186 THE POPULAR SCIENCE MONTHLY. 



wise served to explain some curious forms of expression common to 

 man and the lower animals. The common tendency, when any strong 

 exertion is made with the right hand, to retract the angle of the mouth 

 and open the mouth on the same side, had been stated by Oken, in his 

 "Natur-geschichte" to be due to the homology between the upper limbs 

 and the upper jaw ; the true explanation being that the movements of 

 the fist and of the mouth are in such close relation to each other that, 

 when one is made to act powerfully, the impression diffuses itself to 

 the neighboring part of the brain, and the two act together. 



The experiments have likewise a physiological significance. There 

 is reason to believe that, when the different parts of the brain are stimu- 

 lated, ideas are excited in the animals experimented upon, but it is 

 difficult to say what the ideas are. There is, no doubt, a close relation 

 between certain muscular movements and certain ideas, which may 

 prove capable of explanation. This is supported by the phenomena 

 of epileptic insanity. The most important guide on the psychological 

 aspect of the question is the disease known as aphasia. The part of 

 the brain which is the seat of the memory of words is that which gov- 

 erns the movements of the mouth and the tongue. In aphasia, the 

 disease is generally on the left side of the brain, in the posterior part 

 of the inferior frontal convolution, and it is generally associated with 

 paralysis of the right hand,. and the reason might be supposed to be 

 that the part of the brain affected is nearly related to the part govern- 

 ing the movements of the right hand. 



It is essential to remember that the movements of the mouth are 

 governed bi-laterally from each hemisphere. The brain is symmetrical, 

 and I hold it to be a mistake to suppose that the faculty of speech is 

 localized on the left side of the brain. The reason why an individual 

 loses his speech when the left side of the brain is diseased is simply 

 this : Most persons are right-handed, and therefore left-brained, the 

 left side of the brain governing the right side of the body. Men 

 naturally seize a thing with the right hand, they naturally therefore 

 use rather the left side of the brain than the right, and when there is 

 disease, there the individual feels like one who has suddenly lost the 

 use of his right arm. 



I may, finally, briefly allude to the results of stimulating the dif- 

 ferent ganglia. Stimulation of the corpora striata causes the limbs to 

 be flexed ; the optic thalami produces no result : the corpora quadri- 

 gemina produce, when the anterior tubercles are acted upon, an intense 

 dilatation of the pupil, and a tendency to draw back the head and ex- 

 tend the limbs as in opisthotonos ; while the stimulation of the pos- 

 terior tubercles leads to the production of all kinds of noises. By 

 stimulating the cerebellum, various movements of the eyeballs are 

 produced. — Nature. 



