MUSCULAR POWER. 131 



would be that of extending the fibres of the 

 muscle in a straight line between the points in- 

 tended to be brought nearer to each other. This 

 direct application of the power, however, is 

 seldom compatible with convenience, unless the 

 parts to be moved are of very small size, and 

 require very delicate adjustments. Straight 

 muscles, accordingly, are employed chiefly for 

 the movements of the minuter parts of the ap- 

 paratus belonging to the senses, such as the 

 eye, and the ear, and also that of the voice. 

 In insects, when the hard case, or skeleton, is 

 wholly external, this direct application of the 

 moving force is also very generally employed. 

 The shells of the bivalve mollusca, as of the 

 Oyster and the Cardium, are closed by one or 

 two straight muscles, the fibres of which pass 

 immediately from the inner surface of the one 

 to that of the other. 



In the greater number of cases it is more con- 

 venient to place the muscle in a situation which 

 causes it to act obliquely with respect to the 

 direction of the motion produced in the part to 

 which it is attached. This will, of course, be at- 

 tended with a loss of force corresponding to the 

 degree of obliquity ; but there are, at the same 

 time, advantages gained, both in point of 

 velocity of motion, and also in the effect being 

 produced by a smaller extent of contraction in 

 the fibres of the muscle. Oblique muscles are 



