4 [cmrnal of Comparative Netirology a?td Psychology. 



nerve fiber at the point where it loses its medullary sheath and 

 penetrates the motor plate ; from here it may pass to end on a 

 muscle fiber or in a neuromuscular spindle. 



In any discussion on nerve endings it is well to recognize 

 the facts that are universally accepted. Thus it is well estab- 

 lished that a motor nerve may branch repeatedly before ending, 

 or to put it otherwise, the peripheral ending of a motor neurone 

 is connected with many muscle fibers. This branching occurs 

 at a node. Each branch is a medullated fiber smaller in calibre 

 than the parent stem and it ultimately loses the medullary 

 sheath and breaks up to form a nerve ending usually on one 

 muscle fiber, to which it alone is attached. To this very gen- 

 eral statement there are a variety of exceptions. Thus, two or 

 more endings may go to one muscle fiber ; or a non-medullated 

 nerve may pass off from a node ; occasionally, though more 

 rarely, a non-medullated nerve may be seen leaving a medul- 

 lated nerve where no node is apparent. To define concisely 

 and yet accurately the term motor nerve ending, either from an 

 anatomical or physiological standpoint, is in the present state 

 of our knowledge by no means easy. For our present purpose 

 a motor ending may be regarded as that peripheral part of the 

 nerve which, on reaching a muscle fiber, loses its medullary 

 sheath and breaks up into more or less numerous non-medul- 

 lated ^ branches or end-twigs which enter into a more or less 

 close relation to the muscle fiber. Having thus defined a motor 

 ending, the significance of the term ultraterminal fibrilla is the 

 better understood ; this is a fine non-medullated fibril which 

 passes from one of the twigs of the nerve termination to a re- 

 gion beyond the primary ending. Here it enters into relation 

 with the muscle fiber on which rests the ending from which it 

 originally sprang, or with some adjacent muscle fiber or 

 with a neighboring muscle spindle. 



' DOGIEL has described a medullary sheath as occurring in the nerve end 

 ing (Archiv /. mikr. Anat., Bonn, 1890, p. 314). This I have never seen, 

 though the dye oozing from the axis cylinder at times gives a resemblance 

 to such. 



