100 PSYCHOBIOLOGY 



tubes ; to the gastric glands of the stomach, and possibly to the pancreas ; 

 and to the heart. The effect of vagus currents on the heart is solely in- 

 hibitory, i. e., decreasing the activity of the cardiac muscle. The distribu- 

 tion of the afferent fibers is not so clearly known. 



The pelvic or sacral visceral connections of the central nervous system 

 all run in the pelvic visceral nerve {nervus erigens), and are axons of 

 spinal cell-bodies. These fibers terminate in the pelvic ganglia, lying in 

 the neighborhood of the bladder, from which the further connections are 

 with the muscles of the bladder, colon, rectum and sexual organs (and the 

 blood vessels therein). 



3. Local nervous systems. 



The neurons described under 1 and 2 belong definitely to the central 

 nervous system, as will be explained below. There are, however, certain 

 groups of neurons which have not such direct connection with the cerebro- 

 spinal apparatus. These are the plexuses of Auerbach and of Meissner, 

 located in the walls of the alimentary canal from esophagus to rectum, 

 and serving as ' centers ' for the series of organs. They form, in other 

 words, an independent local system, with afferent and efferent fibers hav- 

 ing no necessary communication with the general nerve system. Stimu- 

 lation of the sensory terminals of neurons in this local system may there- 

 fore be transmitted by a relatively short circuit to the smooth muscle of 

 the coats of the gullet, stomach, and intestines. 



GANGLIA OF THE VISCERAL SYSTEM AND THEIR FUNCTIONS. 



Ignoring now the local visceral systems just described, we find that the 

 visceral system of neurons involves, in addition to the structures in the 

 spinal cord and the spinal ganglia, two sets of ganglia. 1. The chain of 

 lateral ganglia, and the collateral ganglia, of the ' sympathetic ' division ; 

 and 2, certain peripheral ganglia (i. e., ganglia located at a greater or less 

 distance from the cerebro-spinal apparatus) of the cranial, sacral, and 

 vagus visceral nerves. Among peripheral ganglia, for instance, are the 

 otic, orbital, submaxillary, and pelvic ganglia earlier mentioned. These 

 ganglia are sometimes called ' nerve centers ', and properly come under 

 one of the several meanings of that highly confusing term. But they are 

 not (and this is important), structures in which afferent currents are con- 

 verted into efferent currents. No reflex, in other words, can take place 

 through these ganglia alone ; the afferent current must go on into the cord, 

 even if it does not go up to the brain, before it can be redirected outward 

 to any of the effectors. The ganglia of the visceral nerves have merely a 

 distributory function. A current passing out from the spinal cord in an 

 axon which leaves the spinal nerve over the white ramus, is distributed, 



