1932] Poliak: Afferent Fiber Systems, Primate Cerelral Cortex 157 



Chapter XVI 

 VISUAL SYSTEM (DISCUSSION) 



After the preceding^ detailed description of the conditions of the 

 visual system in the present experiments I would give here firstly, a 

 brief summary of the results deduced therefrom, secondly, a discus- 

 sion of the arguments in support of my statements, thirdly, a con- 

 sideration of a few outstanding physiological and pathological prob- 

 lems of vision, and finally, a formulation of further problems relating 

 to this system, as they appear in the light of the present results. 



The present experiments show that : 



(1) The external geniculate body of the between-brain must be 

 recognized at present as the only and the exclusive origin of the visual 

 radiation in primates. 



(2) There exists only one single direct afferent visual path from 

 the subcortical region to the cerebral cortex. (Nothing positive is 

 known of indirect visual paths.) It is the fiber system originating 

 from the external geniculate body. That external geniculo-cortical 

 radiation forms a strong fiber lamina or layer identical with the 

 "primare Sehstrahlung " of Flechsig, with the stratum sagittale 

 laterale of H. Sachs, a portion of which was called by Burdach, 

 Wernicke, and Monakow "fasciculus longitudinalis inferior" of the 

 parieto-occipital and temporal lobes. However, other fibers : efferent, 

 callosal, and associational, mix with the afferent visual fibers. Stratum 

 sagittale internum, "sekundare Sehstrahlung" of Flechsig, is an 

 efferent fiber system. The tapetum is composed exclusively of 

 callosal fibers. 



(3) The cortical region where the visual path terminates is a 

 single, definite, and sharply delimited area which is identical with the 

 area striata of G. E. Smith, field 17 of Brodmann, or area OC of 

 Economo-Koskinas distinguished by the strong intraeortical fiber 

 layer, the stripe of Gennari or Vicq d'Azyr (fig. 21). No other areas 

 of the cerebral cortex receive afferent visual fibers. 



(4) The central visual path above the external geniculate body is 

 strictly unilateral. No evidence exists of a partial decussation of its 

 fibers through the corpus callosum ("fascicidus corporsi callosi cru- 

 ciatus"). The only spot, therefore, where the visual path undergoes a 

 partial decussation is below the between-brain in the optic chiasm. 



