CENTRAL NERVOUS SYSTEM. 



693 



the results are plotted they give a distribution such as is shown in Figure 192. 

 At the same time all such figures are largely compiled from results obtained 

 on the monkey. It is here seen that the two central gyri are the principal 

 seat of these areas, and that it is only along the great longitudinal fissure divid- 

 ing the hemispheres that the motor areas extend beyond this limit in a cephalo- 

 caudad direction. Perhaps the relation most worthy of remark is the com- 

 paratively small fraction of the cortex concerned with the direct control of the 

 spinal cord cells. The motor areas 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 influence of which these areas 

 react. The relation of the areas in a frontal section is shown in Figure 194. 



FIG. 194. Frontal section of the human cerebrum on the left side. The fibres forming the internal 



capsule ( ), the callosum ( ), and the anterior commissure (. . . .) have been 



indicated. T, cortical area for the trunk ; L, cortical area for the leg; A, cortical area for the arm ; F, 

 cortical area for the face ; A, anterior commissure ; C, callosum ; CO, optic chiasma ; NC, caudate nucleus ; 

 NL, lenticular nucleus ; R, fornix ; TO, thalamus ; X, lateral ventricle. 



Sensory and Motor Regions. If an attempt is made to unify the con- 

 struction of the entire cortex by bringing the motor and sensory areas under 

 a common law, it must be based on the fact that the system of neurons bring- 

 ing impulses to the motor region forms part of the afferent pathways from the 

 skin and muscles. To Munk l is due the credit of having from the first looked 

 upon the responsive cortex as marked off into areas within which certain groups 

 of afferent fibres terminated, so that apart from the sensory areas named from 

 the special senses, he calls the area which controls the skeletal muscles the 

 " Fuhlsphare," on the assumption that in it end the fibres bringing in impulses 

 1 Ueber der Functionen der Grosshirnrinde, 1881. 



