PROFESSOR ALISON ON THE NERVES OF THE EYEBALL. 81 



In fact, if it were in consequence of their roots having no connection with 

 the motor portion of the brain and spinal cord, that the ganglionic nerves in the 

 eye or elsewhere are not obedient to the will, and if the nerves underwent no 

 change of endowment in the ganglia, we do not see why the motor nerves of the 

 involuntary muscles (e. g. the motor filaments of the ciliary nerves) should pass 

 through ganglia at all ; they would be fitted for their function merely by their 

 mode of origin. 



Nor does it seem to me difficult to define a little more precisely the modes in 

 which, in this as in other instances, by the connection established in every one of 

 the ganglia of the sympathetic between motor filaments from the anterior, and 

 sensitive filaments from the posterior, column of the spinal cord, the involuntary 

 muscles, although we believe them to be supplied with motor nerves through the 

 ganglia, are withdrawn from the power of the will. 



1. Even if we implicitly rely on the experiments of VALENTIN and others in 

 Germany, tending to correct the previous statements of HALLER, BICHAT, WIL- 

 SON PHILIP, MAYO, and many others, and to shew that all the involuntary 

 muscles may, under certain circumstances, be excited by physical irritations 

 applied to their nerves,* yet I think it cannot be doubted (from the negative 

 result of so many experiments made previously by so many experienced physi- 

 ologists) that the power of the motor nerves to excite muscular contraction is 

 greatly diminished by passing through ganglia. The contractions, so excited in 

 involuntary muscles in these experiments, have followed irritation above the gan- 

 glia, or even in the central masses, much more surely than in the nerves below the 

 ganglia ; and their force, and the certainty with which they can be produced, 

 are certainly much inferior to those of the contractions excited by similar means 

 through nerves not ganglionic, i. e. voluntary muscles. 



2. The vital agency of the sensitive nerves passing through the ganglia seems 

 also to be much modified ; they certainly do not shew on irritation, when in the 

 natural state, nearly as much sensibility as other nerves ; and their grand pecu- 

 liarity seems to be, that although supplying the muscular fibres, they are in- 

 capable of transmitting those muscular sensations by which, in the case of the 

 voluntary muscles, we are continually informed of the contractions we excite. 

 Although the study of the eye teaches us that the influence of volition can tra- 

 verse a ganglion, yet in no one instance in the body is this influence felt to be ex- 

 erted on muscles placed beyond ganglia. And when we reflect on what has been 

 said of the importance of the resulting and guiding sensations, in insulating and 

 directing the efforts of the will, we shall easily perceive that the want of any such 

 sensations in the present case, is sufficient to explain the inefficiency of voluntarv 

 efforts over those muscles. These seem to be results of the degree of intermixture 



* See Valentin Do Functionibus Nervorum, &c, p. 62. 



