102 NERVE. [CH. vn. 



the sympathetic ganglia, whence they emerge as non-medullated 

 fibres, and are distributed to involuntary muscle. They are well 

 seen in sections stained by osmic 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 medullated fibres, and are unaffected in appearance by 



Fig. 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 asso- 

 ciated with the pale olfactory fibres. B. From the sympathetic nerve. X 450. (Max 

 Schultze.) 



osmic acid. They 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. 1 20, 125), and each branch goes to a muscular fibre. Here the 

 neurilemma becomes continuous with the sarcolemma, the medul- 

 lary 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. 



