28 PRINCIPLES OF VETERINARY SURGERY 



sive deposition of tissue, but that is absorbed later through 

 the action of the osteoclasts. These are multinuclear giant 

 ceils situated along the bone-trabeculse. They perform the 

 same function in the repair of bone as in its development, 

 viz: the removal of superfluous tissue both in the periosteum 

 and medullary cavity. 



The periosteal callus may ossify directly through the ac- 

 tion of the osteoblasts, the preliminary cartilaginous stage 

 being dispensed with. They excrete the calcareous salts 

 v\fhich surround them and ultimately convert them into bone 

 corpuscles. 



In from fourteen to twenty-one days, callus-formation 

 has fully begun; twelve or fourteen days later, i. e. during 

 the fourth or fifth week, ossification occurs ; and at the end 

 of one or two months, a mass of spongy bone occupies the 

 seat of fracture. The medullary cavity sometimes takes years 

 to become patulous. The amount of callus varies greatly in 

 different cases. In animals that are allowed to run about 

 during the process of repair, the two ends of the bone are im- 

 bedded in a luxuriant callus which involves a considerable 

 portion of the shaft and this is sometimes impossible to sup- 

 press. 



Sometimes there appears to be an inability on the part of 

 the bone-producing structures to form new bone. The gran- 

 ulation-tissue is either absorbed or becomes fibrous; no new 

 bone is thrown out, and as a result of this we get a non-bony 

 union. The two ends of the bone are united by a ligamentous 

 band. In some cases nature attempts to form a new joint; 

 the fractured ends become covered with hyaline cartilage, 

 and are held together by a capsule, which contains a small 

 amount of clear serum. This condition is known as pseudo- 

 arthrosis. 



The regeneration of fractured and diseased bones varies 

 greatly among the domestic animals. This may be due to 



