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XIV. Of the Fourth and Sixth Nerves of the Brain ; — being the concluding paper on 

 the distinctions of the Nerves of the Encsphalon and Spinal Marrmv. By Sir 

 Charles Bell, K. H., F, B. SS. L. ^ Ed., M. D. H. Gott., Sfc. 



Read 7th May 1838. 



Interesting as theoptical properties of the eye have been to philosophers 

 in every age, there are conditions of this organ which are no less curious, and 

 which have not had their share of attention. 



In the year 1823, I introduced the subject to the Royal Society of London, 

 nearly in the terms I am now using, but there is much more in the subject than 

 I then conceived, although I see no reason to change the mode of contemplating it. 



The eight muscles of the eye, and the five nerves, exclusive of the optic 

 nerve, which pass to them, imply the complex nature of the apparatus exterior 

 to the globe, and I fear it is too plain that the subject has not been satisfactorily 

 treated. 



It is chiefly with respect to the protecting motions of the eye that the diffi- 

 culty occm-s, for I hope the dependence of the proper organ of vision on the vo- 

 luntary muscles of the eye, has been proved and acknowledged. 



Permit me to di-aw the attention of the Society to what appears a very sim- 

 ple piece of anatomy, the circular muscle which closes the eyelids, orbicularis 

 palpebrarum. 



It will be necessary to divide the muscle into three parts — and that not in 

 an arbitrary manner, but according to the action of each division. 



Around the mai-gin of the orbit, there is a portion of the muscle red, fleshy, 

 and strong — within it, and lying on the eyelids, there are fibres, which though 

 they converge to the same point in the angle of the eye, are distinguishable from 

 the outer cii'cle by their delicacy and paleness. Lastly, the ciliaris is a thin slip 

 of muscle which lies along the margin of the lower eyelid. 



These divisions of the muscle authorized by Albinus and others, have dif- 

 ferent actions and different relations. The larger and external circle is brought 

 into action when the eye is irritated or excited. The lesser paler fibres gently 

 close the eyehds as in sleep, or in winking when the eyelids faU together in their 

 usual rapid closing, to moisten the surface of the cornea, — an action which is 

 quite pecuhar, and so quick as not to interfere with the permanence of the un- 

 pression on the retina. 



