OF THE MUSCLES. 95 



powers ; and hence, after exertion, they become fatigued, 

 and at last powerless. 



Voluntary muscles are to be found composing the chief 

 substance of the arms, legs, back, mouth, &c. They have 

 points which are called their origin, or from which they are 

 anatomically said to take their rise ; also other points with 

 which their substance, or the tendons springing from them, 

 are connected ; which are called their points of insertion. 

 The point of origin is generally some bone of somewhat a 

 fixed character ; and that of insertion also a bone, but one 

 that can be moved with more or less ease. It is by moving 

 this last that their power or utility is displayed ; sometimes, 

 however, both insertion and origin are equally moveable ; 

 and then they cannot draw one towards the other, but force 

 the two closer together, by contracting or lessening the 

 space between them. Voluntary muscles have usually 

 antagonists ; whereby the perpetual tendency to contraction 

 is counterbalanced. The muscular masses are commonly 

 invested by a cellular or membranous covering ; which in 

 some instances is very dense, called /«5cm ; whereby they are 

 bound down and assisted in their action. 



There is another kind of muscles denominated mixed ; 

 that is, such as the muscles of respiration ; over which we 

 can exercise a certain, but not an absolute control. Thus 

 we can hold our breath for a limited time ; but by no effort 

 of which he is capable can man prevent his breathing 

 altogether. 



Tendons. — These hang from or form continuations of 

 muscles ; they are almost all of them fixed into the 

 periosteum of bones, which they help to pull ; thus serving to 

 lengthen the muscle, and allowing its action to be asserted 

 at a distant point, without necessitating an increase in 

 either the bulk or weight ; which would have been impera- 

 tive, had the muscle been in substance extended to the 

 point that a comparative small tendon can reach with ease. 

 They are of a firm glossy nature ; and of an almost metallic 

 lustre ; perfectly insensible when in health ; but causing the 

 most intense pain when inflamed. They possess great 

 strength. During life, however, the tendons snap before 

 the nmscles ; after death the muscles always yield the first. 



