CORPUS STRIATUM OF MAMMALS 121 



tural attitudes assumed by animals which have been 

 decerebrated just in front of the midbrain are imme- 

 diately abolished by stimulation of the pyramidal 

 tract. The motor control exerted by the thalamus 

 seems to be essentially similar to that of the mid- 

 brain and lower centers; that exerted by the cortex 

 is an intentional control (phasic) and its motor path 

 (the pyramidal tract) is electrically excitable through- 

 out its entire extent. The motor control exerted by 

 the corpus striatum of higher animals is of still dif- 

 ferent type. Here the striatum itself is electrically in- 

 excitable and (according to Wilson) it is "concerned 

 more with tone control, with steadiness of innerva- 

 tion, than with actual origination of it." 



Wilson says, '*The cardinal features of disease of 

 the corpus striatum may be summed up in three 

 words — variability in muscle tonus, the appearance 

 of involuntary movements, and the absence of paraly- 

 sis." And again, "Relation of the corpus striatum to 

 the rest of the old motor system is one of tone con- 

 trol, and of steadiness of innervation. Remove its 

 influence by disease, and cerebello-mesencephalo- 

 spinal motor mechanisms come into overaction in 

 spite of the normal activity of the pyramidal sys- 

 tem." "The normal cortico-spinal system is unable 

 to prevent the effects of striatal disease from making 

 their appearance. Though we speak of it as the 'last 

 word' in motor control, it cannot inhibit the hyper- 

 tonia and hyperkinesis of striatal disease." It should 



