142 HUMAN PHYSIOLOGY 



of the posterior root. It joins an anterior root (A.R.) 

 coming from the antero-lateral margin. These form the 

 spinal nerve which is distributed to the body wall. Lying in 

 front of this is a swelling or ganglion (S.I.) joined to the 

 nerve by two roots, a white ramus ( W.R.) and a grey ramus 

 (G.R.)', and from this a nerve extends towards the viscera 

 (V.N.). Before this nerve reaches its final distribution it 

 passes through another ganglion. 



Roots of the Spinal Nerves. The posterior root is the 

 great ingoing channel to the spinal cord, and the anterior 

 root is the great outgoing channel. Section of a series 

 of posterior roots leads to (a) loss of sensation in the 

 structures from which the fibres come, and (b) to a loss 

 of muscular co-ordination, as a result of cutting off the 

 afferent impressions connected with the muscle sense 

 (p. 97). 



As a result of this section, the parts of the fibres cut off 

 from the cells of the ganglia on the posterior root die and 

 degenerate. Therefore if the root is cut inside the ganglion, 

 the degeneration extends inwards and up the posterior 

 columns of the cord, and if it is cut outside, the degeneration 

 passes outwards to the periphery. 



Section of the anterior root causes paralysis of the muscles 

 and other structures supplied by the outgoing fibres, and 

 these fibres die and degenerate. 



The nerve to the somatopleur or body wall (S.N.) is 

 composed of incoming and outgoing fibres. 1st, Incoming 

 fibres are medullated and take origin in the various peri- 

 pheral sense organs. As they pass through the ganglion on 

 the posterior root each fibre is connected by a side branch 

 with a nerve cell the trophic centre of the neuron and it 

 then enters the spinal cord, and, passing to the postero- 

 lateral column, it breaks up into an ascending branch and a 

 descending branch (Fig. 40, p. 89). 2nd, Outgoing fibres, 

 which are medullated, take origin from the large cells in the 

 anterior horn of the grey matter of the cord and pass on to 

 be connected with muscle fibres by end plates, or to gland 

 cells by less definite synapses. 



The nerve to the viscera or splanchnopleur (V.N.), and to 

 the involuntary structures in the somatopleur, contains 1st, 



