ed, examination should always be made for the other
before treatment is applied. When a fracture occurs near a joint the force
sufficient to rend the bone is liable to be partly exerted on the immediate
tissues, and when the bone gives way the structures of the joints may be
seriously injured. It occasionally happens that the injury to the joint
becomes the most important complication in the treatment of a fracture. In
order clearly to understand the reason for this a few words are necessary
in relation to the structure of joints.

The different pieces constituting the skeleton of the animal body are
united in such manner as to admit of more or less motion one upon another.
In some of the more simple joints the bones fitting one into another are
held together by the dense structures around them, admitting of very little
or no movement at all, as the bones of the head. In other joints the bones
are bound together by dense, cartilaginous structures, admitting of only
limited motion, such as the union of the small bones at the back part of
the knee and hock (metacarpal and metatarsal). In the more nearly perfect
form of joint the power of motion becomes complete and the structures are
more complex. The substance of the bone on its articular surface is not
covered with periosteum, but is sheathed in a dense, thin layer of
cartilage, shaped to fit the other surfaces with which it comes in contact
(articular). This layer is thickest toward its center when covering bony
eminences, and is elastic, of a pearly whiteness, and resisting, though
soft enough to be easily cut. The bones forming an articulation are bound
together by numerous ligaments attached to bony prominences. The whole
joint is sealed in by a band or ribbonlike ligament (capsular ligament)
extending around the joint and attached at the outer edge of the articular
surface, uniting the bones and hermetically sealing the cavities of the
articulation. This structure and the articular surface of the bone is
covered by a thin, delicate membrane, known as the "synovial membrane,"
which secretes the joint oil (synovia). This fluid is viscid and colorless,
or slightly yellow, and although it does not possess a large quantity of
fat, its character somewhat resembles oil, and it serves the same purpose
in lubricating the joints that oil does to the friction surface of an
engine. Although the tissues of the joint when used in a natural way are
able to withstand the effect of g