XATURAL THEOLOGY. 



149 



IV. Mr. Home has observed,* that the most im- 

 portant and the most delicate actions are per- 

 formed in the body by the smallest muscles; and 

 he mentions, as his examples, the muscles which 

 have been discovered in the iris of the eye, and 

 the drum of the ear. The tenuity of these mus- 

 cles is astonishing: they are microscopic hairs; 

 must be magnified to be visible ; yet are they rea 

 effective muscles : and not only such, but the 

 grandest and most precious of our faculties, sight 

 and hearing, depend upon their health and action. 



[The figure here represents the action of the biceps muscle 

 which Hes on the arm, and is inserted upon the radius of the fore- 

 arm in sustaining a weight in the hand.] 



V. The muscles act in the limbs with what is 

 called a mechanical disadvantage. The muscle 

 at the shoulder, by which the arm is raised, is fixed 

 nearly in the same manner as the load is fixed 

 upon a steelyard, within a few decimals, we will 

 say, of an inch from the centre upon which the 

 steelyard turnsr In this situation, we find that a 



* Phil. Trans, part i. 1800, p. 8. 

 13* 



