SYMPATHETIC NERVOUS SYSTEM. 253 



name. They supph^, also, vasodilator fibers to rectum and anus 

 and motor fibers to the plain muscles of the colon, rectum, and 

 anus. The preganglionic parts of these fibers end in small sympa- 

 thetic ganglia in the pelvic plexus or in the neighborhood of the 

 organs supplied. 



Normal Mode of Stimulation of the Autonomic Werve Fibers. 

 — In distinction from the nerve fibers innervating the skeletal 

 muscles practically the whole set of autonomic fibers is removed 

 from the control of the will. An apparent exception to this general 

 statement is found in the fact that the ciliary muscle of the eye is 

 seemingly under voluntary control. We must suppose that under 

 normal conditions the autonomic fibers are always excited 

 reflexly, and the course of the afferent fibers concerned in these 

 reflexes and the nature of the effective sensory stimulus in 

 each case are important in the consideration of each of the 

 physiological mechanisms involved. The autonomic nerve-fibers 

 control, therefore, the unconscious co-ordinated actions, the so- 

 called vegetative processes, of the body. We are justified in saying 

 that nerve paths that pass through sympathetic nerve cells can- 

 not be excited voluntarily; but the immediate reason for this fact 

 is probably to be found in the ultimate point of origin of these 

 paths in the central nervous system. What we designate as vol- 

 untary motor paths arise in a definite region of the cortex — the 

 motor area in the frontal lobe. Our motor conceptions or ideas 

 can affect the efferent paths arising in this region, but not those, 

 apparently, which originate in other parts of the brain. On the 

 other hand, much recent work* has emphasized the important fact 

 that strong emotional states, such as fear, anger, joy, etc., stimulate 

 the autonomic system, giving rise to changes in the heart-rate, 

 blood-pressure and internal secretions, and causing movements of 

 the bowels, bladder, etc. 



* See Cannon, "Bodily Changes in Pain," etc., 1915. 



