CHAPTER V. 

 JOINTS. 



The movements of the body are brought about by means 

 of soft reddish organs known as the muscles ; the lean of 

 meat is muscle, so every one knows what a dead muscle 

 looks like.* Muscles have the power of shortening with 

 considerable force ; when they do so they pull their ends 

 towards one another and swell out in the middle ; in 

 other words, they become shorter and thicker. With few 

 exceptions the ends of a muscle are attached to separate 

 bones \ between which a joint lies, and when the muscle 

 shortens, or, in physiological language, contracts, it pro- 

 duces movement at the joint. The joints and muscles thus 

 form the chief motor apparatuses of the body. 



What organs produce the movements of the body? What is the 

 technical name of the lean of meat? What power do muscles pos- 

 sess? What happens when they exert it? To what are the ends of 

 most muscles attached? What happens when the muscle contracts? 

 Name the chief motor apparatuses of the body? 



* In many animals some muscles are much redder than others, and it is then 

 found that the deeper colored are those which are kept most constantly in use ; the 

 leg muscles of a chicken, for example, are redder than those of the wings and 

 breast, ard as the coloring matter is turned brown by heat, they form the ' dark 

 meat" after cooking ; in birds which fly a great deal the breast muscles (which 

 chiefly move the wings) are also dark. The heart, which is a muscle always at 

 work, is deep red, even in fishes, most of whose muscles are pale. 



t As an example of a muscle not attached to the skeleton, we may take the orbic- 

 ular'^ oris, which forms a ring around the mouth-opening beneath the skin of the 

 Jip ; when it contracts it closes the mouth, or if it contracts more forcibly purses 

 out the lips. The orbicularis palpebrarum forms a similar ring around the eye 

 opening, and when it contracts closes the f>y e . 



