Part 41

The fibro-cartilages of the grooves, which are found almost all, as we know, situated at the extremities of the long bones, are not, in the first age distinct from the cartilages of ossification, which then form these extremities. Confounded with them, they exhibit no line of demarcation when we cut the lines at that place. This state continues until complete ossification; then the fibro-cartilages of the grooves remain insulated like the cartilages of the osseous extremities.

The interposed gelatinous portion appears to predominate, in childhood, over the fibrous portion in the articular fibro-cartilages and in those of the grooves. It is remarkable in the intervertebral substances, in which this kind of mucilage which occupies the centre, is as to quantity in the inverse ratio of the age, and in which the fibres are also more developed. On the pubis, the whole is almost homogeneous in the fœtus; the transverse fibres do not become very apparent till a more advanced age. The articulations of the knee, the jaw, &c. have in their fibro-cartilages, the same arrangement. Ebullition extracts from them then a much greater quantity of gelatine; they have more the smooth appearance of the cartilages.

The membranous fibro-cartilages are in general developed early, those of the ear, the eyes and the nose especially. We see them very evident in the fœtus. I have observed in two acephalous infants, that, like all the other parts of the face, they were of a remarkable size, and much greater than that of the ordinary state. Besides, the whole fibro-cartilaginous system is, in the fœtus, extremely soft, supple and unresisting.

II. State of the Fibro-Cartilaginous System in the after ages.

This system becomes stronger as we advance in age; in old age, it becomes hard and yields with difficulty from the peculiar nature of its nutritive substances. It is to this circumstance that must be attributed, 1st, the stiffness and inflexibility of the vertebral column, whose fibro-cartilages keep all the pieces in a kind of immobility; 2d, a part of the difficulties which an old person experiences in hearing sounds, the concha not being able to vibrate and reflect them as well as before; 3d, the less susceptibility of his nostrils to dilate, the fibro-cartilages yielding less to the muscular effort, which is besides also less; 4th, the difficulties of the sliding of the tendons, their grooves being much less supple.

The fibro-cartilages have in general much less tendency to ossify in old age, than the cartilages properly so called. I never saw this phenomenon in the membranous ones; perhaps it arises from their peculiar texture, and even the difference of the principles which go to their composition, and from the small quantity of gelatine that enters into them. Among the articular, there are scarcely any but those of the vertebræ, which are sometimes entered by the phosphate of lime; this is however rare. Those of the grooves are like the cartilages of the moveable articulations, they constantly keep their nature; only in extreme old age, their thickness appears to diminish a little by the ossification of their laminæ which correspond to the bone, which besides is not very evident.

MUSCULAR SYSTEM OF ANIMAL LIFE.

The general muscular system very evidently forms two great divisions, differing essentially from each other, by the vital forces that animate them, by their external forms, by their mode of organization, and especially by the parts they perform, the one in animal life, and the other in organic. We shall not then consider them together. Let us begin by the examination of the muscles of animal life; these are spread out in great number in the human body. No system as a whole, is of more considerable size; no one occupies more space in the economy. Besides the numerous regions that the muscles fill, they are generally spread out under the skin, and partake, as it were, of the functions of this organ, protect like it the subjacent parts, like it bear with impunity the action of external bodies, and can even be divided in a more or less considerable extent, without the general functions of life suffering from it; which renders them very fit to defend the deep-seated organs, whose lesion would be very injurious.

ARTICLE FIRST.

Of the Forms of the Muscular System of Animal Life.

From their external forms, the muscles may be divided, like the bones, into long, broad and short. Their arrangement varies according to these three general forms.

I. Forms of the Long Muscles.

The long muscles occupy in general the limbs, to the conformation of which theirs is accommodated. Separated from the skin by the aponeuroses, from the bone by the periosteum, they are situated in a sort of fibrous gutter, which retains them powerfully, and in which they are arranged in layers more or less numerous, the deep ones are confined in their place by the superficial ones, which, in their turn, have the aponeuroses to support them. These last are very long; they commonly belong to the motions of three or four bones and even more, examples of which we have in the sartorius, the semi-tendinosus and membranosus, the biceps, the flexors and the extensors. As they become deeper, they are also shorter and generally destined to the motions of two bones only, as the adductors, the pectineus, &c. are a proof.

Cellular layers separate them; they are loose where great motions take place, more compact where these motions are less, very thick where vessels and nerves go between the muscular fasciculi. Often spaces more or less considerable, filled with cellular texture, separate these fasciculi from each other. We divide the long muscles into simple and compound. They are simple when a single fasciculus forms them, compound when they arise from the union of many. These fasciculi are found then in two different manners; sometimes in fact its division is at the top of the muscle, as we see in the brachial and femoral biceps; sometimes it is at the inferior part, at the most moveable side that this division is met with, as in the flexor and extensor muscles of the leg and the fore-arm.

The long muscles often separate from each other, are sometimes held together by means of aponeuroses, which confound a more or less considerable portion of two, three and even four of these neighbouring organs. The origin of the muscles of the internal and external tuberosities of the humerus exhibits this arrangement, whence results an essential advantage in the general motions of the limb. Then in fact the contraction of each muscle serves, both to cause a motion below in the moveable part to which it is attached, and to strengthen above the fixed point of the neighbouring muscles which contract at the same time with it.

Every long muscle is in general thicker in its middle than at its extremities, a form which arises from the manner of the insertion of the fleshy fibres, which arising above and terminating below, some successively below others, are so much the less numerous as we approach nearer each extremity, whilst in the middle they are all found in juxta-position. The anterior rectus, the long supinator, the external radial muscles, &c. have manifestly this arrangement.

There is a particular kind of long muscles, which has no analogy but in external appearance with that of the muscles of the limbs. They are those that are embedded in front and especially behind the spine. Though they appear simple at first view, these muscles have as many distinct fasciculi as there are vertebræ. The transversalis colli, the sacro-lumbalis, the longus colli, &c. represent very well an elongated fasciculus like the sartorius, the anterior rectus of the thigh, &c.; but the structure of this fasciculus has nothing in common with that of these muscles; it is a series of small fasciculi, which have each their distinct origin and termination, and which appear to be confounded into one muscle only because they are in juxta-position.

II. Forms of the Broad Muscles.

The broad muscles occupy in general the parietes of the cavities of the animal economy, those of the thorax and abdomen especially. They form in part, these parietes, defend the internal organs, and at the same time by their motions assist their functions.

Their thickness is not great; most of them appear like muscular membranes, sometimes arranged in layers, as in the abdomen, sometimes covering the long muscles, as on the back; they are in the first case, much more extensive superficially than deeper seated.

Whenever abroad muscle arises and terminates on one of the great cavities, it preserves everywhere nearly its breadth, because it has a large surface for its insertion. But if from a cavity it goes to a long bone, or to a small apophysis, then its fibres gradually approximate; it loses its breadth, increases in thickness, and terminates in an angle which is succeeded by a tendon, which concentrates into a very small space fibres widely scattered on the side of the cavity. The great dorsal and pectoral muscles present us an example of this arrangement, which is met with also in the iliacus, in the glutæi medius and minimus. The broad muscles of the pectoral cavity have a peculiar arrangement which the ribs require; their origin takes place by serrated points fixed to these bones, and separated by spaces between them.

The broad muscles are most often simple; many rarely unite to form compound ones. Different cellular layers separate them, like the long muscles; but they are hardly ever like them covered by aponeuroses; the greatest number is merely subjacent to the integuments; the reason is that their form naturally protects them from these displacements, of which we have spoken in the article on aponeuroses, and which, without these membranes, would be so frequent in the long muscles. I do not know that the cramp has ever been observed in those of which we are treating. When the abdominal muscles are laid bare by incisions made through the integuments of a living animal, I have observed, that in contracting, the bulk of each preserves the same place.

III. Forms of the Short Muscles.

The short muscles are those in which the three dimensions are nearly equal, having a thickness in proportion to their width and their length. They are found in general in the places, where is required on the one hand much power, and on the other small extent of motion; thus around the temporo-maxillary articulation the masseter and pterygoids, around the ischio-femoral the quadratus the gemini the obturators, &c. around the scapulo-humeral the supra-spinalis and the teres minor, in the hand the muscles of the palmar eminences, in the foot various fleshy fasciculi, in the vertebral column the interspinal, in the head the small and great anterior, posterior and lateral recti, exhibit more or less regularly the form of which we are treating, and answer the double object that I have indicated, on the one hand by the very considerable number and on the other by the shortness of their fibres.

The short muscles are, more often than the broad, united to each other, either in their origin or termination, as we see in the foot and the hand. Sometimes they are of a triangular form, as in these two parts; sometimes they approach to the form of a cube, of which there is an example in the masseter and pterygoid muscles. In general they are rarely covered by aponeuroses, undoubtedly because the shortness of their fibres prevents them from being liable in a great degree to considerable displacements.

Besides, the division of the muscles into long, broad and short, is, like that of the bones, subject to an infinite number of modifications. In fact many of these organs have mixed characters; thus the sub-scapularis and the infra-spinalis have a form intermediate to the broad and short one; thus the cruræus, the gemelli of the leg, &c. cannot be considered precisely long or broad muscles. Nature varies, according to the functions of the organs, the conformation of the agents of their motions, and we can only establish approximations in our anatomical divisions.

ARTICLE SECOND.

ORGANIZATION OF THE MUSCULAR SYSTEM OF ANIMAL LIFE.