MUSCULAR POWER. 



125 



In a great number of muscles, the fibres, instead 

 of running parallel to one another, are made either 

 to converge, or to diverge, in order to suit parti- 

 cular kinds of movements ; and we frequently find 

 that different portions of the same muscle have the 

 power of contracting independently of the rest, so 

 as to be capable of producing very various effects, 

 according as they act separately or in combination. 

 This is exemplified in the muscle of the back, 

 called the trapezius, represented in Fig. 44. In 

 many instances, the fibres radiate in all directions 

 from a common centre : this is the case with the 

 delicate muscle of the ear-drum, as shown in Fig. 

 45. In that of the Elephant, which is about an 

 inch and a half in diameter, these radiating fibres 

 are very conspicuous, even to the naked eye : and 

 they are also visible in the membrane of the human 

 ear, when viewed with a good microscope.* 



At other times, the muscular fibres run in a cir- 

 cular direction, forming what is called an orbicular, 

 or sphincter muscle, of which an example occurs in 

 that which surrounds and closes the eye. (Fig. 46.) 

 Very frequently these two last modes of arrange- 

 ment are united in some part, as appears to be the 



case in the membrane of the eye, called the Iris. 

 (Fig. 47.) The circular fibres of the iris surround 



* Home, Phil. Trans, for 1800, p. 1. 



