an is revealed through a study
of the perimysium. This is not limited to the surface of the muscle, as
the name suggests, but properly includes the sheaths that surround the
bundles of fibers. Furthermore, the surface perimysium and that within the
muscle are both continuous with the strong, white cords, called _tendons_,
that connect the muscles with the bones. By uniting with the bone at one
end and blending with the perimysium and fiber bundles at the other, the
tendon forms a very secure attachment for the muscle. The perimysium and
the tendon are thus the means through which the fiber cells in any
muscle-organ are made to _pull together_ upon the same part of the body
(Fig. 110).

*Purpose of Striated Muscles.*--The striated muscles, by their attachments
to the bones, supply motion to all the mechanical devices, or machines,
located in the skeleton. Through them the body is moved from place to
place and all the external organs are supplied with such motion as they
require. Because of the attachment of the striated muscles to the
skeleton, and their action upon it, they are called _skeletal_ muscles. As
most of them are under the control of the will, they are also called
_voluntary_ muscles. They are of special value in adapting the body to its
surroundings.

*Structure of the Non-striated Muscles.*--The cells of the non-striated
muscles differ from those of the striated muscles in being decidedly
spindle-shaped and in having but a single well-defined nucleus (Fig. 111).
Furthermore, they have no striations, and their connection with the nerve
fibers is less marked. They are also much smaller than the striated cells,
being less than one one-hundredth of an inch in length and one
three-thousandth of an inch in diameter.

In the formation of the non-striated muscles, the cells are attached to
one another by a kind of muscle cement to form thin sheets or slender
bundles. These differ from the striated muscles in several particulars.
They are of a pale, whitish color, and they have no tendons. Instead of
being attached to the bones, they usually form a distinct layer in the
walls of small cavities or of tubes (Fig. 111). Since they are controlled
by the part of the nervous system which acts independently of the will,
they are said to be _involuntary_. They contract and relax slowly.

[Fig. 111]

Fig. 111--*Non-striated muscle cells.* _A._ Cross section of small artery
magnifie