f 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 paralle