370 PHYSIOLOGY CHAP. 



spending spinal nerves, \\hich then pass to the skin, but also send 

 fibres to the viscera (heart, lungs and their blood-vessels, salivary 

 glands). These two ganglia therefore give oft" visceral as well as 

 cutaneous fibres. 



The prevertebral or peripheral ganglia supply the viscera 

 exclusively, and send no fibres to the spinal nerves (Langley). The 

 inferior cervical ganglion sends fibres to the heart : the different 

 ganglia oi' the solar plexus serve the abdominal viscera ; the 

 inferior mesenteric ganglion sends fibres to the lower part of the 

 gut and the urogenital system. 



Langley brings out the striking fact that the ganglia of the 

 sympathetic system nowhere have a special arrangement according 

 to their function ; the cells are not divided into groups with 

 special functions, viz. for the contraction or the relaxation of the 

 unstriated muscles of the gut or arteries. The ganglia are rather 

 cell groups, whence the nerves run out to special regions to inner- 

 vate the whole of the organs controlled by the sympathetic in 

 that region indiscriminately. 



Fig. 197 illustrates diagrammatically the origin, course, and 

 peripheral distribution of the fibres of the sympathetic system. 



IV. Our present knowledge of the course and functional signi- 

 ficance of the afferent fibres of the sympathetic system is compara- 

 tively scanty and incomplete. Every one knows that the visceral 

 organs are sensitive, as violent stimuli can evoke pain, but under 

 normal conditions, the movements of the gut, of the iris, the secretory 

 processes, etc., do not affect consciousness, in other words the 

 afferent impulses that ebb and now in the sympathetic system do 

 not usually pass the threshold of consciousness. That such im- 

 pulses exist may safely be affirmed on the strength of the facts 

 before us, for histology has demonstrated the presence of special 

 sensory end -organs in the viscera, particiilarly the so-called 

 Pacinian corpuscles, which abound, for instance, in the cat's 

 mesentery. 



What, then, do we know of the origin and course of the 

 afferent sympathetic paths, and their relations to the sympathetic 

 ganglia ? Do all organs supplied with efferent sympathetic fibres 

 possess afferent fibres as well ? Do the afferent sympathetic fibres, 

 like the efferent, undergo a break in their passage through the 

 ganglia ? The answers to these important questions, which are 

 essential for a clear understanding of the complex structure of the 

 sympathetic system, will be found in Langley 's review of the 

 experimental work on this subject (1903). 



In this connection it is useful to separate the sympathetic 

 system, in the narrower sense, from the two other functionally 

 related autonomic systems, the bulbar and the sacral. While 

 these two supply afferent fibres to all the peripheral organs to 

 which they send efferent fibres, the same only holds for the 



