106 PHYSICAL EXPEESSION. 



The eyes turn to the right as if looking at a person 

 on the right side. Thus they do not lose their 

 parallelism ; the axes of the eyeballs remain paral- 

 lel there is no strabismus. This lateral deviation 

 of the eyes may show the weakness of one side of 

 the brain, and suggests a one-sided lesion in con- 

 tradistinction to a general brain state, such as 

 poisoning by opium. Now, observe the effect of 

 such a lesion of the right corpus striatum (or of 

 the centres which send their fibres through it) as 

 causes convulsion of the parts previously paralyzed. 

 In such a case we generally speak of an irritative 

 lesion of the nerve-centre as producing the convul- 

 sion or spasm, in contradistinction to a destructive 

 lesion which produces paralysis. 



An irritative lesion of the right corpus striatum 

 causes the head to rotate to the left, and the eyes 

 to deviate to the left, while the left limbs are con- 

 vulsed. 



EIGHT CORPUS STRIATUM. 

 Destructive Lesion. Irritating Lesion. 



Head and eyes turn to the right. 

 Left limbs paralyzed. 

 That is, head and eyes turn 

 away from the side paralyzed. 



Head and eyes turn to the left. 

 Left limbs convulsed. 

 That is, head and eyes turn 

 towards the side convulsed. 



These facts help to give some explanation of cer- 

 tain coincident movements and postures (see p. 151). 

 A destructive lesion on the right side of the brain 

 weakens the left arm and leg, and the head rotates 

 to the right. In an analogous manner we often see 

 the left hand in the nervous posture a sign of 

 weakness of the right hemisphere of the brain ; and 



