THE REGULATING MECHANISM 191 



muscles Thus these large neurones in the 

 anterior part of the grey matter of the cord 

 have fibres reaching them from the posterior 

 roots, and are thus the mechanism of reflex 

 acts, but they are also related to the upper 

 cerebral centres so as to be the mechanism 

 for voluntary acts. It is important to notice 

 that the axons of neurones in the higher 

 parts of the nervous system may become 

 related by arborizations to neurones lower 

 down, and the reverse is also true, lower 

 neurones becoming similarly related to higher 

 ones. It may only be an analogy, but the 

 whole mechanism suggests a series of relays 

 such as one might conceive in a very extensive 

 telegraphic system. In a telegraphic relay 

 the current may be caused to work a mechan- 

 ism a long way off ; by this mechanism another 

 current may be started, and so on, until the 

 terminal station is reached. 



107. It would appear that in movements, 

 such as those of locomotion, caused by 

 antagonist groups of muscles, such as those 

 that bend the forearm on the arm (flexors) 

 and those that extend the arm (extensors), 



