INTRODUCTION. 



THE process leading to the accomplishment of functional localisation in the cerebral 

 cortex is such a complicated one, and involves so many side issues, that perfection cannot 

 be attained or even hoped for until the fruits of investigation in a number of departments 

 are thoroughly weighed, sifted and assorted. It is anticipated that the observations set 

 forth in this research will help to establish the value of histological work as an auxiliary 

 force in the final settlement of that functional subdivision of the cerebral cortex at which 



we aim. 



Methods of Histological Research. 



There are many directions in which the talents of the histologist may be exercised, 

 and these can be arranged in a triad constituted as follows, the study of the brain (1) during 

 development, (2) in conditions of disease, and (3) in the normal state. 



1. The Study of the Brain in Phases of Development. 



The value of embryological researches has already been proved, at any rate in one 

 direction, by taking advantage of the natural law that the maturation or myelinisation of 

 the various tracts of fibres standing in relation with various functions does not occur 

 coincidentally but follows a set sequence. Observing the tenets of this law the surface of 

 the brain can be subdivided in accordance with the different times at which the medullated 

 constituents become apparent. In addition, the embryologist is in the happy position of 

 being able to amplify and confirm assumptions concerning surface realms so demarcated, by 

 his ability to trace the subcortical paths followed by the related axones. To exemplify my 

 meaning I have merely to point to the visuo-sensory area; the calcarine cortex, in which 

 the seeing function concentrates itself, is found to contain myelinised fibres at a relatively 

 early date, certainly at a time when such fibres are absent from the surrounding field, 

 hence its surface distribution is readily determined ; and as the band of fibres bringing 

 this area into association with intermediate visual stations in the thalamic region matures at 

 a corresponding time, its course can be followed with equal facility. In this manner an 

 irrefragable chain of evidence can be welded. 



But unfortunately all tracts and all centres are not so readily determined by developmental 

 methods, also conclusions must be drawn with caution ; indeed, judging from the storm of 

 criticism deluged on the writings of the foremost worker in this province (Flechsig), it seems 

 that the embryologist, almost more than anyone else, must pay the fullest possible regard to 

 the findings of those who have investigated localisation on other lines. 



c2 



