576 'THE NERYOUS SYSTEM. 



have both cerebro-spinal and sympathetic nerves much de- 

 veloped, that the involuntary movements excited by stimuli 

 conveyed through ganglia are orderly and like natural 

 movements, while those excited through nerves without 

 ganglia are convulsive and disorderly ; and the probability 

 is that, in the natural state, it is through the same ganglia 

 that natural stimuli, impressing centripetal nerves, are 

 reflected through centrifugal nerves to the involuntary 

 muscles. As the muscles of respiration are maintained 

 in uniform rhythmic action chiefly by the reflecting and 

 combining power of the medulla oblongata, so, probably, 

 are those of the heart, stomach, and intestines, by their 

 several ganglia. And as with the ganglia of the sympa- 

 thetic and their nerves, so with the medulla oblongata and 

 its nerves distributed to respiratory muscles, if these 

 nerves or the medulla oblongata itself be directly stimu- 

 lated, the movements that follow are convulsive and 

 disorderly ; but if the medulla be stimulated through a 

 centripetal nerve, as when cold is applied to the skin, then 

 the impressions are reflected so as to produce movements 

 which, though they may be very quick and almost con- 

 vulsive, are yet combined in the plan of the proper res- 

 piratory acts. 



Among the ganglia of the sympathetic nerves to which 

 this co-ordination of movements is to be ascribed, must be 

 reckoned, not those alone which are on the principal trunks 

 and branches of the sympathetic external to any organ, 

 but those also which lie in the very substance of the 

 organs ; such as those discovered in the heart by Remak. 

 Those also may be included which have been found in the 

 mesentery close by the intestines, as well as in the sub- 

 mucous tissue of the stomach and intestinal canal (Meissner), 

 and in other parts. The extension of discoveries of such 

 ganglia will probably diminish yet further the number of 

 instances in which the involuntary movements appear to 

 be effected independently of central nervous influence. 



