[ 54 J [Feb. I, 



PROCEEDINGS OF PUBLIC SOCIETIES. 



ROYAL SOCIETY. 



On the Mutioiis of the Eye, in ilhist ration 

 of the uses of the Muscles and Nt-rves 

 if the Orbits. Bt/ Charles Bell, 



' ESQ. 



Il'ROPOSE to show, lliat we must 

 ilistingiiish the motions of the eye 

 accordinjc to their objects or uses, 

 •whether for tliei direct purpose of 

 vision, or for tiie preservation of the, 

 orsan : tliat the eye undergoes a re- 

 volving- motion not hitherto noticed ; 

 that it is suliject to a state of rest and 

 activity, and that the dilTerent condi- 

 tions of tlie retina are accompanied by 

 appropriate conditions of the sur- 

 rounding muscles ; that these muscles 

 are to be distinguished into two natu- 

 ral classes ; and that in sleep, faint- 

 iiess, and insensibility, the eye-ball is 

 given up to tiie one, and in watchful- 

 ness, and the full exercise of the organ, 

 it is given up to the intluence of the 

 other, class of muscICs: and finally, 

 that tlie consideration of these natural 

 conditions of the eye explains its 

 changes as symptomatic of disease, or 

 as expressive of passion. 



The eye is subject to two condi- 

 tions : a state of rest, witli entire obli- 

 vion of sensation, and a state of watch- 

 fulness, during which both tlic optic 

 nerve and the nerve of voluntary mo- 

 tion are in activity. When the eye is 

 at rest, as in sleep, or even when the 

 eye-lids are shut, the sensation on the 

 retina being then neglected, the volun- 

 tary nmsclcs resign tlieir oilice, and 

 the involuntary muscles draw the 

 pupil under the upper eye-lid. This 

 is the condition of the organ during 

 perfect repose. 



On the other hand, there is an inse- 

 parable connection between the exer- 

 cise of tlie sense of vision and the ex- 

 ercise of tlie voluntary muscles of the 

 eye. When an object is seen, wo 

 enjoy two senses ; there is an impres- 

 sion upon the retina ; hut vvc receive 

 also the idea of position or relation 

 which it is not the office of the retina 

 to give. It is by the consciousness of 

 the degree of effort put upon the 

 voluntary muscles, that we know the 

 relative position of an object to our- 

 selves. The relation existing be- 

 Iween the office of the retina and of 

 the voluntary muscles, may be illus- 

 trated in this manner. 



Let the eyes be C.\td upon an illu- 



minated object until the retina be 

 fatigued, and in some measure ex- 

 hausted by the image, then closing the 

 eyes, the figure of the object will eonli- 

 nue present to them : and it is quite 

 clear that nothing can change the 

 place of this impression on the retina. 

 But, notwithstanding that the impres- 

 sion on the retina cannot be changed, 

 the idea thence arising may. For, by 

 an exertion ofthe voluntary muscles of 

 the eye-ball, the body seen will appear 

 to change its place; and it will, to our 

 feeling, assume diftVrent positions ac- 

 cording to the muscle which is exer- 

 cised. If we raise the pupil, we shall 

 see the body elevated, or, if we depress 

 the pupil, we shall see the body 

 placed below us ; and all this takes 

 place while the eye-lids are shut, and 

 when no new impression is conveyed 

 to the retina. The state of the retina 

 is here associated with a conscious- 

 ness of muscular exertion ; and it 

 shows that vision in its extended sense 

 is a compound operation, the idea of 

 position of an object having relatiou 

 to the activity of the muscles. 



In my endeavour to arrange the 

 nerves ofthe orbit, I encounter, in the 

 fust step, all the difficulties of my 

 subject; for, although there be only 

 nine nerves properly enumerated as 

 proceeding from the brain, six of 

 these go to the eye ; the second, third, 

 fourth, part of the fifth, sixth, and se- 

 venth, go into the orbit, and may be 

 said to be concentrated into a spuco 

 no larger than a nut-shell. 



We are, in the first place, to inquire 

 by what nerve t!ie common endow- 

 ment of sensibility is bestowed upon 

 the membranes and surfaces of the 

 eye. On recurring to this subject wo 

 are reminded, that the sensibilities of 

 the body difler as much in kind as in 

 degree; that the sensation of pain is 

 provided to rouse our activity, and 

 guard us against violence, or, by 

 means more direct, to excite instinc- 

 tive motions, which shall anticipate 

 the most rapid actions ofthe will, and 

 serve as a more perfect safeguard. 

 The trii^eminus, or fifth nerve, bestows 

 upon all the surfaces of the head and 

 face, external and internal, that sensi-. 

 bility which is enjoyed by tlie rest of 

 the body through the spinal nerves. 

 But Ihroiigh some of its branches is 

 also bestowed that disthict sense on 

 certain 



