OSSIFTC DISEASE OF JOINTS. 55 



arising from external injury. In spavin, for example, we have 

 disease within the hock joint, and disease without it, the same 

 as we have in several other joint affeclions; and it becomes 

 necessary for us in all such cases to understand the connexion 

 between the internal and external disease, and how either may 

 exist independently of the other. There are few subjects that, 

 heretofore, have had less attention paid to them, and consequently 

 whose real nature has been less understood, than lamenesses arisino* 

 from diseases of the joint : every year of the present age, however, 

 is adding to our knowledge of them ; so much so, indeed, that we 

 may safely predict that lamenesses hitherto classed as " obscure" in 

 their nature, will in a few years become readily explicable by us. 

 And this will be accomplished by observations such as are afforded 

 us by cases we have had opportunities of watching in their progress 

 from their beginning to their very end. 



Concerning the Formation of New Bone, Dr. Watts, 

 from a close and critical observation of four cases of injury and 

 disease of bone, has come to the following conclusions: — 



" 1st. That the theories alleging that new bone is formed only 

 by living parts of old bone, in cases of necrosis and fracture, are 

 incorrect." 



" 2d. That the periosteum has evidently the power to produce 

 new bone of itself, without the aid of the old bone." 



'' 3d. That the formation of new bone by the periosteum consists, 

 at first, in the deposition of osseous matter in the form of a fine 

 microscopic network ; and therefore, that the Haversian canals are 

 only a secondary, not a primary, osseous tissue." 



4th. That in cases of necrosis and fracture, the process of re- 

 production of bone by the periosteum is the same*. 



For the Causes of Bony Formations, in the horse's limbs 

 at least, we must not look to inflammation alone. It has been 

 brought under observation before, that the horse's economy is 

 such as is peculiarly susceptible of action tending to such forma- 

 tions ; to which may be annexed the fact, of our constantly meeting 

 with exostoses, of various descriptions, in young unbroke horses — 



* Edinburgh Med. and Surg. Journal. 



