140 Visuo-Seitsory and Visuo- Psychic Areas [CHAP. 



arrive at the precise localisation of the visual centre, of course provided that full and due 

 regard be paid to the rough guides afforded by the previous findings of the physiologist 

 and the clinician. 



The anatomical researches which have been undertaken with the view of determining 

 the position of the visual area may be divided into three categories ; first, those dealing 

 with the degenerative changes which result from experimental interference with the visual 

 apparatus ; secondly, those in which the course of the various tracts of fibres bearing visual 

 impulses have been studied by the developmental method ; and, lastly, those in which the 

 human brain has been examined, to display degenerative changes in cases of old-standing 

 blindness, to determine the normal histological appearances of the area believed to be concerned 

 with sight, or to fix the course and distribution of bands of visual neurones. 



It cannot be said that the anatomical observations recorded some years ago by von 

 Monakow have assisted in lending preciseness to the definition of the visual area, but at 

 the same time they have no mean value, because they clinched the accuracy of Munk's 

 statement that the visual sense was centred in the occipital lobe, and they gave us much 

 information concerning the path followed by visual impulses in their course from retina 

 to cortex. Thus his enucleations of the eyes of new-born puppies with the subsequent 

 discovery of degenerative alterations in the corpora geniculata externa, the pulvinaria, and 

 the anterior corpora quadrigemina were valuable in proving that the cells in these nuclei 

 formed units of an intermediate station in the visual pathway ; the evidence which he 

 produced to the effect that the same nuclei underwent secondary degeneration in consequence 

 of ablation of the cortical visual area was of importance, inasmuch as it definitely settled 

 the point that the occipital cortex presided over vision ; and it is of even greater interest 

 that von Monakow was able to prove that the human brain resembled that of the lower 

 animal, inasmuch as lesions of the occipital cortex in the calcarine region produced a 

 similar degeneration of the cells of the lateral geniculate body. Further, from von Mona- 

 kow's studies it would appear that the cells of the lateral geniculate bodies serve different 

 functions and therefore are divisible into two categories ; for he has proved clearly that the 

 changes which occur in those bodies after a cortical lesion affect different parts from those 

 involved in disease of or injury to the optic nerve. In the former case, it is the ganglion 

 cells of the lateral geniculate body and the white matter of Wernicke which suffer, while 

 in the latter, it is the fibres of the optic tract and their terminals in the substantia gelatinosa 

 which disappear. 



Other experimental researches having a similar bearing, and also some purely histological 

 observations on the lower animals have been put on record, but I think it unnecessary to 

 discuss them here, because the morphological differences between the brain of any lower animal 

 and that of man in large measure nullify their value as guides to cortical localisation in the 

 human subject. 



We have next to indicate the extent to which developmental researches have added 

 to our knowledge of visual localisation, and I would state at once that although I have 

 little personal experience of this method, yet, when the area to be mapped out contains 

 medullated fibres of large calibre, as does the visual field, it appears to be well-suited for 

 purposes of surface delimitation. For example, if figures 7 and 8, plate IV, in Flechsig's 

 Gehirn und Seele be compared with my figures, a remarkable correspondence will be seen ; 

 his closely-dotted calcarine area agreeing well with my visuo-sensory area, and his more 



