104 



PHYSIOLOGY OF Ml'SCLKS AND M'.KVKS. 



striation, as though it were formed of very delicate 

 fibrillnp, or small tilnvs. It is called the a.i-is-lxi n<L < <r 

 (/o'x-rv// //''. The outer part li;is a crumpled appear- 

 ance, and oo/es at the cut ends of the nerve in drops 

 which soon coagulate; it is called the medullary, or 

 marrow-she ith. The medullary sheath entirely sur- 

 rounds the axis-cylinder; as, however, when in a fresh, 



nncoagnlated condition, it re- 

 fracts light in exactly the same 

 way as the axis-cylinder, it 

 is undistinguishable from the 

 latter, nor do the two become 

 really separately visible till 

 after the conn- Ration of the 

 marrow. The medullary- 

 sheath and the axis-cylinder 

 are further enclosed in a 

 tough elastic tube, which is 

 called the neurilemma or 

 nerve-sheath. 



These three parts are not 

 present in all peripheric 



Q . , , 



Some of the latt.'l 



met j u l] ;ir y <!,,.;,,],, 



and are, therefore, avi>-cylinders immediately sur- 

 rounded by the nerve-sheaths. When many nerve- 

 liln-es are united into a bundle, these marrowless fibres 

 are ^r rev and more t ransjiarent, and ;,re therefore some- 

 times called grev ner\c-libres. Those nerve-tibres which 

 have medtillarv sheaths appear more yellowish white. If 

 the nerves are traced to the periphery, more and more 

 nerve-fibres are continually found to branch off from 

 the common stem, so that the branches ami brailchlets 



FIG. -2.;. NKI:VI: 



a a ,, axte-cylinder, still parly 



Bnirounded by the medullary flheath. 



