ranous sheath.
Each _fasciculus_ contains a number of small fibers, which, when
subjected to a microscopic examination, are found to consist of
_fibrillae_, or little fibers; each of these fibrillae in turn being
invested with a delicate sheath. The fibers terminate in a glistening,
white _tendon_, or hard cord, which is attached to the bone. So firmly
are they united, that the bone will break before the tendon can be
released. When the tendon is spread out, so as to resemble a membrane,
it is called _fascia_. Being of various extent and thickness, it is
distributed over the body, as a covering and protection for the more
delicate parts, and aids also in motion, by firmly uniting the muscular
fibers. The spaces between the muscles are frequently filled with fat,
which gives roundness and beauty to the limbs. The muscles are of
various forms; some are longitudinal, each extremity terminating in a
tendon, which gives them a _fusiform_ or spindle-shaped appearance;
others are either fan-shaped, flat, or cylindrical.

[Illustration: Fig. 20.
1. A spindle-shaped muscle, with tendinous
terminations. 2. Fan-shaped muscle.
3. Penniform muscle. 4. Bipenniform
muscle.]

[Illustration: Fig. 21.
Striped muscular fibre showing cleavage in
opposite directions. 1. Longitudinal cleavage.
2. Transverse cleavage. 3. Transverse section of
disc. 4. Disc nearly detached. 5. Detached disc,
showing the sarcous elements. 6. Fibrillae. 7,8.
Separated fibrillae highly magnified.]

Every muscle has an _origin_ and an _insertion_. The term _origin_ is
applied to the more fixed or central attachment of a muscle, and the
term _insertion_ to the movable point to which the force of the muscle
is directed; but the origin is not absolutely fixed, except in a small
number of muscles, as those of the face, which are attached at one
extremity to the bone, and at the other to the movable integument, or
skin. In most instances, the muscles may act from either extremity. The
muscles are divided into the Voluntary, or muscles of animal life, and
the Involuntary, or muscles of organic life. There are, however, some
muscles which cannot properly be classified with either, termed
Intermediate. The _Voluntary Muscles_ are chiefly controlled by the
will, relaxing and contracting at its pleasure, as in the motion of the
eyes, mouth, and limbs. The fibers are of a dark red color, and possess
great strength. These fibers are parallel, seldom interlacing, but
p