Part 18

In the interior, these bones have nothing peculiar, except an abundance of the texture of the cells which forms them almost wholly, and exposes them to frequent caries.

Nature is not however regular in the division of bones into long, flat and short. Here as elsewhere, she disregards our methodical descriptions, and shows us the bones sometimes exhibiting the character of long ones and short, and sometimes uniting the attributes of both these last with the flat ones. The basilary apophysis and the superior part of the occiput, the body and the lateral portions of the sphenoid, when placed in contrast, prove this assertion. A bone sometimes by its external form belongs to the long ones, but from its internal organization should be classed with the flat, of this the ribs are an example, &c.

IV. Of the Bony Eminences.

The bony eminences have generally the name of apophyses; they are called epiphyses when the cartilage of ossification which unites them to the bone is not yet encrusted with calcareous substance.

These eminences have four great divisions; viz. those, 1st, of articulation; 2d, of insertion; 3d, of reflection; 4th, of impression.

1st. The eminences of articulation vary according as the articulation is moveable or immoveable; I shall not consider them here, as I should be obliged to repeat it in the chapter upon articulations.

2d. The eminences of insertion are very numerous in the bones; they only give attachment to the fibrous organs, as the ligaments, the tendons, the aponeuroses, the dura-mater; no organ differing from these is implanted into the bony eminences, or generally into the bones, except by means of them; the muscles are a remarkable example of this.

These eminences are usually much less in women than in men, in children than in adults, in weak animals than in carnivorous ones who live by attacking and destroying their prey. The prominence of the eminences of insertion is always an index of the force and vigour of the motions. They are the more developed in proportion as the muscles are. Examine comparatively the skeleton of a strong, sanguineous man, whose muscles are powerfully delineated through the integuments, and that of a feeble, phlegmatic man, whose rounded forms like those of women, do not appear prominent, and you will see the difference.

The form of these eminences of insertion varies greatly; sometimes the muscles are inserted by many separate aponeurotic fibres; then they are small, very numerous and form only little asperities imprinted on a greater or less surface; sometimes it is by a single tendon that the muscle takes its origin, then the apophysis is usually very prominent, and occupies a small space. Sometimes a broad aponeurosis gives rise to the fleshy fibres; it is then a bony line, more or less projecting that gives insertion.

The eminences are in general in proportion to the muscles that are attached to them; for example, in three muscles of nearly equal size, one of which is attached by separate fibres, the other by a tendon, and the other by an aponeurosis, we observe that the sum of the asperities of insertion of the first, the separate apophysis of the second, and the prominent line of the third are nearly equal in the quantity of osseous substance that forms them; so that by supposing that the apophysis was divided into asperities, or extended into a line, or that the asperities were united together, or the line concentrated so as to form an apophysis, this quantity of osseous substance would be found to be about the same.

We understand all the advantage of the eminences for the insertion of muscles, which they render distant from the centre of the bone, lessen the parallelism with its axis and consequently favour their motions in an evident manner.

Are these produced by the pulling of the muscles? This opinion borrowed from the laws of the formation of soft and inorganic bodies, does not accord with the known phenomena of vitality, with the existence of eminences where there is no muscular insertion, and which are often more prominent than these, with the disproportion that exists between the elongation of certain apophyses by muscular insertion, that of the styloid, for example, and the force of the muscles that are attached to it, &c.

The eminences for ligamentary insertion have the advantage, by removing a little the ligament from the articulation, of facilitating its motions; this is especially remarkable in the lateral ligaments of the elbow, the knee, &c.

As to the other eminences of insertion, we can hardly consider in a general manner their respective functions.

3d. The eminences of reflection are those under which a tendon passes, in deviating from its primitive course; such is the hook of the pterygoid apophysis, the malleolar extremity of the fibula, &c. Almost all these eminences have a slope or excavation in one direction, connected in the opposite with a ligament, so as to form a ring for the passage of the tendon.

4th. The eminences of impression are those which arise, when the different organs form on the osseous surfaces excavations that separate these eminences, which in fact only appear because the bone at this place remains at its ordinary level. The cerebral and muscular impressions are given as examples of this arrangement. But are these impressions really the effect of the compression of the organs on the bone, or do they arise from the laws of the osseous development, laws which give to the bones forms accommodated to the surrounding organs? I adopt more readily the second than the first of these opinions, which has been thought very probable from the effect of aneurisms upon bones that are contiguous to them, which are worn and gradually destroyed by them. But let us remark that if the muscles, the brain, and the vessels by their pressure, had upon the bones in a natural state, an action analogous to that of aneurism, the state of the parts ought to be the same as in that case. The compact layer ought to be destroyed where these depressions are, and leave in its place an unequal, ragged surface, but the contrary happens, which makes me think, that what is commonly called the impression of organs, is only a natural effect of ossification.

V. Of the Osseous Cavities.

The osseous cavities are very numerous; those only which are found on the exterior of the bones will be treated of. They are divided, like the eminences, into articular and non-articular. The first will be examined, with the analogous eminences, in the chapter on articulations. Among the second there are cavities, 1st, of insertion; 2d, of reception; 3d, of slipping; 4th, of impression; 5th, of transmission; 6th, of nutrition.

1st. The cavities of insertion give attachment to the aponeuroses of the muscles, to the ligaments, &c. They have the advantage, 1st, of multiplying the insertions of the fibres, without increasing the size of the bone, since a concave surface is evidently more extensive than a plain surface would be which should occupy the space between its edges; 2d, of allowing the muscular fibres more room, and consequently giving them greater length than if they arose from an eminence, which also gives more extent to the motions. The pterygoid, digastric cavities, &c. present examples of this arrangement.

2d. The cavities of reception are those which serve to receive an organ, lodge and defend it; such are the fossæ of the bones of the cranium, those of the ossa ilii, &c. These cavities sometimes belong to the whole of the bone, the form of which is concave, as we see in the frontal bone, sometimes they are hollowed out upon an insulated part, like the maxillary depression of the inferior jaw; they are always destined for an essential part, for a gland, a viscus, &c.

3d. The cavities of slipping are in general found at the extremity of the long bones. They are grooves, more or less deep, in which the tendons glide to go to the place in which they are inserted. All are covered with a cartilage and terminated by a very strong ligamentary ring. Do the tendons by their friction form these cavities? This is the common opinion, but it does not appear to me more probable than the theory of muscular, vascular impressions, &c. These cavities ought to be then so much the deeper, in proportion as the muscles are the more exerted; they ought not to exist in subjects paralytic from their infancy; they ought not to exist in the cartilages of ossification in the fœtus, whose limbs have hardly ever moved; but the contrary of all this is constantly observed. Let us describe then all the different configurations of the bones, as a consequence of the laws of ossification, laws in obedience to which the osseous forms, all primitively determined, are made to develop. The size of the extremities of the long bones favours the existence of these different cavities, which cannot on this account injure the osseous solidity.

4th. The cavities of impression correspond with the eminences of the same name. I have spoken of them above.

5th. The cavities of transmission are especially destined for the vessels and the nerves. We find many of them on the head; they have sometimes the form of a groove, sometimes that of a tube and at others that of a slit, according to the thickness or breadth of the bones which these vessels or nerves traverse in order to go from one place to another. The periosteum lines them; they contain more or less cellular texture. The nerves and vessels they transmit are foreign to the bones.

6th. The cavities of nutrition, on the contrary, give passage to vessels which carry to the bones or the medullary organ the substances that repair them. They are of three sorts.

The first form canals that are seen on the long bones exclusively, and go to the medullary cavity. Each bone has but one of these, situated always on its body, directed obliquely between the fibres of the compact texture, running sometimes from below upwards, sometimes from above down into the cavity of the bone, and thus forming a communication from without to within for the vessel of the medullary organ. This foramen serves particularly for the exhalation and nutrition of this organ, and nourishes the bone only secondarily.

The second kind of cavities of nutrition belong especially to the texture of the cells of the bones. Thus they are seen wherever this texture abounds, in the extremities of the long bones, the circumference of the flat ones, and the whole superficies of the short ones. Their diameter is greater than that of the canal which goes to the medullary cavity; it is less than that of the canals of the compact texture. Their number is very considerable; I have counted a hundred and forty upon the tibial extremity of the femur, twenty upon the body of one of the dorsal vertebræ, fifty upon the os calcis, &c. In general this number is always in proportion to the quantity of the texture of the cells that the bone contains. Hence why there are but few on the flat bones of the cranium, why they are more numerous on the flat bones of the pelvis especially where this texture is abundant, as on the ischium, on the iliac portion of the circumference of the ilium, &c. By pouring mercury into the spongy texture, it runs out from all these foramina, and thus proves their communications. They are irregularly scattered wherever they are. They are not met with on the body of the long bones, because the body contains little or none of the texture of the cells.

The third kind of canals of nutrition is only destined to the compact texture. It consists of an infinite number of little pores which the eye can clearly distinguish, and through which small vessels pass, that go to this texture. An evident proof that they do not go to the texture of the cells, is, that in the preceding experiment, the mercury never finds in them a way to escape externally. It is impossible to determine their number; it is prodigious in childhood. As the bones in old age become filled with calcareous substance, they are obliterated, and the vessels they contain become small ligaments, foreign to osseous nutrition, which continually grows weaker, and is soon annihilated, and allows necrosis to seize upon the bones, if general death does not prevent this partial death of the osseous system.

ARTICLE SECOND.