The new bone is laid down on the surface, in the Haversian canals, or in the cancellous spaces and medullary canal, or in all three situations.  The new bone on the surface sometimes takes the form of a diffuse encrustation of porous or spongy bone as in secondary syphilis, sometimes as a uniform increase in the girth of the bone—­hyperostosis, sometimes as a localised heaping up of bone or node, and sometimes in the form of spicules, spoken of as osteophytes.  When the new bone is laid down in the Haversian canals, cancellous spaces and medulla, the bone becomes denser and heavier, and is said to be sclerosed; in extreme instances this may result in obliteration of the medullary canal.  Hyperostosis and sclerosis are frequently met with in combination, a condition that is well illustrated in the femur and tibia in tertiary syphilis; if the subject of this condition is confined to bed for several months before his death, the sclerosis may be undone, and rarefaction may even proceed beyond the normal, the bone becoming lighter and richer in fat, although retaining its abnormal girth.

The function of the epiphysial cartilage is to provide for the growth of the shaft in length.  While all epiphysial cartilages contribute to this result, certain of them functionate more actively and for a longer period than others.  Those at the knee, for example, contribute more to the length of limb than do those at the hip or ankle, and they are also the last to unite.  In the upper limb the more active epiphyses are at the shoulder and wrist, and these also are the last to unite.

The activity of the epiphysial cartilage may be modified as a result of disease.  In rickets, for example, the formation of new bone may take place unequally, and may go on more rapidly in one half of the disc than in the other, with the result that the axis of the shaft comes to deviate from the normal, giving rise to knock-knee or bow-knee.  In bacterial diseases originating in the marrow, if the epiphysial junction is directly involved in the destructive process, its bone-forming functions may be retarded or abolished, and the subsequent growth of the bone be seriously interfered with.  On the other hand, if it is not directly involved but is merely influenced by the proximity of an infective focus, its bone-forming functions may be stimulated by the diluted toxins and the growth of the bone in length exaggerated.  In paralysed limbs the growth from the epiphyses is usually little short of the normal.  The result of interference with growth is more injurious in the lower than in the upper limb, because, from the functional point of view, it is essential that the lower extremities should be approximately of equal length.  In the forearm or leg, where there are two parallel bones, if the growth of one is arrested the continued growth of the other results in a deviation of the hand or foot to one side.