We cannot trace the nerves in the bones, the filaments that enter them are so fine; I do not know that anatomy has any positive data upon this point.
ARTICLE THIRD.
PROPERTIES OF THE OSSEOUS SYSTEM.
I. Physical Properties.
The bones have very strongly marked physical properties. Solidity and hardness are their peculiar portion; they derive these properties from the phosphate of lime which penetrates them, thus they are constantly increasing with age, because this substance becomes more and more predominant. Elasticity is another physical property of the bones, which is found combined with the two preceding, but which is in an inverse order; as it is in the gelatinous substance, in the cartilaginous portion of the bone that it resides, it is, like this portion, greater in childhood. In old age, the bones lose entirely their suppleness and elasticity; they break more easily. Elasticity is more evident in the long and small bones, than in those which are larger; the fibula bends and evidently goes back again, this the tibia could not do without difficulty. It is not that the one is more elastic than the other, but it is that its conformation is more favourable to the development of this property.
II. Properties of Texture.
Although the hardness and solidity of the osseous texture seem to be opposed to every kind of extension and contraction, yet these two phenomena and the properties of texture from which they arise, are often very evident in it.
The extensibility of the osseous fibres is proved by the observation of many diseases, for example, the spina-ventosa, the swelling of the maxillary sinus when it contains a polypus, by the enlargement of the bones of the cranium in hydrocephalus, &c. I would remark on the subject of these different distensions, that often by the influence of analogous causes, the bones which yield and are distended in the above cases, are broken, worn and destroyed in others. A polypus of the nose breaks through the naso-palatine partition, without having first distended it; aneurism of the aorta does not bend the sternum or the vertebræ, but it breaks through and destroys these bones. Whence arises this difference from causes nearly the same? This is not easily determined. The contractility of texture is very evident in the bones, when the cause which distended the fibres is removed. We see the alveoli contract, and become effaced, when a tooth has been drawn from them. The diminution of the thickness of the jaw after cutting the teeth arises only from the contraction of its fibres, which are no longer distended as much, because the root is not so broad as the crown, which had till then been wholly in the bone. The maxillary sinus contracts when a fungus is removed from it, or pus is discharged from the carious bone, &c. If death was not too soon the consequence of the puncture of the head of hydrocephalic patients, I am persuaded that we should see the bones gradually contract, and restore the cavity of the cranium to its natural dimensions. When we remove the dead piece from a long bone in necrosis, the new bone, formed on the exterior by means of the periosteum contracts in an evident manner. In paralysis of the optic nerve, its foramen becomes narrower. The orbit contracts when a cancerous eye has been extirpated. I have dissected the carotid canal in a dog whose carotid I had tied; there was no contraction because the blood coming by anastomoses dilated the artery to the usual size.
This contraction of the bones, by means of the contractility of texture, is not so sudden as that of the muscles, the skin, &c. when they are no longer distended by a tumour, an aqueous collection, &c. This arises from the difference of the organic texture, from the rigidity of osseous fibres owing to the calcareous substance they contain, &c. Thus the organic sensibility is less evident in them.