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 
ought, without the least attention to, or even consciousness 
bf, the direction he is taking; yet he avoids obstacles, and 
Tollows his accustomed course, obviously under the guidance 
‘of his visual sense, whilst the movements of his limbs are 
‘Aept-up by reflex action (§ 471); and on awaking, as it were, 
tom his reverie, he may find that he has thus been automa- 
- IMPORTANCE OF GUIDING SENSATIONS. 383 
