458 ORIGIN AND INSERTION OF MUSCLES. 
usually called the origin , and the other the insertion ,—the 
origin being in the part that is most fixed, and the insertion 
in that which moves upon it. Thus the muscle chiefly con¬ 
cerned in bending the elbow, has its origin at the shoulder 
and its insertion in the bones of the fore-arm; its general 
action being to move the latter, while the former is fixed or 
nearly so. But its attachment to the fore-arm may really 
become its origin, and its other attachment its insertion; for, 
when a person is hanging by his hands from a beam or cord, 
and raises his body by bending his elbows, the fore-arm is 
the fixed point, and the shoulder is moved upon it. In like 
manner, the muscular mass at the bottom of the back, having 
one attachment to the bones of the pelvis and another to the 
thigh-bone, serves to draw the latter backwards when the 
former is made the fixed point, as when we rise-up from the 
sitting posture; but it is also continually serving to keep 
the body upright upon the thighs, the latter being the fixed 
point, and brings it back into this position when it has been 
bent forwards as in stooping.—Muscles are seldom directly 
attached to the hard parts, but are united with them by 
means of the fibrous bands which are called tendons (§ 29). 
Sometimes the tendon is long and round; this is the case with 
several of those that move the hand and fingers (fig. 22 8), which 
arise from the muscles forming the fleshy part of the fore¬ 
arm, and may be felt at the wrists as hard round cords. In 
other instances, however, the tendon is a broad flat band; of 
such we find several within the shell of the body and limbs 
of the Crab or Lobster, when we have removed the muscle 
or flesh. 
606. The action of any muscle, in producing a change in 
the position of a movable bone on which it acts, is deter¬ 
mined in the first place by the nature of the movement of 
which the bone is capable; and in the second, by the direc¬ 
tion in which the power of the muscle is applied to it. 
Having now considered the former of these conditions, we 
proceed to the latter. The contraction of a straight muscle, 
which is attached to a fixed point at one end, and to a 
movable point at the other, will obviously tend to draw the 
latter towards the former. Thus the muscles which bend 
the fingers lie in the palm of the hand and on the correspond¬ 
ing side of the fore-arm; whilst those that straighten tho 
