582 NERVOUS SYSTEM 



Hitzig (1870), Ferrier, Munk, Horsley and many others, that the ques- 

 tion of the existence of motor and sensory centres especially motor 

 centres hardly admits of discussion. The negative results obtained 

 by Flourens were probably due to severe hemorrhage, which, according 

 to Ferrier, rapidly destroys the excitability of the motor cortical areas. 

 Some of the experiments of Goltz, by which it was attempted to prove 

 that circumscribed and invariable motor areas do not exist, are answered 

 by observations showing descending secondary degenerations following 

 injury of certain parts of the cerebral cortex. The earlier observations 

 on cerebral 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 observations in which descending degenerations 

 have been noted as a consequence of destruction of parts of the cerebral 

 cortex, it may be assumed that distinct areas exist which preside over 

 certain localized muscular movements. 



Motor Cortical Zone {Rolandic Area). The motor cortical zone is on 

 either side of the fissure of Rolando. It usually is described as including 

 the ascending frontal and ascending parietal convolutions (see Fig. 139), 

 and the paracentral lobule (see Fig. 140). Faradization of parts in and 

 adjacent to 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 produce a 

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

 followed by partial loss of power in certain sets of muscles and by 

 secondary descending degeneration of nerve-fibres extending through 

 the corona radiata, the internal capsule, the crura cerebri, the anterior 

 pyramids of the bulb and finally the pyramidal tracts of the spinal 

 cord. 



While it can not be doubted that the Rolandic area is made up of a 

 number of motor centres, it is now thought by many physiologists that 

 it receives sensory fibres from the skin and the muscular system ; and 

 therefore it is sometimes called the sensori-motor area. The physio- 

 logical basis of this view is the close association of sensations and 

 voluntary movements ; and it has been proved that extirpation of the 

 Rolandic area in monkeys is followed by impaired sensibility. Recent 

 anatomical researches, made by means of the staining methods of Golgi 

 and Ramon y Cajal, seem to favor this idea, although the tracing of the 

 fibres presents difficulties which render the results somewhat unsatis- 

 factory. 



