THE CEREBRUM. 



5*3 



regions to which it has not been possible to assign specific functions 

 based on physiologic experiments. Three or four such regions 

 separated by the sensor and motor centers are to be recognized on 

 the lateral and mesial aspects of the hemisphere. In Fig. 229 

 the location, extent, and names of these regions are represented. 

 The fibers which are found in these regions belong almost exclusively 

 to the association system, and become medullated at a later period 

 than do the fibers of the projection system; moreover, from the method 

 of their medullization it would appear that many of these fibers grow 

 out directly from the sensor centers into these regions and become 

 related to the nerve-cells of their convolutions, while others grow 

 out from adjacent as well as distant convolutions. From histologic 

 and pathologic evidence these regions were termed by Flechsig 

 association centers or areas, implying the idea that through the in- 

 tervention of their cell mechanisms the sense areas are indirectly 

 associated anatomically and physiologically, and together constitute 

 a mechanism by which sensations are associated and elaborated into 

 concrete forms of knowledge or related to definite forms of move- 

 ment. 



It has been assumed by Flechsig that the frontal association center, 

 from its connections with the sensor and motor areas of the Rolandic 

 region, the olfactory, and perhaps other regions, is engaged in as- 

 sociating and registering body sensations and volitional acts, and 

 that the knowledge thus gained has reference largely to the personal- 

 ity of the individual; that the parieto-occipital association area, from 

 its relation to the visual, auditory, and tactile sense areas, is engaged 

 in associating and registering visual, auditory, and tactile sensations, 

 and that the knowledge thus gained has reference mainly to the 

 external world. These assumptions in a general way are supported 

 by the phenomena of disease. In certain lesions of the frontal lobe 

 the symptoms indicate a loss or change of ideas regarding personality 

 rather than of the objective world, while the reverse is true in disease 

 of the parieto-occipital lobe. 



33 



