558 COURSE OF SWEAT FIBRES. [Boon n. 



corresponding to these ganglia and so the sciatic nerve. Along 

 their course the fibres are connected with nerve-cells in these 

 ganglia, the fibres in a grey ramus starting from cells in the 

 ganglion from which the ramus run, or in the ganglion above 

 it. In the same animal, the sweat-fibres for the fore-feet leave 

 the spinal cord by the anterior roots of the sixth, seventh, and 

 eighth thoracic nerves, but also, to a less extent, by the nerves 

 above and below. Passing into the sympathetic chain, they 

 ascend to the ganglion stellatum, with the nerve-cells of which 

 alone they are connected, and by the branches of this ganglion 

 reach the branchial plexus and so the median and ulnar nerves. 

 The course of the sweat-fibres in other animals is probably very 

 similar to the above. In the horse the sweat-fibres for the side 

 of face and in the pig those for the snout appear to run in 

 branches of the fifth nerve and not in the facial ; in the latter 

 animal at least some of these fibres reach the fifth nerve from 

 the cervical sympathetic, but apparently not all. 



355. The fact mentioned above that in the horse, after 

 section of the cervical sympathetic nerve on one side of the neck, 

 profuse sweating is apt to break out on that side of the face, has 

 suggested the idea that this nerve conveys inhibitory impulses 

 to the sweat-glands of the head and face, and that when it is 

 divided the sweat-fibres running in the fifth nerve, having 

 nothing to counteract them, set up sweating. But it is prob- 

 ably sufficient in this case to suppose that the glands predis- 

 posed to activity by the higher temperature brought about by 

 the section of the sympathetic dilating the blood vessels, are 

 more easily excited by any stimulus working upon them through 

 the fifth nerve. And though the idea of a double nervous 

 mechanism, augmenting and inhibitory, governing the activity 

 of the sweat-glands, is a tempting one, there are at present no 

 satisfactory reasons for adopting it. 



