THE CORTEX OF THE FORE-BRAIN, ETC. 69 



separated. They connect whole lobes with one another. Appar- 

 ently these "association-fibres " are developed when two different 

 regions of the cortex are associated in a common action, or they 



O *- 



arc developed into medullary fibres from among the surrounding 

 mass of indifferent bundles when they are brought into more 

 continuous use than the latter. The association-fibres lie, in 

 great part, close under the cortex; some of them also lie partly 

 in the white substance of the hemispheres. This system of fibres 

 is, as you see, especially adapted to bring all parts of the brain 

 into communication with each other. The manifold processes 

 of association which are indispensable to thought, motion, and 

 sensation possibly have their anatomical substratum in these 

 elements of the brain. It is not 

 improbable that these fibres play 

 an important part in generalizing 

 the movements of epileptic seizures. 

 It is possible, in animals, to 

 produce contractions of the asso- 

 ciated muscles by irritating certain 

 regions of the cortex, and, by in- 

 creasing the irritation, to produce FIG. 39. 



Diagram of tlie fibi^propriae of the 



convulsions of the whole affected cortex. 



side. The order of these convulsions corresponds to the ar- 

 rangement of the affected centres in the cortex. As this irri- 

 tation extends it never skips a neighboring motor centre. 

 The convulsions, when they have affected one-half of the body, 

 pass over to the other half (under certain conditions, intensity 

 of the irritation, disposition of the animal experimented on, 

 etc.). Removal of single motor centres from the cortex causes 

 the muscles directly controlled by them to be omitted from the 

 general convulsive seizure. It is not necessary that the point 

 of cortex so irritated should belong to the motor region. The 

 convulsions thus brought about show the greatest analogy to 

 a partial or general epileptic attack in human beings. Since 

 the writings of Hughlings-Jackson, we are acquainted with forms 



