TUMORS. 



353 



ble for fragments of cartilage to become detached from the primary 

 growth and appear in the secondary tumors, should metastasis 

 occur. 



4. Osteoma. The most important tumors containing bone are 

 mixed tumors that are significant chiefly because of their other 

 constituents. Small growths consisting of bone alone, either in its 

 compact or its spongy form, occur in the lung, walls of the air- 

 passages, and, rarely, in other situations (Fig. 315). Where bony 



FIG. 315. 



Developing osteoma of the arachnoid. (Zanda.) A, dura mater; B, as yet non-calcified 

 osteoid tissue ; G, bloodvessel. 



new formations spring from pre-existent bone e. g., from parts of 

 the skeleton they are usually the result of some inflammatory proc- 

 ess, and are not to be grouped among the tumors. 



In mixed tumors bone is frequently associated with fibrous tissue, 

 myxoma, sarcoma, and chondroma. 



The structure of the bone in tumors presents slight departures 

 from the normal type, just as that of cartilage in chondromata is 

 somewhat atypical. The lacunae are apt to vary in size, shape, and 

 distribution more than in normal bone, and the system of canaliculi 

 is less perfectly developed. 



5. Myxoma. The mucous tissue of myxomata has its normal 

 prototype in the Whartonian jelly of the umbilical cord. In its 

 purest form it consists of stellate or spindle-shaped cells, with long 

 fibrous processes that lie in a clear, soft, gelatinous, intercellular sub- 



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