H1STOR Y OF THE INVOL UNTAR Y NER VO US S YSTEM 2 1 



it is no longer suitable. So far as the term system can be used 

 at all, we are dealing only with motor cells and motor nerves to 

 a special set of tissues, and with the connexions of such motor 

 neurons with the central nervous system. There is one charac- 

 teristic common to these special tissues, they are not directly 

 under the command of the will. The motor nerve cells in ques- 

 tion invariably send motor nerve fibres to involuntary muscles or 

 glands, just as the motor nerve cells in the central nervous system 

 send motor nerve fibres to voluntary muscles. The natural term 

 then to use, if we wish to group together these vagrant motor 

 cells and their connexions into one system, is to speak of it as the 

 involuntary nervous system in contradistinction to the voluntary 

 nervous system ; meaning thereby a system of motor nerve cells 

 to involuntary structures, which have left the central nervous 

 system and have migrated out to a greater or lesser distance. 



Now the vertebrate body is undoubtedly segmented ; that 

 segmentation is shown on the motor side by the segmentation of 

 the body muscles in the trunk region to form the myotomes, and 

 by their innervation by the motor nerves, which pass from the 

 anterior horn cells into each spinal nerve ; again on the sensory 

 side it is shown by the presence of the posterior root ganglion in 

 each segment and the distribution of its sensory nerves to a de- 

 finite segmental skin area. Each spinal nerve then is a segmental 

 nerve as far as concerns the central and peripheral distribution of 

 its motor and sensory components. We may then inquire how 

 far such an arrangement also obtains in the case of its sym- 

 pathetic components. The motor fibres which supply the 

 muscles of the involuntary system arise from the vagrant 

 ganglion cells of that system, and in the case of the so-called 

 sympathetic part of that system, form the grey rami communi- 

 cantes. These grey rami from each of the ganglia of the lateral 

 or main chain supply the corresponding spinal nerve, and, as 

 Langley has shown in the case of the pilo-motor muscles, reach 

 their destination by way of the cutaneous branches of that nerve ; 

 they thus afford evidence that these segmentally arranged motor 

 neurons are closely associated in the adult with the segmental 

 cutaneous sensory neurons, which must be the case if they have 

 separated out from a conjoined mass of sensory and motor 

 neurons, as Onodi has shown. Here then in the lateral ganglia 

 of the sympathetic chain we find the true segmental motor nerve 



