xt 



FUNCTIONS OF NERVE ROOTS 



471 



root to the spinal cord. Hence the nerve-cells of the 

 ganglion appear to be lateral appendages of the nerve- 

 fibres, forming a junction with them after the fashion of 

 a T-piece. On the central side of the ganglion the fibres 

 continue their course into the substance of the spinal 

 cord towards the posterior horn. Like the motor 

 nerves they lose their neurilemma as they enter the 

 cord. The majority of them turn aside as they enter the 

 cord and run upwards in the posterior column of the cord 



Fio. 151.— A Nerve Cell from the Ganomov ok thk Postertor Root 

 OK A [Spinal Nerve. 



The nerve cell, with n, nucleus, 71', nucleolus, p, protoplasmic body; 

 f, capsule of the nerve cell ; n", nuclei of the capsule ; n.f. the nerve 

 fibre which, at the node, d, divides into two. At a the neuraxis of the 

 fibre is lost in the substance of the cell ; at b it acquires a medulla; at 

 n'" nuclei are seen on the fibre. At. the division the neuraxis J is seen 

 to divide, and besides the neurilemma, n.l., the fibre has an additional 

 sheath, s, continuous with the capsule tif the nerve cell. 



to the brain. On their way thither the fibres give off 

 numerous branches called collaterals ; these are fine 

 medullated fibres, they pass into the grey matter of the 

 posterior horn and if their connections were traced ihey 

 would lead for the most part to cells of the anterior horn 

 or those of Clarke's column. They or their connections 

 end in contact with these cells (A Fig. 150). Some of the 

 posterior root fibres cross the cord and connect with 

 neurons which ascend the opposite side. Therefore an 

 impulse started in the skin would ultimately pass from 

 the sensory neuron in either one or more of three direc- 

 tions : (1) To the sensory portion of the brain, (2) To 



