122 THE MECHANICAL FUNCTIONS. 



and the Canhuni, are closed by one or two straight 

 muscles, the fibres of v/hich 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 attended 

 with a loss of force corresponding to the degree of 

 obliquity ; but there are, at the same time, advan- 

 tages gained, not only in point of velocity of motion, 

 but also in the effect being produced by a smaller 

 extent of contraction in the fibres of the muscle. 

 Oblique muscles are frequently employed in pairs, 

 and are made to act on opposite sides of the line 

 of the intended motion, which is, in this case, the 

 diagonal between the direction of the two equal 

 forces. Thus, in order to bring a bone at p. Fig. 

 39, down to the point q, the two muscles a and b, 

 extending from the fixed points m and n, may be 

 employed ; for as they exert forces in the directions 

 p M and p N, there will result a force in the inter- 

 mediate direction p o : and the effect desired will 

 be accomplished more quickly, and with a smaller 

 extent of contraction in the muscles producing it, 

 than if the same power had been applied by means 

 of a straight muscle in the direction p o.* It is by 

 means of two sets of muscles, acting thus obliquely, 

 that the ribs are brought in closer approximation 

 every time that the chest is elevated in breathing. 

 Thus carefully does nature dispose the muscular 

 fibres so as to obviate the necessity of their being 



* See a paper by Dr. Monro, in the Transactions of the Royal 

 Society of Edinburgh, vol. iii. p. 250. 



