ARTICLE SECOND.
ORGANIZATION OF THE OSSEOUS SYSTEM.
The peculiar texture of the osseous system forms in it the principal and predominant part, especially as we advance in age. The common organs are in much less proportion.
I. Texture Peculiar to the Osseous System.
The texture of the bones, like that of most of the other organs, presents itself under the aspect of fibres whose nature is everywhere the same, but which differently arranged, form two principal modifications; in the one, these fibres being more or less scattered, exhibit many cells; in the other being close to each other, they form a compact substance in which it is difficult to distinguish them. Hence two sub-divisions of the osseous texture, that with cells, and the compact. Authors admit a third one, the reticular; but this is included in the first.
Texture with Cells.
The texture with cells does not exist in the first periods of ossification. The time of its formation is when the phosphate of lime is added to the gelatine of the primitive cartilage, and gives to the organ the bony nature. Then an infinite number of cells is formed in the solid mass of cartilage, because the gelatine, taken up by the absorbents, disappears in the place they occupy. No more is brought by the exhalants, which begin to carry the phosphate of lime to the fibrous cross-pieces, whose interlacing forms these cells; so that the development of the texture of the cells belongs evidently to the disproportion that takes place in the bones at a certain period of their growth, between the functions of the exhalant and absorbent system, until then in equilibrium. We know not the cause of this disproportion, it appears to be a law of ossification. It is by virtue of this law and by an analogous mechanism, that the os ethmoides, at first solid and full when it is cartilage, is hollowed out at the period of its ossification, into a great number of cells. It is thus that the sphenoidal, frontal sinuses, &c. are formed and enlarged.
The formation of the texture of the cells ceases when all the epiphyses have disappeared. At this period it exhibits to us an infinite number of fibres which appear to arise from the internal surface of the compact texture, go in different directions, cross, unite, separate, bifurcate, in a word, pursue such irregular courses, that it is impossible to follow them. Their size is not less variable; sometimes their delicacy is such, that they can hardly be touched without breaking; at others they are quite large. Often instead of fibres there are layers, of more or less considerable size, from which arise other smaller ones, which appear to ramify, and from which result, when they are near each other, species of canals, which are seen very well by sawing transversely the extremity of a long bone, so as to have a segment of half an inch.
The cells which are made by their separation, are of very unequal form and capacity.
All communicate together; the following experiments prove this. 1st. If we make a hole in the extremity of a long bone, or upon the surface of a short or flat one, and pour in mercury, it passes through all the communications, and comes out of the natural foramina on the surface of the bone, which also open into the cells. 2d. Saw a long bone at one of its extremities, cover its whole surface with something that shuts up its pores, then expose it to the sun; the medullary fluid not being able to escape by the external pores, will come out at the sawed place, after passing successively through all the cells. 3d. By varnishing a dry bone, and opening it only in two opposite points, we can force air, water and every kind of fluid through these communications, from one opening to the other.
We can then consider the interior of every bone as forming a general cavity that is filled by many interlaced fibres. I have not observed a sensible difference in the direction of these fibres in the three kinds of bones.