60 THE INVOL UNTAR Y NER VO US S YSTEM 



favour of the view that the connector nerve fibres of the involun- 

 tary nervous system, which constitute the thoracico-lumbar out- 

 flow, behave like those of the voluntary nervous system, and give 

 off collaterals to a number of ganglion cells ; in consequence of 

 such collaterals an axon reflex can take place in organs entirely 

 separated from the central nervous system. Further there is no 

 reason to suppose that one part of the involuntary nervous system 

 differs in essentials from another. I imagine therefore that the 

 cranial connector fibres in the vagus nerve and the sacral con- 

 nector fibres in the pelvic nerve also send off collaterals, so as to 

 connect with more than one motor nerve cell ; that therefore, 

 when the organs supplied by such motor cells are isolated from 

 the central nervous system, reflexes can take place in them which 

 are also of the nature of axon reflexes, and thus may account 

 for the reflexes observed in the isolated heart, intestine, and 

 bladder. This question will receive further consideration in a 

 later chapter. 



The sympathetic musculature, which becomes part of the 

 bladder musculature, may have arisen from one or both of the 

 two systems, which I have called the uro-genito-dermal and the 

 sphincter systems, by means of the involvement of the musculature 

 of the ureters in the one case, and of the sphincter muscles of the 

 bladder and urethra in the other. The physiological evidence is 

 in favour of the vesical sphincter system as playing the chief part 

 in the formation of the muscles in question, for the phenomenon 

 of the axon reflex shows that the two marked reflex contractions, 

 which take place through the medium of the mesenteric ganglia 

 upon stimulation of the central end of the hypogastric nerve, are 

 those of the trigonal region of the bladder and of the sphincter 

 ani, and further that the motor fibres to the muscles in each case 

 arise from cells in the inferior mesenteric ganglion. In other 

 words, the vesicular musculature involved in this reflex is inner- 

 vated in the same manner as the internal sphincter ani, and 

 belongs to the sphincter muscular group and not to the uro-genito- 

 dermal. 



As already stated, the axon reflex is brought about by the 

 presence of collaterals in a connector fibre belonging to the 

 lumbar splanchnic nerves, one of which connects with a motor 

 cell in the inferior mesenteric ganglion and the other with a nerve 

 cell near the muscle itself. This motor cell sends motor fibres 



