CHAPTER VIll 



THE NERVOUS SYSTEM 



Ev«iry 'nerve' or nerve-trunk is composed of a number of 

 fibres arranged in bundles and separated by connective tissue. 

 The fvmctional jiart of the nerve fibre is called the axon, and this 

 in medullated nerves is surrounded by an insulated jacket com- 

 posed of phosphorised fat and called the medulla or myelin. The 



Fig. 45. Section through sciatic nerve of cat showing con- 

 stituent fibres of different sizes (from Schafer). 



medulla is broken at certain intervals to admit of the passage 

 of nutriment to the axon from the tissue outside. The axons 

 are extensions of nerve cells, and a nerve cell may have a number 

 of such extensions. The name 'neuron' is given to a nerve cell 

 together with all its extending axons, and the whole of the 

 nervous system is composed of vast numbers of neurons. 



