RELATIONS OF SPEECH TO HUMAN PROGRESS 529 



of a bony prominence ; in all the lower Primates it comes out of 

 a pit. Moreover, in the apes it is found not only to be much 

 smaller than in man — which is a sure sign that it meets certain 

 specific human needs — but it lis also obviously much less versa- 

 tile,-in that the separate fasciculi of the muscle are bound closely 

 together. In several of the lower monkeys dissected by the 

 writer no trace could be found of that curious splitting of the 

 hypo-glossal nerve before it enters the muscle found in the 

 human subject. Further information on this detail of compara- 

 tive anatomy is very desirable. 



Why should the genio-gloss us muscle appear so much larger 

 in man than in his nearest congeners the great apes? As far 

 as the other, and especially the intrinsic, muscles of the tongue 

 are concerned, I have not been able to discern very much 

 difference between our tongues and those of gorillas and chim- 

 panzees. It cannot be because we want to sort our food with 

 our tongue to a greater degree than do the monkeys. We have 

 no cheek pouches, which among many of the Old World apes 

 form a kind of banking account, of which the tongue plays the 

 part of the cashier. Man's intelligence, inventiveness, and 

 versatile hands free the tongue from many of the discriminating 

 duties it has to exercise lower down the scale. 



It is only I think when we consider the functions of the 

 genio-glossus muscle as an important aid in articulate speech 

 that we are able to account for new facts. The mechanism 

 of speech is exceedingly complex, and here it must suffice to 

 discuss the part of it which refers more particularly to the 

 question before us. When we speak at the rate of (let us 

 say) 150 words a minute the number of separate tongue 

 movements involved must come to nearly 500. These move- 

 ments are following one another in ever-varying order, and 

 most of them are composite, i.e. several groups of muscles 

 are brought into action at practically the same time and must 

 act in harmony with one another. Moreover, absolute preci- 

 sion in all these movements is necessary, and any failure re- 

 sults in a breakdown of clear articulation. Stammering is 

 undoubtedly due to such failures of co-ordination, for any hitch 

 in the exact timing of the muscle contractions (at the rate of 

 nearly ten per second) causes a clashing of the forces brought 

 into play comparable to the result of commutator troubles in 

 internal combustion engines. 



