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



The spinal pilo-motor fibres run into the sympathetic trunk, there 

 they become connected with nerve-cells ; on leaving the sympathetic 

 chain, they run to their peripheral endings in cranial or spinal 

 nerves. The fibres to the body accompany those dorsal cutaneous 

 branches of the spinal nerves which supply the skin over and close 

 to the vertebrae. 



Broadly speaking, the pilo-motor fibres run from the sympathetic 

 chain to the cranial and spinal nerves in the grey ranai, but a few 

 fibres may run out in the white rami ; and in some of the upper 

 thoracic rami, as is well known, no anatomically separable white rami 

 occur. 



Broadly speaking, the fibres issuing from any one ganglion are con- 

 nected with nerve- cells in that ganglion, and with no other sympa- 

 thetic nerve-cell. In some cases a certain number of such fibres are 

 connected with nerve-cells, not in the ganglion from which they issue, 

 but in the ganglion immediately above or below it. In the following 

 statement these fibres, and those which may take the course of the 

 white rami, are, for the sake of simplicity, left out of account. 



The fibres, before and after they have joined nerve-cells, I shall call 

 respectively pre-ganglionic or pre-cellular, and post-ganglionic or 

 post-cellular. 



Each ganglion, by its post-ganglionic fibres, supplies, in any one 

 individual, a definite portion of skin. This portion varies somewhat 

 in different individuals. The more important variations only will be 

 mentioned here. 



The areas supplied by the ganglia from above downwards, starting 

 with the superior cervical ganglion, are, apart from a variable amount 

 of overlapping, successive areas. 



An overlapping of the areas occurs when one nerve receives post- 

 ganglionic fibres by more than one ramus; thus the 3rd cervical 

 nerve, and so the skin of the upper part of the neck, may receive 

 pilo-motor fibres from the superior cervical ganglion by one grey 

 ramus, and from the ganglion stellatum by another grey ramus ; not 

 uncommonly the 7th lumbar nerve, and so the skin over the upper 

 coccygeal vertebrae, receives pilo-motor fibres by two separate grey 

 rami, one from the 7th lumbar ganglion, and the other from the 

 1st sacral ganglion. Similarly, also, a lower thoracic, or upper 

 lumbar, nerve may receive pilo-raotor fibres by the grey ramus of its 

 own ganglion, and others by the white ramus which it gives off to 

 the ganglion below. 



A second cause of overlapping is a spreading out of the pilo-motor 

 fibres in the skin itself. When two successive grey rami, or two 

 successive dorsal cutaneous branches, are stimulated one after the 

 other, the area of skin affected by both of them may be not more 

 than J to 1 mm. ; but it may be about 5 mm., and in such case the 



