These membranes which comprehend, as has been said, the periosteum, the
dura-mater, the sclerotica, the albuginea, the peculiar membrane of the
spleen, the kidneys, the corpus cavernosum, &c. are almost all destined
to form external coverings, kind of sacs in which are contained the
organs they invest.
These organs are not, like those around which the serous surfaces are
spread, as the stomach, the intestines, the bladder and the lungs,
subject to alternate dilatations and contractions. This would not
accord with their degree of extensibility. They are fitted exactly to
the form of these organs, and have none of those numerous folds which
we see in the serous membranes, if we except however the dura-mater.
Their two surfaces are adherent; a character which distinguishes them
especially from the preceding membranes, as well as from the mucous.
One of these surfaces, intimately united to the organ, appears to send
various elongations into it, which identify at first view its existence
with that of the membrane. Many fibres detached from the albuginea,
from the covering of the corpus cavernosum, from the peculiar tunic
of the spleen, &c. or rather adhering to these tunics, penetrate the
respective organs of these membranes, and crossing there in various
directions, form as it were the outline and frame, around which are
arranged and supported the other constituent parts of these organs,
which seem from this to have the external membranes for a mould; as we
see when these moulds are removed, irregular vegetations shooting up
here and there. The callus, in displacements too great to allow the
periosteum to extend over the divided surfaces, is rough and uneven.
The form of the testicle alters, when the albuginea has been divided at
any part. This adherence of the fibrous membrane which covers different
organs, to the internal elongations of these organs, and the fibres
which compose their outline, has made anatomists believe that the
nature of one was the same as that of the others, that these were but
elongations of the membrane. I thought so when I published my Treatise
on the Membranes; but new experiments have since convinced me of the
contrary.
I am confident that the membrane of the corpora cavernosa belongs to
the fibrous system alone. The internal spongy texture, contained in
the cavity of this membrane, has not the nature of it, is not as all
anatomists say an elongation of it. The spongy texture is not made by
laminæ, which, according to the common expression, are detached from
the membrane and produce it by their interlacing. This is a separate
body, unlike in its life and its properties.
By exposing a corpus cavernosum to ebullition, I have evidently
observed this difference; the external membrane does, like all the
fibrous organs, become thick, yellowish, semi-transparent, then melts
more or less into gelatine; the spongy texture, on the contrary,
remains white, soft, does not increase in size, hardly crisps at all
from the action of fire, exhibits, in a word, an appearance which I can
compare to no texture treated in the same way by ebullition.
Maceration also answers very well to distinguish these two textures.
The first yields but slowly to it; its fibres remain a long time
distinct; they have still their natural arrangement, when the second
is already reduced to a homogeneous, reddish pulp, in which nothing
fibrous, nothing organized can be any longer traced. In general, it
appears that the spongy texture of the corpora cavernosa is their
essential part, that in which the great phenomena of erection take
place, that which animates the peculiar kind of mobility which
distinguishes it from the other organs. The fibrous shell is only
accessory to its functions; it is but a covering; it is only formed to
obey in erection the impulse which is communicated to it.
When we expose the corpus cavernosum to the action of the nitric acid,
the spongy texture, freed from the blood it contained, becomes of
a much deeper yellow than the fibrous membrane; this enables us to
distinguish them clearly from each other.
By exposing the testicle to the action of boiling water, we also
observe that its internal texture assumes an aspect wholly different
from that of its external membrane; it becomes of a deep brown, whilst
the other remains white; it does not assume the gelatinous appearance
in so decided or in so prompt a manner as that of the corpus cavernosum.
Subjected to maceration, the testicle is also wholly different in its
covering and in its internal texture.
The surface of the fibrous membranes, opposite to that which
corresponds to their organ, is joined to the neighbouring parts,
sometimes in a loose manner, as the covering of the corpus cavernosum,
sometimes by very tight bands, as the dura-mater. In general the
membranes, and even all the fibrous organs, have a singular tendency
to unite intimately to the serous and mucous surfaces. We find examples
of this in the serous membranes in the union of the dura-mater with
the arachnoides, of the albuginea with the tunica vaginalis, and the
fibrous capsules with the synovial. Such is the intimacy of this
adhesion, that the most careful dissection cannot destroy it in adult
age. In infancy, it is much less, as we see very well especially in
the relation that exists between the base of the pericardium and
the phrenic centre, a relation which is such, that we can with ease
separate in the first age the two surfaces which are rather contiguous
than continuous, whilst in the after ages we are unable to do it.
As to the union of the mucous surfaces with the fibrous, when they are
found contiguous, they are entirely confounded; this is observed in
the pituitary membrane, in that of the sinuses, of the ear, &c. The
perichondrium of the larynx and of the trachea is only a part of their
internal membrane. In all these parts, the periosteum so intermixes
with the mucous surface, that it is impossible to separate them, and
they are removed together from the bone, which then remains bare. The
vas deferens, the fallopian tubes, the ureters, &c. are also very
evidently fibro-mucous.