250 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



By a few direct experiments and by many pathological observations some- 

 thing is known of the motor centres in the human cerebral cortex. When 



K 1 1 ; . 107.— Mesial view of a human hemisphere, showing motor areas. Formed in the same way as 



Fig. 100. 



the results are plotted they give a distrib 

 At the same time all such figures arc lari 



FlG. 108.— Frontal section of human cerebrum on 

 the left side. The fibres forming the internal capsule 



( ), the callosum ( ), and the anterior 



COmmisMirr i . - . — . — ) have been i mlic:i t <■<! : T. cor- 

 tical area for the trunk ; /,. cortical area tor the leg: A, 

 cortical area for the arm; /•'. cortical area for the face; 

 A, anterior commissure ; C, callosum ; CO, optic chias- 

 ina : NC, caudate nucleus ; NL, lenticular nucleus; i: 

 fornix; TO, thalamus; .V, lateral ventricle. 



to the cord. The relation of the ana- in 

 Multiple Control from the Cortex. 



ution such as is shown in Fig. 106. 

 elv based on results obtained from 

 the monkey. It is here seen that 

 the two central gyri are the princi- 

 pal seat of these areas, and that it 

 is only along the great longitudinal 

 fissure separating the hemispheres 

 that the motor areas extend beyond 

 this limit in a cephalo-caudad direc- 

 tion. Perhaps the relation most 

 worthy of remark is the compara- 

 tively small fraction of the cortex 

 concerned with the direct control 

 of the spinal cord cells. The motor 

 anas in man are elaborated not so 

 much by the increase in the number 

 of the cells controlling the lower 

 centres, as by an increase in the 

 number of those cells under the in- 

 fluence of which these areas react. 

 According to the estimates of Miss 

 Thompson, 1 there are in man 9200 

 millions of cells in the entire cere- 

 bral cortex of both hemispheres. 

 In the motor region about the cen- 

 tral fissures there appear to be only 

 159,600 cells concerned in the pro- 

 duction of pyramidal fibres going 



a frontal -eel ion is shown in Fig 10<S. 



— It has been found that stimulation 



1 Helen B. Thompson: Journal of ComjMtrative Neuroloyy, 1899, vol. ix. No. 2. 



