NERVE ENDINGS IN MUSCLE AND TENDON 



173 



connected with the tendon, or they may join other muscle fiber bundles. 

 The muscle spindles are usually found in the fibrous septa of the peri- 

 mysium. Compared with the adjacent muscle fibers, the intrafusal fibers 

 have a smaller diameter, are less distinctly but more coarsely striped, 

 and contain some centrally located nuclei. 



Either one or several nerve trunks enter the spindle, usually near 

 its equator rather than at its poles. The nerve fibers branch repeatedly 



FIG. 192. MIDDLE THIRD OF A TERMINAL PLAQUE IN THE MUSCLE SPINDLE OF AN 

 ADULT CAT. 



A, rings; F, dendritic branchings; S, spirals. Chlorid of gold preparation. Highly 

 magnified. (After Ruffini.) 



in the intracapsular connective tissue, and finally pierce the axial sheath 

 as naked processes which form a rich arborization of terminal fibrils 

 about the intrafusal muscle fibers. Euffini distinguishes three types of 

 terminal nerve fibrils: (1) annular, which form rings around the muscle 

 fibers; (2) spiral, which are spirally twisted about the intrafusal fibers; 

 and (3) dendritic branchings, in which the axons break into numerous 

 irregular processes with laminate expansions. 



Motor end-plates for the muscle fibers of the spindle as well as sym- 

 pathetic vasomotor nerves for its blood-vessels have also been demon- 

 strated within the muscle spindles. 



That the muscle spindles are sensory and not motor organs has been 



