THE AE-G-UMENT APPLIED. ' 53 



In the configuration of the muscle which, though placed 

 behind the eye, draws the nictitating membrane over the 

 eye, there is what the authors just now quoted deservedly 

 call a marvellous mechanism. I suppose this structure to 

 be found in other animals ; but in the memoirs from which 

 this account is taken, it is anatomically demonstrated only 

 in the cassowary. The muscle is passed through a loop 

 formed by another muscle, and is there inflected as if it 

 were round a pulley. This is a peculiarity — and observe 

 the advantage of it. A single muscle with a straight ten- 

 don, which is the common, muscular form, would have bee.n 

 sufficient, if it had had power to draw far enough. But the 

 contraction necessary to draw the membrane over the whole 

 eye, required a longer muscle than could lie straight at the 

 bottom of the eye. Therefore, in order to have a greater 

 length in a less compass, the chord of the main ra,uscla 

 makes an angle. This so far answers the end ; but still fur- 

 ther, it makes an angle, not round a fixed pivot, but round 

 a loop formed by another muscle, which second muscle, 

 whenever it contracts, of course twitches the first muscle at 

 the point of inflection, and thereby assists the action designed 

 by both. 



One question may possibly have dwelt in the rea-der's 

 mind during the perusal of these observations, namely. Why 

 should not the Deity have given to the animal the faculty oi 

 vision at once ? "Why this circuitous perception ; the minis- 

 try of so many means ; an element provided for the purpose ; 

 reflected from opaque substances, refracted through trans- 

 parent ones, and both according to precise laws ; then a 

 complex organ, an intricate and artificial apparatus, in or- 

 der, by the operation of this element and in conformity with 

 the restrictions of these laws, to produce an image upon a 

 membrane communicating with the brain ? WLerefore all 

 this ? Why make the difficulty in order to surmount it ? li 

 to perceive objects by some other mode than that of touch, 

 or objects which lay out of the reach of that sense, were the 



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