Ossification does not take place with equal rapidity in every bone; the ribs and clavicles are completely converted into bone long before birth, while the bones of the _carpus_, _tarsus_, and more particularly the _patella_, are not completed until some years afterwards; certain parts of bones are not formed until after birth, as the _mastoid processes_, and the projections of the _frontal sinus_; nor are the _epiphyses_ consolidated with the body of the bones, so as to constitute _apophyses_, until many years. With regard to the general developement of the skeleton after birth, it may be observed, that the proportion of cartilage is in an inverse ratio to the age; reckoning from the twentieth year backwards, the younger the subject the larger is its head, compared with the trunk and limbs; the smaller the bones of the face, but the larger the fontanelles; the flatter is the lower part of the face; the larger the chest, in relation to the pelvis; the shorter the limbs; the larger the clavicles; the smoother and flatter the broad bones, but the rounder those that are cylindrical. (_See Albert Durer on the proportions of the bones_, _Lib._ 1.) The chemical composition of the bones, in relation to their _phosphate of lime_, and _gelatine_, varies also very materially at different ages. It may be stated that the quantity of the former substance deposited in the texture of bones, is in the direct ratio of the age; the bones of the fœtus are at first entirely gelatinous; at the time of birth, and during the first years of life the organic part superabounds; in youth the quantity of each constituent is nearly equal; in adults the calcareous earth forms almost two-thirds of their substance; and finally, by gradual accumulation in old age, its excess obliterates the organized parts; so that the skeleton of the aged person may be distinctly recognised; besides which, the sutures of the skull are generally lost, and the absorption of the alveolar processes again imparts to the face the physiognomy of the infant.