CH. XVII.] THE AUTONOMIC NERVOUS SYSTEM 197 



arranged, and these ganglia are called the vertebral or the lateral 

 ganglia. 



In connection with the lateral chain are other outlying ganglia, 

 such as the semilunar ganglion, from which the coeliac plexus takes 

 origin ; the superior mesenteric ganglion, and the inferior mesenteric 

 ganglion, from which the hypogastric nerve takes origin. These 

 outlying ganglia are called the collateral or the prevertebral ganglia. 

 These differ from the lateral ganglia in not sending any fibres back 

 to the spinal nerves; their fibres pass onwards to the thoracic, 

 abdominal, and pelvic viscera. 



Finally, there are ganglia situated in the walls of the organs 

 themselves, as, for instance, those in the heart wall, and those in the 

 plexuses of the wall of the alimentary canal (the plexuses of 

 Auerbach and of Meissner). By some, these ganglia are included 

 with the collateral ganglia, but it appears better for descriptive 

 purposes to speak of them as Gaskell does, as a third group, and 

 name them the terminal ganglia. 



The sympathetic system thus consists of three sets of ganglia 

 with strands connecting them together, and all come into ultimate 

 connection with fibres which leave the spinal cord. 



There is, however, another set of ganglia which are related 

 anatomically in a similar way to some of the cranial nerves, and 

 physiologically with the involuntary muscles and glands in the head 

 region as well as with some of the thoracic and abdominal organs. 

 Thus we have the ciliary ganglion in connection with the third 

 cranial nerve; then there are such ganglia as the spheno-palatine, 

 otic, and submaxillary, in connection with other cranial nerves. 



It has been considered wise not to extend the terra sympathetic 

 to these, but to include both them and the sympathetic system under 

 one common term, and Langley's suggestion that this word should be 

 autonomic has been very generally adopted. The word indicates 

 that they possess a certain power of self-government, and are to 

 some extent, at any rate, independent of the central nervous system. 



The impulses that pass to the involuntary musculature of the 

 body arise in the central nervous system, and travel to the ganglia 

 of the autonomic system by means of fine medullated nerve-fibres ; 

 the diameter of these fibres varies from 1-8 to 3-6 /*; the fibres 

 therefore contrast with the motor fibres which pass to voluntary 

 muscles; the diameter of these being 14 to 19 /x (see fig. 95, p. 77). 

 There is a further contrast in the two cases; the motor fibres to 

 voluntary muscles pass uninterruptedly from the brain or cord until 

 they terminate in the end-plates of the voluntary muscles. The 

 autonomic fibres, on the other hand, terminate by arborising around 

 cells in one or other of the autonomic ganglia, and from the ganglion 

 cells a fresh relay of nerve-fibres carries on the impulse to the 



