XI MOTOR NERVE-ENDINGS 463 



contains the continuation of a certain number of the fibres 

 of the nerve trunk, bound up into a bundle by themselves. 

 In these larger ramifications of the nerve trunk there is 

 no branching of the nerve fibres themselves (at any rate 

 as a rule), but merely a separation of the fibres of 

 the compound nerve bundles. In the finer branches, 

 however, the nerve fibres themselves may divide ; the 

 division, which always takes place at a )>ode, is generally 

 dichotomous — that is, one fibre divides into two, each of 

 these again into two, and so on. An ultimate branch 

 consisting of one or two nerve fibres, or of one only, with 

 a very delicate connective tissue envelope (Fig. 146, 

 E c), passes to some single muscle fibre, and each nerve 

 fibre applies itself to the outer surface of the sarcolemma. 

 At this point, if it has not done so before, the medulla 

 disappears, the neurilemma becomes continuous with 

 the sarcolemma, and the axis-cylinder ending abruptly is 

 applied to a disc of protoplasmic substance containing 

 many nuclei, thus forming what is called a motor 

 end-organ or end-plate,' which is interposed be- 

 tween the striated nmscle substance and the sarco- 

 lemma at this point. Before ending the axis-cylinder 

 divides and its divisions anastomose freely, but the exact 

 relations of the various parts of the end-plate to the 

 muscle-substance have not yet been clearly made out. 

 The whole appears, however, to constitute an apparatus by 

 which the molecular disturbances of the substance of the 

 axis-cylinder (the essential part of the nerve) may be 

 efficiently propagated to the substance of the muscle. 



If, instead of following the motor nerve to its distribu- 

 tion in the muscle, we trace it the other way, towards 

 the spinal cord, we shall find no alteration of any moment 

 until we arrive at the point at which the anterior root 

 enters the cord. From the finest branches of the motor 

 nerve (in which, as has been stated, the nerve-fibres 



1 This is tlie arr.an£remei;t in most vertehnited animals. In the frog the 

 axifl-cylinder branches out without entering a distinct motor end-pla^e. 



