648 SYMPATHETIC AND OTHER SYSTEMS OF NERVES 



gastric nerves after section of the roots of the lumbar nerves. 1 And 

 this is, no doubt, also the case with the solar ganglion ; some fibres traverse 

 it and run to small peripheral groups of ganglion cells, such as those 

 which occur in the pancreas. Whether such fibres send a branch to the 

 main pre-vertebral ganglion, as they traverse it, requires experiments of a 

 different kind to determine (cf. p. 679). We may for the present regard 

 the splanchnic and inferior splanchnic nerve fibres as arranged as in 

 Fig. 313 ; the great majority, as in A ; comparatively few, as in B ; and 

 possibly, occasionally, a few as in C. 



It has long been known that the major splanchnic contains a con- 

 siderable number of non-medullated fibres, and it is in large part this 

 fact which has led to the unquestioned belief that the ganglia of the 

 sympathetic chain send fibres to the solar ganglia or to the abdominal 

 viscera. It is a priori possible that the non-medullated fibres in the 

 splanchnic nerve should arise from the solar ganglion and run to the 

 ganglia of the sympathetic chain, or to their grey rami. But this 

 possibility I put on one side, since I have not observed any pilo-motor, 

 vasomotor, or other similar effect, on stimulating the central end of the 

 splanchnic nerve after removal of the spinal cord. If, then, the view I 

 have given above be accepted, namely, that very few if any fibres pass 

 from the cells of the vertebral ganglia to the splanchnic nerves, we 

 must take the non-medullated fibres to be pre-ganglionic fibres which 

 have lost their medulla (cf. p. 650). 



The Nerve Fibres of the Sympathetic System. 



Distribution of medullated and of non-medullated fibres.— A strik- 

 ing feature of the sympathetic system is the predominance of small 

 medullated fibres in it. This was pointed out by Bidder and Volk- 

 mann 2 in 1842. The great majority of its medullated fibres vary 

 from 2 ijj to 3*5 n in diameter. 



Other larger medullated fibres are present to about 12 [i. These 

 vary in number in the different strands, and although all sizes, from 3 - 5 

 to 12 //,, occur, they may, broadly speaking, be divided into two classes — 

 medium-sized fibres about 5 >x, and large fibres of about 8 (i. The size of 

 small, medium, and large vary somewhat in different animals. Very large 

 medullated fibres, 15 to 20 ,«,, which are common in the roots of the spinal 

 nerves, do not occur in the sympathetic system. 



The large fibres of the sympathetic occasionally divide. In this case 

 the branches are of somewhat less diameter than the parent fibre. Most 

 of the large fibres in the cat can be traced to Pacinian bodies. 



In the trunk of the sympathetic the large and medium fibres are 

 most numerous in the lower dorsal and upper lumbar regions. Here, 

 too, they are somewhat larger than in the lower lumbar region. Most of 

 them pass outwards in the superior and inferior splanchnics. Below 

 the lowest inferior splanchnic strand, there are few fibres larger than 

 5 jjj in diameter, and they diminish in number in passing downwards. 

 In the cervical sympathetic there are sometimes a few medium and 



1 Langley and Anderson, Joum. Physiol., Cambridge and London, 1894, vol. xvii. 

 p. 183. 



2 " Die Selbststandigkeit dessympathischen Nervensystems," Leipzig, 1842. Numerous 

 observations of the size of the medullated fibres in the different nerves of vertebrates are 

 here given. 



