fibro-cartilaginous pad that is firmly attached to the articular faces of
the bones, and by peripheral ligaments that may be flat or formed by
scattered fibres. All _movable articulations_ are formed by bony surfaces
encrusted with a thin cartilaginous layer that makes them perfectly smooth,
ligaments and complimentary cartilages. Sometimes the bony surfaces do not
fit each other, and we find between them _fibro-cartilages_ that complete
the articulation by adapting the articular surfaces to each other. _Round_
or _flat ligaments_ may extend from one articular surface to the other, and
attached to the margins of the articulation are _membranous, flat_ or
_round ligaments_. Muscles and tendons that cross the articulations should
be included among the structures binding them together.

[Illustration: FIG. 29.--Photograph of model of stifle joint, showing:
ligaments; complementary cartilages; femur; and tibia.]

Movable joints possess a _synovial membrane_. This membrane lines the
structures that enclose the articulation and secretes a fluid, _the
synovia_, that lubricates the surfaces.

_The muscles_ are the contractile organs that move the body. The movement
of the different parts of the body is rendered possible through the manner
in which the skeletal muscles are inserted into the long bones, by which
the lever motion is possible. A muscle originating on one bone and
terminating on another either moves both bones toward each other or, if one
attachment is fixed, the movable is drawn toward the fixed part.

We may class muscles as _striated_ or _voluntary_ and _unstriated_ or
_involuntary._ A third class, _mixed,_ is represented by the heart muscle.
The striated is represented by the skeletal muscles, and the unstriated by
the thin muscular layers that form part of the wall of the stomach,