xviii Introduction 



way as the nerve cells and fibres do. The second component forms that cortical " terra 

 incognita " which remains over when cells, fibres, and neuroglia, are subtracted, and the 

 evident truth that its bulk must vary in proportion with the representation of the other 

 elements may be significant. 



Hitherto means to localisation restricted entirely to the domain of histology have been 

 spoken of; it is now to be mentioned that facts pertaining to the kindred science, anatomy, 

 and more especially the findings of the comparative anatomist have already assisted us to 

 some extent, and may guide us a great deal further in the final determination of many 

 points bearing on localisation in the human being. Passing through the phylogenic scale 

 from the invertebrata upwards, we have watched with interest the progressive development 

 of the nervous system from a rudimentary chain of ganglia to the highly elaborated and 

 extremely complex human organ ; we have observed that in the lowest mammals the brain 

 is developed only to that degree which will meet and ensure existence, that is to say, it 

 is simply composed of centres for the control of motion and intrinsic physical functions ; 

 we have also been taught that the representation of these essential centres, common to all 

 animals, undergoes changes in accordance with environmental circumstances, that, for instance, 

 the centres for smell, sight, hearing, touch and motion, exhibit developmental variations in 

 relation to the degree in which the animal relies upon any one of these functions for its 

 well-being or self-preservation. Therefore by carefully observing the area supposed to preside 

 over any one of these functions, watching its behaviour in order after order, and eventually 

 making comparisons with the human being, invaluable clues to localisation should be forth- 

 coming. Indeed in this very way, we have already derived the most important and direct 

 information we possess on the localisation of one primary sense, that pertaining to smell, 

 and although homologies in regard to other senses and functions are not yet satisfactorily 

 established, I would point out that this is a branch of study which is as yet in its 

 infancy, and I venture to predict that the examination of a series of animal brains in 

 the comprehensive manner advocated in these pages will serve to settle many points which 

 at the present moment rest on inference and form matter for argument. 



So much for comparative histology. We have next to consider whether any structural 

 features, gross and macroscopic in character, may be taken as finger-posts to the orientation 

 of function. It appears that some can, but at the same time their utility is restricted. 

 The guides alluded to consist of fissures. It will be noticed on consulting the map 

 of localisation submitted herewith that the fields of cortex dominating the primary and 

 essential functions are all deposited in relation to important fissures: thus the visual area 

 is associated in the closest manner possible with the calcarine fissure, the olfactory with 

 the hippocampal, the motor and the common sensory with the Rolandic and the auditory 

 with the Sylvian ; and it may be further observed that all these fissures, with one ex- 

 ception, are admitted, by those who have studied the developing brain, into the category 

 of " primary " fissures ; the exception is the Sylvian fissure, and about this opinions are 

 divided, some including His advocating, and others including Cunningham denying its 

 " primary " character. This seems to be a deliberately planned ontogenetic result more than 

 an accidental occurrence, to those interested in homologies it is a relation worthy of 

 further study, and so also is the subject of the influence of phylogenesis in the production 

 of fissural limits. Save these " primary " fissures there is really no practical naked-eye 

 guide to the localisation of the different areas, for all the " so-called " secondary fissures 

 bear a very inconstant relation to given fields and cannot be utilised as fixed boundary lines. 



