672 PHYSIOLOGY 



by voluntary impulses, shows that this sense is in large part, if not 

 entirely, peripheral. It is, however, very complex in nature, and 

 is served by a whole array of different end-organs in the skin, joints, 

 tendons, and muscles. The muscles themselves are known to be 

 well supplied with afferent nerves. Stimulation of the central end 



pr.e. 



FIG. 308. A neuro-muscular spindle of the' 

 c, capsule ; pr.e, primary ending ; s.e, secondary ending ; pl.e, plate ending 

 (all these are probably sensory in function). 



FIG. 309. Part of a muscle-spindle more highly magnified. 

 n, nerve-fibres passing to spindle ; a, annular endings of axis cylinders ; 

 s, spiral endings ; d, dendritic endings ; sh, connective-tissue sheath of 

 spindle. 



of a muscular nerve may renexly excite or inhibit movements of 

 other muscles. Sherrington has shown that, after section of the 

 motor roots, over one-third of the fibres in a muscular nerve remain 

 undegenerated, proving their connection with the posterior root 

 ganglia. The sensory nerve- endings in the muscle are represented 

 partly by the tendon nerve-endings and partly by the muscle-spindles. 

 The former are richly branched end-arborisations of nerve fibres 

 on the surface of the tendon bundles. The muscle-spindles consist 

 of one or more muscle fibres, often continuous with normal fibres, 

 enclosed in a sheath composed of several layers of fibrous tissue with 



