THE AUTONOMIC NERVE SYSTEM 657 



Lar the group of nerve-cells which gives origin to the nerve-fibers for the sphincter 

 luscle of the iris. It is also believed that the accelerator nerves for the heart 

 Ihich emerge from the spinal cord in the second and third thoracic nerves come 

 lorn a center lying in the bulbar region not far from the center from which the 

 ihibitor fibers in the vagus come. 



Nevertheless there are other instances in which this antagonism does exist, e.g., 

 I the effects of the efferent fibers of the vagus and the splanchnic nerves on the 

 Jtuscle-wall of the intestine, the former augmenting, the latter inhibiting the con- 

 J action and so in other regions. But this does not necessitate the employment of 

 jw terms. It suffices to say that there is a difference in the action of different 

 arts of the general autonomic system. It is just as probable, however, that the 

 difference in the effects observed following stimulation of the two classes of nerves 

 epends on the character of their peripheral terminations rather than on a differ- 

 nce in the character of the central cells. 



Huber, in a recent review of the morphology of the sympathetic system, says 

 ,1 regard to the foregoing division, "such a division of the autonomic nerve system 

 oes not seem justifiable when viewed in the light of a morphologic study of the 

 anglia with their constituent neurons, the terminations of the neuraxis of the 

 .eurones in the various tissues, and the connections of these neurones with the 

 erebrospinal axis by means of the pre-ganglionic fibers; morphologically con- 

 idered, the entire autonomic system is- a unit and will be treated as such. The 

 ninor structural differences, more apparent than real, observed in the neurons of 

 :ertain of the cranial autonomic ganglia and in the entire system, do not warrant, 

 t would seem to me, a regional subdivision of the autonomic system, whencon- 

 idered from the viewpoint of structure." 



