THE VASOMOTOR NERVES. 



599 



of the trunk and extremities pass from the ganghon to the cor- 

 responding spinal nerve by way of the ramus commumcans gray 

 ramus) and after reaching the spinal nerve they are distributed with 

 it to its corresponding region (Fig. 251). In the general region 



Fig. 252.-Vasomotor effect of stimulation of the s,,lanchnio nerve-peripheral e^^ 



\n ihVf\no- (Dawson)- 1 The Una of zero pressure; 2, tlie hne of the stimulating pen, on 



^nrlo/marktL beginning an l end of the stimulation ;. 3, the tune record m seconds; 4. 



owing to the constriction of its arterioles. 



under consideration (lower cervical to upper lumbar) each ramus 

 communicans between a spinal nerve and a sympathetic ganglion 

 consists, therefore, of two parts, one (white ramus) of preganglionic 

 fibers passing from the spinal nerve to the ganglion, the other 

 (gray ramus) of postganglionic fibers coming from the ganglion to 

 the spinal nerve for distribution to the peripheral tissues. It should 

 be borne in mind that the fibers in the wliite ramus do not 

 return to the spinal nerve by the gray portion of the same ramus. 



