Functions of the Basal Ganglia. 633 



lyzed, unless the deficient sensorial guidance be replaced by some other, 

 and in similar affections of the upper extremities, there is a like inabil- 

 ity to raise a limb, or to sustain a weight. But in such cases the defi- 

 ciency of the ' muscular sense ' may be made good by the visual ; thus 

 the patient who cannot feel either the contact of his foot with the ground, 

 or the muscular effort he is making, can manage to stand and walk by 

 looking at his limbs ; and the woman who cannot feel the pressure of 

 her child upon her arms, can yet sustain it so long as she keeps her eyes 

 fixed upon it, but no longer, the muscles ceasing to contract and the 

 limb dropping powerless the moment that the eyes are withdrawn from 

 it. Thus it is, too, that when we are about to make a muscular effort, 

 the amount of force " used accords with our conception of what will be 

 required, as indicated by the experience of former sensations. If the 

 estimate is wrong, we will exert too much or too little effort. The move- 

 ments of the eyeball are directed by the visual sense ( and not by the 

 muscular sense ) in the same way that most muscles are directed by their 

 own muscular sense. When we close our eyes .we cannot move them in 

 any required direction without an effort that strongly calls forth the mus- 

 cular sense. 



The auditory sense governs the movement of muscles that are con- 

 cerned in the production of vocal sounds. People who never heard a 

 sound, cannot articulate, although they possess all the necessary mus- 

 cles in good order. Through the visual sense, however, and long train- 

 ing, people born deaf have learned to talk imperfectly. 



The muscular, tactile and visual senses are combined in the movements 

 and balancing of the body. If a person be blindfolded he cannot walk 

 straight toward an object at any considerable distance, because deprived 

 of the guidance of the visual sense. A blind man can do much better, 

 because his muscular sense is so much more acute by use, that it in con- 

 siderable part, supplies the visual deficiency. < < When our vision, how- 

 ever, instead of aiding and guiding us, brings to the mind sensations of 

 an antagonistic character, our movements become uncertain from the 

 loss of that power of guidance and control over them which the har- 

 mony of the two sensations usualty gives. " A person feels insecure 

 when looking down a precipice. If he attempts to walk a plank ele- 

 vated 50 feet in the air, his muscles become almost paralyzed, and he loses 

 the power of equilibrium, although he could walk the plank with ease 

 if it were on the ground. He may become dizzy and lose his balance if he 

 attempts to walk a plank or foot-bridge over a running brook. The 

 muscular sense alone is more reliable than when it is counteracted and 

 confused by an unsteady and uneducated visual sense. So, in such sit- 

 uations, it is safer to look up, and ignore, as far as possible, the influence 

 of vision. In somnambulism the subject is guided by the muscular 



