The cartilaginous system, like the osseous, is often developed
in organs to which it is naturally a stranger. But there is this
difference, that this phenomenon appears to be an effect of age
in the first, whereas in the second it is always the effect of
disease. Nothing is more common than to find cartilaginous balls in
scirrhous, cancerous tumours, &c.; in the middle of those frequent
morbid productions, in which the parts have an appearance like
lard, in the lungs, liver, &c. when enlarged. I do not know why the
peculiar membrane of the spleen has a great tendency to be encrusted
with gelatine; it is perhaps of all the organs, that in which the
preternatural cartilages are the most frequent. It is usually by
irregular scales that the cartilaginous development appears; sometimes
it attacks the whole membrane, which then presents a convex surface
analogous to the convex surfaces of the moveable articulations, which
the peritoneum covers, as these are covered by the synovial membrane.
Can the spleen, when thus cartilaginous externally, yield to the
changes of size that it often undergoes? I know not.
We know that there are often moveable and loose cartilaginous
substances in the articulations. Do they arise from the ossification
of a portion of the synovial membrane? I presume they do; for we
frequently see them hold to the cartilage by membranous expansions. I
have seen in a dead body, within the last year, the portion of synovial
membrane that goes from the fatty substance behind the patella, to the
depression that separates the condyles of the femur, almost wholly
cartilaginous. If during life it had been detached by the effect of
the motions, it would have formed one of these moveable and loose
cartilages. Besides, as I know but this fact which seems peculiarly
applicable to this point, I can only offer conjectures, especially as
we know that the synovial and serous membranes are of the same nature,
and yet these last hardly ever become cartilaginous.
Moreover these productions follow entirely the ordinary progress
of ossification. At first cartilaginous and without blood vessels,
they soon acquire a red centre, then osseous, which extends from
the centre to the circumference, and which sometimes terminates by
seizing upon the whole cartilage; so that they are real bones. This
last circumstance is however very rare. The state in which we most
commonly find these productions, is that in which they are osseous in
the middle, and cartilaginous at the circumference. I found one of them
in the articulation of the pisiform bone, of the size of the head of a
great pin, and which, in its whole thickness was harder than ivory.