GROWTH OF CRANIAL FIBRES INTO GANGLIA. 691 



valuable work on this subject, considers that the skin areas of the body 

 correspond to segments of the spinal cord, and not to the peripheral 

 distribution of the posterior roots. 



Ross, as we said, supposed that the visceral fibres affect the cutaneous 

 fibres by some action on the grey matter of the spinal cord. This sup- 

 position does not at present rest on any satisfactory histological basis. 



If the arrangement suggested by Dogiel (cf. p. 686) exists, it affords 

 a fairly satisfactory basis for explaining the referred pain in visceral 

 disease, so far as regards the trunk of the body. For referred pain in 

 the head, however, an explanation based on some action in the central 

 nervous system does not seem avoidable. 



It must be borne in mind that a transference of impulses might take place 

 in the spinal ganglia in other ways than that just mentioned, for example, by 

 the collaterals which some of the nerve fibres are said to give off to the cells of 

 the spinal ganglion. And it may be noticed that, so far as we know, diseases of 

 the viscera do not cause referred pain in the muscles, and that diseases in the 

 areas of the somatic nerves do not cause referred pain in the viscera. 



Growth of Pke-Ganglionic Cranial Fibres into Sympathetic 



Ganglia. 



We have seen (p. 652) that the pre-ganglionic fibres of the sym- 

 pathetic, after section, readily re-form connections with sympathetic 

 nerve cells. We have seen also that the fibres may in certain circum- 

 stances form connections with sympathetic nerve cells of a different 

 class. The general similarity which exists between all pre-ganglionic 



X 



S.C&. °V Sy 



Fig. 318. 



fibres suggested the possibility that cranial autonomic fibres might be 

 able to form synapses with sympathetic cells. And experiment has 

 shown that this is in fact the case. 1 If the central end of the vagus be 

 joined to the peripheral end of the cervical sympathetic (as in Fig. 318), 

 it will in about a month make connection with the cells of the superior 

 cervical ganglion of such nature that stimulation of the peripheral end of 

 the nerve will cause dilatation of the pupil, contraction of the vessels of 

 the ear, and the other effects which are normally produced by stimula- 

 tion of the cervical sympathetic itself. In this formation of new con- 

 nections some of the fibres of the vagus must change their function ; 

 since there are normally no pilo-motor fibres in the vagus, and some are 

 found in it after union with the cervical sympathetic. 



Probably a more striking instance of change of function is afforded 

 by joining the central end of the lingual nerve 2 with the peripheral end 

 of the cervical sympathetic. The lingual nerve contains vaso-dilator 

 and secretory fibres derived from the chorda tympani. After it has 

 been allowed time to unite with the cervical sympathetic, it is found on 

 stimulation to cause, amongst other effects, constriction of the arteries of 

 the ear. It is difficult here to avoid the conclusion that some of the 



1 Langley, Proc. Roy. Soc. London, 1898, vol. lxii. p, 331 ; Jowrn. Physiol., Cambridge 

 and London, 1898, vol. xxiii. p. 240. 



2 One experiment only of this nature has as yet been made. 



