tis Deformans--Paget's Disease of Bone.#--This rare disease was
first described by Sir James Paget in 1877. In the early stages, the
marrow is transformed into a vascular connective tissue; its bone-eating
functions are exaggerated, and the framework of the bone becomes
rarefied, so that it bends under pressure as in osteomalacia. In course
of time, however, new bone is formed in great abundance; it is at first
devoid of lime salts, but later becomes calcified, so that the bones
regain their rigidity. This formation of new bone is much in excess of
the normal, the bones become large and bulky, their surfaces rough and
uneven, their texture sclerosed in parts, and the medullary canal is
frequently obliterated. These changes are well brought out in X-ray
photographs. The curving of the long bones, which is such a striking
feature of the disease, may be associated with actual lengthening, and
the changes are sometimes remarkably symmetrical (Fig. 135). The bones
forming the cranium may be enormously thickened, the sutures are
obliterated, the distinction into tables and diploe is lost, and, while
the general texture is finely porous, there may be areas as dense as
ivory (Fig. 134).

[Illustration: FIG. 134.--Changes in the Skull resulting from Ostitis
Deformans.

(Anatomical Museum, University of Edinburgh.)]

_Clinical Features._--The disease is usually met with in persons over
fifty years of age. It is insidious in its onset, and, the patient's
attention may be first attracted by the occurrence of vague pains in the
back or limbs; by the enlargement and bending of such bones as the tibia
or femur; or by a gradual increase in the size of the head,
necessitating the wearing of larger hats. When the condition is fully
developed, the attitude and general appearance are eminently
characteristic. The height is diminished, and, owing to the curving of
the lower limbs and spine, the arms appear unnaturally long; the head
and upper part of the spine are bent forwards; the legs are held apart,
slightly flexed at the knees, and are rotated out as well as curved; the
whole appearance suggests that of one of the large anthropoid apes. The
muscles of the limbs may waste to such an extent as to leave the large,
curved, misshapen bones covered only by the skin (Fig. 135). In the
majority of cases the bones of the lower extremities are much earlier
and more severely affected than those of the upper extremity, but the
capacity of walki