered.) 



To the question of the internal organization of the auditory radia- 

 tion these studies can give only a general answer. However, the 

 present observation that the internal geniculo-cortical radiation forms 

 a thin fiber sheet or lamina composed of regularly or "spatially" 

 arranged, parallel fibers and fiber bundles, each terminating in a 

 different segment of the auditory projection cortex, together with 

 other evidence collected previously (see my papers, 1925, 1926, 1927), 

 corroborates the view of a fixed or stable projection of the auditory 

 peripheral receptive surface (papilla basilaris of the cochlea) upon 

 the cerebral cortex. 



Since the uppermost link of the central auditory path is a definite 

 anatomical and functional entity confined to a comparatively narrow 

 space in the hemisphere and since it terminates in a definite circum- 

 scribed area of the temporal cortex, we are permitted to conclude that 

 the entire auditory radiation can easily be interrupted by a single sub- 

 cortical lesion. This will more readily occur when the seat of the 

 lesion is close to the origin of the auditory radiation where all its 

 fibers are assembled into one bundle ("handle" of the fiber "fan" 

 of the radiation), while nearer the cortex small lesions will be likely 

 to interrupt only a portion or portions of the radiation and thus pro- 

 duce one or several gaps in tone perception comparable to scotomata 

 of the visual fields. A similar partial loss of the auditory function 

 can be expected from small injuries to the auditory projection cortex 

 because of the unequal functional significance of different segments 

 of that area. 



