IV. On certain Physiological Inferences which may be drawn from the Study of the. 

 Nerves of the Eyeball. By W. P. ALISON, M.D., Professor of the Theory of 

 Medicine. 



(Read 7th December 1840.) 



IT has been justly observed that the great discovery of the appropriation of 

 the different portions of the Nervous System to the exercise of different functions, 

 would never have been clearly established, but for the fortunate circumstance 

 that, in certain parts of the body, especially on the face, the nerves of sense and 

 of voluntary motion are distinct throughout their whole course. And this consi- 

 deration may instruct us that, when we have an organ supplied with a variety of 

 nerves, known to be of perfectly different endowments, the study of the peculi- 

 arities of these nerves may give us an insight into the purpose or use of some 

 of those pieces of structure in all parts of the Nervous System, in which we must 

 still admit that we see much contrivance, without understanding its intention. * 



In the case of the Eyeball, it is generally allowed that we see, separated for 

 us by Nature, almost every kind of nerve which the physiology of any part of 

 the body includes ; we have the nerve of the special sensation, and that of com- 

 mon sensation ; we have the nerves which excite motion in obedience to the will, 

 and those which excite motion over which the will has no control ; we can point 

 out the incident nerve and the efferent nerve, concerned in two distinct examples 

 of the reflex function of the spinal cord; and we can specify the nerve by 

 which the nutrition of the whole organ, and more than one secretion contained 

 in it, are liable to be influenced and controlled. And when we attend to the 

 peculiarities of these nerves, and to facts which have been observed in regard 

 to then* action, I think we have sufficient data for certain inferences appli- 

 cable to other parts of the Nervous System, which have not yet been distinctly 

 pointed out, and which are steps in the progress of that most difficult, but like- 

 wise most interesting department of Physiology, where our object is to detect 

 the laws by which mental acts are connected with the physical changes of living 

 beings ; and where, accordingly, the intimations of our own consciousness must 

 be admitted as part of the foundation of our inferences. 



I. The first peculiarity in the nerves of the eyeball to which I wish to direct 

 attention is this, that those supplying the muscles by which the eyeball is instinc- 



VOL. XV. PART I. T 



