574 THE NERVOUS SYSTEM. 



none but involuntary movements, and when the mind acts 

 on them at all, it is only through the strong excitement or 

 depressing influence of some passion, or through some 

 voluntary movement with which the actions of the involun- 

 tary part are commonly associated. The heart, stomach, 

 and intestines are examples of these statements ; for the 

 heart and stomach, though supplied in large measure from 

 the pneumogastric nerves, yet probably derive through 

 them few filaments except such as have arisen from their 

 ganglia, and are therefore of the nature of sympathetic 

 fibres. 



The parts which are supplied with motor power by the 

 sympathetic nerve continue to move, though more feebly 

 than before, when they are separated from their natural 

 connections with the rest of the sympathetic system, and 

 wholly removed from the body. Thus, the heart, after it 

 is taken from the body, continues to beat in Mammalia for 

 one or two minutes, in reptiles and Amphibia for hours ; 

 and the peristaltic motions of the intestine continue under 

 the same circumstances. Hence the motion of the parts 

 supplied with nerves from the sympathetic are shown to 

 be, in a measure, independent of the brain and spinal 

 cord. 



It seems to be a general rule, at least in animals that 

 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 



