Elementary Biology. 



cord. Externally to the pia mater is a strong protective 

 sheath, which does not follow the pia mater into the fissures : 

 to this the name of dura mater is given. 



A nerve consists of a large number of ultimate nerve- 

 fibres bound together by connective tissue. The connec- 



FIG. 170. TRANSVERSE SECTION OF A LARGE NERVE. (Schaftr.) 



?', ?', blood-vessels ; end, endoneurium ; per, perineurium ; ep, epineurium. 



tive tissue receives different names according as it binds 

 together ultimate nerve-fibres (endoneurium), simple bundles 

 of nerve-fibres (perineurium), or compound bundles (epi- 

 neurium). An ultimate nerve-fibre consists of an axial 

 cylinder of nerve-fibrillse, surrounded by one or two 

 sheaths. The inner sheath, composed of a fatty substance. 



