CHAPTER VIII. 



THE RHYTHMIC AND PERISTALTIC MOVEMENTS IN THE 

 INVOLUNTARY MUSCLES OF THE VERTEBRATE. 



WE may profitably embody the arguments in the previous chap- 

 ters in the following conception of the nature of the innervation 

 of all involuntary muscle. 



The motor nerve cells of all involuntary muscles (including in 

 this term also those giving off inhibitory fibres) were originally, 

 like those of voluntary muscles, situated within the central 

 nervous system, and corresponded therefore to the anterior horn 

 cells which send motor fibres directly to the voluntary muscles. 

 They have left the central nervous system and formed the various 

 groups of peripheral nerve cells, being still joined by connector 

 fibres with connector cells in the central nervous system. These 

 connector fibres form three main outflows, bulbar, thoracico- 

 lumbar and sacral, known respectively as the vagus group of 

 nerves, the white rami communicantes and the pelvic nerves. 



Further the evidence shows that the afferent nerves belong- 

 ing to the involuntary nervous system are in connexion with 

 these motor nerve cells only by way of the central nervous 

 system, for all the afferent nerve cells of the system are found in 

 the posterior root ganglia, and none of them among the vagrant 

 cells. 



It looks as though the evolutionary process had acted in op- 

 posite directions in the case of afferent and efferent nerve cells of 

 the involuntary system ; causing in the former case a movement 

 towards the central nervous system, in the latter, away from it. 



This conception implies that there is no complete peripheral 

 nervous system belonging to the involuntary muscles, but only 

 motor neurons. 



Another school of thought exists, which argues that a com- 

 plete peripheral involuntary nervous system does exist and per- 

 vades all involuntary muscles ; and is acted upon by regulating 



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