Enchondroma, springing from hone, is in vested or not with a bony capsule. When it grows in the interior of a long bone, expan sion, and not perforation of the shell, occurs; the cancellated structure first.. and then the cortical, undergo softening and rarefaction, and are gradually spread out into a globular sac. New bony matter is also thrown out, help ing to complete the capsule, which is, even with this assistance, commonly imperfect. When developed in bones of very spongy texture, perforation may, according to Midler, occur, instead of expansion; we believe that, in at least some such cases, the growth originates in the sub-periosteal cellular membrane. In this latter variety the form is less regularly spheroidal than in the other ; but the texture is the same in both.
The progress of enchondroma is slow; its effects fundamentally are purely mechanical. Adhesion of the skin only occurs as an acci dental effect of inflammation : rupture of that membrane only from excessive distension; the resulting ulcer may discharge abundantly, and inflammation arise from this cause, as from external injuries, but not apparently from in trinsic spontaneous changes.
Enchondronia of the bones, like every other affection of those organs attended with en largement, has been described under the names osteosarcoma, osteosteatoma, andspina ventosa — terms devoid of definite significa tion. Scarpa speaks of it as " malignant
exostosis," a double misnomer—for its course differs essentially, as has been seen, from that of cancerous maladies, and it does not necessarily spring from bone.
Colloid cancer might possiblybe confounded with enchondroma. We have already alluded to a rude mark of distinction between the two products ; further, colloid cancer rarely (never so far as our experience goes) occurs in bone, the chosen site of enchondroma ; the effects of the two products on adjoining tissues are essentially different — enchon droma never infiltrates structures, colloid fre quently does ; colloid never contains patches of bone, enchondroma does -so commonly ; colloid is of protein basis, enehondroma yields chondrin, or (rarely) glutin.
Certain sarcomata of the maxillm have much outward resemblance to enchondroma ; but they contain spherical,cells with granules and fusiform corpuscles, and are besides of albuminous composition.