292 MUSCULAR SENSE. 



The Muscular Sense. As an example, we will take the 

 case of estimating the weight of an object by holding it in the 

 hand. Our estimate is thought by some to be the result of 

 (1) direct consciousness of the degree of effort put forth; 

 but probably it is (2) a sensation, or complex of sensations, 

 aroused by nerve impulses from the organs used. There are 

 afferent nerve fibers with endings in (1) the skin, (2) the 

 muscles and tendons, (3) the joints. In extending the arm 

 and moving it up and down, all three of these sets of nerve 

 endings are probably stimulated, and impulses thence con- 

 veyed to the brain. 



It is matter of doubt whether or not the impulses from the 

 muscles are predominant, and consequently, whether the term 

 " muscular sense " is the most appropriate. Peciiliar nerve 

 endings have been found in the tendons, and the joints are 

 believed to have an especially rich nerve supply. It is not 

 necessary that we actively use the muscles to have sensations 

 of this kind. In passive moments, as the raising of the arm 

 by another person, we have a " sense of position " of the 

 parts, a considerable share of which is probably due to the 

 tension of the skin and changes in the joints. There is, of 

 course, some tension of the muscle, even in this passive move- 

 ment, that might affect nerve endings in it. The muscular 

 sense is closely related to the general sensibility already men- 

 tioned, if not a modified form of it. 



It is difficult to realize the importance of this sense in our 

 daily experience. We probably underestimate it, and attrib- 

 ute to sight too much of our knowledge of the external world. 

 The fundamental facts concerning the objects about us are 

 not obtained through sight alone. Such knowledge is based 

 on complex judgments concerning the meaning of auditory 

 and visual phenomena, according as they have, in past expe- 

 rience, been interpreted by tactile and muscular perceptions. 



