6 14 THE POPULAR SCIENCE MONTHLY. 



patient could still understand tunes, and, further, could imagine 

 tunes " in his head " (what the French call interieur), while he 

 could not sing them. This shows a close connection in locality 

 between motor speech and motor music function, while a slight 

 separateness of the two centers in locality in the left hemisphere, 

 explains cases of motor aphasia in which musical execution is 

 preserved. Further, Frankl-Hochwart declares that no cases are 

 recorded of amusia from lesion in the right hemisphere,* and 

 Starr says (in a private letter) of a patient of his : t " My patient 

 is right-handed, and music does follow speech in being unilater- 

 ally located ; ... it is well proved that the musical faculty is one- 

 sided in location." Despite these positive opinions, I think more 

 critical cases with autopsy are necessary to make the position 

 quite secure. 



All this means simply that the general cause to which is due 

 the fact of right-handedness is also the cause, through further dif- 

 ferentiation and emphasis in the same local seat, of the develop- 

 ment of musical ability and of speech. It now remains to ask : 

 What was or is this cause, and when in the race-history series did 

 it begin to operate ? There are only two hypotheses of any force 

 either " experience " or " spontaneous variation " at some stage 

 in biological development. 



It is extremely improbable that dextrality should have arisen 

 among the quadrupeds (or amanous bipeds), for experience was 

 lacking of unilateral stimulation, and a spontaneous variation of 

 this kind would have produced such inconvenience of locomotion 

 and ultimately such asymmetry of form that it would have been 

 weeded out. J As an extreme example, fancj^ a bird which is dex- 

 tral in its flight.* 



As soon as we come to bipeds with hands, however, these rea- 

 sons do not hold. Their locomotion does not depend on manual 

 symmetry, and any dextrality, however slight, would be of direct 

 advantage in climbing, fighting, breaking sticks, and pulling 

 fruit ; since a disproportionate growth of one side would give that 

 side greater strength than either side would possess in animals 

 of symmetrical development in the same environment. A very 

 strong one-armed man can keep at bay a weaker man with two 

 arms, or destroy him, and this is emphasized in animals, where 

 brute force is the only resource. It is difficult to find, however, 

 in the habits of simians any ground for believing that there has 



* This meaus that all cases noted have been right-handed. Deutsche Zeitsch. fur Ner- 

 venheilkunde, 1891, i, p. 295 and foot-note. 



f Referred to in The Psychological Review, January, 1894, p. 92. 



X For this reason the human leg, as Brown-Sdquard says, is not as right-sided as the arm. 



* The only evidence I know of such a thing is that a cat swims in a circle ; but then 

 dogs and horses do not. 



