134 MECHANISM OF THE MUSCLES. 



Fig. 26. 



c, the gaff or rod upon which the sail is suspended, elevated by 

 a rope b, passing through a pulley at a, above the sail, exactly 

 as in the bird's wing, and for the same reason, viz. the ne- 

 cessity of applying the power below the part which is to be 

 raised. 



T. You have mentioned several examples which 

 illustrate applications of the mechanical powers in 

 the animal structure, which are among the most con- 

 fessed proofs of skill and contrivance in our own 

 mechanism. Besides many more that might be 

 added, there is one which Dr. Paley calls, "that 

 most exquisite of all contrivances, the nictitating 

 membrane," (from a Latin word, signifying to wink,) 

 which is found in the eyes of birds and of many 

 quadrupeds. 



A. The white skin which we sometimes see 

 fowls and birds suddenly twitching over their eye 

 balls, is this membrane, " and the use is to sweep the 



