BONE. 273 BONE. ■versian canal. These spaces are known as ?«- cun<F, and each one has passing off from it. in a radiate manner, nvimerous small canals or <-anaUcuU, which anastomose with canallciili from other lacuna' belonpinj; to the same system, and probably serve as lymph-channels for the mitrition of the hone. The lacunae are not empty, but contain bone cells or corpuscles, which are nucleated bodies and send out fine processes into the canaliculi. In addition to the Haversian systems are irregular lamellw, or lay- ers of bone, which fill in the spaces left l>etween the systems, and are known as interstitial la- mellw. Along the surface of the bone, and also along the side of the central canal, the Inmcllw are arranged parallel to the surface, and are known as circumferential lameltrr. The cavities of bones and the various nutrient channels which run through them are filled with a substance called nrnrrow. In all bones of young animals the marrow is red in color, and is known as red marrow. As the bone grows older the marrow becomes lighter in color from the accumulation of fat, and is known as yellow marrow, itar- row consists of a delicate connective-tissue net- work, in which ramify numerous small blood- vessels. In the meshes of this network are found various kinds of cells — marrow-cells, or rather large oval cells; giant cells, or myeloplaxes; large cells containing several nuclei ; red-blood cells; nucleated red-blood cells; white-blood cells; connective-tissue cells; and fat-cells. The periosteum is a connective - tissue membrane, rich in blood-vessels, Avhich invests the surface of all bones except where they articulate with other bones. Connective-tissue fibres ('Sharpey's fibres') extend from the periosteum into the superficial layers of the bone. With the exception of the flat bones of the head, all bones are first represented by masses of hyaline cartilage which resemble in shape the future bone. The cartilage is covered over with the primitive periosteum, or perichondrium. From this membrane blood-vessels extend into the cartilage at some point, usually near the centre of a long bone, and a rearrangement of the car- tilage-cells occurs. This point is known as the centre of ossification. Xew cells, probably de- rived from the white-blood cells, appear and are known as osteoblasts. Each osteoblast sur- rounds itself with a little layer of bone, and is then known as a bone-cell. In compact bone the formation of the Haversian sj-stems is due to the laying down of the bone in concentric lay- ers around the blood-vessels. During the devel- opment of bone witliin the cartilage ( intra-carti- laginous development), bone is also being formed imder the periosteum (subperiosteal develop- ment). Here, also, the bone is formed by the osteoblasts surrounding themselves by bone. The flat bones like those of the skull are not laid down in cartilage like the long bones, but de- velop in a membranous connective-tissue matrix (intra membranous development). Except for the absence of the preexisting cartilage, the process is q<iite similar to that which occurs in intracartilaginous development. Neres may be seen entering bone, and the acute pain felt in some of its diseased conditions proves their existence ; but they have not yet been actually demonstrated in the osseous tis- sue; neither have lymphatics, though we sup- pose, from analogy, that bones are supplied with them. The several bones composing the animal frame will be treated of tinder the head Skele- ton ; any important peculiarities in the bones of dilTerent classes of animals, under the heads of these classes. C'uEiiiCAL CojrposiTiox OF Bone. The prin- cipal chemical ingredients present in bone are gelatin and phosphate of lime: and the follow- ing table represents the composition in 100 parts of bone of average quality: CON'STITCENTS Human Bones Ox-bonea Gelatin 33.30 53.04 11.30 1.16 1.20 Phosphate of lime 67.35 3.85 Carbonate of linif Pho.sjihate c)f nuii^nesia.. . . 2 05 Carbonate and chloride of sodium 3.45 100.00 lOO.OO The gelatin of bones remaining behind after treatment with dilute hydrochloric acid has the size and shape of the original bone, but is, of course, soft, somewhat transparent, flexible, and even elastic. If this soft, gelatinous residue of bone be boiled with water, it dissolves in great part therein, and yields a solution which sets, or gelatinizes, on cooling. A more common way of extracting the gelatin from bone is to heat the bones covered with water in a digester to a temperature of 270° to 280° F., when much of the gelatin dissolves out and leaves the earthy salts with the remainder of the gelatin. Be- sides the marrow (q.v.), a little fat is gener- ally found permeating the entire structure of the bone, which can be extracted by throwing the bones into hot water, when the grease or fat exudes and floats to the surface. In some of the larger bones of man and other mammalia, there is a central cavity containing a consider- able amount of fatty matter, popularly known as marrow. These cavities are not found in the bones of the young animal, but gradually form as the animal approaches maturity. In the sloth, cetacea. seals, and a few other animals, the cavities are not found. Occasionally, as in man, the elepliant. girafl'e, etc., the bones in the head have cavities filled with air instead of marrow. The uses to which a bone may be put are various. In the cooking of soups, bones form a constant ingredient, and become useful in -supplying gelatin, which gives a body to the soup it would not otherwise possess. How far gelatin is of itself nutritious is a disputed question. (See Gelatix and Xutritio.v.) Ani- mals, however, like the dog. which masticate, devour, and digest the entire bone, do derive benefit therefrom, in part from the gelatin and in other part from the earthy substances: and the same remark applies to the use sometimes made of small fish, where, after being thorough- ly bro«-ned, they are entirely eaten. In times of s<-arcity in Xorway and Sweden, the jjwirer people even eat the bones of mackerel and otlier fish. Bone is largely used in making the handles of small brushes, the more common table knives and forks, and penknives, and in the manufac- ture of the cheaper sort of combs (q.v.). Our forefathers, before the metals were known, fash- ioned fish-hooks out of bone, and used the spinee
