THE MUSCLES. 5Ir 
in sheaths of another kind of tissue. Fig. 46 represents such a bundle of 
fibres. The individual fibres, again, are streaked in two ways—lengthwise 
and crosswise. When separated from each other, they often split up into 
fibrille} or little fibres, as 
seen in fig. 47. Other fibres, 
when extended, separate, ac- 
cording to the cross streaks, 
into discs, as seen in fig. 47, 
a,b; and when this separation ceguer seein 
takes place both ways at once, . Fig. 47. 
the fibre is separated into a 
mass of particles, b/ in fig. 47. When a muscle is being contracted, 
these cross discs of the individual fibres become more closely squeezed 
together, and the fibre becomes thicker as it is shortened, in a manner 
similar to what is seen to take place in the’ body of a worm, when it is 
drawing itself up after having put forward its head. 
The muscles are attached to the bones by means of tendons,? which are 
white, smooth, non-elastic bands at the ends of the muscles, of a different 
structure from the muscle itself. Of the two component parts of fibrous 
tissue, the elastic and the non-elastic, only the non-elastic, which is white, 
is found in tendons ; a tendon being formed of fibres of this white tissue, 
one fibre coming from each fibre of the muscle. The tendon itself is a 
tough, white mass, attached to the bones by the individual fibres becoming 
fixed in depressions in the bones, and also by becoming amalgamated with 
the hard outer part of the bone called the periosteum. The muscle being 
thus attached at its ends to two bones, a distinction is made between the 
two ends ; the point of attachment to the less movable bone is called the 
origin, while that to the bone specially to be moved is called the insertion ; 
thus, the muscle which bends the elbow is attached to the shoulder and to 
the fore-arm ; the point of attachment of this muscle at the shoulder is its 
origin, and the point of attachment in the fore-arm its insertion. Muscles 
such as the one here alluded to—that is, those that bend joints, the best 
example being the muscles that bend the fingers on the palm—have a 
particular name, flexors, or benders, from Latin flecto, to bend. Where such 
muscles exist, there is always, of course, another set that reverse this 
bending action, or extend the bones connected with the joint, and are 
hence called extensors, from Latin extendo, to extend; such are the muscles 
that open the hand, by extending the fingers. Muscles which act in 
opposition to each other in this way, as flexors and extensors, are said to 
be antagonistic, or the one is said to be the antagonist of the other. 
The various bones acted on by the muscles. are like so many levers 

1 Latin, diminutive of fibre, threads. 2 From Latin tendo, to stretch. a 
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