INTRODUCTION TO SOCIOLOGY 801
membrane, which shows a considerably different development in man, where the zones of association are the centers of intellectual functions.
The essential point of the tneory of Flechsig is that, contrary to what was accepted, all the zones of the cerebral cortex are not connected by bundles of fibers to the lower part of the gray mat- ter. The cerebral cortex is divided into (a) zones or centers of projection, or sensorial spheres, and (b) zones of the mem- brane, comprising all the parts of the latter with exception of those connected with the fibers of projection, but connected by numerous fibers of association to the sensorial spheres and to one another. The centers of projection are both sensitive and motor. Their extent or limits are determined by the number of fibers they receive and send out in proportion to their surface. There are three zones of association: (i) the large posterior center of association, comprising a part of the lingual convolution, the fusi- form convolution, the two parietal convolutions, the lower tem- poral and anterior part of the occipital lobe ; (2)' the middle center of association, comprising the insula de Reil; (3) the anterior center of association, formed by the anterior part of all the frontal convolutions and then by the convolutions on the orbital surface.
In comparing the results of the researches of Flechsig, it is shown that the zones of association in man correspond to two- thirds of the cortical surface, and the zones of projection to only one-third. As one descends the animal scale, one sees that in the monkey the proportion is the same for each of the parts ; then in the mammalia the zones of association diminish more and more until the zones of projection exist almost alone.
The essential character of the zones of association is in not having a direct connection with the lower gray masses that is, in being independent. No impression from the periphery reaches them without the mediation of the centers of projection, and no imitation can emanate from the zones of association without passing by those of projection.
The centers of association receive impressions by the sen- sorial spheres, focus and compare them, and form the substratum
