Metazoa Rana, 



FlG. 171. NON-MEDtTLLATED NERVE-FIBRES. 



(Schafer.) 



is spoken of as the medullary sheath, 

 and fibres which possess it are 

 spoken of as medullated fibres. ' 

 Many nerve- fibres, however, are non- 

 medullated, and in that case possess 

 only the outer sheath, or neuri- 

 lemma, which corresponds to the 

 sarcolemma of the muscle-fibre, and 

 with which it is homologous. 



Nerve-cells are extremely vari- 

 able in size and shape. They are, 

 however, usually branched, and are 

 termed unipolar, bipolar, or multi- 

 polar, according to the number of 

 poles or branches they possess. The 

 poles are continuous 



