CEREBRAL LOCALIZATION. 



613 



according to Ferrier, rapidly destroys the excitability of the motor cortical 

 areas. Some of the experiments of Goltz, by which it has been attempted to 

 prove that circumscribed and invariable motor areas do not exist, are an- 

 swered by observations showing descending secondary degenerations following 

 injury of certain parts of the cerebral cortex. The earlier observations on cere- 

 bral localization were made on dogs. Later, experiments have been made 

 on monkeys, and the results of these have been to a certain extent confirmed 

 by pathological observations on the human subject. Beginning with the ob- 

 servations in which descending degenerations have been noted as a consequence 

 of destruction of parts of the cerebral cortex, it may be assumed that a distinct 

 area exists which presides over certain localized muscular movements. 



Motor Cortical Zone. The motor cortical zone is on either side of the 

 fissure of Rolando. It is usually described as including the anterior and pos- 



Fio. 226. Motor cortical zone, on the outer surface of the cerebrum (Exner). 



terior central convolutions (see Fig. 221) and the paracentral lobule (see Fig. 

 222). Faradization of parts in this zone is followed by localized muscular 

 movements. In fact, the motor areas seem to be subject to nearly the 

 same laws, as regards their reactions to Faradic stimulation, as are the 

 motor nerves. Forty Faradic shocks per second produce a corresponding 

 number of single muscular contractions. Forty-six shocks per second pro- 

 duce a tetanic contraction (Franck and Pitres). Destruction of motor areas 

 is followed by partial loss of power in certain sets of muscles, and by descend- 

 ing secondary degeneration of nerve-fibres, extending through the corona 

 radiata, the internal capsule, the crura cerebri, the anterior pyramids of the 

 medulla oblongata and finally the pyramidal tracts of the spinal cord. 



