THE SPINAL NERVES 297 



root are outgrowths of cells in the ganglion of that root, as indi- 

 cated in Fig. 87. This accounts for the arborization of the differ- 

 ent fibers around cells in the cord instead of an actual connection 

 with them. These facts should not be lost sight of though it is 

 customary to speak of an efferent fiber as passing directly to a 

 cord cell itself. The anterior root is entirely motor except for 

 a degree of "recurrent" sensibility which is due to the presence 

 in it of posterior root fibers which have passed backward from 

 the point of junction of the two probably to supply the mem- 

 branes of the cord. The common trunk is, of course, mixed, as 

 are the anterior and posterior branches passing from it. 



These spinal nerves are distributed to the muscles of the trunk 

 and extremities, to the integument of almost the entire body 

 and to some mucous membranes; and from what has been said 

 in speaking of the cord about the connection between it and 

 these nerves, and their connection through it with the higher 

 centers, it is evident that they are most important factors which, 

 acting under the guidance of the sensorium, on the one hand, 

 tell of the condition of the organism its relations and environ- 

 ments and, on the other, control the voluntary movements of 

 the body. 



The spinal nerve fibers come in part directly from the brain 

 and in part from the gray cells of the cord. 



THE SYMPATHETIC SYSTEM. 



The sympathetic has been separated from the cerebro-spinal 

 system only for the sake of convenience. The former sends 

 filaments to the latter and receives both motor and sensory fibers 

 in return, while the cooperation of the two systems, regulating in 

 harmony all the physiological processes going on in the body, 

 is too evident to be questioned. 



The sympathetic system is remarkable for the number of 

 ganglia connected with it. These may be divided into (a} those 

 along the vertebral column, as the thoracic, (6) those in close 



