554 Mr. J. N. Langley. On the Arrangement [Feb. 9, 



whenever the matter was tested the pilo-motor area of a cutaneous 

 branch was found to be supplied with sensory fibres from the same 

 branch ; that there is a certain amount of overlapping in the pilo- 

 motor areas of successive cutaneous branches ; and that the sym- 

 pathetic fibres of any given kind may have a rather less or rather 

 greater extension than the sensory fibres with which they run. 



Of the distribution of sympathetic fibres to muscles we have no 

 information, but, if the view I have given above is true, it establishes 

 a probability that such of these fibres as may run in a given grey 

 ramus to a nerve would have approximately the same distribution as 

 the muscular branches of the nerve. 



We have seen that at the origin of the nerves for the arm and for 

 the leg, one, two, or three grey rami contain no pilo-motor fibres. 

 Let us consider a simple case, say, when the 6th lumbar grey ramus 

 has no pilo-motor fibres. Five spinal nerves, the 12th, 13th thoracic, 

 the 1st, 2nd, 3rd lumbar, give off nerve-fibres, which leave the sym- 

 pathetic by each of the grey rami of six or seven ganglia in the 

 neighbourhood of, and including, the 6th lumbar ganglion.* Of this 

 series of rami, the 6th lumbar is about the last supplied by the 

 12fch thoracic, and about the first supplied by the 3rd lumbar nerve 

 (c/. table above). Further, each of these spinal nerves has abundant 

 pilo-motor fibres, and sends them to every ramus except the 6th 

 lumbar. Why is it that the pilo-motor fibres of each nerve skip this 

 particular ramus, skipping it wherever it comes in the series of rami 

 supplied by the nerve ? And, further, why do variations occur in 

 different animals, so that any one or all of the grey rami of the 5th, 

 6th, or 7th lumbar ganglion may have no pilo-motor fibres ? 



The proximate explanation I take to be that the sympathetic ganglia 

 develop in connexion with the spinal nerve-roots ; f that, as is now 

 generally believed, the number of consecutive nerve-roots passing 

 out in a particular spinal nerve varies ; that the sympathetic fibres 

 issuing from the sympathetic ganglion to run to the nerve follow 

 in the main the course of the nerve ; and that probably the connexion 

 of the ganglion with the cord by the white rami is a subsequent 

 event. The following diagram represents the chief points of this 

 explanation. 



A detailed account of the facts summarised above I hope to be 

 able to give in no long time, and then, also, I hope to deal with one 

 or two problems of the sympathetic system which I have omitted 

 here. 



Cf. Langley, ' Journ. of Physiol.,' vol. 12, p. 347, 1891. 



f According to Hi 8 and others, a common mass of cells gives rise to both sympa- 

 thetic and spinal ganglia. * 



