CHAP. XXVIII.] AND PHYSIOLOGICAL PROCESSES. 605 



system Even though the child acquires the 



power of uttering articulate sounds slowly, still when we 

 think of the delicacy of the muscular combinations 

 necessary, and of the almost instinctive way in which 

 they are brought about, we shall rather be impressed with 

 the notion that this could not have been accomplished at 

 all had not the infant been born with a nervous system 

 tending to develop itself in certain special directions, and 

 thus making the performance of the highly complex 

 muscular acts necessary for articulate speech a possibility. 

 Slowly elaborated developments of the parts of the 

 Medulla and of the Brain concerned in the acts of speech, 

 we may presume had taken place in remote individuals 

 of the parent race, as they acquired additional powers 

 in this respect ; and the power of developing similar 

 structural connections between nerve cells and nerve 

 fibres, thus established, having been handed down and 

 gradually rendered more perfect by hereditary transmis- 

 sion through countless succeeding generations, the infant of 

 to-day is born, perchance, with the potentiality of develop- 

 ing a nervous system as complex and as perfect in this 

 respect as any which may have preceded it in its own 

 ancestral line." A slowly growing mechanism of this kind 

 becomes perfected under the influence of suitable stimuli 

 of a volitional order, which here, as in the case of the 

 acquirement of new motor powers by an adult, have an 

 unquestionable though an unexplained influence in bring- 

 ing about the development of nerve-tissues in the Centres 

 to which they are directed (see p. 563). " This impetus, 

 we may presume, is given by the passage of nerve-currents 

 downwards from those superficial portions of the cerebral 

 hemispheres concerned in the acts of intellectual percep- 

 tion and of memory, to those parts which are the motor 

 centres concerned in articulate speech." 



