2 o THE INVOL UNTA R Y NER VO US S YSTEM 



of things is seen in the young crocodile, where the rami com- 

 municantes between the nerve and the ganglionic chain are very 

 short, so that the posterior root ganglion is very near the corre- 

 sponding sympathetic ganglion, and in the tortoise, where the 

 ramus communicans in the thoracic region springs directly out of 

 the posterior root ganglion. According to Giacomini in Bufo 

 and Bombinator the two ganglia actually touch one another. 



This fact, that the sympathetic system of cells has split off 

 from a cell mass in the position of the posterior root ganglion, 

 has led many anatomists to look upon the sympathetic ganglia as 

 offshoots of the posterior root ganglia, and therefore mainly 

 sensory in function. Langley's evidence makes it clear that it 

 is only the motor cells which have passed peripheral-wards, while 

 the sensory cells of the system have remained in their original 

 position in the ganglion of the posterior root. 



Further, those who hold that the sympathetic system is an 

 independent nervous system, not only find a necessity for the 

 presence of sensory cells in that system, but also consider that 

 the cells of the different ganglia are connected together, thus 

 forming a system of relays, as in the central nervous system. 

 Acting on the principle that a nerve cell keeps alive that part 

 of the nerve fibre which is in connexion with it, Langley argued 

 that, after section of the spinal roots and after time had been 

 allowed for degeneration of their peripheral ends, stimulation 

 of the splanchnic nerves (rami efferentes) ought still to produce 

 an effect, if the cells of the lateral chain communicated with cells 

 of the collateral chain. He, however, found no effect under 

 these conditions ; there is therefore no commissural system be- 

 tween these two sets of sympathetic ganglia. Similarly he 

 showed that the cells in separate ganglia of the vertebral chain 

 do not connect with each other. Therefore this characteristic 

 of relays of cells which connect with each other, which is so im- 

 portant a factor in the making of a central nervous system, is 

 not to be found in the sympathetic nervous system. 



I have made use hitherto of the term organic system in ac- 

 cordance with old usages to represent in part the nerve cells and 

 nerve fibres of this thoracico-lumbar outflow ; but this term is so 

 bound up with the ideas of the independence of the organic and 

 animalic systems an objection which applies on the face of it 

 also to Langley's substitution of " autonomic " for organic that 



