238 SIR CHARLES BELL ON THE FOURTH AND SIXTH 



The ciliaris draws the lower eyelid horizontally, and belongs properly to the 

 sacculus lacrymalis, squeezing and emptying the sac. 



Let us observe the necessity of certain relations between the larger and 

 fleshy circle of the orbicularis when the eye is excited, as when something offen- 

 sive is thrown into it. It is here necessary to notice the resemblance in action 

 of the human eye to that of quadrupeds which possess the haw. 



In the caruncula lacrymalis and memhrana semilunaris, we have an appara- 

 tus less perfect, certainly, than that of the horse — but for the same pm-pose, to 

 gather together and thrust out what is UTitating the eye. 



To the exercise of these parts, however, other muscles must consent, so that 

 the cornea shall be turned in towards the inner canthus of the eye at the moment 

 that the eyebaU is forcibly squeezed by the action of the orbicularis. The diffi- 

 culty which the oculist encounters, is to prevent the cornea turning into the 

 lesser angle of the eyelids ; for this direction of the eye towards the nose, is 

 taken the instant that the knife or needle touches the eye. This action of the 

 muscles which is a provision for the protection of the eye, is often the source of 

 mishap in operation. 



The position of the eyeball in which it is drawn towards the os planum, and 

 the axis turned inwards, could not be the effect of the external orbicular muscle 

 alone — nor could it be performed by the combined action of the recti. It is ob- 

 vious that a relaxation must take place in the rectus externus or abducens muscle. 

 How is this relaxation to be effected in correspondence with the action of the 

 larger or outer portion of the orbicularis f There is no direct connection between 

 these muscles: they do not touch: no nervous filaments pass between them. 

 We must therefore turn to the origins of the nerves which supply these muscles. 

 We find them related at their origins though proceeding by different courses to 

 their destination. 



Here let us consider the nature of that relation which exists between two 

 classes of muscles engaged in any action. I mean not those only which are ex- 

 cited together to contraction, but those also which are relaxed, and which re- 

 laxation is as necessary to the effort or movement, as the contraction of their op- 

 ponents. 



In every action there are two conditions of the muscles, and philosophically 

 considered, both might be called states of action, for that which is called relax- 

 ation, is not like the throwing loose of a rope which gives no resistance, but 

 a condition of yielding, apportioned in the finest degree to the state of contrac- 

 tion of the other class. 



This relation established between the two opposite classes of muscles is not 

 always as in the limbs where they lie in juxta-position, — but often, more espe- 

 cially where the muscular action is related to the internal functions, muscles 

 may be far apart, which yet through nervous connection are in intimate cor- 



