CH. VII.] END-PLATES 95 



sections stained by osiiiic acid, the black rings being the stained 

 medullary sheaths (fig. 123). 



The non-medullated fibres or fibres of Remak have no medullary 

 sheath, and are therefore devoid of the double contour of the medul- 

 lated fibres, and are unaffected in appearance by osmic acid. They 



Fio. 124. Grey, or non-medullated nerve-fibres. A. From a branch of the olfactory nerve of the 

 sheep ; two dark-bordered or white fibres from the fifth pair are associated with the pale olfactory 

 tibres. B. From the sympathetic nerve, x 450. (Max Schultze.) 



consist of an axis cylinder covered by a nucleated fibrillated sheath. 

 They branch frequently. 



Though principally found in the sympathetic nerves, a few are 

 found in the spinal nerves mixed with the medullated fibres. 



Termination of Nerves in Muscle. 



In the voluntary 'muscles the motor nerve-fibres have special end 

 organs called end-plates. The fibre branches two or three times (figs. 

 120, 125), and each branch goes to a muscular fibre. Here the 

 neurilemma becomes continuous with the sarcolemma, the medullary 

 sheath stops short, and the axis cylinder branches repeatedly. This 

 ramification is embedded in a layer of granular protoplasm containing 

 numerous nuclei. Considerable variation in shape of the end-plates 

 occurs in different parts of the animal kingdom. Somewhat similar 

 nerve-endings are seen in tendon; these, however, are doubtless 

 sensory (figs. 126, 127). 



In the involuntary muscles, the fibres which are for the most part 

 non-medullated form complicated plexuses near their termination. 

 The plexus of Auerbach (fig. 128) between the muscular coats of the 

 intestine is a typical case. Groups of nerve-cells will be noticed at 

 the junctions of the fine nervous cords. From these plexuses fine 

 branches pass off and bifurcate at frequent intervals, until at last 

 ultimate fibrillae are reached. These subdivisions of the axis cylinders 

 do not anastomose with one another, but they come into close relation- 



