[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, the vertebral border of the scapula, and the cristal border of the ilium.  They exhibit a rough symmetry; they rarely attain any size; and they usually cease growing when the skeleton attains maturity—­the conversion of cartilage into bone being then completed.  While they originate from the ossifying junctions of the long bones, they tend, as the shaft increases in length, to project from the surface of the bone at some distance from the ossifying junction and to “point” away from it.  They may cause symptoms by “locking” the adjacent joint or by pressing upon nerve-trunks or blood vessels.

In a considerable proportion of cases, the disturbance of growth is further manifested by dwarfing of the long bones; these are not only deficient in length but are sometimes also curved and misshapen, which accounts for the condition being occasionally confused with the disturbances of growth resulting from rickets.  In about one-third of the recorded cases there is a dislocation of the head of the radius on one or on both sides, a result of unequal growth between the bones of the forearm.

[Illustration:  FIG. 140.—­Multiple Cartilaginous Exostoses in a man aet. 27.  The scapular tumour projecting above the right clavicle has taken on active growth and pressed injuriously on the cords of the brachial plexus.]

In early adult life, one of the tumours, instead of undergoing ossification, may take on active growth and exhibit the features of a chondro-sarcoma, pressing injuriously upon adjacent structures (Fig. 140) and giving rise later to metastases in the lungs.