1893.] of the Sympathetic Nervous System. 549 



*' exclusive " area of a ramus may be about a half only of the total 

 area supplied by it. 



A third cause of over-lapping may be the formation of a plexus in 

 the dorsal cutaneous branches of the spinal nerves ; this is, perhaps, 

 the cause of some of the cases of over-lapping of areas which I have 

 observed in the sacral and coccygeal regions. 



Most of the details with regard to the over-lapping of the areas we 

 may leave on one side, and, treating the areas as successive, proceed 

 to consider their position. 



The cranial rami of the superior cervical ganglion supply the 

 skin of the dorsal part of the head, except a posterior portion, begin- 

 ning about 1^ cm. behind the anterior level of the ears ; this unaffected 

 region we may call the occipital region. 



The cervical rami of the superior cervical ganglion supply the 

 skin of the occipital region of the head by fibres running in the great 

 occipital (2nd cervical) nerve, and the skin over the first three or 

 four cervical vertebras by fibres running in the 3rd cervical nerve. 



The ganglion stellatum, by its cervical rami, supplies the skin from 

 the 3rd and 4th cervical vertebrae to some point between the spine 

 of the 2nd and 3rd thoracic vertebras. Often its area extends 

 upwards to join the occipital region. 



The areas supplied by the post-ganglionic pilo-motor fibres of the 

 3rd 4th, 5th, and 6th cervical nerves vary in relative size in different 

 individuals ; roughly, we may take the 3rd nerve as supplying the 

 skin over the first three and a half vertebras, and the others as supply- 

 ing successive strips of about two vertebrae each. 



We come now to the fore leg region, in which one, two, or three 

 spinal nerves send no cutaneous branches to the mid-line of the back. 

 These are the 7th and 8th cervical, and the 1st thoracic, nerves. 



Sometimes the 7th, sometimes the 1st, thoracic has such a cutaneous 

 branch ; when it is present it contains pilo-motor nerves. I have 

 not, in any case, observed any such cutaneous branch from the 

 8th cervical nerve. Corresponding to the presence or absence of these 

 cutaneous branches so far as my experiments go is the presence or 

 absence of pilo-motor fibres in the rami which pass from the ganglion 

 stellatum to the respective nerves. Thus, if the 1st thoracic nerve 

 sends a branch to the skin over the vertebrae, stimulation of its ramus, 

 as of the branch itself, causes a movement of hairs. 



In the two experiments in which there was a mid-line cutaneous 

 branch from the 7th cervical nerve, it supplied the lower part of the 

 area usually supplied by the 6th nerve, the area of this and of the 5th 

 .and 4th nerves lying a little more anteriorly than usual. 



The ganglion stellatum also sends pilo-motor fibres to the first four 

 thoracic nerves. From the 5th thoracic nerve downwards (and some- 

 times from the 4th) there is a ganglion and ramus for each nerve. 



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