Chapter VII: Part 7

The bones have hardly any animal properties in a natural state. Their sensibility is nothing; the saw, the mallet, and the chisel act upon their texture almost with impunity; an obscure feeling is the only result of the action of these instruments; fire even can act upon them without making the animal suffer much. But in a morbid state, the sensibility is developed to the greatest extent; we know the horrible pains that attend spina-ventosa, and those not less severe that caries produces in certain cases. If a bone is inflamed, as for example the sawed extremity of a stump after amputation, this bone which in a natural state had borne, without transmitting any painful impression, the action of the saw, becomes as it were a new sensitive organ, to which the least touch is painful. The animal contractility is nothing in the osseous system.

The organic properties give life to this system as to all the others. The sensibility of this kind certainly exists in it; the fluids that penetrate it are felt, and by virtue of this feeling, those are appropriated to it which are proper for its nutrition. But is there in the osseous system a reaction upon these fluids? are there those insensible oscillations which compose insensible organic contractility? Its hardness seems to prevent them. But yet the circulation is carried on there; it performs a constant work, an habitual composition and decomposition, which can hardly be conceived of without reaction on the part of the osseous system. Besides this reaction is more slow, more difficult on account of its structure; and hence without doubt the slowness, of which we shall speak, in the vital phenomena of the osseous system. Sensible organic contractility is foreign to it.

_Character of the Vital Properties._

The peculiar life of the bones is composed then of only two vital properties, organic sensibility and insensible organic contractility. From these two properties are derived all the vital phenomena that these organs exhibit, inflammations, formation of tumours, cicatrization of solutions of continuity, &c. This peculiar life is remarkable in general, as I have just observed, when compared with the peculiar lives of the other organs, by its slowness, by the tardy concatenation of its phenomena. All things being equal as to ages, and the different proportions of the earthy and cartilaginous substances, inflammation is more slow there than in the other parts. Callus is remarkable among the other cicatrices by the length of its formation; compare an exostosis in its origin, its progress and its development, with a tumour of the soft parts, a phlegmon for example, and you will see the difference. Who does not know, that whilst suppuration often requires only a few days in the other organs, it is whole months in forming in the middle of the bones? Observe the difference that there is between a gangrene of the soft parts, in which death takes place in a short time, with caries and necrosis of the bones, in which a long period elapses between disease and death of the part. In general we can say, when inflammation exists in a bone, that it is chronic.

_Sympathies._

This character of the vital properties imprints an analogous one upon the sympathetic relations of the osseous system with the other systems. At first the animal contractility and the sensible organic contractility cannot be put in action in these relations, as they do not exist in the bones. The animal sensibility being developed in them with difficulty and slowly by the diseases that essentially affect them, the sympathies can be brought into action in them only in an obscure manner. These sympathies then should act essentially upon the organic sensibility and upon the insensible organic contractility, and as these two properties are developed slowly, the different sympathies should not be connected with the acute affections of the other organs, and this is what is clearly proved by observation. In fact observe that whilst many other systems respond with great quickness to the acute diseases of an organ, this, as well as the cartilaginous, fibro-cartilaginous systems, &c. remain then almost always in inaction. Let the stomach, the lungs, the brain, &c. be the seat of a severe acute disease, you see immediately many sympathetic phenomena arise in the nervous, vascular, muscular, glandular, cutaneous, mucous systems, &c. &c.; all seem to feel the trouble of the affected organ; each, according to the vital forces that predominate there, exhibit different phenomena, which are only aberrations, irregular developments of these forces; in the animal muscular system, it is the animal contractility which is especially raised; hence spasms and convulsions; in the glandular, the serous, the cutaneous, the mucous, &c. the insensible organic contractility and the organic sensibility principally experience alterations; hence the different sympathetic derangements of the secretions, of the sweat, of the exhalations; in the nervous, it is the animal sensibility which is especially brought sympathetically into action; hence the wandering or fixed pains in different parts; in the organic muscular, it is the organic contractility which is raised; hence the irregular motions of the heart, the stomach and the intestines. In all the acute diseases of an organ there are always two orders of symptoms, the one relative to the affected organ, as are the cough, the pain in the side, the spitting of blood, the difficulty of respiration, &c. in peripneumonia; the others purely sympathetic and arising from the relations which connect the vitality of this organ with that of all the others; now these last are often much more numerous than the others.

Observe the bones in the midst of all that general sympathetic derangement of the systems in which life is very active; they undergo no alteration; their life, more slow than that of the other systems, is not connected with these phenomena which have an acute character; neither is that of the cartilages, the fibro-cartilages, the hair, the aponeuroses, &c. All these systems, remarkable by the same character of vitality, do not respond to the acute affections of the other systems; they are not sympathetically affected, during these affections, at least in an evident manner. Observe all the acute fevers; their numerous phenomena have an effect only upon those systems in which life is very active; those in which it is distinguished by an opposite character, have uniformly no connexion with these phenomena; they are, if we may so say, calm and tranquil in the midst of the tempest which agitates the others. Let us take for example the different eruptions that appear in fevers; it is upon the skin, the mucous surfaces, &c. that they come; they arise during the fever and they disappear with it; now the bones, the cartilages, &c. could not, from their kind of life, admit of this sudden origin and disappearance.

It is then in the slow and chronic affections that we must seek for examples of sympathies of the osseous, cartilaginous systems, &c. In the first stages of the venereal disease, in which it is marked only by acute symptoms, or in which at least its progress is not very slow, as when it appears in buboes, in inflammations of the urethra, &c. it has no influence upon the osseous system; it is only when it is of long standing, when it has, as it were, degenerated, and become chronic, that it makes the bones the seat of pains, of different tumours, &c. Besides, I do not know, that we have yet thoroughly analyzed the osseous sympathies. I have shown only their general character. We shall understand them better, when we have given more attention to the relation that there is in diseases between the affection of each organ, and its kind of vitality.

_Seat of the Vital Properties._

The bones penetrated by saline substances which tend continually to obey the laws of affinity and attraction, and to make these laws predominate over those of sensibility and organic mobility, seem to hold a middle place in living bodies, between these bodies and inanimate ones. There is truly but one part of their osseous texture which partakes of the vital phenomena, viz. their cartilaginous substance; the other part or calcareous substance is foreign to them; thus the proportion of each of these substances determines in the bones their degree of life. In infancy, in which the first predominates, in the early stages of the formation of callus, in which it is exclusively found, in the softening of the bones in which it remains almost alone, all the vital phenomena become more evident and more powerful. On the contrary, as age accumulates in the bones the saline substance, as in certain animals this accumulation takes place by the natural laws of ossification in some external portions of the system with calcareous base, as in the horns of stags, the shells of crustaceous animals, &c. so life is, if we may so say, successively destroyed in the bones; it becomes nothing, when this calcareous portion predominates considerably; this is what happens in the necrosis which produces the fall of the horns, the casting of the shells of crustaceous animals, &c.

Besides, that which shows the vital energy in an organ, is the rapidity with which inflammation goes through its periods in it, and the frequency of this affection, &c. Now in the bones inflammation is so much the more rapid, in proportion to the greater quantity of cartilaginous texture they contain; observe the periods of the formation of the callus in the different ages, periods which are determined by the duration of the inflammation necessary for its formation, you will see that in infancy they are short, that they are much longer in old age, and that often even consolidation does not take place, whilst it is effected with facility in all the soft parts. The general weakness no doubt of all the vital forces which takes place from the effect of age is one cause of this slowness and this rapidity in the formation of the callus at the two extreme periods of life; but the different proportions of gelatinous and calcareous substances contribute much to it also; for when we compare other cicatrices with this, the cutaneous, for example, we see that age establishes in them an infinitely less sensible difference as it respects the slowness and rapidity of this reunion, than in the osseous system. The bones have not sufficient life to inflame and unite, like the skin, the muscles also exhibit this phenomenon in a very evident manner. I have seen an old man, the neck of whose fractured thigh-bone remained a long time without reunion, and in whom a wound of the face was healed very speedily by the first intention.

Finally, there is a simple experiment that I have often made, and which proves as well as the preceding facts, that the cartilage is truly the animal part of the bone. We know that one of the great attributes of animal substances, is to contract and exhibit the horny hardening when burnt; now when the bone is penetrated with its earthy salt, it has not this kind of combustion; deprived of this salt by an acid, the cartilaginous parenchyma which remains burns in this manner. The flat bones in infancy in which this parenchyma predominates, exhibits also this phenomenon in burning; it forces the calcareous portion, which is in small quantity to obey the impulse that it gives it, and turns it in various directions; but in the adult in whom the calcareous portion is the largest, the bone remains unmoved while the fire penetrates it, and its whole cartilage is taken away, without its fibres being able to obey their tendency to the horny hardening which combustion imprints upon them.

ARTICLE FOURTH.

OF THE ARTICULATIONS OF THE OSSEOUS SYSTEM.

All the bones are united together, and thus form the skeleton. The manner of their union varies, but whatever it may be, it is known under the general name of articulation.

I. _Division of the Articulations._

All the articulations can be referred to two general classes. Mobility is the character of the first, immobility that of the second.

One belongs to all the bones which serve for locomotion, to some of those destined to internal functions, as the ribs, the lower jaw, &c. The other is especially met with in the bones, the union of which forms the cavities designed to defend the organs; this we see in the head, the pelvis, &c.

_Moveable Articulations. Observations upon their Motions._

I divide moveable articulations into four kinds, the characters of which are borrowed from the different motions they execute. To understand this division, it is necessary previously to know the motions of the articulations in general. These motions can be included under four species, which are, 1st, opposition; 2d, circumduction; 3d, rotation; 4th, sliding.

1st. The motion of opposition is that which is made in two opposite directions, for example, from flexion to extension, from adduction to abduction, and vice versa. This motion is extensive or limited; extensive when it is made in all directions, first in the four named above, then in all the intermediate ones; limited, when it only takes place from flexion to extension, from adduction to abduction, &c. The thigh in its articulation with the pelvis enjoys an extensive motion of opposition. The tibia in its articulation with the femur has a limited motion of opposition.

2d. Circumduction is the motion in which the bone describes a kind of cone, the summit of which is in its superior articulation, and the base in the inferior; so that it is found successively in flexion, adduction, extension and abduction, or in abduction, extension, adduction and flexion, according to the motion by which it begins, and that moreover it goes through all the intermediate directions. Hence we see that circumduction is a motion composed of all those of opposition, and in which the bone, instead of moving from one direction to an opposite one, as in the preceding case, moves from one direction to another nearest to it, describing thus by its extremity a circle which is the base of a cone of which I have spoken, and which is so much the greater as the bone is so much the longer. We easily understand that among the bones, those only whose motion of opposition is loose, enjoy that of circumduction.

3d. Rotation is wholly different from the preceding motion. In this there was locomotion, a moving of the bone from one place to another; here it remains always in the same place; it only turns upon its axis. The humerus and the femur enjoy this motion which is simple.

4th. Sliding belongs to all the articulations. It is an obscure motion, by which two surfaces go in an opposite direction, by sliding as it were upon each other. In all the other motions, this is met with; but it often exists without them.

It is easy to understand, from these views upon the articular motions, the division into genera of the class of moveable articulations. In fact, there are articulations in which all the motions are united; in others, there is no rotation; in many rotation and circumduction are wanting, and opposition exists only in one direction; some have only rotation. Finally, there are those in which rotation, circumduction and opposition are nothing, and sliding alone remains.

Hence we see that nature moves here as elsewhere by gradation, that from the most moveable articulations to those that are the least so, there are different degrees of decrease, that she descends gradually to the immoveable articulations, that she is finally reduced to the motion of sliding alone, like that which exists at the carpus, the tarsus, &c. There is even an intermediate one between sliding and immobility; it is the articulation of the symphysis pubis; which can be considered with that of the humerus as forming the two extremes of the series of moveable articulations.

All the articulations of which I have spoken are with contiguous surfaces; this is the general character of those which are moveable. There is however an exception to this rule; it is the articulation of the body of the vertebræ, in which there is continuity and mobility. The symphysis pubis is also in part continuous in its surfaces, and yet has sometimes obscure motions. Hence arises a division of the moveable articulations, into those with continuous surfaces, and into those with contiguous ones.

_Immoveable Articulations._

The immoveable articulations are sometimes with surfaces inserted into each other, as the bones of the cranium, in which many projections and depressions reciprocally receive each other; sometimes with surfaces in juxta-position, as in the articulation of the temporal with the parietal, the two superior maxillary bones with each other; sometimes with implanted surfaces, as in the teeth.

All the different divisions that I have mentioned will be easily understood by the following table; it is not the same as that which I have given in my treatise on the membranes; I think it presents a classification a little more useful in this, that it offers for a characteristic two things essential to be known in all kinds of moveable articulations, viz. 1st, the relation of the articular surfaces which characterizes the orders; 2d, the number of motions of each which distinguishes the genera. There are no orders in the immoveable articulations because, except the relation of surfaces, the articulations have not differences sufficient to occasion them to be sub-divided.

_Table of the Articulations._

┌ CLASSES. ┌ ORDERS. ┌ GENERA.
│ │ │1st. Extensive Opposition,
│ │ │ Circumduction and
│ │ │ Rotation.
│ │1st. With │2d. Extensive Opposition
│ │ Contiguous │ and Circumduction.
│1st. Moveable. │ Surfaces. │3d. Limited Opposition.
│ │ │4th. Rotation.
│ │ └5th. Sliding.
ARTICULATIONS. │ │2d. With Continuous
│ └ Surfaces.
│
│ ┌1st. With Surfaces
│ │ in juxta-position.
│ │2d. With Surfaces
│ │ inserted
└2d. Immoveable. │ into each other.
│3d. With Surfaces
└ implanted.

After having thus divided the articulations, let us offer upon each class some general observations. But let us first remark that the preceding table, considered in respect to the moveable articulations with contiguous surfaces, indicates perfectly the disposition of these articulations as to luxations, which are so much the more frequent as the motions are more extensive. The first genus is the most exposed to it, the last the least so; and the others are more or less so according to their distance from the first.

II. _Observations upon the Moveable Articulations._

The class of moveable articulations is the most important to be considered, because their mechanism is the most complicated of the two orders composing this class, as we have seen. The latter, or that of the articulations with continuous surfaces, will not be considered in our general observations, as it embraces only one species of motion, that of the vertebræ, this motion will be noticed in the examination of the spine. The order of the moveable articulations with contiguous surfaces, comprises, as we have said, five genera characterized by their respective motions.

_First Genus._

Extensive opposition, circumduction and rotation characterize this genus. The first by the extent and number of its motions. The articulations of the humerus with the scapula and the femur with the ilium are examples of it; they even exclusively compose it.

We see why it is at the superior part of the limbs that nature has placed this genus. A double advantage results from this situation. On the one hand, very far from the part of the limb immediately exposed to the action of external bodies, it more easily escapes luxations to which its want of solidity renders it liable. On the other hand, it can by this situation give to the limb the motions of a whole which compensate for those of the inferior articulations, the solidity of which prevents the power of motion in all directions. For example, the two articulations of which I have just spoken, are not only the articulations of the bones that form them, of the humerus and the femur, but also the articulations of the whole limb, which they direct in different directions; thus the anchylosis of these articulations renders the limb completely useless, whilst that of the inferior articulations only destroys partial motions.

The kind of motion of this genus of articulation requires a rounded form in the articular surfaces, whether they be concave that receive and convex that are received. This form is in fact the only one that can accommodate itself to extensive opposition, rotation and circumduction united; this is the form of the superior parts of the humerus with the scapula, and the femur with the os innominatum. The bone which moves has a convex surface, that which serves for support a concave one. There are in animals examples of an opposite arrangement: that is to say that a concavity is moved in all directions upon a convexity; but this is not found in man.

Though the two limbs have between them the greatest analogy in their motions, yet there are some differences relative especially to their respective uses, which in the one are for seizing and repelling bodies, in the other destined to locomotion. The principal of these differences is, that rotation and circumduction are found in them in an exactly inverse ratio. The mechanical reason and advantages of this arrangement are easily understood.

In the femur the length of the neck which is the lever of rotation, gives much extent to this motion, which supplies the pronation and supination that are wanting in the leg; so that every rotation of the foot is a motion of the whole of the limb. In the humerus on the contrary, the neck being very short and bringing the axis of the bone near the centre of the motion, limits rotation, which is less necessary on account of that of the fore-arm; the motion of the hand without or within is never communicated but by a part of the limb.

As to circumduction, the length of the neck of the thigh is an obstacle to it. In fact, let us remark that this motion is much the more easy, when it is performed by a rectilinear lever, because then the axis of the motion is the axis of the lever; that on the contrary, if the lever is angular, the motion becomes so much the more difficult because the axis of the motion is not that of the lever; and in general we can say, that the difficulty of the motion is in the direct ratio of the distance of the two axes.

This being settled, let us observe that the axis of the motion of circumduction of the thigh is evidently a straight line, obliquely directed from the head to the condyles, and distant consequently above from the axis of the bone, the whole length of the neck. Now, from what has just been said, it is evident, that the difficulty of circumduction will be in the direct ratio of the length of the neck, and consequently very great. In the humerus, on the contrary, the neck being very short, the axis of the bone and that of the motion are almost the same; hence the facility and extent of the circumduction. We might fix precisely the relation of these motions by this proportion; the circumduction of the humerus is to that of the femur, as the length of the neck of the humerus is to the length of the neck of the femur; which shows us how much more difficult the circumduction of the femur is than that of the humerus. To know this, it is sufficient in fact to know the excess of the length of the neck of the first over that of the second.

It is easy to perceive the advantages of this very great extent in the circumduction of the superior limbs destined to seize, and of the limits placed by nature to that of the inferior limbs destined to standing and locomotion. We understand also why luxations are more easy in the first than in the second. The displacement almost always takes place in fact, in one of the simple motions, the succession of which forms the compound motion of circumduction, for example, in elevation or depression, in adduction or abduction, &c. Now all these motions being carried much further in the humerus than in the femur, the surfaces are more easily separated.

_Second Genus._

This genus differs from the first by the absence of the motion of rotation. Opposition and circumduction are alone met with in it. We find examples of it in the temporal maxillary, sterno-clavicular, radio-carpal, meta-carpo-phalangeal articulations, &c.

The want of rotation evidently supposes, from what has been said above, the absence of an osseous head, the axis of which would make, as in the preceding genus, an angle with the axis of the body of the bone. Thus in all the bones of the articulations that I have just mentioned, the articular surface is at the extremity even of the bone, and not upon the side; the axis is the same in both cases. They form a rectilinear lever, instead of an angular one.

The articular surfaces are in general, as in the preceding case, uniform, without eminences and reciprocal depressions; which would embarrass and even prevent circumduction. In the bone which serves for support, there is a cavity more or less deep; in the bone which is moved, there is an analogous convexity. The corresponding surfaces of the temporal and the inferior maxillary bone, of the bones of the metacarpus and the first phalanges, are examples of this arrangement.

This articular mode is the most favourably disposed for circumduction, which is, as we have seen, constantly in the inverse ratio of rotation, and which consequently has the greatest possible facility when the lever is rectilinear, a circumstance that destroys rotation. Yet in many articulations of this genus, circumduction is evidently less extensive than in the humerus and the femur; but this arises from the arrangement of the moving powers which being in much greater number in the articulations of these two bones, compensate for the bad arrangement of the articular surfaces for circumduction.

In the genus of articulations of which we are treating, there is always one direction in which the motion of opposition is more easy than in the others; for example, it is elevation and depression in the jaw, flexion and extension in the first phalanges, in the wrist, &c. In general there are two lateral ligaments and the capsule in the direction in which the motions are most limited, the capsule only in that in which they are the most extensive.

_Third Genus._

As we advance in the examination of these articular genera, the extent of their motion diminishes. This has less opposition in many directions than the preceding, and less circumduction which always supposes an extensive opposition. Here this opposition is always limited to one direction only, to that of flexion and extension, for example.

We find this articular genus especially in the middle of the limbs, as at the elbow, the knee, the middle of the fingers in the articulations of the phalanges. Though the bone which composes them, inferiorly can move by itself but in one direction, yet it borrows from the loose motions of the superior articulation of the limb, so as to be able to be turned in every way.

The articular surfaces are found here as in the preceding genus, at the extremity of the bone, having the same axis as the bone; but they differ, 1st, in this that there are many eminences and cavities fitted to each other, an arrangement, which, by permitting the motion in one direction, prevents it in the others. Very commonly there are two kinds of round prominences, called condyles, which roll from before behind, or from without within, &c. upon two analogous cavities, that are separated by an eminence, which is received in the space between the condyles, as we see in the femoro-tibial, phalangeal articulations, &c. 2d. The breadth of the surfaces also distinguishes this genus from the preceding; this breadth insures its solidity, and prevents luxations, which besides are more to be feared when they happen here where more ligaments must be broken than elsewhere.

There is always in this genus greater extent of motion on one side, than on the opposite. In general flexion has always more extended limits than extension; observe in fact the condyles of the femur, of the phalanges, &c. they are extended much further in the first than the second direction; why? because all our principal motions are those of flexion, and the motions of extension are as it were but to moderate the first, and have for their object only to bring back the limb to the position from which it can be bent again. Hence why the number, and the strength of the fibres are much greater in the flexors than in the extensors; why the great vascular and nervous trunks are always on the side of flexion, as we see in the thigh, the leg, the fore-arm, the phalanges, &c. There is always something which limits the motion of extension, as the olecranon in the humero-cubital articulation, the crucial ligaments in the femoro-tibial articulation.

Though in the genus which we are describing, there is no well marked motion of circumduction, yet when the leg or the fore-arm are in flexion, they can move laterally and even in the form of a cone, but not in a very evident manner. In extension this is impossible, because the lateral ligaments being much stretched, do not yield enough to allow the bone to incline from one side to the other.

_Fourth Genus._

Every kind of opposition and circumduction is wanting in this genus, which presents rotation alone, as we see in the articulations of the ulna with the radius, and the atlas with the odontoid process. Sometimes it is a concave surface rolling upon a convex one, as at the lower end of the radius, and at the odontoid process; sometimes it is a convex surface moving upon a concave one, as at the head of the radius; there is always a kind of ligament which completes the concave surface, and which thus forms a ring turning upon the bone, or in which the bone turns.

Luxations are here very difficult, because the rotation being made upon the axis of the bone, the ligaments are hardly more distended on one side than the other, and are hence broken with difficulty, whatever may be the extent of the motion. The inferior part of the radius forms a slight exception to this rule, because it is upon the ulna, and not exactly upon its own axis, that the bone turns in this place.

There is no rotation in the leg as in the fore-arm, because, as we have seen, that of the thigh which is very extensive, supplies the place of it; which the humerus could hardly do for the fore-arm, as we know when this last is anchylosed.

_Fifth Genus._

Every kind of rotation, opposition and circumduction are wanting in this genus, which is the most numerous, and which embraces the articulations of the carpus, the metacarpus, the tarsus and metatarsus, of the vertebræ between themselves by their articular processes, of the atlas with the occiput, of the humeral extremity of the clavicle, the sternal of the ribs, and the superior of the fibula. There is only a kind of slipping more or less obscure, and in which the osseous surfaces hardly ever leave each other. These surfaces are almost all plain, very close together, united by a considerable number of ligaments, and so strong in their connexion, that luxations hardly ever happen to them. Another reason moreover which renders them difficult, is that all this genus of articulations belongs almost wholly to short bones; now we know, that the motion imparted to a bone has a power of action which is in direct ratio of its length, and in the inverse of its smallness; for example, the same power applied to the tibial extremity of the femur, would luxate much more easily the ischiatic extremity, than if it acted upon the middle of this bone.

As the separate motion of each of the articulations of the fifth genus is almost nothing, nature usually unites several at the same place, for the purpose of producing a sensible, general motion, as we see in the carpus, the tarsus, the vertebræ, &c.; this is also a reason of the difficulty there is in luxating this genus of articulations. In fact, how great the general motions may be, two bones, taken separately, move but little upon each other; now it is only the extent of the motion of the two separate bones from each other, that can produce the displacement.

III. _Observations upon the Immoveable Articulations._

We have only pointed out orders in this class, because its varieties are not sufficiently great to assign genera for them.

1st. The order of immoveable articulations with surfaces in juxta-position, is met with where the mechanism of the part alone is almost sufficient to insure the solidity of the bones which are found only placed at the side of each other, without holding by any insertion, and having only between them a slight cartilaginous layer; the superior maxillary bones, wedged in between the malar bones, the ossa ungues, the ethmoid, the ossa palati, the vomer, and the frontal bone, are supported more by the general mechanism of the face, than by any articular attachments that unite them to each other; thus the squamous portion of the temporal bone supports the parietal, more by the abutting arches, than by the manner of the union of their respective surfaces. Remove this general mechanism of the part, you will soon see all the articulations separate.

2d. The order of immoveable articulations with inserted surfaces, owes also in some measure its solidity to the general mechanism of the part; but this mechanism would be insufficient to insure this solidity; thus the bones, instead of having almost plain surfaces, exhibit very evident prominences and depressions which are inserted into each other, as we see in the articulations of the parietal bones with each other, with the sphenoid, the occipital, the frontal, &c.; these are called sutures. This order sometimes approximates the preceding, as in the union of the parietal and frontal bones, which, reciprocally aiding each other, are supported by this mechanism, more than by their insertions; sometimes it resembles the following order, as in the articulation of the occipital and parietal bones, in which the very deep insertions almost alone insure the solidity of the union. This order is never seen except upon the edges of the flat bones; the insertion of these edges compensates for their want of size, by multiplying the points of contact. The eminences and depressions forming the insertion are always of an irregular form and size. They are exactly fitted to each other, they are not alike in two bones of the same species, taken from two different subjects; so that we cannot unite to a detached left parietal bone, the right parietal bone of another individual. There has been much dispute upon the formation of the sutures; they are an effect of the laws of ossification, an effect which we can account for no more than we can for all the others, and all the general phenomena of growth; we shall see the progress they follow in this formation. This articular order is gradually effaced with age, and the bones unite together by the ossification of the thin intermediate cartilage. It is more rare that the preceding order disappears. I have seen, however, in extreme old age, different articulations of this order cease to be evident, those of the maxillary bones between themselves especially.

3d. The order of articulations with implanted surfaces borrows none of its solidity from the mechanism of the part; it owes it entirely to the relation of the surfaces, which are so united and embraced by each other, that displacement is impossible. There is but one example of this articular order, it is the teeth with the jaws.

Age does not here efface the articulation, and thus confound the two bones as in the preceding orders, because the medium of union is the palatine membrane, which belongs to the mucous system, and which by its organization has no tendency to ossification; whereas in the preceding cases, the intermediate cartilage has a natural disposition to become encrusted with the phosphate of lime.

IV. _Of the Means of Union between the Articular Surfaces._

The articular surfaces would soon separate, if different organs did not retain them in place. These organs are the cartilages and the membranes for the immoveable articulations, the ligaments and the muscles for the moveable.

_Union of the Immoveable Articulations._

The two first orders of immoveable articulations, those with inserted surfaces and those with surfaces in juxta-position, have cartilages between the osseous surfaces, the breadth and thickness of which are found so much the greater in proportion as they are examined in subjects nearest infancy. Almost all the bones of the head are held together in this manner, which allows them to yield a little, and consequently prevents their fracture.

In the articulations of the pelvis, there are besides the cartilages, ligaments; but as these articulations perform in certain cases small sliding motions, we can consider them as intermediate between the moveable and immoveable articulations; it is on this account that they have the two kinds of organs especially destined to strengthen the articular surfaces of each of the classes, viz. the cartilages and the ligaments.

The immoveable articulations with implanted surfaces, an order which comprehends only the teeth, have nothing between the surfaces as a means of union, but a mucous membrane, the palatine. Hence why in the swellings of this membrane, in scorbutic affections, after the use of mercury, &c. the teeth become loose.

_Union of the Moveable Articulations._

The moveable articulations with contiguous surfaces have the ligaments especially as a means of union, which are found in the five genera, but under different forms which will be examined hereafter. This kind of organ unites much suppleness with great resistance, a double attribute which it derives from its peculiar texture, and which renders it very proper for this function. Let us observe however that these two properties are in an inverse ratio in the two extreme ages of life, that suppleness is the companion of infancy, that stiffness and resistance are the character of the ligaments in old age. Hence in part the multiplicity of motions in one age, and their slowness and difficulty in the other.

The cartilages are not in this articular order, as in the preceding, means of union, but means of motion, by their smooth and polished surfaces.

As to the synovial membrane that is found exclusively in this order, such is its extreme tenuity, that it can hardly be considered as uniting the surfaces, and its use appears to be confined to the exhalation of synovia.

It is not the same with the muscles; they can be considered as forming at the same time around the moveable articulations, a power for the whole of the bone, and a resistance for its extremities, which they prevent from being displaced, by forming around them supports, the efficiency of which is in proportion to the efforts that are made to displace these extremities. In fact, it is in the great motions that these efforts are the most considerable; now then the neighbouring muscles of articulation strongly contracted, hard during their contractions, have a powerful tendency to prevent the osseous extremity from abandoning that which corresponds with it. In rest when the relaxed muscles offer but little resistance, the effort for support is nothing. A paralyzed limb can be luxated much more easily than another, by external violence.

The order of moveable articulations with contiguous surfaces, has as a means of union, a substance, the nature of which is between that of the ligaments and that of the cartilages.

ARTICLE FIFTH.

DEVELOPMENT OF THE OSSEOUS SYSTEM.

There is no system in which anatomists have traced in a more accurate manner than in this, the different states in the different periods of life. The remarkable difference of a bone examined in the first months when gelatine almost alone composes it, compared with a bone of an adult in which the calcareous substance predominates, has especially arrested their attention upon this point. Let us examine the phenomena of ossification in all the ages; these phenomena should be considered during and after growth. In general, while this continues, there are some portions of the osseous system not ossified, as the neck of the femur, for example; ossification is not complete, the bones are not perfectly developed until towards the sixteenth or eighteenth year, and sometimes even later.

I. _State of the Osseous System during Growth._

We commonly distinguish three states in the development of the bones, viz. the mucous, the cartilaginous and the osseous states.

_Mucous State._

The mucous state may be considered as existing at two periods: 1st. In the first days of the development of the embryo, a period in which the whole of its organs forms only a homogeneous and mucous mass, in which it is not possible to distinguish any line of demarcation, and in which the parenchymas of nutrition alone exist. All the organs are then of the same nature; the bones are in fact mucous like all the other organs, if by this word we understand a state in which the cellular texture existing alone with the vessels and the nerves, is penetrated by so large a quantity of juices, that it has the form of a mucilage, and gives the appearance of it to the embryo. 2d. We may understand by the words mucous state, that more advanced period of osseous nutrition, in which the bones can be already distinguished, seen through the transparency that the other parts of the limb still have, and in which they have a consistence much greater than that of the parts which surround them; now this state is only the commencement of that of cartilage; for the parenchyma of nutrition takes the cartilaginous character when it begins to be penetrated by gelatine, and it is in fact penetrated by this substance when it has more consistence, since it is that which gives it this consistence, and hence an existence distinct from the surrounding parts. If in the early periods, this cartilage is softer, if it flattens under the finger when pressed, if it even has an appearance partly mucous, it is because the gelatine is not yet in sufficiently large proportion, and because the nutritive parenchyma still predominates; gradually its quantity increases, and then the cartilaginous nature is more evidently developed.

It follows hence that the bones have three periods in their development; one is common to them with all the other organs; it is the mucous period; the two others especially characterize them; these are the cartilaginous and osseous periods. Let us examine their phenomena.

_Cartilaginous State._

All the bones are cartilaginous before taking their last form. This state of cartilage begins at a period that is difficult to be determined; it is when on the one hand the circulating system begins to carry gelatine and present it to the organs, and when on the other the organic sensibility of the parenchyma of nutrition of the bones is put in relation with this substance. Then the consistence of the bone is constantly increasing, because the gelatine is constantly accumulating; now it accumulates in the same direction that the phosphate of lime afterwards takes; that is to say, in the long bones it is in the middle of the body, in the flat bones it is in the centre, and in the short ones it is in the centre also, that this substance is at first exhaled, which afterwards extends gradually to the extremities of the first, the circumference of the second and the surface of the third. I would observe however that we do not see, during the formation of the cartilaginous bone, those longitudinal striæ in the long bones, radiated ones in the flat, irregularly crossed ones in the short, which distinguish the osseous state in its formation, and which seem to indicate to the eye the course of the phosphate of lime.

The cartilaginous state exhibits a peculiarity that distinguishes it from the osseous state; it is that all the bones that are to be afterwards united by means of cartilage, such as those of the cranium, the face, the vertebral column and the pelvis make only one piece; whilst all those that are to be held together by ligaments, whose articulations are consequently moveable, are found very distinct, as the femur, the tibia, the clavicle, &c.

The broad bones, those of the cranium especially, do not exhibit in so distinct a manner the cartilaginous state. Their appearance, at this period of ossification, is even rather membranous. It arises from this; as they are found interposed between the periosteum and the dura mater, and as their tenuity is very great, we can with difficulty distinguish them on the interior of these two membranes. But when we dissect the parts with care, we can distinguish the bone yet soft, from this double covering.

The cartilaginous state appears in the clavicle, the scapula, the ribs, before being discoverable in the other bones in which it is afterwards seen. When we examine the bones in this state, we find them of different consistence and solidity; where the exhalation of gelatine has commenced, they are incompletely cartilaginous; as we go from this point, they partake more or less of the mucous state. The cartilaginous bone has no internal cavity, no medullary system, &c.

_Osseous State._

When the whole bone is cartilaginous, and even when some points appear to be still mucous, the exhalation of calcareous substance begins, and then the osseous state manifests itself; the following is the manner; the bone becomes more dense, then of a deeper colour, and finally of a very evident yellow in its middle, that is to say where the ossification should begin; gradually a red point appears; these are the vessels that begin to receive the red portion of the blood, and not to be developed as some anatomists pretend, to be hollowed out according to their expression, by the force of the impulse of the heart. They always existed; the white fluids alone penetrated them before, then the red globules are admitted into them. At the same time the neighbouring parts are encrusted with calcareous substance. This period is then remarkable in two particulars, viz. in respect to the entrance of the blood into the cartilaginous bone, and in regard to the exhalation of the phosphate of lime. These two phenomena are always inseparable; when there is redness in one part of the cartilages, there are also osseous points; this is observed not only in common ossification, but also in those which are not so, such as the ossifications of the cartilages of the larynx, of the ribs, &c. When we examine the progress of the exhalation of the earthy substance, we see always in the bones, whether long, flat or short, a very red vascular layer, between the cartilage and the portion of ossified bone. This layer seems to serve as a precursor to the osseous state. Why do the vessels of the bones which before had admitted only white fluids, receive then red globules? It is not, as Boerhaave would have said, had he treated of ossification, because their caliber increases, but because the sum of their organic sensibility increasing, they are then found in relation with the red portion, which until then was foreign to them. Their caliber might be treble or quadruple the diameter of the red globules, but these would not enter if the organic sensibility repelled them, as the larynx rises against a body which attempts to enter it, though this body may be infinitely less than the glottis. It is by an increase of organic sensibility, that must also be explained how the bone, until then a stranger to calcareous substance, being in relation only with the gelatine, appropriates also to itself the first of these substances, and is penetrated with ease.

I will observe only that there is this difference between the exhalation of the two, that the first comes immediately from the red portion of the blood, since wherever it is deposited, there is, as I have said, blood vessels; whilst the second appears to come immediately from the white fluids, since the vessels of the tendons, the cartilages and the other parts that they nourish, do not evidently receive in their natural state any red globules, and all that circulates in them appears to be white.

The osseous state commences with the end of the first month in the clavicle, the ribs, &c.; it is a little more slow in the other bones; we know not its precise period. The following is its progress in the three kinds of bones.

_Progress of the Osseous State in the Long Bones._

We distinguish at first in the middle of these bones, a small osseous cylinder, very slender in its centre, enlarging towards the extremities, hollow in the interior for the rudiments of the medullary system, perforated by a nourishing foramen whose size is then in proportion very great, receiving also a very large vessel. This osseous cylinder, at first very slender in comparison with the cartilaginous extremities of the bone, is in a very evident disproportion to them in this respect; it is formed of very delicate fibres, and is gradually enlarged and extended, until it reaches near the extremities where it is found at birth; the most of these extremities are not then bony. Some time after, and at a period which varies in the different bones, there is developed in these extremities an osseous point which begins at the centre, and which is always preceded by the passage of the blood in the vessels. These new germs increase at the expense of the cartilage which is gradually lessened between the body and the extremity of the bone; at the end of some time there remains only a slight partition which ossification also seizes upon; so that the bone is then wholly osseous from one extremity to the other. The secondary points which are developed in the different apophyses, also unite; so that its substance is everywhere homogeneous. It is not until the age of sixteen or eighteen years, that nature has completely finished this work.

_Progress of the Osseous State in the Broad Bones._

The mode of origin of ossification varies in this kind of bones. Those which are symmetrical, have always two points or more, which correspond upon each side of the median line; sometimes one of them is found upon this line. When these points of ossification are in equal number, they are always upon the sides; if they are in unequal number, one of them is upon the line.

The irregular bones sometimes have but one of them, as in the parietal; at other times many appear in them, as in the temporal; but there is never a similar arrangement among them; only they correspond with those of the opposite bone.

At the first point of ossification in a broad bone, we perceive at first reddish spots, then we observe the phosphate of lime spreading in rays from the centre to the circumference of the bone. The osseous rays are very evident upon the bones of the cranium. Portions not ossified at first fill their interstices, which new rays afterwards occupy. All terminate in an unequal manner, without touching, so that by separating an ossified portion of a broad bone from the membranous portion to which it belongs, its circumference looks cut like the extremity of a comb; hence, as we shall see, the origin of sutures.

The delicacy of these bones is extreme in the early periods; they have not then any of the texture of the cells. At birth but few of the osseous centres are yet united; cartilaginous and membranous spaces separate them; these spaces are greater towards the angles than towards the edges, and generally at points the most distant from the primitive osseous centres. The bones with many points of ossification are formed of separate pieces, more or less distant from each other. Those with one point only, have but one piece.

After birth these bones extend more and more, their thickness and hardness increase; they are divided into two compact layers, the space between which is filled by the texture of the cells; gradually they touch at their edges, and then the sutures are formed in the cranium; for there is this difference between their ossification and that of the long bones, that it takes place always from the centre to the circumference, and that new osseous points are not developed at the circumference to meet those of the centre. But when this happens, the union does not then take place as in the long bones, but sutures are formed; and it is this which occasions the ossa wormiana, which are so much the larger as the osseous point is the sooner developed, because it has had time to extend itself more, before meeting the general ossification of the bone.