760 VOLUNTARY MUSCLE. 



the internal organs, may occur in muscles which are adjacent to other 

 parts which are the seat of chronic inflammatory processes. It may 

 occur in muscles which are not used. The new formation of fibrous tis- 

 sue seems in some cases to be secondary to atrophy of the muscle fibres. 

 In this case it would more appropriately be called replacement fibrous 

 hyperplasia. 



Myositis Ossificans. Under conditions and for reasons which we do 

 not understand, there occasionally occurs, usually in young persons, a 

 new formation of bone in the interstitial tissue of muscles, and in ten- 

 dons, ligaments, fasciae, and aponeu- 



roses. This sometimes apparently ~^^T~' v ~--r~^'~~*&rr ^ 



starts as outgrowths from the perios- 

 teum, sometimes not. The bone for- ?C~ -c~ 

 mations are apt to commence about _ ^ ^ 

 the neck and back, and may become j^g 

 very widespread over the body. So 

 far as the muscles are concerned, 

 there is usually an increase of con- 

 nective tissue between the fibres and % <*jJ^~.^~ ; 

 bundles, in which new bone is formed, jj^S! 

 usually in elongated and sometimes --w^ -.<-<> :^ 



in Spicula-like masses. The muscle FIG. 499. -CHRONIC INTERSTITIAL MYOSITIS. 



fibres undergo secondarily a greater 



or less degree of atrophy or degeneration. There may be fatty infiltra- 

 tion between the fibres, and various deformities are produced by the 

 shortening and progressive immobility of the affected parts. 



While the above disease is a progressive and frequently a general one, 

 there may be new formation of bone in muscle as a result of prolonged 

 or repeated mechanical irritation. Thus in the adductors of the thigh 

 in persons who are constantly in the saddle, or in the deltoid muscle of 

 soldiers who strike this part with their weapons in drill, there may be a 

 formation of bone. ' 



Tuberculous and Syphilitic Inflammation in the muscle is of occasional 

 occurrence ; the active processes are in the connective tissue and blood- 

 vessels, the muscle fibres being secondarily involved in various phases 

 of atrophy and degeneration. 



TUMORS. 



The tumors of the muscles usually develop in the connective tissue. 

 Fibroma, chondroma, lipoma, myxoma, sarcoma may occur as primary 

 tumors. Carcinoma and sarcoma may occur secondarily in the muscles 

 as a result of local extension from adjacent parts. The muscle fibres 

 are, as a rule, only secondarily affected by pressure, etc., in tumors of 



Consult for a study of myositis ossificans De Witt, Am. Jour. Med. Sciences, vol. 

 xx., p. 295, bibliography. 



