180 VETERINARY PATHOLOGY. 



of the tendon are firmly united by the mass of newly formed 

 fibrous tissue the extravasate and the fibres, excepting those ex- 

 tending in a longitudinal direction, are absorbed. Finalh' the 

 repair is so complete that the defect is not visible to the unaided 

 eye and is difficult to detect microscopically. Scars are bands, 

 sheets or masses of white fibrous tissue and indicate imperfect 

 regeneration, the fibrous tissue in scars being largely a suljstitu- 

 tion tissue. 



Ycllozv clastic tissue is not as perfectly regenerated as white 

 fibrous tissue. White fibrous tissue usually is substituted for 

 yellow elastic tissue when the latter has been destroyed. 



Rcgoicration of cartilage is very imperfect probably because 

 of its irregular supply of nourishment. Destroyed cartilage is 

 usually replaced by fibrous tissue. In some instances injuries 

 to cartilage are succeeded by excessive cartilaginous prolifera- 

 tion. A case was observed in which the ar^-tenoid cartilage was 

 severed in an operation to relieve roaring; six months later there 

 had developed at the point of operation a cartilaginous mass as 

 large as a goose egg. Perfect regeneration of cartilage does 

 occur, although it is rare. Regenerating cartilage cells are de- 

 rived from the inner portion of the perichondrium. Fil^rous 

 tissue formation usually precedes the regeneration of cartilage, 

 althf^-'.gh it maj' be formed from the beginning. 



Osseous tissue is usually perfectly regenerated . The cells 

 that produce osseous tissue are called osteoblasts. Osteoblasts 

 are usually derived from the osteogenetic layer of the perios- 

 teum, although they ma^- have their origin from undift'erentiated 

 connective tissue cells. The formation of osseous tissue is usu- 

 ally preceded by mucoid, fibrous or cartilaginous tissue. The 

 various stages of osseous regeneration are very similar to those 

 of normal bone formation. Osseous regeneration may be illus- 

 trated b}' the union of a fracture as follows : Blood and lymph 

 vessels are ruptured when the fracture is produced. Blood and 

 lymph escapes into the surrounding tissues and the interstice 

 between the twn ends of the fractured bone. The injury pro- 

 duces necrosis and establishes inflammation. \^ascularization of 

 the injured area initiates the process, after which there is solu- 

 tion of the extravasate, exudate and necrotic tissue. Osteo- 

 blasts accompany the newly formed vessels and produce irregu- 

 lar masses of fibrous tissue which later calcify. The calcareous 

 tissue is infiltrated with osteoclasts derived from the blood wdiich 

 dissolve out regular canals in the regeneration of long bones, 

 and irregular cavities in the regeneration of flat or irregular 

 bones. Osteoblasts appear in the canals and cavities, formed 



