[Illustration: FIG. 156.--Section of Upper End of Fibula, showing
caseating focus in marrow, erupting on articular surface and infecting
joint.]
_Changes in the Synovial Membrane._--In the majority of cases there is a
_diffuse thickening of the synovial membrane_, due to the formation of
granulation tissue, or of young connective tissue, in its substance.
This new tissue is arranged in two layers--the outer composed of fully
formed connective or fibrous tissue, the inner of embryonic tissue,
usually permeated with miliary tubercles. On opening the joint, these
tubercles may be seen on the surface of the membrane, or the surface may
be covered with a layer of fibrinous or caseating tissue. Where there is
greater resistance on the part of the tissues, there is active formation
of young connective tissue which circumscribes or encapsulates the
tubercles, so that they remain embedded in the substance of the
membrane, and are only seen on cutting into it.
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