ON THE FUNCTIONS OF THE CEREBRUM 301 



exist in the association centres, and that association systems exist 

 in the sensory spheres. 



In the whole cerebrum he described in 1898 no less than forty 

 separate myelogenetic fields which develop at different periods. 

 In 1901 he reduced these to thirty-six, and in 1903 he made no 

 alteration in the number although he stated that later investi- 

 gat'on might eventually cause him to do so. 



Of the sensory spheres he describes four, namely, for (1) bodily 

 sensibility ; (2) visual ; (3) auditory ; and (4) olfactory and gus- 

 tatory sensations. (1) has eight separate myelogenetic fields, and 

 each of the others has three each. 



Of the centres of association he originally described four, namely, 

 the frontal, the parietal, the temporal, and the insular. Later he 

 combined the temporal and parietal centres into one, the great 

 posterior centre of association. In 1900, however, owing to his 

 discovery of a centre of projection in the gyrus subangularis, he 

 again separated these centres. 



In Fig. 2 these sensory spheres and centres of association are 

 indicated. 



In the temporal and parietal centres of association there exist, 

 according to Flechsig, peripheral zones, which develop earlier, and 

 central zones, which develop later ; the former adjoin the sensory 

 centres, and are united to them by numerous arcuate fibres. 



In the frontal centre of association similar zones exist, but 

 their disposition is much more complex. 



The insular centre of association, and also that in the precuneus, 

 consist of peripheral zones only. Flechsig is of opinion that the 

 peripheral zones may be intermediate types between the central 

 territories of association and the sensory projection spheres. 



Hence, of the centres of association, the frontal exhibits the 

 greatest complexity, the temporal and. parietal are intermediate in 

 structure, and the insular and that in the precuneus are the least 

 complex of the types. 



Flechsig's views on the functions of the central territories of the 

 areas of association are as follows : " The central territories of the 

 zones of association (especially the middle of the angular gyrus, the 

 third temporal convolution, and the anterior half of the second frontal 

 convolution) are apparently the nodal points of the long systems of 

 association, whilst the peripheral zones only feebly show these char- 

 acteristics. 



