190 University of California Publications in Anntomy \yoh.. 2 



radiation. That such an arrang-ement indeed exists is further proved 

 by one's ability to trace separate, individual bundles along their 

 entire course corticalward. (Compare also Putnam.) The course of 

 individual bundles of the radiation is, however, only approximately 

 parallel. In places they diverge somewhat or approach one another 

 since the visual fiber lamina adapts itself to tlie available space inside 

 the hemisphere. Yet, on the whole, that entire lamina is composed 

 of parallel bundles, which only gradually leave it to enter their 

 respective cortical segments. 



In addition to this in Experiment V-c, as also in other similar 

 experiments not further reported here, where small lesions of various 

 sizes and locations were made either in the \asual cortex alone or also 

 in the visual radiation, various parts of the external geniculate body 

 degenerated. The size, location, and shape of the degenerated zones 

 were in a fair proportion and agreement with that of the lesions. 

 This means, of course, a point-to-point projection of the external 

 geniculate body (and hence of the retina) upon the striate area. 



The facts to which the present investigations have led, do not leave 

 room for doubt as to the fundamental principle of the organization of 

 the whole afferent visual system. Certainly no anatomical evidence 

 exists for an "irregular" or a ''diffuse" arrangement of bundles 

 composing the central portion of the visual path. The evidence 

 secured decidedly favors the "principle of localization," that is, of 

 the projection of definite segments of the external geniculate body 

 (and thus of the retinae) upon definite segments of the striate area. 

 This is obser\^ed with all the rigidness of the logic postulated by the 

 exquisite "spatial" function of the visual system and by the laws of 

 physical optics. (Compare Chapter XIX.) Since this principle was 

 found to be valid for the peripheral portion of the visual system, 

 from the retina to the external geniculate body (Ronne, Brouwer- 

 Zeeman, Overbosch), this means that the whole visual system is 

 "spatially" organized. The collected evidence also refutes the suppo- 

 sition of an arrangement differing for the macular and extramacular 

 portions. This also disproves the assertion that no finer, detailed 

 projection of the retina upon the cerebral cortex exists, and that no 

 such detailed projection can be proved. Another question, however, 

 is whether the exactness and sharpness of the projection of the extra- 

 macular retina is the same as that of the macular portion. No doubt, 

 however, can exist as to the actual projection of the extramaeular or 

 "peripheral" portions of the retina. In the macular portion of the 



