84 University of California Puhlications in Anatomy [Vol. 2 



most dorsal and at the same time the most caudal bundles turn later- 

 ally into the upper lip of the superior temporal convolution which here, 

 in the posterior coruer of the Sylvian fossa, shows an elevation compar- 

 able to the transverse convolution of Ileschl in the human brain {Ttr 

 in figs 30, 50, 51). Farther on orally, the successive ventral bundles, 

 these being at the same time more rostral, turn toward the upper lip 

 of the superior temporal convolution, and toward its successive rostral 

 segments. Accordingly, the ventral bundles of the auditory radiation 

 run for a short stretch in the sagittal direction as the sagittal stratum. 

 The longest sagittal course is taken by the most oral-ventral bundles 

 running to the most oral portions or segments of the auditory projec- 

 tion cortex, and the shortest course by the postero-dorsal bundles 

 destined for the posterior or caudal segments of the auditory projec- 

 tion cortex around the posterior corner of the Sylvian fossa. It is, 

 therefore, easy to understand why the same bundles appear on certain 

 sections as cross-sectioned bundles of the sagittal stratum, while on 

 others they appear as long fibers taking a transverse direction in the 

 white substance of the superior temporal convolution. These trans- 

 versely running fibers were naturally found in greater numbers in 

 sections corresponding with the posterior region of the Sylvian fossa, 

 in small numbers in sections through anterior planes. Fibers which 

 do not reach directly the posterior segment of the auditory projection 

 cortex coating the most posterior portion of the Sylvian fossa, do so 

 gradually as they approach the more orally situated portion of the 

 same cortex. The more anterior sections of the series show a gradual 

 decrease in the number of degenerated auditory fibers until they com- 

 pletely disappear {ar in figs. 26, 27 and 47, 48). 



The regular arrangement and distribution of fibers of the auditory 

 radiation during their course toward the cortex is remarkable, espe- 

 cially in the white substance beneath the Sylvian fossa. Here, as well 

 as in the internal capsule, they almost all lie apparently parallel to one 

 another, excepting such fibers as leave their common fiber layer to 

 enter various segments of the auditory projection cortex. The entire 

 auditory radiation, accordingly, represents a thin, regularly arranged 

 fiber system or lamina whose shape resembles that of an irregular 

 "fan," the radii of which are represented by individual fibers and 

 fiber bundles. These radii or ribs of the fan are, close to their origin 

 within the internal geniculate body, closely assembled into one single 

 bundle ("handle" of the fan) gradually diverging as they approach 

 the cortex. Consequently, the radii or bundles composing the auditory 

 radiation are not mixed one with another in an irregular way. Each 



