IMPORTANCE OF GUIDING SENSATIONS. 383 



in Man and the highest Vertebrata, not merely in their direct 

 and independent operation on the Muscles, but also in the 

 manner in which they participate in all voluntary action. 

 For it is now well established, that the Will cannot bring 

 about any definite movement, except under the guidance of 

 sensations, derived either from the muscles themselves, or 

 through some channel of information which indicates what 

 the muscles are doing. It is for want of the guiding sensa- 

 tions afforded by the ear, that persons who are born deaf are 

 also dumb, the will not being able to make use of the muscles 

 concerned in vocalization ; and where, by long training, some 

 imperfect power of speech has been acquired, it has been 

 gained by attention to the sensations arising from the mus- 

 cular exertion of the organs themselves. It is by the guiding 

 influence of the visual sensations, that the movements of the 

 two eye-balls are made to correspond ; and, in children born 

 completely blind, it may be observed that the eyes roll about 

 without any harmony, though a very slight perception of light 

 is sufficient to bring their motions into consent. So, again, 

 if the arm or the leg be so paralysed that its sensibility is 

 lost whilst its muscles are still under the power of the will, 

 that power can only be exerted to occasion movement by the 

 assistance of the sight ; a mother, for example, so affected, 

 being only able to hold her infant upon her arm so long as 

 she looks at it ; and a man, whose legs are thus paralysed, 

 being only able to sustain himself in standing or walking by 

 constantly looking at his legs. 



479. It seems to be obviously through the shorter channel 

 afforded by the Sensory Ganglia, that those actions are per- 

 formed, which, though originally directed by Intelligence and 

 Will, come by frequent repetition to be so completely auto- 

 matic as to resemble the instinctive actions of the lower 

 animals. Thus it is within the experience of almost every 

 one, that he occasionally walks through the streets with his 

 mind intently and continuously engaged on some train of 

 thought, without the least attention to, or even consciousness 

 of, the direction he is taking; yet he avoids obstacles, and 

 follows his accustomed course, obviously under the guidance 

 of his visual sense, whilst the movements of his limbs are 

 kept-up by reflex action (471); and on awaking, as it were, 

 from his reverie, he may find that he has thus been automa- 



