44 University of Calif ornia PuUications in Anatomy i^^^^- 2 



radiation as demonstrated here forms a well defined fiber system: a 

 fiber lamina slightly t^^^sted as it passes through the white substance 

 of the hemisphere, with its fibers close to the internal capsule forming 

 a compact "handle" of the "fan," and with its cortical end spread- 

 ing into an elongated ' ' umbrella, ' ' that envelops the sulcus centralis 

 on both its sides. 



The cortical region receiving the degenerated afferent fibers in the 

 present experiment is, first, the cortex lining the floor and both the 

 lips of the central sulcus (C) along its entire dorso-ventral length, 

 which corresponds well with field 3 and probably also field 1 of 

 Brodmann (fig. 4, compare wdth fig. 7). In front of the sulcus cen- 

 tralis a more extensive zone receives afferent fibers corresponding 

 well in shape and position with the agranular, giganto-pjTamidal or 

 the so-called "motor" area, field 4 of Brodmann. Further, the 

 receptive region of the cerebral cortex in this case spreads ventrally 

 over a part of the operculum almost to the Sylvian fissure (FS) ; over 

 the interhemispheric cortex it just reaches the cingular sulcus {Sc). 

 Altogether, the somato-sensory region as delimited in the present 

 experiment corresponds to the combined areas 1, 3, 4, and 43 of 

 Brodmann. 



As to the meaning of the result of the present experiment — it is 

 significant that a single bundle or fan, the intermediate one, of the 

 thalamo-cortical radiation, interrupted within the internal capsule, 

 terminates in a cortical zone which according to its position along the 

 central sulcus, according to its extent in front and behind that sulcus 

 and on the inner face of the hemisphere, and according to its wedge- 

 like shape, corresponds almost exactly with the combined cyto- 

 architeetural areas 1, 3, 4, and probably 43 of Brodmann. Especially 

 remarkable appeal- the sharp boundaries of the delimited zone with 

 the sudden cessation of the degenerated afferent fibers streaming into 

 the cortex, which recalls the abrupt cessation of the afferent visual 

 fibers at the point of disappearance of the stria Gennari-Vicq d 'Azyr. 

 All this means, in connection with Experiment I, II, and III, that in 

 the present experiment one single segment or "fan" of the thalamo- 

 cortical radiation, the intermediate one, was interrupted accidentally, 

 and further that this fan corresponds with a few adjoining cy to- 

 architectural areas of the central region. It does not appear to be an 

 unreasonable conclusion that the entire thalamo-cortical radiation is 

 organized on a functional basis: to each cyto-architeetural area or 

 field corresponds a sheet, or lamina of fibers, wdth its plane approxi- 



