Part 24

The general sheaths are seen especially at the wrist and the instep, where they have the name of annular ligaments. They are destined to confine many tendons together. As in these two places, all those of the hand and the foot pass in a very narrow space, it is necessary that they should be strongly supported. Besides, these sheaths serve also sometimes to change their direction, as we see in those that go to the thumb, whether to its palmar or its dorsal face, and which evidently make an angle at the place of their passage under the sheath. The tendons of the little finger have also an analogous arrangement.

These sheaths exhibit also two great modifications; in the one, as on the anterior part of the wrist, all the tendons are found contiguous, separated only by a kind of loose membrane which is placed between them; in the others, as on the posterior part of the wrist, under the general sheath, are found small fibrous partitions, which separate the tendons from each other. In general, the resistance of these sheaths is very considerable.

ARTICLE EIGHTH.

OF THE APONEUROSES.

We have distinguished aponeuroses as being of two classes, those for covering and those for insertion.

I. _Of the Aponeuroses for Covering._

The aponeuroses for covering are general or partial.

_Aponeuroses for General Covering._

They are found around the limbs, whose muscles they tie down. The arm, the fore-arm and the hand, the thigh, the leg and the foot, are provided with them.

_Forms._

They are, in their conformation, analogous to the form of the limb, which they in part determine, and which they especially maintain, by preventing the displacement of the subjacent parts, a displacement which would continually take place, from the laxity of the cutaneous organ. Their thickness varies. In general, the greater the number of the muscles they cover, the greater their thickness; hence why the aponeurosis of the fascia lata is superior in this respect to the brachial; why that of the fore-arm is thicker in front than behind; why the plantar and palmar are so considerable, whilst hardly any fibres are found on the back part of the foot and the hand. There are however some exceptions to this rule; for example, the aponeurotic covering of the posterior part of the leg is not in proportion to the power of the gastrocnemii and solæus muscles; thus these muscles are more than all the others exposed to displacements, frequently very painful, which constitute cramp, and which it is necessary to distinguish from the pains or numbness which result from the compression of one of the nerves of the lower limbs, as of the sciatic, or the external plantar, a compression produced by a bad position, or any other analogous cause.

Externally, the aponeuroses of the general covering are contiguous to the integuments. A very loose texture unites them, so that the latter can easily slide over them in external pressures. Immoveable between these motions and those of the muscles, they entirely separate them; so that the skin and the muscles that correspond to it, have not, in this respect, any influence upon each other.

Within, these aponeuroses are in general loosely joined to the muscles by cellular texture. Here and there they send between the different muscular layers numerous elongations, which are afterwards attached to the bone, and which, at the same time that they furnish points of attachment, increase the solidity of the covering of the limb.

_Tensor Muscles._

The aponeuroses for general covering have almost all one or two particular muscles that are inserted in them in whole or in part, and which are destined to give them a degree of tension or relaxation proportioned to the state of the limb. This arrangement is remarkable in the insertion, 1st, of the great dorsal and pectoral muscles in the brachial aponeurosis; 2d, of the biceps in that of the fore-arm; 3d, of the palmaris longus in the palmar; 4th, of the glutæus maximus and of the fascia lata in the aponeuroses of that name; 5th, of the semi-tendinosus, semi-membranosus and biceps in the tibial.

As in the great motions of the limbs, in which all the muscles are the most liable to be displaced, these are necessarily in action, they distend powerfully the aponeurosis, which thus reflects the motion that is communicated to it, and resists especially every displacement. When the limb is at rest, the tensor muscles cease their contraction, and the aponeurosis is relaxed. I would observe, that the muscles attached to the fibrous capsules, as to that of the humerus, for example, perform for them the same functions, that the tensor muscles do for their respective aponeuroses.

The colour of these last is a brilliant white; in this respect they differ from all the fibrous organs thus far examined, and are analogous to the tendons, from which they differ a little however in their nature; in fact, they yield less quickly to maceration and ebullition; their fibres are more stiff and resisting. There are no aponeuroses exactly like the tendons, except those which are essentially formed by their expansion or which are at their origin, as those spread upon the anterior rectus of the thigh, those which are concealed in the fleshy fibres of a muscle, and afterwards go out of it to become a tendon. In certain parts of the limbs, as at the top of the arm, for example, the aponeuroses of general covering are insensibly lost in the cellular texture, without our being able to draw the line of demarcation. This arrangement is almost peculiar to the fibrous system; at least I know of no one which thus intermixes and loses its fibres in the cellular texture; it is so much the more remarkable, as the nature of the two textures is essentially different; they do not yield the same products, and they have not the same organic arrangement.

The fibres of the general aponeuroses are only interlaced in two or three directions; this interlacing is almost always very evident to the naked eye. But I have observed that by plunging an aponeurosis into boiling water, and leaving it there for some time, its fibres, in the horny hardening they then undergo, become still much more evident. This observation is moreover applicable to the whole fibrous system, to its organs especially, whose texture but little apparent seems at first view to be homogeneous. In this way, we distinguish very well the fibres of the dura-mater.

_Functions._

The constant compression made upon the limbs by their aponeuroses, besides the uses pointed out, has that of favouring the circulation of the red and white fluids. Thus varices, which are very rare in the deep veins which accompany the arteries, are extremely common in the superficial ones placed beyond the influence of this compression, which art imitates by the application of tight bandages, the effect of which is so advantageous in many external diseases arising from the want of tone, and the relaxation of the parts. I have uniformly observed that the serous infiltrations always begin in the sub-cutaneous cellular texture, that it is only in an advanced stage of dropsy, that we find effusion in that which is under the aponeuroses, and that in general it does not contain as much serum in proportion as the other. In most of the great distensions of dropsical limbs, when the skin is removed and the subjacent water has flown off, the limb covered by its aponeurosis, is scarcely larger than in the ordinary state. The muscles not protected by these coverings, like those situated on the sides of the abdomen for example, become dropsical much more easily.

_Aponeuroses for Partial Covering._

These aponeuroses are met with in insulated parts, in front of the abdomen, on the head, the back, &c.; they are usually destined to retain in place a certain number of muscles which they do not surround on all sides, like the preceding, but with which they correspond only in one direction. Their thickness is much less than that of the preceding ones; it is adapted to the efforts that they are to support.

All have a tensor muscle which proportions their degree of relaxation or of tension to the effort of the neighbouring muscles. The anterior rectus, by means of its intersections, and the pyramidalis, perform this office for the abdominal aponeuroses; the small posterior dorsocostals do it for that which covers the muscles of the vertebral foramina; the auricular, the frontal and the occipital for that of the cranium.

The aponeuroses of covering, whose use is limited to one muscle only, like that, for example, of the temporal, want the tensor muscle, and have consequently the same degree of tension always; it is on this account no doubt that they have a very compact and thick texture, as that which I have just mentioned is an example.

In general, the use of all the aponeuroses of covering whether general or partial, relative to the compression of muscles, is required by the displacements of which they would be susceptible in contracting, displacements evident, 1st, when we place the hand upon a muscle in action, and which is destitute of aponeurosis, as the masseter; 2d, when a wound having injured a considerable part of an aponeurosis of covering, the subjacent muscles become accidentally contiguous to the integuments; 3d, when in an animal we lay bare the muscles of a limb, and leave only the cellular texture to confine them, and in this state excite their contraction; 4th, in certain wounds of the muscles happening at the instant of their contraction, it is difficult to probe these wounds, because in their relaxation the muscles taking a different position, the relations change between the parts that formed the two edges of the wound.

_Of the Aponeuroses of Insertion._

We have divided into three species the aponeuroses of insertion.

_Aponeuroses of Insertion with a Broad Surface._

They are very numerous. Sometimes they arise from the expansion of a tendon, as we see in those of the anterior rectus of the thigh; sometimes, as in the masseter, they derive their origin immediately from the bones. Sometimes it is on one side only that the insertion is made; at others it is on both at the same time, and then they appear like partitions placed between the fleshy fasciæ, which they serve at the same time to separate and unite, as we observe in the muscles that arise from each of the condyles of the humerus.

These aponeuroses always receive in a very oblique direction the insertion of the fleshy fibres. Their mutual adhesion is intimate; I shall speak of it in treating of the tendons.

They have the great advantage of multiplying prodigiously the points of insertion, without requiring great osseous surfaces. The width of the whole of the temporal fossa would not be sufficient for the masseter, if it was inserted by separate fibres. By means of the aponeurotic partitions which receive its fibres and are afterwards fixed in the bone, its insertion is concentrated upon one of the edges of the zygomatic arch. Thus in general, all the very strong muscles, whose fibres are consequently very numerous, are crossed by similar aponeuroses, as the deltoid, the pterygoids, &c. are a proof.

Almost all these aponeuroses are exactly like the tendons; many are continuous with them and then their fibres remain in the same direction. In general, it is a character of these aponeuroses not to have their fibres crossed in different directions, like those of the aponeuroses of covering; the reason of it is plain; the fleshy fibres to which they give attachment being all nearly in one direction, or at least not crossing, it is necessary that these should be like them as they are continuous with them.

I have made an experiment which shows very evidently the identity of the tendons with these aponeuroses; it consists in macerating for some days a tendon; it then becomes supple; its fibres separate; by stretching in the direction of its width, it forms a kind of membrane which it would be impossible to distinguish from a true aponeurosis.

_Aponeuroses of Insertion in the form of an Arch._

They are much more rare than the preceding. When a great vessel passes under a muscle, nature employs this means, so as not to interrupt the insertion of the fleshy fibres. The diaphragm for the aorta, the solæus for the tibial artery, exhibit an arrangement of this kind. The insertion is made on the convexity, and the passage of the vessel under the concavity of the arch, both extremities of which are fixed in the bone. It has been thought for a long time that the arteries could be compressed under these arches; and hence the explanation of popliteal aneurisms, of apoplexy by the reflux towards the head of the blood interrupted in the aorta, &c. But it is very evident that by contracting, the fleshy fibres would enlarge the passage, instead of contracting it, since the necessary effect of these contractions is to enlarge in all directions the aponeurotic curve, an effect which would be directly opposite, if their insertion was made at the concavity. These aponeuroses are strongly interlaced and very resisting.

_Aponeuroses of Insertion with Separate Fibres._

They are a collection of an infinite number of small fibrous bodies wholly distinct from each other, which seem to be detached from the periosteum, as the threads of velvet go off from their common woof. Each is continuous with a fleshy fibre; so that when by maceration we remove all those fibres, these small bodies become floating and are seen perfectly well, especially when the periosteum which has been detached is plunged into water.

It is evident that this mode of insertion on the part of the muscles requires always broad osseous surfaces, since each fibre has a place of its own; we have an example of it in the superior part of the iliacus, of the anterior tibialis, of the temporal, &c. If all the muscles were inserted in this manner, ten times more surface in the skeleton would not be sufficient to receive them.

ARTICLE NINTH.

OF THE TENDONS.

The tendons are a kind of fibrous cords, intermediate to the muscles and the bones, transmitting to the second the motion of the first, and performing in this function a part wholly passive.

I. _Form of the Tendons._

Usually situated at the extremities of the fleshy fascia, they sometimes however occupy the middle, as we see in the digastric muscle; they are almost always found at the most moveable extremity, that which serves for support having aponeuroses for insertion, as we see especially on the fore-arm and the leg, of which all the muscles inserted above by broad osseous or aponeurotic surfaces, terminate below by a more or less slender tendon. From this arrangement result, 1st, little thickness at the extremity of the limbs, and consequently facility in their motions; 2d, great resistance to external pressures very frequent in this place, the fibrous texture being, as we have said, very resisting; 3d, the concentration of the whole effort of a muscle oftentimes very thick upon a very narrow osseous surface, and for the same reason the extent and force of the motions of the bone.

The tendinous forms are usually round, no doubt because they are those in which, with the least size the greatest quantity of matter enters. Sometimes however as in the tendons of the extensors of the leg and the fore-arm, they are flat.

Sometimes bifurcated or divided into many secondary elongations, the tendons are inserted into the bones, or receive fleshy fibres in two or many different points. All are covered by a loose texture which allows them to slide easily upon each other, or upon the neighbouring parts. Sometimes this texture is wanting, and then the synovial capsules surround them to favour their motions. Their extremity, in which the fleshy fibres are fixed, receives these fibres differently. Sometimes it is to one side only that they are attached; hence the semi-penniform muscles; at other times it is to both sides at the same time; this constitutes the penniform. Frequently the tendon is buried so deep in them, that it cannot be laid bare, but by dividing them longitudinally.

The adhesion is very great between the fleshy and tendinous fibre. Yet by macerating them a long time or subjecting them to ebullition, they gradually separate from each other. I have observed that in young subjects the union was much less intimate; thus by scraping at this age the tendon with a scalpel, we remove from it the muscle, without its ever appearing again; the polish is almost the same where the fibres are inserted, as where they are naturally wanting. The extremity of the tendon fixed to the bone, intermixes with the periosteum as it usually expands; so that it is with this membrane, and not with the bone itself, that the tendon makes part, because in fact it is the membrane which is of the same nature; thus if it finds an analogous membrane, it fixes to it equally, as we see in the insertion of the straight and oblique muscles in the sclerotica, of the ischio and bulbo-cavernous ones in the membrane of the corpus cavernosum. In general the tendons never unite but to fibrous membranes; the serous, the mucous, every organ in a word, foreign to the fibrous system, is also heterogeneous to them.

II. _Organization of the Tendons._

The fibrous texture is extremely compact in the tendons; many appear homogeneous at first view; but by examining them with care, we soon distinguish fibres, connected by a small quantity of compact cellular texture. Ebullition renders these fibres very evident; when we plunge suddenly the tendon into boiling water at the place where it has been cut transversely, they become a little thicker at this divided extremity, swell as it were and are thus very evident. At the place where they expand to form an aponeurosis or to unite to the periosteum, these fibres can be distinctly seen without any preparation. On the other hand, as we can always, as I have said, reduce artificially a macerated tendon to an aponeurosis, and as in this state of maceration, soft and loose, it yields to all the forms we wish to give it, it is an excellent means of distinguishing the tendinous fibres. In this experiment so easily repeated, I have never seen the spiral form of the tendinous cylinders, of which some modern authors have spoken. These fibres are in the tendon as at the place where they separate to form an aponeurosis, that is to say in a right line.

Blood scarcely enters the vascular system of the tendons; but in some inflammations, they are wholly penetrated by it. I have seen one of those of the extensors, laid bare in a whitlow, so red, that it had the appearance of a phlegmon. Yet I observed that this colour was not, as in many other inflamed organs, dependant on the small red striæ, an indication that the exhalants are filled with blood; but it was uniform, as for example a body dyed red. In general, it appears that of the whole fibrous system, it is the tendons which have the least energetic degree of vitality, and the most obscure vital forces. By dissecting them in a living animal I have found that they have exactly the same arrangement as in the dead body; the white fluids that penetrate them do not flow under the scalpel; they are dry and can be removed by layers. They appear to have a very low temperature; for, in general, the degree of heat of an organ is in proportion to the quantity of blood vessels it receives.

If in the body they are at the general temperature, it is only because the neighbouring organs communicate theirs to them. Caloric is not disengaged in their texture.

The tendons have a remarkable affinity to gelatine and even the phosphate of lime; where they slide upon a bone, and where they suffer a great friction, they exhibit a hardness which authors attribute to pressure, by comparing it to the callous hardening of the sole of the feet, but which is owing evidently to an exhalation in the tendinous texture of the two preceding substances, an exhalation which the motion produces and from which arises a real ossification.

It is thus as we have said, that the different sesamoid bones are formed, and the patella in particular, a bone the texture of which evidently differs from that of the others, because in the midst of the gelatine and of the phosphate of lime that penetrate it, there remains in it a part of fibrous texture which is not seized upon by these substances, and which is so considerable that its kind of vitality and organization belong as much and more to that of the fibrous system, than to that of the osseous.

Besides, if we detach the patella or any sesamoid bone, leaving with it a tendinous portion of each side, and expose them to the action of an acid, this calcareous substance is removed, the fibres of the bone are exposed, and we see that they are a continuation of those of the tendon which is then softened.

The muscles of organic life, and most of those which in animal life form the sphincters, are destitute of tendons. This white texture, those silver cords that are found in the heart, have not the nature of the tendons of the limbs.

ARTICLE TENTH.

OF THE LIGAMENTS.

We have divided the ligaments into those with regular fasciæ, and into those with irregular ones.

I. _Ligaments with Regular Fasciæ._

They are met with in general in almost all the moveable articulations, and especially upon their sides; hence the name of lateral ligaments by which most of them are designated. Some however are foreign to the articulations, as we see an example in that extending from the coracoid to the acromion process, in those which complete the different osseous fissures, the orbitary for example.

These organs form fasciæ sometimes round, sometimes flat, fixed to, or rather intermixed with the periosteum by their two extremities, easily removed with it in childhood, holding to the bone in the adult by the ossification of the internal layers of this membrane.

Their analogy with the tendons is very striking; the external difference is that they hold to the periosteum at both sides, whilst on one side the tendons are contiguous with the muscles. We see sometimes that the same organ is a tendon at one age, and a ligament at another. This arrangement is remarkable in the inferior ligament of the patella. Yet there are, as we have remarked, differences of composition between them. All result from an assemblage of fibres parallel in the middle, diverging at the extremities, united by a cellular texture more loose than that of the tendons, and which often contains some fatty flakes. This substance is sometimes so abundant in them, that they have an appearance analogous to that of the fatty muscles; I have made this observation on the ligaments of the knee, in a subject elsewhere very thin.

There are some blood vessels in the ligaments. In certain diseases of the articulations, their vascular system is developed in a very remarkable manner, and they are penetrated by a great quantity of blood; no nerve is discoverable in them.

Sometimes the ligamentary texture is changed into a matter like lard, in which every kind of fibre disappears, which rarely returns to its primitive state, and which is met with almost always in organic affections, fatal to the patient.

The ligaments unite strongly the osseous surfaces, prevent their displacement, and yet allow easy motions; a double function which they perform in virtue of a double property, of their resistance on the one part, of their softness and flexibility on the other; sometimes externally, they serve for some muscular insertions.

II. _Of Ligaments with Irregular Fasciæ._