This membrane surrounds all the bones. Hard, resisting, of a grey
colour, it forms for them a covering which extends everywhere, except
where the cartilages cover them. Its thickness is remarkable in
infancy; it is thinner in proportion in the adult and becomes more firm
and compact.
The ancients described it as extending from one bone to another over
the articulation, and thus forming a continuous sac for the whole
skeleton. This idea is incorrect. At the junction of the bones, the
periosteum intermixes with the ligaments which serve it as a means of
communication, and it is in this way only that we can understand its
continuity. The crown of the teeth is destitute of it, as well as all
the osseous productions that grow upon the head of certain animals.
The periosteum is feebly united to the bone in infancy; it can then be
separated with great ease, especially on the middle part of the long
bones. In the adult, as the calcareous substance gradually encrusts its
most internal fibres, the adhesion becomes very strong; it is extreme
in old age, in which this membrane is often reduced to a very delicate
layer by the progress of ossification. The constant pressure exerted
by the muscles in their contractions, can also have a little influence
upon this adhesion. Various elongations pass from the periosteum to the
bone. They are much more numerous at the extremities of the long bones
and upon the short bones, than upon the middle of the long bones, or
the broad ones; which may easily be conceived of, from the much greater
number of foramina in one than the other part. These elongations
accompany the vessels, line the canals which pierce through the bone,
are lost in those which terminate in its substance, do not penetrate
the medullary cavity, and confined to the osseous texture alone,
establish, between it and the membrane from which they arise, immediate
relations.
It is the destruction of these relations, when the periosteum is
diseased or destroyed for a considerable extent, that produces the
death and separation of the bone. There is however this difference
between this phenomenon and the death of the bone by the injury of the
medullary membrane, that if this is disorganized, necrosis seizes upon
the whole bone, whilst if we irritate and tear the periosteum in the
middle part of a long bone, for an extent nearly equal to that of this
medullary membrane, the external laminæ of the compact texture alone
are detached by exfoliation, and the bone remains the same. I have made
this experiment the year past upon two dogs. As to that which consists
in removing the periosteum, not only from the middle part, but from the
whole surface of the bone, I do not know that any one has been able to
try it; it has appeared to me impossible; it might be practicable, but
the animal would soon die from the extent of the injury, and thus we
could have no result from it.
The relations of the periosteum with the neighbouring organs vary
remarkably. In the greatest number of bones, there are muscles that
slide upon it; the cellular texture unites it to them more or less
closely according as the motions are more or less considerable. In
consequence of inflammations, it loses this laxity, and often all
motion ceases.
_Organization of the Periosteum._
The direction of the fibres of the periosteum is nearly analogous to
that of the bones, the long bones especially as well as the short; but
it has not the radiated structure of the flat bones that it covers.
These fibres placed upon each other, have different lengths; the
superficial ones are the longest; those which correspond immediately
with the bone run but a short distance. In general all become very
evident in some diseases of the bones. I recollect among other examples
of the preternatural development of the fibres, a man affected with
elephantiasis, and at the same time a swelling of the compact texture
of the tibia, which was of a remarkable thickness. The periosteum of
this bone was very thick, and adhered so little to the bone, that
the slightest effort was sufficient to raise it in its whole extent,
and its fibres were so distinct, that it might have been taken, when
separated from the bone, for a portion of plantar or palmar aponeurosis.
The periosteum borrows its vessels from those of the neighbouring
parts. Their innumerable branches ramify in it ad infinitum, form there
a net-work, which injections, especially in infants, make very evident,
they are afterwards lost in it, or penetrate the compact texture of the
bone, or return to the neighbouring parts to form anastomoses.
This membrane receives, as we have said, the insertion of almost all
the fibrous system, of the tendons, the ligaments and especially the
aponeuroses. This insertion has no connexion with the bone in infancy;
but ossification soon seizing upon the most internal laminæ, all the
fibrous organs appear to be identified with the bone in the adult. I
would observe that this arrangement coincides with the prodigious power
of drawing that the muscles, having become more developed, often exert
at this age, and which only spent upon the periosteum, as it would have
been without its ossification, would not have found in it a sufficient
resistance, whereas acting also upon the bone, it moves it without
endangering its covering. The general organization, the properties and
the life of the periosteum are the same as those of the fibrous system;
I shall not treat of them.
_Development of the Periosteum._
In the fœtus, this membrane is soft, spongy, containing much gelatinous
fluid; it melts easily in water; its fibres are not distinct; they
become so as we advance in age, and at the same time the softness
diminishes and the resistance increases. The periosteum in old age
has extreme tenacity; it resists ebullition almost as much as the
ligaments; those who prepare skeletons know this very well. It tears in
various places, because its fibres in contracting are detached from the
bone; but what remains becomes with great difficulty gelatinous.
_Functions of the Periosteum._
The periosteum defends the bones which it covers from the impression
of the moveable parts that surround it, from that of the muscles, of
the arteries, whose pulsation would wear them, as happens in certain
aneurismal tumours near the sternum, the vertebræ, &c.
It is a kind of parenchyma of nutrition in reserve, if I may so express
myself, always ready to receive the phosphate of lime, when it cannot
be carried upon the bone that has become diseased; hence natural and
artificial necroses which never take place in the teeth, from the
want of this membrane. These little bones have caries and various
alterations, but not true necrosis.
We cannot doubt that the internal laminæ of the periosteum are
successively ossified, and thus contribute not a little to increase
the bone in thickness, when its increase in length is finished. I
would observe upon this subject, that not only it, but all the fibrous
system, has a singular affinity with the phosphate of lime. Next to
the cartilaginous system, it has the greatest tendency to be encrusted
with it, no doubt because its kind of general vitality, of organic
sensibility in particular, has much analogy with that of the bones.
Where the tendons in sliding upon the bones experience great friction
they become osseous. The dura-mater and the tunica albuginea are very
often ossified; the sclerotica serves as a parenchyma for much earthy
substance in birds, which in consequence have it extremely hard.
The periosteum has no connexion with the formation of the bones; it
is only accessory to that of the callus; it is a kind of limit which
circumscribes within its natural bounds the progress of ossification,
and keeps it from irregular aberrations. Does it prepare the blood
which serves to nourish the bones? This question cannot be settled by
any experiment; but we are sure that the vital properties which it
enjoys, do not enable it to accelerate the circulation of the blood
arriving at the bones, as some authors have thought.
It seems to me moreover that they have described the periosteum too
exclusively in relation to the bones; no doubt it is necessary to these
organs; but perhaps it performs in relation to the fibrous organs a
still more important part. If nature has placed it everywhere on the
osseous system, it is probably in great part, as I have said, because
it finds in this system a general, solid and resisting support, which
enables it to resist the various drawings, that the whole fibrous
system makes upon it, drawings which are sometimes communicated to this
last system. This is a new point of view in which the periosteum should
be described, and it will yield much more to general considerations,
than that in which Duhamel, Fougeroux, &c. have considered this
membrane.