=Composition of Bone.=—Bone consists of organic and inorganic matter. Organic matter gives toughness and elasticity to the bone, and inorganic matter hardness. The organic substance of bone is called ossein. When boiled in water ossein is resolved into gelatin. The following tables[1] give the results of an analysis of the femur, fresh, of a mature hen. Footnote 1: Grateful acknowledgment is hereby made to Dan M. McCarty, Chemist, Animal Industry Division, North Carolina Agricultural Experiment Station, for this analysis. Fresh femur: Water 18.23 per cent. Dry matter 81.77 per cent. Dry matter: Organic matter 63.09 parts Inorganic matter 18.68 parts Salts in dry matter: Calcium 6.970 per cent. Magnesium 0.283 per cent. Potassium 0.004 per cent. Sodium 0.276 per cent. Iron 0.020 per cent. Phosphorus 3.210 per cent. Sulphur 0.085 per cent. Chlorine 0.520 per cent. Carbon dioxid 0.550 per cent. The inorganic matter of the femur of the hen consists of 18.68 parts or 22.84 per cent. of dry matter, and the organic matter of 77.16 per cent. Stated in other words the femur, including its contained marrow, consists of organic and inorganic matter in the ratio of 3.4, approximately, to 1. =The Skeleton of the Fowl.=—The skeleton of a bird is remarkable for the rapidity of its ossification. It is worthy of note that other parts of the bodies of adult birds also become ossified. Among such parts are the tendons of the muscles of the legs, of the feet, and of the neck; the plates of the corneal margin of the sclerotic tunic of the eye; and the stapes of the ear. Ossification in birds at the attachments of the semi-lunar valves of the aorta and of the pulmonary artery has been reported by Owen. The bony structure is compact, and the bones contain a greater proportion of phosphate of lime than do the osseous structures of mammals. Especially is this the case in those parts of the skeleton which are permeated by air. THE DIVISIONS OF THE SKELETON