PRINCIPLES Of Veterinary surgery 31 



myelin sheath also breaks down into small fragments and 

 particles, and the nuclei of the sheath of Schwann begin an 

 active cell proliferation. They swell up and seek the centre 

 of the nerve fibre among the fragments of myelin, forming 

 small cellular tubules at various intervals apart. Regenera- 

 tion begins long before the retrogressive changes are com- 

 plete, and is accomplished by an outgrowth of the axis- 

 cylinder of the central end, which splits up into several small 

 fibrils, often spiral, and sometimes one coiled within the 

 other. These early receive a covering of delicate medullary 

 sheaths, and may enter the old sheaths of the peripheral por- 

 tion of the nerve and there complete their structure. How- 

 ever, they may also extend into the adjacent tissue. This is 

 more likely to occur if much scar-tissue has formed in the 

 healing of the wound, the cicatrix preventing the downward 

 growth of the fibres. 



The cells of the sheath of Schwann are connective-tissue 

 cells and their functions in the regeneration of nerve seem 

 to be phagocytic, rather than forming a part of the neurones 

 proper. (Hektoen). 



When a section of a nerve is removed or when a limb 

 is amputated, the axis-cylinders may permeate the scar tis- 

 sue of the wound in every direction and form a very sensitive 

 scar which has been erroneously included among the true 

 tumors. In human surgery it is designated as "amputation 

 neuroma." The so-called neuroma following. neurotomy of 

 the plantars is an example of this regenerative process. It 

 is an unsuccessful effort to restore the function of the cut, 

 nerve. The axis-cylinders, in their effort to grow into the 

 unnerved area, become lost in the intervening cicatrix. 



The regeneration of nerves has been the subject of nu- 

 merous clinical and experimental observations which have 

 yielded a fairly accurate knowledge of the process. It is now. 

 well known that a divided nerve trunk will slowly re-estab- 



