22 PHYSIOLOGY AND ANATOMY. 
at the shoulder we had had the hinge-joint, like the one at 
the arm, then we could only havemoved our arm and shoulder — 
upward | and downward, which would be more inconvenient 
than it is now, when we can turn it in every direction. 
When we wish to raise our arm our minds speak to the 
muscles leading to the arm and tell them to contract, or 
shorten, and they instantly obey and the arm is raised. 
When we desire to put it down our minds. speak to Santer 
set of muscles, which expand, and the arm drops. 
‘In no part of the system is the variety, quickness and ac- 
curacy of muscular motion so remarkable as when we move 
our tongue in speaking. Every word we speak, every syla- 
ble we utter, requires a distinct action of a muscle. We also 
move a great variety of muscles in our hands when we write 
or otherwise use them ; also in our feet when we walk; and 
whet at, and in every thing else that we do. You will 
t what is meant by the contraction and ex- 
pansion of muscles if you will take a piece of India rubber 
and stretch it—this will show the expansion; and when you 
remove your hand it will take its original ‘size and appear- 
ance—this will show the contraction ; but in our bodies there 
are two sets of muscles, one for utah and the other for 
expansion, as you will see in the cut of the arm, and also the 
manner in which they are joined to the arm. Our muscles 
— and shorten to move our bones. 
