other portions may be soft and fluctuating as a result of myxomatous degeneration and liquefaction.  These tumours grow slowly and painlessly, and may surround nerves and arteries without injuring them.  They may cause a deep hollow in the bone from which they originate.  All intermediate forms between the innocent chondroma and the malignant chondro-sarcoma are met with.  Chondroma may occur in a multiple form, especially in relation to the phalanges and metacarpal bones.  When growing in the interior of a bone it causes a spindle-shaped enlargement of the shaft, which in the case of a phalanx or metacarpal bone may resemble the dactylitis resulting from tubercle or syphilis.  A chondroma appears as a clear area in a skiagram.

A skiagram of a bone in which there is a chondroma shows a clear rounded area in the position of the tumour, 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.