6i2 THE POPULAR SCIENCE MONTHLY. 



urged as reasons for riglit-liandedness are not present ; animals do 

 not carry tlieir young, nor pat them to sleep, nor do animals shake 

 hands! It must therefore be shown that animals are right or 

 left handed, or that they differ in some marked respect in regard 

 to function, in their nervous make-up, from man. Admitting the 

 need of meeting these requirements; admitting again that we have 

 little evidence that animals are dextral in their functions ; admit- 

 ting also the known results as to the control of the two halves 

 of the muscular system by the opposite brain hemispheres respect- 

 ively ; admitting further that the motor speech function is per- 

 formed by the hemisphere which controls the stronger side of the 

 body, and is adjacent to the motor arm center in that hemisphere ; 

 and admitting, finally, that the speech function is one in which the 

 animals have little share all these admissions lead us at once to 

 the view that there is a fundamental connection between the rise 

 of speech and the rise of right-handedness,* 



Looking broadly at the methods of nervous and muscular 

 development, and accepting all the results of neurology we are 

 able to gather, we may say that in the differentiation of func- 

 tions in the animal series certain principles may be recognized : 

 1. The deep-seated vital functions represent least nervous differen- 

 tiation, as is seen in the simple organs known as the lower nerv- 

 ous centers. 2. New unsymmetrical functions give a differential 

 or twofold organic development, the great instance of which is 

 found in the cerebral hemispheres. 3. New symmetrical or uni- 

 lateral functions find their counterpart each in one of three kinds 

 of nervous adaptation : (a) co-ordination of the hemispheres in a 

 single function i. e., functions which are crippled if either hemi- 

 sphere is damaged ; (b) co-ordination of particular functions in each 

 hemisphere i. e., functions which are not crippled unless both 

 hemispheres are damaged ; and (c) co-ordination of particular func- 

 tions in one hemisphere only i. e,, functions which are crippled 

 if one selected hemisphere is damaged. All these kinds of co-or- 

 dination exist. 



It is easy to see that both speech and right-handed function 

 belong under the last head of the last class co-ordinations of 

 particular functions in one hemisphere only and that they be- 

 long in the same hemisphere. Why is this ? What have they in 

 common ? 



A very essential kind of hand movements are the so-called " ex- 

 pressive" movements, meaning those which serve to convey a 

 meaning, or express a state of consciousness. Of course, speech is 



* This much has been before surmised (see Mazel, Kevue Scientifique, 1892, i, p. 113). 

 He makes no attempt, however, to account for the association, except by calling both func- 

 tions expressive. 



