GENERAL PHYSIOLOGY OF THE CEREBRUM. 



199 



must be applied with caution to the conditions in man. As 

 we have seen, the entire cerebral cortex may be removed from 

 the frog, the pigeon, and the dog without causing permanent 

 paralysis, although in the animal 

 last named there is at first a more 

 or less marked loss of voluntary 

 control. In man and the anthro- 

 poid apes the pyramidal system is 

 more highly developed and, in ac- (J 

 cordance with this fact, we might 

 expect paralyses resulting from le- 

 sions of the motor cortex to before 

 permanent. In regard to man it is 

 difficult to get exact data, but it has 

 been stated, on the basis of surgical 

 operations, that the paralysis does 

 not pass off completely with time; 

 there remains some degree of pare- 

 sis. The more complete observa- 

 tions made on the anthropoids* 

 indicate, on the contrary, that after 

 ablations of considerable extent in 

 the limb areas the initial paralysis 

 soon disappears almost completely, 

 and when a second operation is 

 made on the corresponding area in 

 the other hemisphere, there is no 

 recrudescence of paresis in the limb 

 which had recovered from the first 

 operation. The way in which this 

 vicarious substitution is effected is 

 not definitely known. In the dog 

 and animals still lower in the scale 

 of development one thinks of theru- 

 brospinal tract and its connections 

 with the basal ganglion of the cere- 

 brum as offering a mechanism, in addition to the pyramidal system, 

 for carrying out the highly co-ordinated movements of locomotion, 

 etc., but the exact distribution of function between the pyramidal 

 (cortical) and the subcortical motor systems is not understood. 



The Crossed Control of the Muscles and Bilateral Represen- 

 tation in the Cortex. It has been known from very ancient times 

 that an injury to the brain on one side is accompanied by a paral- 

 ysis of voluntary movement on the other side of the body, a condi- 

 * Leyton and Sherrington, Loc. tit. 



Fig. 89. Schema representing 

 the course of the fibers of the pyra- 

 midal system: 1, Fibers to the nuclei of 

 the cranial nerve ; 2, uncrossed fibers 

 to the lateral pyramidal fasciculus ; 

 3, fibers to the anterior pyramidal 

 fasciculus crossing in the cord ; 4 and 

 5, fibers that cross in the pyramidal 

 decussation to make the lateral 

 pyramidal 'tract of the opposite side. 



