We may divide the fibro-cartilaginous organs into three classes.
The first comprehends those which are found in the ears, the alæ of
the nose, the trachea, the eye-lids, &c. They are very delicate, like
membranes, sometimes arranged in an uniform manner, sometimes bent in
various directions. As neither their position nor functions have any
thing in common, we cannot give them a denomination derived from their
forms. We may designate these substances by the name of membranous
fibro-cartilages. Besides it is not only in its form, but also in its
nature, that this class differs from the others, as we shall see.
In the second class are ranked the inter-articular substances, which
occupy the interstices of the moveable articulations, whether they
are in part loose in the cavity, like those of the knee, of the lower
jaw, &c. and go in different directions according to the motions, or
whether, like that of the body of the vertebræ, they are fixed in a
solid, though moveable manner, on the osseous surfaces. These organs
are in general thicker than the preceding, very various in their form,
representing commonly a kind of laminæ, sometimes perforated through
the middle in the articular cavities, arranged in very thick fasciæ,
and formed like the body of the vertebræ in the vertebral column. We
may designate them under the name of articular fibro-cartilages.
I refer to the third class certain portions of the periosteum in which
the nature of this membrane is entirely changed, becomes penetrated
with gelatine and exhibits an aspect at first analogous to that of
the cartilages, but in which it is easy however to distinguish the
fibrous texture. These portions are found in the tendinous sheaths, in
which they facilitate the sliding of the tendons, and defend the bones
from their impression. They may be called the fibro-cartilages of the
tendinous sheaths.
These three classes of fibro-cartilages, though very analogous, have
not exactly the same structure, the same vital properties, nor the
same life; so that the system they form is not as homogeneous in its
different divisions, as the osseous, animal muscular systems, &c.