LESSON XIV. 



NERVE FIBRES. 



1. Spinal Nerves. Cut off J to f of a centimetre 

 of a small, perfectly fresh nerve (e.g. a branch of the 

 sciatic of a frog), and place it on a glass slide without 

 any fluid. Fixing one end by pressing on it with the 

 blunt end of a scalpel, pass a needle through the other 

 end in the direction of the nerve fibres, and so spread 

 them out into the shape of a fan ; add a drop of normal 

 saline solution, and cover with the cover-slip. Observe 

 (h. p.) 



The medullated nerve fibres of variable size; 

 about 3/4 to 18/z in diameter. Measure some (Less. 

 IV.). 



In each fibre the double contour, due to the 

 medullary sheath. 



The primitive sheath or neurilemma; this is 

 seen with difficulty except at points where the me- 

 dullary sheath has been displaced in mounting. 



The nodes ; these will be seen as short but distinct 

 breaks in the medullary sheath. 



Drops and fragments of the medullary sheath, 



