Bones, if they have arteries, must have accompanying veins, and they have also absorbents; for a diseased bony part is absorbed as well as other parts of the body: and the cavities of the round bones bear the same proportion to the whole bulk of the bone in the foetus and the adult. The earth when out of the circulation has no longer any peculiar quality; and when dissolved by spirit of salt, the vessels and membranes remain unchanged, displaying the same laminated arrangement as the bony parts. The earth of bone is however valued as a material for cupells in the nice assays of silver, and styled virgin earth; but its properties arc owing to a portion of the phosphoric acid. The circulation in the bones is peculiar. The vessels run in the direction of the fibres in the long bones longitudinally, occasionally dipping perpendicularly; in the fiat bones they are radiated, diminishing towards the centre. The bones are full of pores for the admission of vessels: in the middle they are large and few; at the extremities smaller and more numerous. In every long bone, there is about the middle a hole for the passage of an artery and vein: the artery passes slantingly through the bone, branches on the internal periosteum, and externally again through the bone. These branches freely anastomose, and thus form an uninterrupted circulation between the internal and external parts. In the flat bones, the vessels anastomose in the meditullium or diploe.

In their external form bones greatly vary. Besides the epiphesis, they rise, we have said, in various protuberances, named processes, and they are sometimes depressed in cavities. These if deep, with large brims, are called cotylae; if shallow, glenae or glenoid. Anatomists have employed other appropriate terms. Thus, pits are small roundish cavities; furrows, long narrow canals; niches, small breaches; sinuosities, broad superficial depressions without brims; sinuses, large cavities within the bones, opening by a small aperture; foramina, holes that pierce through the bone. Bones are usually divided into, 1st. spherical, which arc spongy, except a thin plate on the surface: 2dly, cylindrical, which are compact in their middle, and spongy at their extremities; 3dly, the fat, which are compact on both sides, but spongy in the middle; 4thly, the irregular, which when thick arc like the round, and when thin like the fiat bones. It will be sufficiently obvious that these terms are not mathematically accurate.

Bones, we have said, owe their solidity to phosphorated lime. They contain also gelatine, and the proportion of each differs in different animals, and at different periods. The bones of an adult contain the greatest proportion of earth; those of a foetus, of gelatine. Fish bones, from Mr. Accum's experiments, contain one-sixth part more of phosphoric acid than the bones of quadrupeds. Carbonated alkalis decompose the phos-phat of lime in bones. They contain also a small proportion of selenite, carbonate of lime, and, according to Proust, of mineral alkali. Mr. Hatchett's late experiments in the Philosophical Transactions, greatly illustrate the chemical analysis of bone, horn, zoophytes, etc. but as less applicable to human bones, they fall not within our immediate province. See Hair and Horn.

Bones are covered with a strong, firm, fibrous substance, styled periosteum, which-is acutely sensible when inflamed, as indeed all the denser membranes are. Its chief use is to defend the bone, and perhaps to prevent its irregular growth. Bones themselves when inflamed are also highly sensible.

The internal parts of bones and the minutest cells are filled with marrow; a fluid fat contained in membranes, forming, in the language of some authors, the internal periosteum. The marrow does not differ in its analysis from suet and fat, or perhaps it has not been minutely examined. The marrow of herbaceous ani-.mals hardens when cold; that of carnivorous remains fluid; and in young animals a little blood is occasionally deposited. We suspect that the harder fats are distin guished by their containing a larger proportion of oxygen, and the softer by a greater proportionof hydrogen or carbon. Marrow is contained in follicles not communicating With each other: at the heads of the bones these follicles are supported by the cancelli,but in the middle they have no such support, though the marrow is still confined by follicles, which lessen its weight on the lower parts of the bone, where the cancelli again lend their assistance. The bone is apparently always full. It has been supposed that the larger arteries which penetrate the middle of the bone, are exclusively appropriated to the nutrition of the marrow. The facts however lately noticed of the mutual anastomoses of the internal and external vessels, oppose this opinion, which, we believe, is not supported by any well authenticated observation. The use of the marrow is not known: it is a part of the adipose system, and perhaps intended for occasional support, and to correct the acrimony produced by inanition. Animals that remain torpid during the winter repair to their retreats with considerable coverings of fat, and leave them in a most impoverished state. We suspect also that the fat may be a reservoir of oxygen; for when this principle is exhausted little fat remains. In the last stage of phthisis some fat is found in the adipose membrane, and in this disease the oxygen is not deficient: but in dropsy it is quite exhausted; and in this complaint the retention of the excrementitious urine would be soon injurious, were not its acrimony blunted by either an oleaginous or an oxygenated fluid.

The products of bones employed in medicine are the empyreumatic oil, styled Dippel's animal oil, highly rectified. When distilled they afford ammonia; and from these the spiritus cornu cervi is now exclusively prepared. Bones calcined in open vessels are styled cornu cervi calcinatum, now seldom employed. The oil remaining after distillation burnt with the earth produces lamp black; the finest kinds of which are furnished by the more compact bones, and the horns of animals, thence called ivory black. Bones rasped and macerated in hot water, or exposed to considerable heats in Papin's digester, furnish a nutritious soup; and in a more condensed state a valuable glue. Six pounds of dry bone shavings produced fifteen ounces of clear glue; and fifty pounds of ivory shavings yielded nine pounds and a half of transparent glue. The exact proportion of gelatine in bones has not however been ascertained, since the driest glue contains some water. These preparations were made by boiling only; but the soluble parts are more perfectly extracted in Papin's digester, though the fat acquires an un-pleasing empyreumatic flavour. Proust informs us, that the enlarged extremities of the bones, boiled for a quarter of an hour in water, yield one-fourth of their weight in fat, and the haunch bones one-eighth. The hard bones must be powdered, reduced to a fine paste by trituration with water, and boiled for a longer time. See Proust's ' Memoir for Meliorating the Condition of a Soldier,'published at Madrid 1791; an abstract of which may be found in the 53d volume of the Journal de Physique.

The diseases of the bones, independent of fractures and Dislocations, are wounds, necrosis,