534 



THE NEKVOUS SYSTEM 



PATH "II." The second subdivision of the dorsal nerve 

 roots includes many fibres and collaterals from the dorsal root 



fibres which enter the 

 grey matter 

 medio - lateral 



the 



from 



root zone 



and pass directly to the 

 ventral horns, where they 

 end in relation with the 

 dendrites or cell bodies of 

 the large motor cells. This 

 group of fibres forms the 

 great pathway for reflex 

 impulses. It includes de- 

 scending branches of the 

 peripheral sensory neu- 

 rones as well as collaterals 

 from many of their as- 

 cending branches. 



PATH "III." Begin- 

 ning in the lumbar region 

 and extending upward 

 through the greater por- 

 tion of the thoracic spinal 

 cord is a sharply defined 

 oval cell column, situated 

 in the grey matter at the 

 base of the dorsal horn 

 where it joins the grey 

 commissure on either side 

 of the median line ; this 

 group is the "vesicular 

 cell column of Lockhart 

 Clarke." 



In the lower lumbar 



scending, ?, branch from both of which numerous and SaCral regions a simi- 

 collaterals, A, enter the grey matter and terminate larly situated but Smaller 

 in fine end brushes. The peripheral branch of the an( j ] egs we jj d e fi ne d group 

 spinal ganglion cell enters a spinal nerve and finds . . 

 its way to its termination which is here represented of nerve cells IS found 111 

 in the. skin; it terminates partly by free endings the base of the dorsal 

 among the epithelial cells, *, and partly in connec- \* nrn ~ flT1( i forms thp mo- 

 tion with a sensory end organ, *, in this case a tac- nOrnS > 3 

 tile corpuscle of Meissner. (After von Lenhossek.) Called " nucleus of Still- 



FIG. 410. DIAGRAM or THE ORIGIN AND RELATIONS 



OF THE PERIPHERAL MOTOR AND SENSORY NEU- 

 RONES. 



A cylindrical section of the spinal cord, with 

 its ventral and dorsal nerve roots, is shown, a, nerve 

 cell of the ventral horn whose neuraxis passes 

 through the ventral nerve root, J, to its peripheral 

 termination, c; at rf, is a unipolar sensory nerve 

 cell in the dorsal root ganglion : its process imme- 

 diately divides into a peripheral and a central 

 branch. The central branch enters the spinal cord 

 and at 0, divides into an ascending, /, and a de- 



