92 DIRECTION OF MtTSCLES. 



on the application of stimuli, and again relaxing when 

 the stimulus is withdrawn. 



The direction in which the fleshy fibres run de- 

 termines the direction of the motion effected by 

 their contraction. In some muscles the fibres are 

 nearly parallel, and act consequently in a straight 

 line. In others they run obliquely, producing a cor- 

 responding obliquity of motion ; while in others they 

 are disposed like feathers in relation to a quill, and 

 are, therefore, styled penniform. A few are cir- 

 cularly disposed round openings, and contract 

 towards a common centre, like the mouth of a purse 

 closed by its strings. When the direction varies, it 

 is always to effect a particular kind of action. Re- 

 markable contrivances appear for this end : one 

 muscle of the lower jaw, for example, is divided into 

 two distinct fleshy bellies by an intermediate thin 

 strong tendon, which passes through and plays in a 

 pulley adapted for its reception ; its two portions 

 being by this means enabled to operate with full 

 effect almost at right angles to each other. A sim- 

 ilar arrangement is found in the trochlearis or pulley- 

 muscle of the eyeball ; and modifications of a dif- 

 ferent kind occur in other muscles, as in those of 

 the fingers and toes, wherever a particular object is 

 to be accomplished. 



The chief purpose of the muscles is obviously to 

 enable us to carry into effect the various resolutions 

 and designs or volitions, as they are termed by 

 philosophers which have been formed by the mind. 

 But while fulfilling this grand object, their active 

 exercise is at the same time highly conducive to 

 the well-being of many other important functions. 

 By muscular contraction, the blood is gentty as- 

 sisted in its course through the smaller vessels and 

 more distant parts of the body, and its undue accu- 

 mulation in the internal organs is prevented. The 

 important processes of digestion, respiration, secre- 

 tion, absorption, and nutrition are promoted, and 



