Spinal Nerves 



215 



the anterior containing motor, and the posterior sensory fibres. The 

 posterior, the larger root, has a ganglion upon it just as has the 

 posterior or sensory division of the fifth cranial nerve. Just beyond 

 the ganglion, which lies in the inter-vertebral foramen, the roots join. 

 The mixed nerve then breaks into an anterior and a posterior primary 

 division, each of which contains both motor and sensory fibres. The 

 posterior primary divisions pass backwards to supply the erector 

 spinae and other muscles, and to carry sensory twigs to the back of the 

 head, neck, and trunk, whilst the anterior divisions end, for the most 

 part, in plexuses, except in the dorsal region, where they run forwards 

 in the intercostal spaces. 



Nerve-roots. The filaments of the anterior root arise from the 

 ganglionic cells in the anterior cornu 

 of the grey crescent and pass out 

 to the muscles. They are zmder 

 the control of the motor strands 

 descending from the brain in the 

 direct cohtmns of Tiirck and in the 

 crossed Pyramidal tracts. 



In the posterior root, which is 

 afferent, or sensory, are also fila- 

 ments which preside over the nutri- 

 tion of the skin trophic filaments 

 (rpe$o), nourish). Bed-sores are apt 

 to occur when the function of the 

 posterior roots is disturbed as when 

 disease or pressure interferes with 

 the posterior columns. When the 

 anterior roots or columns, however, 

 are in distress, as in angular curva- 

 ture of the spine, dermal trophic 

 changes are conspicuous by their 

 absence. 



Of the fibres of the posterior 

 root some straightway enter the tail 

 of the grey crescent, but others pass D.C\ 



\Q.C 



into the pOSterO-extemal Column Of D c, direct cerebellar tracts ; c p, crossed 



Burdach, as shown in the adjacent 



diagram. All these sensory fibres 



pass over into the opposite half of 



the cord, and so up to the brain. 



If, therefore, the right half of the 



cord be destroyed, there is loss of 



sensation in the parts below on the left side of the body, the motor 



paralysis being on the right side, for the motor strands cross in the 



medulla oblongata (p. 55) and not in the cord. In the case of a lesion 



pyramidal tracts ; G, Coil's sensory 

 columns ; T, direct pyramidal (motor) 

 tracts Turck's columns ; M, motor ; 

 s s', sensory roots of spinal nerve ; of 

 these sensory filaments some pass 

 through the posterior cornu of the grey 

 crescent, and some through postero- 

 external or Burdach's column. (After 

 RANNEY.) 



