mour, which must be differentiated
from similar clear areas due to other kinds of tumour, especially the
myeloma; when it has undergone calcification or ossification, it gives a
shadow as dark as bone.

[Illustration: FIG. 50.--Chondroma growing from infraspinous fossa of
Scapula.]

[Illustration: FIG. 51.--Chondroma of Metacarpal Bone of Thumb.]

_Treatment._--In view of the unstable quality of the chondroma,
especially of its liability to become malignant, it should be removed as
soon as it is recognised. In those projecting from the surface of a
bone, both the tumour and its capsule should be removed. If in the
interior, a sufficient amount of the cortex should be removed to allow
of the tumour being scraped out, and care must be taken that no nodules
of cartilage are left behind. In multiple chondromas of the hand, when
the fingers are crippled and useless, exposure to the X-rays should be
given a trial, and in extreme cases the question of amputation may have
to be considered. When a cartilaginous tumour takes on active growth, it
must be treated as malignant.

The chondromas that are met with at the ends of the long bones in
children and young adults form a group by themselves. They are usually
related to the epiphysial cartilage, and it was suggested by Virchow
that they take origin from islands of cartilage which have not been used
up in the process of ossification. They are believed to occur more
frequently in those who have suffered from rickets. They have no
malignant tendencies and tend to undergo ossification concurrently with
the epiphysial cartilage from which they take origin, and constitute
what are known as _cartilaginous exostoses_. These are sometimes met
with in a multiple form, and may occur in several generations of the
same family. They are considered in greater detail in the chapter
dealing with tumours of bone.

Minute nodules of cartilage sometimes form in the synovial membrane of
joints and lining of tendon sheaths and bursae: they tend to become
detached from the membrane and constitute loose bodies; they also
undergo a variable amount of calcification and ossification, so as to be
visible in skiagrams. They are further considered with loose bodies in
joints.

Cartilaginous tumours in the parotid, submaxillary gland, and testicle
belong to a class of "mixed tumours" that will be referred to later.

#Osteoma.#--The true osteoma is composed of bony tissue, and originates
from the skel