MUSCULAR POWER. 107 



in opposite directions, and greatly facilitating the varied 

 movements of the animal.* 



A variety of still more complicated arrangements may be 

 traced in the fibres of those muscles which invest hollow 

 sacs, or receptjicles, such as the stomach, (Fig. 51,) and the 

 heart, (Fig. 52.) We find, in the substance of these organs, 

 sets of fibres, which pass in a spiral direction, and which, 

 consequently, unite the effects of both longitudinal and cir- 

 cular fibres; and, when combined with either of these, they 

 serve to modify and regulate the actions of each organ in a 

 great variety of ways.t 



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 man- 

 ner, in the execution of the smaller motions, requiring the 

 most accurate regulation, and the nicest adjustments. We 

 cannot but be struck with the accordance which may often, 

 in these instances, be traced with human contrivances, when 

 the greater motions are rapidly executed by one set of 

 agents, acting with considerable power and velocity, while 

 the minuter approximations to the exact positions are eflfect- 

 ed by a distinct part of the apparatus, capable of more deli- 

 cate action, though with a smaller force. Thus, while the 

 astronomer brings his telescope round by powerful machi- 

 nery, so as to direct it to that part of the heavens, where 

 the object he wishes to view is situated, a more nice me- 

 chanism is employed to direct the instrument accurately to 

 the exact point; and, again, another is provided for making 

 the proper focal adjustments. Many parallel cases occur in 



* Carus, Tabulae Anat. Comp. fol. Tab. I. Fig". 6. 



•j- 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 combina- 

 tion of oblique muscles already explained. Thus beautifully is the arrange- 

 ment of tiie muscular fibres of the heart calculated to produce the rapid and 

 complete expulsion of its contained blood, with tlie smallest amount of con- 

 traction in the individual fibres. 



