g() PROFESSOR ALISON ON THE NERVES OF THE EYEBALL. 



vous actions which attend sensations) certainly exciting movements through 

 motor nerves destitute of ganglia. Of this, the portio dura and phrenic nerve 

 furnish sufficient examples. 



But setting aside the supposition that the ganglia are necessary to enable 

 the involuntary affections of mind to act on the muscles, let us inquire how far 

 the opinion long ago stated by Dr JOHNSTON and others is correct, that the 

 ganglia intercept the influence of the Will, prevent the voluntary acts of mind 

 from acting on the muscles which have their nerves only through them. 



A decided opinion is given against this supposition, both by MULLER, and by 

 liis very intelligent translator Dr BALY. The reason given by MULLER is this, 

 that as we know from the experiment formerly mentioned of forcibly acting on 

 the muscles of the eyeball, and thereby causing contraction of the iris, that a mo- 

 tor influence can traverse the ciliary ganglion, there is no reason to suppose that 

 a voluntary motor infmence should be arrested in it, if really brought to it. He 

 considers it, therefore, more probable, that the fibres of the " sympathetic, at 

 their origin in the spinal cord and brain, are not in communication with the 

 source of the voluntary influence ;" i. e. that they are not set on the fibres by 

 which the will acts downwards from the source of voluntary power ; to which 

 Dr BALY adds, that to suppose the admixture of other fibres in the sympathetic 

 to have the effect of removing the motor cerebro-spinal nerves from the action of 

 the will, is in opposition to one of the fundamental principles in physiology, that 

 of the course and influence of nerves in their " peripheral part," i. e. at a distance 

 from the brain and spinal cord, being insulated, i. e. admitting of no admixture 

 or transference of power from one filament to another. These authors, therefore, 

 regard the ciliary nerves as beyond the influence of the will, by reason of the 

 mode of their origin, not of their passing through the ciliary ganglion. 



But, on the other hand, if we attend to the experiment insisted on by MULLER, 

 we shall see that its result is not correctly stated by his expression, that it shews 

 that a motor influence can be transmitted through a ganglion, and therefore gives 

 us reason to presume that an effort of volition could traverse the ganglion also, 

 if really carried to it. When the 3d nerve transmits an effort of volition to the 

 muscles of the eyeball, and at the same time causes contraction of the pupil, it is 

 plain that the influence which affects the iris has originated in the " source of vo- 

 luntary influence" in the brain, that it is not only a motor influence, but one 

 consequent on a voluntary effort, which has traversed the ciliary ganglion. The 

 ganglion has not prevented the influence of volition from acting on the nerves 

 and muscular fibres which it supplies, although the will has no power of regulat- 

 ing the movement of these fibres ; and this being so, I do not see how it can be 

 denied that it has modified, in one way or other, the endowments of the nerves 

 entering it; rendering them incapable, not of transmitting the influence of the vo- 

 lition, but of obeying any specific efforts of the will. 



