FUNCTIONS OF THE SENSORY GANGLIA. 725 



are directed and controlled, in virtue of the guiding sensations which they 

 furnish, but that they are actually the immediate centres of the motor influence 

 which excites muscular contractions, in obedience to impulses transmitted 

 downwards from the Cerebrum. It has usually been considered that the Cere- 

 brum acts directly upon the muscles through the motor nerves, in virtue of a 

 direct continuity of fibres from the gray matter of its convolutions, through the 

 Corpora Striata, the motor tract of the Medulla Oblongata, the anterior portion 

 of the Spinal Cord, and the anterior roots of the nerves ; and that in the per- 

 formance of any voluntary movement, the Will determines the motor force to 

 the muscle or set of muscles by whose instrumentality it may be produced. To 

 this doctrine, however, the anatomical facts already stated ( 730) constitute a 

 very serious objection; for the motor tract cannot be stated with certainty to 

 have any higher origin than the Corpora Striata; and it is impossible to imagine 

 that the fibres which converge towards the surface of these bodies from all parts 

 of the Cerebrum can be so closely compacted together as to be included in the 

 motor columns of the Spinal Axis. The fact would rather seem to be that 

 these converging fibres bear the same kind of anatomical relation to the Cor- 

 pora Striata and the other Sensorial centres of motor power, as do the fibres of 

 the afferent nerves which proceed to them from the Retina, the Schneiderian 

 membrane, and other peripheral expansions of nervous matter; and hence we 

 might infer that the nerve-force generated in the convolutions, instead of acting 

 immediately on the motor nerves, is first directed towards the Automatic centres, 

 and excites the same kind of motor response in them as would be given to an 

 impression transmitted to them through a sensory nerve. We shall find that 

 such a view of the structural arrangements of these parts is in remarkable 

 accordance with their functional relations, as indicated by a careful analysis of the 

 mechanism of what is commonly regarded as voluntary movement. The Cerebrum, 

 as will be shown hereafter (Sect. 5), may thus call the Automatic apparatus into 

 action, as the instrument either of ideas, of emotions, or of volitional determi- 

 nations; but as both the ideo-motor and the emotional movements have much 

 in common with the automatic, there is no occasion for at present specially 

 inquiring into their mechanism, and we may limit our examination to voluntary 

 movements alone, which have been usually regarded as in such complete an- 

 tagonism to those of the automatic group, that even distinct sets of nerve-fibres 

 have been thought requisite to account for the transmission of these two sets of 

 motor impulses to the muscles. 



754. Now in the first place it may be asserted with some confidence, that no 

 effort of the Will can exert that direct influence on the muscles which our 

 ordinary phraseology, and even the language of scientific reasoners, would seem 

 to imply ; but, on the other hand, that the Will is solely concerned in deter- 

 mining the result, the selection and combination of muscular movements required 

 to bring about this result not being effected by the Will, but by some inter- 

 mediate agency. If it were otherwise, we should be dependent upon anatomical 

 knowledge for our power of performing the simplest movement of the body ; 

 whereas we find the fact to be, that the man who has not the least idea of the 

 mechanism of muscular action can acquire the most perfect command over his 

 movements, and can adapt them as perfectly to the desired end as the most 

 accomplished anatomist could do. Further, we cannot, by any exertion of the 

 will, single out a particular muscle and throw it into contraction by itself, unless 

 that muscle be one which is alone concerned in an action that we can voluntarily 

 perform; and even then we single it out by willing the action. Thus we can 

 put the levator palpebrse in action by itself; but this we do, not by any conscious 

 determination of power to the muscle itself, but by willing to raise the eyelids; 

 and it is only by our anatomical knowledge that we know that but a single 

 muscle is concerned in this movement. So far as our own consciousness can 



