300 RESEARCHES ON CORTICAL LOCALISATION AND 



rise in the scale of primates this associational zone increases with 

 the more perfect specialisation of the fore-limbs for manipulation 

 and the erect posture, and this we may correlate with the increase 

 in area of the associational or visuo-psychic zone, the increasing 

 development of the parietal lobe, and the pushing back and infolding 

 of the striate visuo-sensory cortex, so that in the highest types of 

 man it conies to occupy the infolded calcarine region of the mesial 

 surface, although some lower types still preserve the anthropoidal 

 character. It is probable that the same causes give rise to the shifting 

 forward of the anterior motor eye centres." 



In this connection reference may be made to a paper by Wilfred 

 Harris. This writer discusses the question of binocular and stereo- 

 scopic vision in man and other vertebrates, with regard to the de- 

 cussation of the optic nerves, ocular movements, and the pupil light 

 reflex. 



CORTICAL LOCALISATION BY MEANS OF THE HISTOLOGICAL 



METHOD 



The researches of Flechsig on the development of the human 

 brain by a study of the process of myelination are so well known 

 to neurologists that any description of them may seem superfluous. 



The conclusions at which he arrived are, however, of funda- 

 mental importance, and form the origin, if not entirely the basis, 

 of our present knowledge of cortical localisation by histological 

 methods. Again, his generalisations in the gross have success- 

 fully passed through a storm of discussion and dissent which is 

 almost unsurpassed in the history of research. Lastly, even at 

 the present time, except by neurologists, the researches of Flechsig 

 are by no means as generally understood and appreciated as they 

 merit. A short description of the main features of the investiga- 

 tions of this writer is therefore perhaps not entirely out of place 

 as an introduction to the subject under consideration. 



By studying the exact period of myelination of different parts 

 of the cerebrum in the human foetus and infant, Flechsig was 

 enabled to divide the cortex cerebri into the two great classes 

 of " sensory centres " and " centres of association." The former 

 myelinate earlier than the latter, and possess a well-marked system 

 of fibres of projection. The latter myelinate later and are rich in 

 long systems of fibres of association. The difference is really one 

 of degree only, as Flechsig does not deny that fibres of projection 



