THE SENSES 



97 



B. MUSCLE AND JOINT SENSE. 



Closely allied to the mechanism of common sensibility is 

 the arrangement by which we are made aware of the 

 movements and thus of the position of various parts of 

 the body. A double mechanism is here involved 1st, 

 A mechanism stimulated by the contraction of the muscles ; 

 and 2nd, a mechanism acted on by movements at the 

 joints. 



(1st) Muscle Spindles. Among the fibres of the muscles 

 are found long fusiform structures containing modified parts 

 of the muscle fibres. Into each spindle a medullated nerve 

 passes and breaks up into a non-medullated plexus round 

 the fibres. (Fig. 41.) 



(2nd) Organs of Golgi are swellings 

 in the tendons near the muscle fibres 

 into which a medullated fibre enters, and 

 losing its white sheath forms a plexus 

 of fibrils with varicosities upon them. 



(3rd) Varicose terminations of axons 

 surrounded by fibrous tissues are found 

 in the synovial membranes and round 

 joints. 



Through these mechanisms informa- Fia 4L "structure 

 tion is transmitted to the central nervous 

 system as to the position and move- 

 ments of the various parts, and this, 

 although not necessarily modifying the 

 consciousness, is of service in guiding 

 the movements. When the conscious- 

 ness is affected, valuable information as to the conditions of 

 the surroundings may be gained. In estimating the weight 

 of bodies, these sensations are much used. The body is taken 

 in the hand, and by determining the amount of muscular 

 contraction required to support or raise it, the weight is 

 estimated. The shape and size of objects are also determined 

 by this sense in conjunction with the sense of touch. If 

 we touch a book on the table we can form an idea of its 

 shape and size by estimating the distance through which 



' 7 



of 



muscle spindle only 

 one fibre represented. 

 6, capsular space ; c, 

 capsule; p, motor ter- 

 mination ; T.S., sen- 

 sory termination on the 

 spindle fibre. (From 

 EEGAUD and FAVRB. ) 



