CEREBRAL LOCALIZATION 681 



ciated with contractures of the paralyzed muscles, while paraplegia 

 resulting in consequence of the division of the spinal cord or higher 

 conducting paths, is not. This hypertonic setting of the muscles 

 may be explained by the assumption that the injury to the cerebrum 

 has removed those inhibitory impulses which ordinarily tend to hold 

 the tonic discharges of the ganglion cells in check. In consequence of 

 this removal of cerebral inhibition the lower reflexes have full sway 

 and are enabled to play upon these muscles repeatedly until they 

 are thrown into a state of spastic rigidity or contracture. "High" 

 lesions, therefore, increase the spinal reflexes, while "low" lesions tend 

 to diminish them, thereby allowing the muscles to remain continuously 

 in a flaccid condition. 



The foregoing discussion should also have made it clear that the 

 motor area constitutes a center for voluntary movements. This 

 statement, however, does not imply that this area, in conjunction with 

 the faculty of volition, is the primary exciting agent of all muscular 

 movements. A conclusion of this kind cannot be correct for the reason 

 that all our actions result in consequence of sensory impressions, and 

 are, therefore, not spontaneous. As the motor area, together with the 

 pyramidal system, forms merely the efferent arc of the association or 

 reaction circuit necessary for motion, it cannot be regarded as a thor- 

 oughly independent unit capable of generating centrifugal impulses 

 unaided. The afferent impulses and subsequent sensory impressions 

 ordinarily responsible for the activation of this motor system, are 

 derived from the different association centers of the cerebrum with 

 which we will become acquainted in the chapter now following. 



CHAPTER LVI 



CEREBRAL LOCALIZATION (CONTINUED) 

 THE BODY -SENSE AREA 



The Location of the Body-sense Area. While it is undoubtedly 

 true that, in the lower animals, the sensory and motor areas overlap 

 to such an extent that it has been suggested by Bastian to apply 

 to them the more general term of kinesthetic area, 1 the more recent 

 experimental work has shown that, in the apes and man, these fields 

 find a natural boundary in the fissure of Rolando. 2 Thus, it is now 

 commonly accepted that the motor area lies in front of this sulcus and 

 the sensory area posterior to it. It must be evident, therefore, 

 that a hemiplegia need not be associated with a hemianesthesia, unless 



1 Luciani and Seppilli, Le Localsizzazioni funz. del cervello, Napoli, 1885. 



2 Von Monakow, Ergebn. der. Physiol., 1902. 



