v] Anatomical Evidence rcfjardin;/ Function 141 



openly dotted field being not unlike inv visuo-psychic area. Arid apart from the value of 

 developmental methods in determining surface areas, a glance at Flechsig's illustrations, and 

 at the beautiful reproductions in Vogt's recently published woik, suffices to show that this 

 method has no equal in giving a demonstration of the subcortical bands of fibres running 

 in connection with the surface field. As a guide to cortical localisation a clear display of 

 these subcortical bands is of extreme value, and of the highest importance is the fact that 

 developmental studies have supplied one of the strongest links in the chain of evidence which 

 we can now adduce in support of the limited sensory localisation in the calcarine region. 

 I refer to the appearances presented by the radiations of Gratiolet. Preparations of the 

 t'oi'tal brain stained for medullated nerve fibres conclusively prove that, at birth, only a 

 poll ion of these radiating fibres have acquired their myelinic investment, namely, those 

 related to the lateral geniculate bodies ; all the other fibres of Gratiolet's radiation remain 

 unmedullated, and this early-medullated band of fibres can be distinctly followed to that 

 part of the occipital cortex which coats the calcarine fissure. Flechsig, who was the first to 

 describe this band, speaks of it as " the optic radiation in the narrow sense," in contra- 

 distinction to the remaining fibres of Gratiolet which he calls " the optic radiation in the 

 wiiler sense," and which he regards as corticifugal instead of corticipetal in direction. It 

 seems that this band of fibres (the optic radiation in the narrow sense) was that along 

 which von Monakow traced acute degeneration after lesions in the occipital cortex in man, 

 and it is evidently of important functional significance, since it constitutes a direct line of 

 communication between the calcarine cortex and the lateral geniculate bodies. 



Of the remaining fibres of the radiation of Gratiolet (Flechsig's radiations in the wider 

 sense) we do not possess such definite information, but apparently the majority originate 

 in the pulvinar, and at first occupying a position dorsal to those derived from the lateral 

 geniculate bodies, are distributed ultimately to the occipital cortex outside the calcarine 

 region. 



Of the function of other bands of nerve fibres discoverable in the white substance of 

 this region, some of which are autochthonous and may serve to bring different gyri of 

 the occipital lobe into association with one another, while others seem to connect the oc- 

 cipital gyri with parts of the brain lying further afield, our knowledge is still less certain. 

 But as their anatomical position is more or less definite, a short description of them will 

 be necessary to complete this section. 



Taking first the autochthonous bands, or as Barker calls them, the short association 

 neurones. These bands correspond with the fibrae arcuatae of Arnold and the U-shaped 

 fibres of Meynert, and the following systems have been identified in the occipital lobe. 



( 1 ) The stratum calcarinum is figured and described by Dejerine and Sachs as curving 

 round the floor of the calcarine fissure, for the purpose of uniting the cortex of the convo- 

 lutions lying immediately above and below that fissure. But while the appearance of a band 

 in this situation is undeniable, and while some of the fibres are undoubtedly of associative 

 nature, I cannot help thinking that the appearance is due mainly to the presence of the 

 terminal portions of the calcarine division of the optic radiations arching up to the cortex. 



(2) The stratum proprium cunei is a bundle recognised by Sachs as consisting of 

 vertical fibres issuing from the upper wall of the calcarine fissure and spreading up in 

 the cuneus in radiate fashion to terminate along the margin of the hemisphere, and viewed 



