On certain physiological inferences which may be drawn from the study of the nerves of the eyeball / by William Pulteney Alison.

  • Alison, William Pulteney, 1790-1859.
Date:
1841
Catalogue details

Licence: Public Domain Mark

Credit: On certain physiological inferences which may be drawn from the study of the nerves of the eyeball / by William Pulteney Alison. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    10/24 (page 74)
    power at the origins of these nerves cannot he very strong, and, therefore, that proximity of origin can afford hut a very imperfect explanation of the very strong tendency to consentience remarked in almost all the motions of the trunk of the body. Consciousness informs us that, although it is very difficult to act at the same moment on dissimilar portions of the same pair of nerves, yet there is in general no difficulty in refraining from acting at the same moment on the cor- responding portions; and in no case any difficulty in acting, at the same mo- ment, on dissimilar and distant nerves. And there are facts observed in the eye, which have quite the value of the experimentum crucis, as shewing, that the chief cause of consentience of movement in our muscular organs is very different from the connection of nerves, at their roots or in their course. These facts are, that while those corresponding portions of the 3d nerve, which elevate and depress the eyeball, i. e. those which go to the superior and inferior recti, always act simul- taneously ; those which go the rectus internus and inferior oblique do not usually act together in the two eyes. Again, the 4th and 6th nerves never act together on the two sides of the body, but each is uniformly combined in its movement with a portion of the 3d on the other side. The reason obviously is, that the Sensations which result from the action of the 4th and 6th nerves of the one eye, cannot be identified with those which result from the action of the nerves of the same pair in the other eye, and cannot be separated from those which result from the action of that portion of the 3d pair in the other eye. There is no other circumstance, but the identity of the resulting and guiding sensation, which can be pointed out as existing where the consentience is observed, and not existing where it is not observed. From these facts, therefore, we learn that the main cause of Consentience of muscular movement is simply Identity of the Guiding Sensations. Whether it is by an original instinct, or by repeated trials and acquired experience, that the acts of volition are directed to the nerves in each eye, which so turn the eyeballs as to keep the optic axes parallel, and so produce the single sensations, is a dif- ferent question; but what has been stated seems to me quite enough to shew, that it is because the single sensations result, that these nerves are consentient. I have no doubt that this principle, deduced from the movements of the eye- ball, is strictly applicable to all the cases of consentient movement excited by the nerves of the same pairs on the face, fauces, thorax, abdomen, and pelvis, in the different actions which have been already mentioned. The movements which these nerves excite, are always followed by certain sensations, generally grateful, influenced by the degree in which the actions are performed; and by these sen- sations, the extent to which the actions are carried, and the energy with which they are performed, are felt to be habitually regulated. These resulting and guid- ing sensations are felt to be affected exactly alike by the movement which is