494 THE NERVOUS SYSTEM. 



anterior and posterior branch, each containing 1 fibres from 

 both the roots (fig. 141). 



According to Kolliker the posterior root-fibres of the 

 cord enter into no connection with the nerve-corpuscles in 

 the ganglion, but pass directly through, in one or more 

 bundles, which are collected into a trunk beyond the gan- 

 glion, and then join the motor root. From most, if not all, 

 of the ganglionic corpuscles, one or two, rarely more, 

 nerve-fibres arise and pass out of the ganglion, in a peri- 

 pheral direction, in company with the posterior root-fibres 

 of the cord. Each spinal ganglion, therefore, is to be 

 regarded as a source of new nerve-fibres, which Kolliker 

 names ganglionic fibres. The destination of these fibres is 

 not yet determined : probably they pass especially into the 

 vascular branches of the nerves which they accompany. 



The anterior root of each spinal nerve arises by nume- 

 rous separate and converging fasciculi from the anterior 

 column of the cord ; the posterior root by more numerous 

 parallel fasciculi, from the posterior column, or, rather, 

 from the posterior part of the lateral column ; for if a 

 fissure be directed inwards from the groove between the 

 middle and posterior columns, the posterior roots will 

 remain attached to the former. The anterior roots of each 

 spinal nerve consist exclusively of motor fibres; the 

 posterior as exclusively of sensitive fibres. For the know- 

 ledge of this important fact, and much of the consequent 

 progress of the physiology of the nervous system, science 

 is indebted to Sir Charles Bell. The fact is proved in 

 various ways. Division of the anterior roots of one or 

 more nerves is followed by complete loss of motion in the 

 parts supplied by the fibres of such, roots ; but the sensa- 

 tion of the same parts remains perfect. Division of the 

 posterior roots destroys the sensibility of the parts supplied 

 by their fibres, while the power of motion continues unim- 

 paired. Moreover, irritation of the ends of the distal 

 portions of the divided anterior roots of a nerve excites 



