DEXTRALITY AND SINISTRALITY. 365 



are dual in nature, requiring dual centers of coordination and innerva- 

 tion in the two halves of the brain. But speech, being a single func- 

 tion, can have but one center, and that, of course, must be located, not 

 in any median place, because there is no such place, but in one or the 

 other side. We also know by physiology and pathology that in the 

 dextral it is in the third left frontal convolution, and in the sinistral 

 it is in the corresponding position on the right side. We know, 

 furthermore, that it is the intellectual act of writing, rather than 

 the grosser acts and functions, which localizes the speech center. A 

 man may be left-handed for everything but writing and the judgments 

 issuing in the correlations of spoken words are formed and innervated 

 from Broca's convolution. Or vice versa in the case of I;he sinistro- 

 manual writer who is dextromanual for all other acts. 



The reason why dextromanuality, dextrocularity, etc., must coexist 

 with sinistrocerebrality becomes manifest. The function of speech or 

 writing is the method whereby judgment or volition passes into action. 

 The initial, dominating and guiding motility to vocal organs, to hand, 

 and even to foot, springing from closely contiguous, and hence more 

 quickly and accurately acting, cerebral centers, will be better correlated 

 and certain than if the centers were in opposite cerebral hemispheres. 

 The indicator of all action, the very creator of intellect, is vision. 

 Hence all right-handed people are also right-eyed.* The centers for 

 right vision, right motion, and for speech are thus in close relationship 

 and upon the same side of the brain. As I have said (Science, April 

 8, 1904) : 



The unification and perfection of innervation and cerebration must be better 

 if initiated and executed with the cerebral centers mainly upon one side of the 

 brain, than if the unity is gained by means of the longer and more distant 

 commissural fibers extending between the two sides of the brain. In the 

 right-handed the speech center is in the left side of the brain, as is also 

 the motor center for the right hand, and the optical center of the right 

 eye. The dependence of all motion upon a perfect correlation of vision 

 and judgment needs only to be mentioned. That all intellect is psychologically 

 the product of vision is less recognized, but is not less absolute truth. The 

 right hand writes, possibly because the right eye looks down upon the writing 

 more accurately than would the left; both depend upon the synchronous and 



* One of the best tests of predominant dextrality or sinistrality is the 

 ' sighting ' of a stick to see if it is straight, or the sighting of a gun or pistol. 

 Dextrocularity is largely a dictator of general dextrality. And of dextropedality 

 also, for the dextral is right-footed also. Errors of judgment, however, have 

 been frequent as to the function of the feet. The ' spade-foot ' is the left, nat- 

 urally, because the right leg and foot are the directing ones, in the dextral, who 

 also, as the masonic ritual directs, steps off with the left foot first. The 

 dextral must spring from the right foot. It has been said that the oblique 

 line of the body of the dog in trotting is due to incipient right or left-footedness. 

 But all soft-footed animals avoid ' interfering ' by this obliquity of progression. 

 The much discussed knockout blow of the pugilist with the left is, I suspect, 

 because of the better spring from the firmer right foot. 



