BONES

are adapted to form a fenevesk capable = eementing i ight, of giving attachment to pow muscles wi sop learting: ate certain cases of protecting the organs they enclose, e.g. the brain or the heart and lungs. They develop either from gristle or from membrane, and some bones, e.g. tho collar-bone from both; and differ from other organs of the body chiefly in the high percentage of miner a) matter they contain. They consist of about two-thirds mineral matter, which is mainly chalk and phosphate of calcium, but in advanced life the percentage of mineral matter is highcr and the bones in consequence more brittle at this time. In certain cases the bones are lightened by containing cavities full of air, thus the et pe jaw is hollow and communicates with the nose. In birds this arrangement is present in nearly al! the bones. The long bones, e.g., those of the arm or leg, contain marrow pavities. These contain in the child a red marrow that is concerned in the making of blood, but after growth is over the red marrow is largely replaced by yellow marrow. composed merely of fat. (Reefer to Broken Bone.} [s. 338]