NERVE-ENDINGS. 313 



the nerve fibre enters the muscle fibre. The axis cylinder 

 breaks up into an end arborization. The relation of this to 

 the protoplasm of the muscle fibre is described variously by 

 different authors. According to some, it lies on the sar- 

 colemma. Other authors who believe that the sarcolemma 

 and the sheath of Sehwann fuse together, hold that the end 

 arborization of the axis cylinder lies under the sarcolemma 

 in immediate contact with the sarcoplasm. There can often 

 be observed at the place where the nerve fibre enters the 



FIG. 236. 



Motor nerve-endings in striated muscle fibres (abdominal muscle) of a rat. X 170. 



muscle fibre an elevation, which in optical section has the 

 form of a hillock. This was observed first by Doyere in the 

 muscles of insects, and hence is known as Doyere' s hillock. 



The end arborization of the axis cylinder varies in form 

 according to the animal in which it is observed. In amphib- 

 ians the branches are more or less straight and simple (Fig. 

 230) ; in reptiles, birds, and mammals, on the contrary, they 

 are S-shaped (Fig. 231). 



Around the end arborization there is a larger or smaller 

 quantity of a finely granular substance, which is called the gran- 

 ulosa or granular bed. Authors differ as to the significance of 



