TERMINATION OF MOTOR NERVES IN VERTEBRATA. 227 



contractile substance. This last idea is, however, opposed, 

 from a morphological point of view, by a consideration of the 

 mode of nerve termination in the frog ; since, if there be a 

 fact in the whole range of this inquiry capable of being easily 

 ascertained, it is the invariably sharply defined and distinct 

 termination of the intra-muscular axis cylinder in the Amphibia. 

 That view is also, and has long been, opposed by physiological 

 considerations ; for it is demonstrable that the muscle does not 

 act upon the nerve fibre, but that, on the contrar}^ all stimuli 

 are conducted from the nerve to the muscle, and never in the 

 inverse direction ; and for this purpose the nerve termination 

 forms, as we now know, the visible structure. It may indeed 

 be that a finer series of radiating processes from the nerve 

 plate may penetrate between the granules of the substratum 

 than we are at present disposed to admit ; and many circum- 

 stances may be adduced in favour of this supposition, as, for 

 example, the intimate adhesion of the two parts to one another, 

 even when the contents of the eminence no longer rest upon 

 the muscle. It is obvious, then, that it remains to be shown 

 that the substratum constitutes a direct transition to the con- 

 tractile, since there are muscles, especially amongst the Am- 

 phibia, in which this structural characteristic is entirely absent. 



The present state of our information upon these points may 

 be shortly expressed as follows : 



In all transversely striated muscles the nerves terminate 

 beneath the sarcolemma, the sheath of Schwann becoming 

 continuous with the latter. Up to this point the axis cylinder 

 is accompanied by the medullary sheath. The extremity of 

 the axis cylinder always corresponds to a remarkably broad 

 expansion, which constantly forms a flat branching mass. 

 This terminal nerve plate sometimes presents the character of 

 a membrane, and at others resembles a system of fibres. In 

 the greater number of cases the plate rests upon a substratum 

 of nuclei and finely granular protoplasm, whilst in others this 

 material is absent, and the nerve plates possess the so-called 

 terminal nerve bulbs. The extremity of the nerve never 

 penetrates into the interior of the contractile cylinder, and, on 

 the other hand, never entirely invests it. Short muscular fibres 

 usually receive only one nerve ; but long fibres have several. 



