yo MICROSCOPICAL DIAGNOSIS. 



variable. Some are spindle-shaped, some stellate and movable. Usu- 

 ally, however, they resemble the cells of normal cartilage. The en- 

 chondromata vary in size, are usually single, occasionally multiple. 

 They occur in the early part of life, even in the new born. By far 

 the greater number affect the bones and most frequently the medul- 

 la. Thus the articulating surfaces are rarely affected. They may 

 arise from cartilage itself : their likeness to normal cartilage is then 

 more exact. In some of the. softer forms there is a tendency to re- 

 turn after removal, affecting even the lymphatics, and in the young 

 causing cachexia. The malignant properties of the encondromata, 

 when present, are probably due to the fact that sarcorrratous ele- 

 ments are associated with them. However healing almost invaria- 

 bly occurs after complete extirpation, and in the case of a pure en- 

 chondroma malignancy may be said to be entirely absent. Of the 

 many degenerations to which this tumor is subject calcification is 

 the most common. Ossification sometimes affects the periphery of 

 the growth so that it is surrounded by a thin bony wall. Spiculrc 

 of bone are frequently found through the growth. A specimen in 

 the author's possession shows about one-third of the growth truly 

 ossified, the remainder resembling normal cartilage. The line be- 

 tween the two being sharp and distinct. 



TYPE OK BONN STRUCTURE. 



Osseous tumor, Osteoma. In the case of this tumor the bony 

 appearance is the natural result of development, whereas in many 

 other cases tumors having undergone osseous degeneration it is 

 accidental. It has an independent growth and is not to be con- 

 founded with the products of inflammation of bone, as the callus 

 after fractures, etc. Most of the osteomata arise from connective- 

 tissue. They may have their origin from cartilage, bone, or the 

 periosteum of bone. Those having their origin apart from bone, 

 heterologous, are known as osteophytes. They are found near 

 diseased joints, near the seat of inflammatory processes and in many 

 other situations. They are found not uncommonly in the lungs 

 and brain. They are to be carefully distinguished from growths 

 that have become partly ossified, for in the latter case they might 

 be more or less malignant, while a true osteoma is perfectly inno- 

 cent. The homologous exostoses are found most frequently on the 

 external and internal surfaces of the skull, in the orbit, on the up- 



