The texture of the bones, like that of most of the other organs,
presents itself under the aspect of fibres whose nature is everywhere
the same, but which differently arranged, form two principal
modifications; in the one, these fibres being more or less scattered,
exhibit many cells; in the other being close to each other, they form a
compact substance in which it is difficult to distinguish them. Hence
two sub-divisions of the osseous texture, that with cells, and the
compact. Authors admit a third one, the reticular; but this is included
in the first.
_Texture with Cells._
The texture with cells does not exist in the first periods of
ossification. The time of its formation is when the phosphate of lime
is added to the gelatine of the primitive cartilage, and gives to the
organ the bony nature. Then an infinite number of cells is formed in
the solid mass of cartilage, because the gelatine, taken up by the
absorbents, disappears in the place they occupy. No more is brought
by the exhalants, which begin to carry the phosphate of lime to the
fibrous cross-pieces, whose interlacing forms these cells; so that
the development of the texture of the cells belongs evidently to the
disproportion that takes place in the bones at a certain period of
their growth, between the functions of the exhalant and absorbent
system, until then in equilibrium. We know not the cause of this
disproportion, it appears to be a law of ossification. It is by virtue
of this law and by an analogous mechanism, that the os ethmoides, at
first solid and full when it is cartilage, is hollowed out at the
period of its ossification, into a great number of cells. It is thus
that the sphenoidal, frontal sinuses, &c. are formed and enlarged.
The formation of the texture of the cells ceases when all the epiphyses
have disappeared. At this period it exhibits to us an infinite number
of fibres which appear to arise from the internal surface of the
compact texture, go in different directions, cross, unite, separate,
bifurcate, in a word, pursue such irregular courses, that it is
impossible to follow them. Their size is not less variable; sometimes
their delicacy is such, that they can hardly be touched without
breaking; at others they are quite large. Often instead of fibres there
are layers, of more or less considerable size, from which arise other
smaller ones, which appear to ramify, and from which result, when
they are near each other, species of canals, which are seen very well
by sawing transversely the extremity of a long bone, so as to have a
segment of half an inch.
The cells which are made by their separation, are of very unequal form
and capacity.
All communicate together; the following experiments prove this. 1st.
If we make a hole in the extremity of a long bone, or upon the surface
of a short or flat one, and pour in mercury, it passes through all the
communications, and comes out of the natural foramina on the surface
of the bone, which also open into the cells. 2d. Saw a long bone at one
of its extremities, cover its whole surface with something that shuts
up its pores, then expose it to the sun; the medullary fluid not being
able to escape by the external pores, will come out at the sawed place,
after passing successively through all the cells. 3d. By varnishing a
dry bone, and opening it only in two opposite points, we can force air,
water and every kind of fluid through these communications, from one
opening to the other.
We can then consider the interior of every bone as forming a general
cavity that is filled by many interlaced fibres. I have not observed a
sensible difference in the direction of these fibres in the three kinds
of bones.
_Compact Texture._
The fibres that form the compact texture are not the same as those
of the preceding. These fibres, being in juxta-position, not leaving
any space between them, giving by their approximation a remarkable
density to the texture they form, have a longitudinal direction in the
long bones, are in the form of rays in the flat ones, and cross each
other in all directions in the short ones. This triple arrangement of
the fibres of the compact texture appears to be wholly owing to the
manner of ossification. In fact, when we examine its progress in the
primitive cartilages, we see these organs encrusted with the phosphate
of lime, in the same direction which these fibres afterwards take.
Thus these fibres are very evident in the first age, on the bones of
the cranium in particular. When the phosphate of lime, successively
deposited on the cartilaginous parenchyma, predominates there, then
the whole is confounded in the compact texture in one homogeneous
mass. But still there are different circumstances that indicate the
primitive direction of the fibres: 1st. When by an acid we remove from
bones their calcareous part, then the cartilaginous portion keeps as a
kind of mould, the form of the substances that filled it, and exhibits
fibres whose direction is the same as that pointed out for the three
species of bones. If we wish to separate the cartilaginous layers, it
is in this direction that it is most easily done. 2d. The fissures that
come in bones long exposed to the air follow in general the natural
direction of the fibres. 3d. Calcined bones exhibit nearly the same
phenomenon.
The direction of the fibres of the compact texture is changed entirely
in the apophyses, in which it does not follow that of the principal
bone. In those, which by their form, partake of the character of the
long bones, as in the styloid, these fibres are longitudinal; they
go in all directions in those, which like the mastoid, the different
species of condyles, &c. resemble in their shape the short bones.
The assemblage of the fibres forms, according to anatomists, layers
which they have considered as in juxta-position, and held together
by little pins according to some, and by the interlacing of fibres
according to others. These osseous layers do not appear to me to exist
in nature. All the fibres of the compact texture adhere to each other,
cross and form a whole that we cannot conceive of in this manner, and
which besides does not accord with the irregularity of the distribution
of the vessels. Art separates here fibres layer by layer, as it is
done in a muscle, in a ligament, &c.; but these layers are wholly
factitious; to exhibit the bones as formed by an union of these layers
is to give a very inaccurate idea of their structure. It is still
more inaccurate to consider these layers as attached to each other by
osseous pins, by attraction, or by a glutinous matter which serves as
a glue. All these ideas, contrary to anatomical examination, suggested
by a false application of the laws of the adhesion of inorganic bodies
to the adhesion of organized fibres, now belong only to the history
of physiological errors. There is a circumstance, it is said, that
very evidently proves the lamellated structure of the bones, it is
their exfoliation. It is true that often very distinct layers are
separated from the living bone, but these layers are only the product
of exfoliation itself. Then in fact the bone dies on the surface;
the superficial vessels receive no more blood; this fluid is stopped
under the portion deprived of life, the exhalation of the phosphate of
lime ceases there, every kind of sanguineous, exhalant and absorbent
vessel is destroyed; a slow inflammation, with suppuration, comes on,
and fixes the line of demarcation; and as this line is often at the
same place, all which is above it becomes an inorganic layer which
gradually falls off, and preserves its osseous solidity, because the
dead absorbents were not able to remove the phosphate of lime. Besides,
nothing is more common than to see exfoliation take place not by
layers, and the bone afterwards exhibit an unequal surface, the effect
of the inequality of the thickness of the exfoliated portions. Finally,
exfoliation often takes place in a direction opposite to that which the
layers are thought to have; this is what we see in the separation of
the extremity of the long bones, that have been exposed to the air or
too much irritated after amputation, in the shedding of the horns of
animals, &c. Let us consider the compact texture as an assemblage of
condensed fibres, not separated by layers, which we can only consider
as imaginary.
The fibres of the compact texture differ in their organic arrangement,
from the muscular fibres in this, that frequent elongations unite them
to each other, whereas the muscular have only the cellular organ, the
vessels and the nerves as the means of union. Such is the intimate
juxta-position of the fibres of the compact texture, that they leave
between them only pores hardly sensible to the naked eye, but which
become so however with a glass, and which the medullary juice and
vessels fill. In the rickets this density of texture disappears, and
we observe in the middle part of the long bones and under the layer of
periosteum more thick than common, an osseous texture, easily bent in
all directions, forming an infinity of cells and taking the place of
the compact texture that ought to be there. It appears that this change
of compact texture into that of cells is made less by the absorption of
a part of the phosphate of lime, than by the extension of the osseous
fibres which separate from each other, and leave between them spaces
that did not before exist; this gives to the bodies of long rickety
bones a very considerable thickness. I have many times made this remark.
_Arrangement of the two Osseous Textures in the three kinds of Bones._
The osseous textures, considered in the different kinds of bones, are
differently arranged. In general the compact forms the exterior, the
covering of the bone, and that of the cells occupies the interior. The
ossa spongiosa form an exception to this rule, the modifications of
which we shall now examine.
1st. In the long bones, the compact texture has a very remarkable
thickness in the centre, where it serves the triple purpose, first
of protecting the medullary organ, of which it is the covering,
then of giving solidity to the bone in this place, which more than
the extremities, is exposed to great efforts in locomotion, falls,
concussion, &c. and where the bone, traversed only by some very weak
fibres of the cells, cannot borrow its resistance but from its external
parietes; finally, of thus diminishing without danger the size of the
bone in the middle part of the limb, the form of which, becomes by
this means much more regular. So that as we go from the centre, we see
in a long bone, sawed longitudinally, the compact texture diminish
in thickness, and form at last at the extremities only a delicate
layer analogous to that which covers the short bones. Thus the power
of resistance of the long bones, at their extremity, is less in their
compact shell, than in the great quantity of the texture of the cells
deposited under it; it is this especially that prevents fractures;
hence we see how the proportion of the compact texture and that of the
cells being inverse in the two parts of the bone, the manner of their
resistance is also inverse.
The texture of the cells differs a little when examined in the
medullary canal and in the extremities. In the canal there are
extremely delicate filaments, continued from larger fibres which fill
above and below the extremities of the bone, and the compact portion
which forms the osseous cylinder. Few and scattered at random in the
middle of the canal, these filaments approximate each other, and form
a kind of net-work, as they go from it; hence the name of reticular
substance by which it is designated. But it is not a distinct texture,
it is only a modification of that of the cells; a modification, which
is especially characterized, 1st, by the delicacy of the fibres; 2d,
by the uniform absence of those fine and short layers which frequently
belong to this texture in other parts. Besides, the manifest use of
this portion of the texture of the cells, too weak to contribute to
the resistance of the bone, is evidently to serve as a support to the
medullary system, and insertion for its membrane. At the extremities
of the long bones, the fibres of the texture of the cells increase
a little, approximate each other, are scattered in layers, and give
to the bone by their union and number, a remarkable thickness and
resistance, without however increasing the weight, which very much
favours locomotion, considering that this weight placed at the
extremity of the lever would have been very painful to raise.
2d. In the flat bones, the compact texture forms two external layers,
the thickness of which is between that of the middle of the long bones,
and that of the extremity of the same bones, or that of the short ones.
Between these two layers is found the texture of the cells, similar
in general to that of the extremity of the long bones, a little more
lamellated however, thicker usually at the circumference, often almost
wanting in the middle of the bone, where its two compact layers in
juxta-position allow a light to be seen through it, when placed behind.
In general wherever the broad bones are so thin, from the want of the
texture of the cells, there are very strong muscles, which by their
thick layers give solidity to the bone. We see examples of this in the
iliac, sub-scapular, inferior-occipital fossæ, &c.
3d. In the short bones, the texture of the cells always predominates;
the bone is almost wholly formed of it, a delicate layer of compact
texture forms only its covering, and in this respect, the organization
of these bones is the same as that of the long bones at their
extremities; thus the resistance of the bone depends on the whole of
its mass, and no part makes a greater resistance than another against
fractures. We see, from all that has thus far been said, the successive
manner of the solidity of the different bones. In the middle of the
long bones, there is hardly any thing but compact texture to which it
is owing; in the flat bones it is as much to this texture as to that of
the cells; in the extremities of the long bones and in the short ones
it is almost to this last only that its solidity is owing.
4th. In the osseous eminences, the compact texture is more abundant
than elsewhere, especially in those of insertion, as in the prominent
lines of the long bones, which are all formed of it, in the asperities
of the osseous surfaces, in their angles. If the eminence is
considerable, there enters into it also more or less of the texture
of the cells as we see in the spinous and transverse processes of the
vertebræ, in the coracoid, mastoid, &c. processes. The eminences of the
moveable articulations have in general less of the compact texture,
solidity is given to the bone by the articular cartilage. Those of the
immoveable articulations, on the contrary, in general smaller, as the
sutures of the bones of the cranium, for example, are in proportion
more compact than cellular.
5th. In the osseous cavities, all those which serve for moveable
articulations, are only furnished with a very delicate compact layer;
it is thicker when the articulations are immoveable. In general all
the foramina, cavities and canals that transmit from one region to
another vessels, nerves or other organs are everywhere lined with a
compact layer that defends them from the impression of these parts.
The foramina at the base of the cranium, the dental canals, the vidian
foramina, &c. are examples of this arrangement.
_Of the Composition of the Osseous Texture._
Whatever may be the modifications under which it is exhibited, the
osseous texture has everywhere the same nature; the same elements form
it; now these substances are especially a saline calcareous substance
and a gelatinous one.
The existence of the saline substance in the bones is proved in
different ways. 1st. Combustion, by destroying the gelatinous portion,
leaves a friable, brittle body, of a form analogous to that of the bone
and which is nothing but this saline substance, which resembles, if
we may so say, a moulded body that keeps the form of the mould after
it has been taken away. If the combustion is pushed very far, and a
red heat produced on the calcined bones, they undergo a semi-fusion,
which makes them resemble the state of porcelain; they have then a
very compact, fine, semi-vitreous grain, a semi-transparency, and an
appearance like that of the vitrified earths. 2d. The long continued
exposure of the bones to the air produces an effect very similar to
that of the first degree of combustion, though however the gelatine
is rarely so thoroughly removed, and the saline portion so perfectly
exposed as by the action of fire. Besides, it requires a very long time
to produce this effect, especially upon the thick bones; the thin ones
are more easily altered; I have often made this observation. After ten
years exposure to the air and rain, I have observed that clavicles
taken from the cemetery of Clamart, exhibited upon the action of the
acids, a cartilaginous parenchyma almost equal to that of a bone that
had been some time dried. But this parenchyma finally disappears, and
the bone falls to powder, when it is no longer supported by it, and the
particles of the remaining calcareous substance have been disunited
by time. 3d. In the last stages of all cancerous diseases, the bones
have a friability which is only owing to the greater proportion of this
last substance, a proportion arising itself from the small quantity
of gelatine that is then exhaled in the bones. 4th. When a bone has
been for some time exposed to the action of an acid, the nitric for
example, a portion of its substance is taken from it by this acid,
which is evidently a calcareous salt, as can be seen by mixing it
with a solution of an alkali, which uniting immediately to the acid,
exposes this salt, by making it precipitate. 5th. Papins digester, by
dissolving by the action of water reduced to vapour the gelatinous
portion, shows also this saline calcareous part.
Scheele has found that this portion is a neutral salt with an earthy
base, the phosphate of lime. Frequently the phosphorus in fresh bones
give them a luminous appearance, that can be seen very far in the
night. It is sometimes the whole of the bone, sometimes some parts only
that become luminous. I have always observed in the illuminated places
an oily exudation, either that comes from the medullary juice, or is
furnished by the fat of the neighbouring soft parts of the bone.
Different facts as evident as the preceding, prove in a manner not less
certain, the existence of a gelatinous substance in the bones. 1st.
When in the solution of the bones in the acids, the phosphate of lime
has left them, there remains a cartilaginous, flexible, elastic body,
yellowish when nitric acid is employed, of the same form as the bone.
Now we know that the gelatine especially nourishes the cartilages. 2d.
If besides we subject this cartilaginous residue to ebullition, we
extract a very great quantity of gelatine which is dissolved in the
water and can be afterwards precipitated by tannin. This substance
can even be removed from the bones without the previous extraction of
the phosphate of lime; it is thus that with bones stripped of every
surrounding organ, and reduced to very small fragments or even to
powder by the action of a rasp, very nourishing broths and jellies
are made. It is not without reason that in the preparation of boiled
meat, the bone is left attached to the meat; besides the white organs
that surround it, and the medullary oil that it contains, it furnishes
to the broth a substance that is peculiar to it. 3d. The combustion
of the bones, and especially of their cartilaginous residue, gives
an odour exactly similar to that of the combustion of the different
animal glues, which, as we know, the gelatine especially forms. 4th.
In the different affections in which the bones become soft, the earthy
substance is diminished more or less sensibly, and the gelatinous
remains more abundant in proportion than common.
These two substances, the gelatinous and saline, which enter
essentially into the composition of the bones, imprint upon them
very different characters. The phosphate of lime, almost foreign to
vitality, is only destined to give to the bones the solidity and
resistance that characterize them. The gelatinous substance, on the
contrary, has especially the animal character; thus the vital activity
is in the inverse ratio of one and the direct ratio of the other, as
we shall see. Deprived of gelatine, the bones are not capable of being
digested, they offer nothing for the gastric juices to act upon, they
cannot extract nutritive matter from them, because they act upon them
nearly as water does, which dissolves the gelatinous substance and
extracts it from the saline portion. Different animals that swallow
fresh bones for nourishment, would die from eating a calcined one; thus
the more the bones contain of this substance, the more nourishing they
are; those of young animals are on this account more proper to make
gelatinous broths, more suitable to be digested raw by the stomachs
of certain species, &c. If we expose a bone to the action of an acid,
so as to have only its cartilaginous parenchyma left, and afterwards
soften this parenchyma in boiling water, it becomes an aliment that can
be eaten.
Besides phosphate of lime and gelatine, the bones contain also some
saline principles, as the sulphate and carbonate of soda, &c. But this
proportion is too small to be noticed. Upon this point, I refer to
chemical books, especially to the great work of Fourcroy.
II. _Common Parts which enter into the organization of the Osseous
System._
The ancients ranked the bones among the white parts, among the tendons,
the cartilages, &c. It is sufficient however to examine the interior of
them to see, by the redness that distinguishes them, that much blood
enters them. This blood penetrates in three orders of vessels; one
belonging to the medullary cavity of the long bones, another to the
texture of the cells, and the other to the compact texture. These two
last orders distributed in the osseous texture, appear to be especially
destined to deposit the phosphate of lime; for in the cartilages of
ossification, the white vessels alone carry the gelatine; in other
cartilages it is the same; so that I think that this kind of vessels is
also destined in the bones which are perfectly formed to nourish their
cartilaginous parenchyma, whilst the red vessels belong more to their
calcareous portion.
Each medullary cavity has only one vessel, and only one foramen of
nutrition. This vessel has a diameter proportioned to that of the bone
which it penetrates, and in which it is divided immediately into two
branches, without permitting any ramification on the compact texture.
These go in an opposite direction to the two extremities of the bone,
ramify ad infinitum in the medullary organ, and their last branches
are lost in the commencement of the texture of the cells, where they
anastomose with the vessels of this texture; that which occupies the
medullary cavity under the name of reticular, and the internal surface
of the compact texture, receive also some branches. A vein everywhere
accompanies the artery, and follows the different distributions of it.
The vessels of the second order belong to the texture of the cells
of the long, flat and short bones; they are equal in number to the
foramina of this texture, and ramify on its cells; they communicate
with those of the marrow and of the compact texture. At death, the
small arteries in general remain full of red blood, which indicates
their course which their minuteness would conceal, and which injections
can rarely demonstrate with accuracy. The accompanying veins of these
arteries can hardly be seen.
The blood-vessels of the third order are only the last ramifications
of the arteries surrounding the bones, ramifications which enter in
great number the compact texture, and stop there. The existence of
these vessels may be proved in different ways. 1st. By detaching the
dura mater from the internal surface of the cranium, many small
sanguineous drops prove their rupture. 2d. By raising on a subject
of a middle age the periosteum, we make the same observation. I have
remarked that these experiments succeed especially on those that have
been drowned, or on animals destroyed by asphyxia, on account of the
great quantity of blood their vessels contain. 3d. If we fracture a
long bone in the middle, the compact portion, which forms the medullary
canal, exhibits small reddish striæ, which are nothing but these small
vessels still full of blood, and of which we thus discover a greater or
less number, according to the manner in which the blood was arrested in
the capillary system at the instant of death. 4th. The saw-dust of the
compact texture in living animals is red, though less evidently so than
that of the texture of the cells; a proof that these vessels have been
divided.
The vessels of the bones are very numerous in childhood; they diminish
in the adult, and become scarce in old age. The facility of the
formation of callus follows the same proportion in the different ages
of life. Often in affections of the osseous parenchyma they have a
remarkable development, which much exceeds their natural diameter.
Osteo-sarcoma, spina-ventosa, &c. exhibit this, which is much oftener
observed in cancerous tumours than any other.
These vessels communicate with each other by numerous anastomoses;
this is what we see especially in the long bones, between those of
the medullary organ and those of the texture of the cells. By these
communications, they mutually assist each other's functions. I have
seen the nourishing foramen of the tibia completely obliterated in a
body that I injected. A sort of cartilage filled this foramen; the
artery formed a real ligament. Yet its bifurcation in the medullary
canal was found very well injected, and besides no alteration appeared
in the nutrition of the medullary organ, which had probably received
as much blood as usual. I found nothing in the neighbourhood of
the foramen, which showed the cause of this obliteration, which an
exostosis, an affection of the periosteum, or an inflammation can very
easily produce.
On the other hand we know that very considerable osseous layers are
often taken from the extremity of the long bones by caries, which
consequently destroys all the vessels corresponding to these layers,
and yet the bone beneath lives, principally by the blood that it
receives by the extremities of the artery of the medullary organ. This
is nearly what happens to the long bones in the first age, in which the
cartilaginous extremities have not vessels of the second order, and in
which consequently almost all the blood comes from this same artery
of the medullary organ; thus it is much larger in proportion, and the
foramen which receives it much more considerable.
Nothing is yet known upon the systems of absorbent and exhalant vessels
of the bones, and we can reason upon this point only from analogy.
Besides the nutritive process evidently supposes them there.
As to their cellular texture, it appears to be almost nothing; we can
even say that in whatever place we break the compact fibres or those
of the cells, its filaments are not distinct; but it is their dense
and compact texture that conceals them from us. In fact, 1st, when
this texture is softened, and the bone has become flesh, as it is
called, the cellular texture is very apparent there. 2d. The fleshy
granulations, rising on places that have been fractured or laid bare,
are only the extension of the cellular texture which has too much
calcareous substance to allow it to be seen in the natural state.
3d. After having removed from a fresh bone all this substance by an
acid, I have sometimes observed cellular filaments by separating the
cartilaginous fibres which form the parenchyma that is left. 4th. When
we boil this cartilaginous parenchyma in order to extract the gelatine
from it, there remains portions of membranes which are evidently
cellular.
We cannot trace the nerves in the bones, the filaments that enter them
are so fine; I do not know that anatomy has any positive data upon this
point.