SENSATIONS OF MOVEMENT AND POSITION 073 



intervening lymph-spaces. One or more nerve fibres pierce this 

 sheath and, after making many spiral turns round the muscle fibres, 

 branch freely and terminate in little knobs on the surface of the 

 fibres (Fig. 308, 309) . The cross-striation of the muscle fibres within 

 the spindle is but faintly marked. It is evident that the continuity 

 of these sense-organs with the contracting muscle ensures in the best 

 possible way that the organs should be affected by the slightest change 

 of tension of the muscle, and should transmit information of the state 

 of tension to the central nervous system. 



THE PSYCHOLOGICAL SIGNIFICANCE OF SENSATIONS OF 

 MOVEMENT. Not only are these organic sensations of importance 

 as affording us information of the condition of our own bodies as 

 distinct from the objects in the world around, but they enter into 

 and qualify our judgments derived from all the sensations which 

 arise in the special sense-organs. 



When we regard the continuous aimless activity of a healthy 

 baby, we see that all ideas of space, of extension, of relative position 

 are wanting, or at any rate are not present to guide the movements. 

 Bit by bit muscular experience is acquired. The child learns that a 

 given movement of the right arm will bring the hand in contact 

 with something which is exciting the left side of his retina. The 

 surface of the thing, if of sufficient extension, can excite tactile 

 sensations in all the fingers of the right hand. By moving one finger 

 over the object the tactile sensations are found to be continuous ; 

 by moving the whole hand forwards the thing is found to possess 

 extension in a direction away from the body, and therefore in the 

 third plane of space. Thus gradually is acquired not only ideas 

 of extension, distance, and space, but certain movements are cor- 

 related with stimulation of definite regions of the skin or of the retina. 

 Tactile and retinal impressions therefore acquire local sign, and 

 power is acquired of moving the limbs to a degree and in a direction 

 adapted to stimuli arising from any part of the tactile or retinal 

 surfaces. The child gradually acquires the power of following a 

 bright object with its eyes, i.e. of contracting the ocular muscles 

 so as to keep the retinal image of the object on the fovea 

 centralis, and up to adult age we are still engaged in this balancing 

 of muscular movement against sense impressions a balancing 

 in which the muscular sensations are the constant guide and 

 criterion of success. Only by the muscular sensations are we 

 informed whether our willed movement has been carried out or not. 

 It is in virtue of the muscular and allied sensations that we are 

 able to clothe our visual and tactile sensations with properties of 

 extension, solidity, and resistance, which create them in consciousness 

 as parts of a material world. 



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