CH. XVII.] AUTONOMIC PATHS 201 



ganglionic fibres are stimulated, the usual effects (for instance, 

 constriction of blood-vessels, erection of the hairs, etc.) take place. 

 If instead of injecting nicotine into the circulation, and so producing 

 a general effect, the nicotine is painted over one or more ganglia, 

 there will be a block in those fibres only which have their cell- 

 stations in those particular ganglia. By patiently examining all the 

 ganglia in this way in turn, stimulating the fibres that enter it and 

 those that leave it, Langley and his colleagues, after years of work, 

 have been successful in localising the cell-stations on most of the 

 autonomic paths in the body. 



We shall in later chapters be considering the autonomic nerve 

 supply of the individual organs, but it will be convenient here to 

 state in a general way the main course of the distribution of these 

 nerves; we have seen that the outflow from the central nervous 

 system occurs in four regions, and therefore we may take these 

 seriatim. 



1. The autonomic nerve-fibres which arise from the mid-brain. 

 These emerge by the third nerve ; the pre-ganglionic fibres pass to 

 the ciliary ganglion; the post-ganglionic arising from the cells of 

 this ganglion run in the short ciliary nerves to supply the intrinsic 

 muscles of the eyeball (sphincter iridis and ciliary muscle). 



2. The autonomic nerve-fibres which arise from the medulla 

 dblongata. These emerge by the following nerves : 



(a) Seventh and ninth nerves. These supply the blood-vessels 

 with vaso-dilator fibres and also the secreting glands in the nose and 

 mouth region. Many of these fibres (for instance, those in the 

 chorda tympani) get bound up with branches of the fifth nerve, and 

 are distributed with them. The ganglia on the course of these 

 fibres are the spheno-palatine, otic, submaxillary, and sublingual 

 ganglia. 



(b) Tenth and eleventh nerves. These are distributed by the 

 branches of the tenth or vagus nerve to the oesophagus, stomach, and 

 part of the intestine, to the bronchial muscles, to the heart, and to 

 the gastric and pancreatic secretory mechanism. Here our know- 

 ledge of the localisation of the cell-stations is not so exact as it is in 

 other parts ; some of the fibres appear to have their cell-stations in 

 the ganglion on the trunk of the vagus, but in most cases they do not 

 become post-ganglionic until the terminal ganglia in the walls of the 

 various organs mentioned are reached. 



3. The autonomic fibres which arise from the thoracic region of the 

 spinal cord. These constitute the best known of the autonomic 

 fibres, and we may describe them according to their distribution 

 under the following two headings : 



(a) The white rami leave the spinal nerves and find their cell- 

 stations in lateral ganglia, returning by the grey rami for distribution 



