268 THE NERVOUS SYSTEM 



missural fibers there are those of the anterior and posterior 

 white commissures. Fibers in the anterior connect the tem- 

 poro-sphenoidal lobes and probably the corpora striata with 

 each other ; fibers in the posterior connect the temporo-sphe- 

 noidal lobes with the optic thalami of the opposite side. 



(d) The arcuate fibers connect different convolutions of 

 the same lobe and the convolutions of different lobes with 

 each other. Some of these are the jornix, in the corpus 

 callosum } and in the other parts, as well as running along 

 the concave surface of the cortex. 



Cerebral Localization. There are certain cortical areas 

 which have certain fixed functions. There are certainly such 

 areas for motion and for the reception of impressions con- 

 veyed by the nerves of special sense; areas for the reception 

 of impressions conveyed by the nerves of general sensation 

 have not been definitely determined. 



Motor Centers. Electrical stimulation of the convex sur- 

 face of the cerebrum shows that the anterior part is motor 

 and the posterior part non-motor; that stimulation of the 

 motor portion produces muscular contractions on the oppo- 

 site side of the body, that stimulation in the same spot is al- 

 ways followed by the same contractions; and that when the 

 current is quite weak the contractions are limited to distinct 

 muscles or sets of muscles. It may be further said that while 

 the experiments establishing these facts have been largely 

 limited to inferior animals, the deductions have been made 

 applicable to man by pathological observations and by the 

 fact that in different animals stimulation of anatomically 

 corresponding parts is followed by corresponding results. 

 Destruction of motor areas is followed by descending sec- 

 ondary degeneration of fibers through the corona radiata, 

 internal capsule, crura cerebri (crusta), anterior pyramids 

 of the medulla and the pyramidal tracts of the cord; the 

 resulting paralysis is on the side opposite the lesion. 



The motor cortical zone, so far as can now be said, cor- 

 responds to the ascending frontal and parietal convolutions 



