]'28 THE MECHANICAL FUNCTIONS. 



these, they serve to modify and regulate the actions 

 of each organ in a great variety of ways. The 

 muscular fibres of the heart are disposed in two 

 layers ; each set passing in a spiral course from the 

 basis, or broad part, to the point or apex ; but the 

 direction of the turns being different in each, the 

 two layers cross or decussate, producing the effect, 

 and procuring the advantages of a combination of 

 oblique muscles already explained. Thus beauti- 

 fully is the arrangement of the muscular fibres of 

 the heart calculated to produce the rapid and com- 

 plete expulsion of its contained blood, with the 

 smallest amount of contraction in the individual 

 fibres. 



The infinite mechanical skill, with which the 

 moving power has been applied to the purposes to 

 be accomplished, is displayed not only in the larger 

 organs, where great force is to be exerted, but also, 

 in a still more conspicuous manner, in the execu- 

 tion of the smaller motions, requiring the most ac- 

 curate regulation, and the nicest adjustments. We 

 cannot but be struck with the accordance which 

 may often, in these instances, be traced with human 

 contrivances, where the greater motions are rapidly 

 executed by one set of agents, acting with consi- 

 derable power and velocity, while the minuter ap- 

 proximations to the exact positions are eftected by 

 a distinct part of the apparatus, capable of more 

 delicate action, though with a smaller force. Thus, 

 while the astronomer brings his telescope round by 

 powerful machinery, so as rapidly to direct it to 

 that part of the heavens, where the object he wishes 

 to view is situated, a more nice mechanism is em- 

 ployed to direct the instrument accurately to the 



