TUMORS. 327 



designated. Bone tissue often occurs in tumors of the connective-tissue 

 group as a secondary or complicating structure osteo -fibroma, osteo-chon- 

 droma, osteo -sarcoma, etc. It may occur in muscles as a result of certain 

 exercises, or as a result of a peculiar inflammatory process, or it may 

 occur in connection with chronic inflammation in a variety of tissues. A 

 circumscribed mass of abnormal bone, not of inflammatory origin, may 

 be called an osteoma. Small masses of new-formed bone of various 

 shape, projecting from a bony surface and frequently of inflammatory 

 origin, are usually called osteophytes. Bony tumors projecting from the 

 surface of bones are frequently called exostoses. 



An osteoma may be loose in texture, consisting of bone tissue similar 

 to cancellous tissue ; or it may be very hard and dense like ivory, so- 

 called ivory exostoses. The difference between these forms lies chiefly 

 in the varying number and size of the vascular and medullary spaces 

 which they contain. The growth of the osteomata is, as a rule, slow. 

 They are benign tumors, and are not infrequently multiple. 



Osteomata may develop in connection with the bone or periosteum, 

 which is most frequently the case, or, independently of bone, in soft 

 parts. 



New-formed bone has been found in the soft parts of the body ; in the 

 brain substance, dura mater, and pia mater ; in the pleura, diaphragm, 

 and pericardium; in the skin, choroid, air passages, lungs, and penis, 

 and in other places. To what extent some of these bone formations may 

 have been due to inflammatory action it is not possible to say. 



Odontoma. Tumors are sometimes formed from the pulp during the 

 development of the teeth. When these contain dentin they are called 

 odontoinata. 



GLIOMA. 



The gliomata are developed from the characteristic framework of 

 nerve tissue, the neuroglia, which in structure many, though usually not 

 all, of its cells closely resemble. 

 Small cells with inconspicuous 

 bodies and numerous delicate 

 branching processes are most 

 characteristic ; but in connection 

 with these there is usually a 

 greater or less number of small 

 spheroidal cells with proportion- 

 ally large nuclei (Fig. 171). It 

 is usually necessary to shake sec- 

 tions in water or carefully tease FIG . IH.-GLIOMA OF BRAIN. 

 fragments of the tumor in order 



to see the characteristic neuroglia or so-called "spider" cells (Fig. 172). 

 These tumors may contain very numerous and frequently dilated thin- 

 walled blood-vessels. They may be very soft or moderately hard ; and, 

 especially when occurring in the substance of the brain, are frequently 



