This system becomes stronger as we advance in age; in old age, it
becomes hard and yields with difficulty from the peculiar nature of
its nutritive substances. It is to this circumstance that must be
attributed, 1st, the stiffness and inflexibility of the vertebral
column, whose fibro-cartilages keep all the pieces in a kind of
immobility; 2d, a part of the difficulties which an old person
experiences in hearing sounds, the concha not being able to vibrate
and reflect them as well as before; 3d, the less susceptibility of his
nostrils to dilate, the fibro-cartilages yielding less to the muscular
effort, which is besides also less; 4th, the difficulties of the
sliding of the tendons, their grooves being much less supple.
The fibro-cartilages have in general much less tendency to ossify in
old age, than the cartilages properly so called. I never saw this
phenomenon in the membranous ones; perhaps it arises from their
peculiar texture, and even the difference of the principles which go to
their composition, and from the small quantity of gelatine that enters
into them. Among the articular, there are scarcely any but those of
the vertebræ, which are sometimes entered by the phosphate of lime;
this is however rare. Those of the grooves are like the cartilages of
the moveable articulations, they constantly keep their nature; only
in extreme old age, their thickness appears to diminish a little by
the ossification of their laminæ which correspond to the bone, which
besides is not very evident.