24 APPLICATION OF THE ARGUMENT* 



in order to fit it up for its office it is connected by a ten- 

 don or thread with a muscle in the back part of the eye ; 

 this tendon or thread, though strong, is so fine, as not to 

 obstruct the sight, even when it passes across it ; and the 

 muscle itself being placed in the hack part of the eye, de- 

 rives from its situation the advantage, not only of being 

 secure, but of being out of the way ; which it could hard- 

 ly have been in any position that could be assigned to it 

 in the anterior part of the orb, where its function lies. 

 When the muscle behind the eye contracts, the membrance, 

 by means of the communicating thread, is instantly drawn 

 over the forepart of it. When the muscular contraction 

 (which is a positive, and, most probably a voluntary effort,) 

 ceases to be exerted, the elasticity alone of the membrance 

 brings it back again to its position.* Does not this, if any 

 thing can do it, bespeak an artist, master of his work, ac- 

 quainted with his materials? "Of a thousand other 

 things," say the French Academicians, " we perceive not 

 the contrivance, because we understand them only by the 

 effects of which we know not the causes ; but we here 

 treat of a machine, all the parts whereof are visible ; and 

 which needs only to be looked upon to discover the rea- 

 sons of its motion and action."! 



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, deserved- 

 ly 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 demonstrat- 

 ed only in liie cassowary. The muscle is passed through 

 a loop f >rmfd hif another muscle; and is tliere inflected, 

 as if it were round a pulley. This is a peculiarity; and 

 observe the advantage of it. A single ruuscle with a 

 straight tendon, whi h is the common muscular form, would 

 have been sufficient, if it had had the power to draw far 

 enough. But the contraction, necessary to draw the mem- 

 brane over the whole eye, required a longer muscle than 

 couH lie straight at the bottom of the eye. Therefore, 

 in order to have a greater length in a less compass, the 

 cord of the main muscle makes an angle. This, so far. 



« Phil. Tran. 1796. 



t Memoirs for a Natural History of Animals by the Royal Academy 

 of Sciences at Paris, done into English by order of the Royal Society.- 

 1701, p. 249. 



