THE SYMPATHETIC SYSTEM. 



2I 3 



devised. It is also uncertain as yet whether these fibers run from 

 one of the chain ganglia to a more peripheral ganglion or from a 

 more peripheral to a more proximal ganglion. The important 

 question regarding these endings is whether the visceral excitatory 

 chain consists of more than two links. The physiologists claim 

 that only one sympathetic cell intervenes in any case between 

 the efferent cerebro-spinal fiber and the muscle or gland innervated. 

 The existence of sympathetic endings in sympathetic ganglia, if 

 clearly established, would seem to show that in some cases two 

 such neurones enter into the excitatory chain. 



(4) Sympathetic sensory cells. Certain cells in the peripheral 

 ganglia, as in Auerbach's plexus, have longer dendrites than 

 those of ordinary sympathetic cells and these dendrites are sup- 

 posed to be distributed to the mucosae and to serve as sensory 

 fibers. The neurites of these cells pass through one or more 

 sympathetic ganglia to which they give branches. These branches 



Symp. g. 



Inf.mes.gangr^' 



Postg. fiber 



Fig. no. A diagram to illustrate Langley's "axone reflex". After Langley. 

 Preg. fiber, preganglionic fiber; Postg. fiber, postganglionic fibers; Inf. mes. gang., 

 inferior mesenteric ganglion; b, bladder. 



enter into the plexus of dendrites in the ganglion and may serve 

 to arouse peripheral reflexes by stimulating the excitatory cells 

 in the ganglion. It is stated as probable (Dogiel) that these 

 neurites run on through the gray rami communicantes and form 

 the pericellular endings which are known to occur in the spinal 

 ganglia of several classes of vertebrates. These are complex 

 endings immediately around the bodies of certain spinal ganglion 

 cells which are described as cells of type II. These second type 



