392 NEKVOUS ACTION. 



definite number of fibres at its point of origin from the 

 nervous centre, and has neither more nor less at its peri- 

 pheral extremity, each fibre passing in an unmodified con- 

 dition from its origin to that part of the tissue or organ in 

 which it is destined to ramify. Nerves, it is true, frequently 

 become connected or anastomose with each other, but this 

 union results alone from an interchange of fibres, while 

 each of these continues to maintain its distinct individuality. 

 The anastomoses of nerves is thus principally intended to 

 ensure a wider distribution of nervous fibres coming from 

 the same centre, and to obviate to some extent the occur- 

 rence of paralysis from injury to a single centre or nervous 

 trunk. Where a free anastomosis of this kind take place 

 between a number of nerves, the structure is known as a 

 plexus. 



Eegarding the origin of fibres in a nervous centre, there 

 is some difference of opinion. Some anatomists assert that 

 the fibres form loops which lie in the grey substance and 

 in contact with the nerve-cells, with which, however, they 

 have no direct structural connection. On the other hand 

 it ha.s been clearly demonstrated that in the ganglia the 

 fibres arise directly from the tails of the caudate (stellate) 

 cells, and Schroder van der Kolk and others have satis- 

 factorily shown that a similar origin is at least frequent in 

 the spinal cord. 



The modes in which nervous fibres terminate in the 

 tissues are varied. The nerves commonly break up into 

 small branches, which arrange themselves in plexuses, and 

 from these individual fibres are given off to terminate as 

 follows : 1st, In loops, a single fibre bending backward in 

 the substance of the tissue and entering either the same 

 or an adjacent nervous trunk, in which it is understood to 

 follow a retrograde course to the nervous centre ; 2d, Some- 



