APPLICATION OF THE ARGUMENT. 
25 
to its position.* Does not this, if anything can do it, be¬ 
speak an artist, master of his work, acquainted 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 need only to be 
looked upon to discover the reasons of its motion and ac¬ 
tion.”! 
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 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 tendon, which is the common muscular form, would 
have been sufficient, if it had had power to draw far 
enough. But the contraction, necessary to draw the mem¬ 
brane 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 
cord of the main muscle makes an angle. This, so far, 
answers the end; but, still farther, 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 reader’s 
mind during the perusal of these observations, namely, Why 
should not the Deity have given to the animal the faculty 
of vision at once ? Why this circuitous perception; the 
ministry of so many means; an element provided for the 
purpose; reflected from opaque substances, refracted 
through transparent ones; and both according to precise 
laws; then, a complex organ, an intricate and artificial ap¬ 
paratus, in order, 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? 
♦Phil. Tran. 1796. 
f 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. 
C 
