102 THE MUSCLES. 



oones are joined to each other by articular surfaces, the contact 

 and junction of which are secured by fibrous ligaments. 



OF THE MUSCLR3. 



Fig. 40. 58. All the great motions of the body are caused 

 by the displacement or movement of some of the 

 bones which form the skeleton; but these bones can- 

 , .\\.d not move of themselves, and only change their posi- 

 tion through the action of other organs attached to 

 them, which, by contracting, draw the bones after 

 them. 



b 59. These motor organs are the mnsvlea. They 

 are very numerous and constitute what is commonly 

 called flesh, and form nearly one half of the total mass 

 of the body. They are a species of ribbon or fleshy 

 cords composed of fasciculi or bundles of fibres united 

 > AW! together, and which have the property of contraction 

 or elongation, (Fiy. 40.) All the muscles destined to 

 produce the great movements of the body, are fixed 

 to the skeleton by their two extremities. Tt, therefore, 

 follows, that when they contract they displace those 

 bones which offer the least resistance, and -draw them 

 towards those which are not moveable, but serve as points of sup- 

 port for moving the first. Now, in most instances, the bones are 

 more moveable in proportion as they are more distant from the 

 centre of the body: and .the muscles which are fixed between 

 two bones, generally act upon that which is most distant, and we 

 always tind the muscles, destined to move a bone, extend from it 

 towards the trunk ; for example, the muscles which move the 

 fingers, occupy the palm of the hand, and the fore-arm ; those 

 which flex the fore-arm upon the arm, occupy the arm, and those 

 which move the arm on the shoulder, are placed upon the shoulder, 

 (Pig. 40.) 



Under ordinary circumstances, however, the muscles displace 

 the bones which serve them as points of support. When the body 

 is suspended by the hands, and we endeavour to raise it, the 

 flexor muscles of the fore-arm, not being able to displace the latter, 

 approximate the arm, and thus draw the whole body after it. 



Explanation of Fig, 40. The muscles of the superior extremity, d. the 

 deltoid muscle, which extends from the shoulder to the arm, and by contract* 

 ng, elevates the litter, b. the biceps muscle w.iich bends the arm, -f. one 

 of the flexor muscles of the fingers. 



58. How are the great motions of the body produced ? 



59. What are muscles ? 



