orbit it displaces the eyeball; in the nasal fossae
and in the external auditory meatus it causes obstruction, which may be
attended with ulceration and discharge. In the skull it may project
from the outer table, forming a smooth rounded swelling, or it may
project from the inner table and press upon the brain.

The diagnosis is to be made by the slow growth of the tumour, its
hardness, and by the shadow which it presents with the X-rays (Fig. 138).

An osteoma which does not cause symptoms may be left alone, as it ceases
to grow when the skeleton is mature and has no tendency to change its
benign character. If causing symptoms, it is removed by dividing the
neck or base of the tumour with a chisel, care being taken to remove the
whole of the overlying cartilage. The dense varieties met with in the
bones of the skull present greater difficulties; if it is necessary to
remove them, the base or neck of the tumour is perforated in many
directions with highly tempered drills rotated by some form of engine,
and the division is completed with the chisel.

[Illustration: FIG. 139.--Multiple Exotoses of both limbs.

(Photograph lent by Sir George T. Beatson.)]

#Multiple Exostoses.#--This disease, which, by custom, is still placed
in the category of tumours, is to be regarded as a disorder of growth,
dating from intra-uterine life and probably due to a disturbance in the
function of the glands of internal secretion, the thyreoid being the one
which is most likely to be at fault (Arthur Keith). The disorder of
growth is confined to those elements of the skeleton where a core of
bone formed in cartilage comes to be encased in a sheath of bone formed
beneath the periosteum. To indicate this abnormality the name
_diaphysial aclasis_ has been employed by Arthur Keith at the suggestion
of Morley Roberts.

Bones formed entirely in cartilage are exempt, namely, the tarsal and
carpal bones, the epiphyses of the long bones, the sternum, and the
bodies of the vertebrae. Bones formed entirely in membrane, that is,
those of the face and of the cranial vault, are also exempt. The
disorder mainly affects the ossifying junctions of the long bones of the
extremities, the vertebral border of the scapula, and the cristal border
of the ilium.

_Clinically_ the disease is attended with the gradual and painless
development during childhood or adolescence of a number of tumours or
irregular projections of bone, at the ends of the long bones,