y68 



THE CEREBRAL CORTEX. 



various parts is located in the motor areas of the Rolandic region, 

 cannot be substantiated. This no doubt lands us in the unsatisfactory 

 position that we are unable certainly to say in what part we are to localise 

 cutaneous sensibility, or even if it is localised at all in the cortex. This 

 difficulty may, however, arise from the great extent of cortex to which 

 the tactile projection fibres are distributed. It is, I think, quite certain 

 that the sensory projection of any part of the general surface of the 

 body is not localised, as Munk teaches and as is believed by many 

 neurologists, to the part of the Eolandic cortex stimulation of which 



produces movements of that part. 

 It is possible, as suggested by 

 Mott, 1 that the sensory fibres 

 branch out to a large area of the 

 cortex, so that only a very ex- 

 tensive lesion will remove all 

 their ramifications; but this is 

 at present purely conjectural. It 

 is also possible that there may 

 not be any intra-areal localisation 

 for cutaneous sensibility, so that, 

 should any portion of the gre} r 

 matter which is concerned with 

 it remain intact, cutaneous sen- 

 sibility is nowhere wholly lost. 



The sensory tracts are ulti- 

 mately traceable to the optic 

 thalamus, which must be regarded 

 as a great sensory centre. But 

 at which Jacksonian level we are 

 to place this centre, is by no 

 means clear. According to v. 

 Monakow 2 and Dejerine, 3 it is 

 connected by fibres of the corona 

 radiata with all regions of the 

 cortex. According to Flechsig, 4 

 the fibres which conduct centri- 

 petal impulses form three systems, 

 which are developed at different 



FIG. 350. Diagram of a frontal section 

 through the brain of a new-born child, to 

 show the course and destination of fibres 

 from the optic thalamus to the cortex. Cc, 

 Corpus callosum ; Gf, gyrus fornicatus ; gh, 

 gyrus hippocampi ; Gsm, gyrus supramar- 

 ginalis ; jR, Rolandic region ; 1,1, fibres 



belonging to the first system ; 2, 2, fibres 

 belonging to the second system ; a, fibres 

 passing to the superior and transverse tem- 

 poral gyri. Flechsig. 



periods. Of these three the first 

 (Fig. 350 1, 1) (which begin to 

 show a myelin sheath at the 

 commencement of the ninth 



month of foetal life) are situated in the part of the internal capsule 

 immediately behind the pyramidal fibres, and pass almost entirely 

 to the two central or Rolandic gyri (but some go to the visual 

 sphere) ; the second (Fig. 350, 2, 2), which appear about a month after 

 the first, go partly to the Rolandic region, partly to the gyrus 

 fornicatus and the cornu ammonis (the latter by way of the cingulum), 



1 Journ. PhysioL, Cambridge and London, 1894, vol. xv. p. 469. 



2 Arch. f. Psychiat., Berlin, Bde. xiv., xvi., xxiii., xxv., xxvii. 



3 Compt. rend. Soc. de biol., Paris, 1897, p. 178. 



4 ' ' Die Localisation der geistigen Vorgange insbesondere der Sinnesempfindungen des 

 Menschen," Leipzig, 1896. 



