92 



HANDBOOK OF PHYSIOLOGY. 



the following parts :-(!.) An external sheath called ft* primitive nerv 

 sheath, or nucleated sheath of Schwann; (2.) An intermediate or pad 

 ing substance known as the medullary or myelin sheath, or white su" 

 stance of Schwann; and (3) internally the axis-cylinder, primitive bane 

 axis band, or axial fibre. 



Although these parts can be made out in nerves examined soir 



ie alter death, m a recent specimen the contents of the nerve-shea! 



appear to be homogeneous. Lut by degrees they undergo changes whic 



M.Ncui-cn^ 



S-tfeuronJS. 



^4^^ 



/ 



a kind of coaguation At tl 



ou sl y tra D spaL i d H 1 ^7^^ f ' 



