LAMENESS. 177 



There is another form of hone spavin in which there is a 

 slight or possibly no external development at all. In this form 

 of spavin there ma)- be diseases of the bones in the deeper parts ; 

 particularly erosions of the articular cartilages. Bone spavins 

 have a tendency to recover without treatment, although in many 

 cases tire period required for natural recovery is very long, ex- 

 tending through a period of years. In other cases recovery can 

 never occur. Recovery when brought about by natural or artifi- 

 cial conditions implies that certain of the tarsal bones have united 

 in the process called technically, anchylosis, and the inflamed sur- 

 faces are no longer rubbing together as the limb moves. 



FIG. 65. SIDEBONES. (M. II. R.) 

 Due to an inflammation and ossification of the lateral cartilages. 1, Nor- 

 mal os pedis; 2, 3, 4, varying types of sidebones. 



Many bone spavins doubtless appear as the result of slight 

 injuries in susceptible subjects, particularly those that have a 

 strong hereditary tendency to diseases of this kind. 



Bone spavin is one of the most serious forms of unsoundness 

 of the organs of locomotion. 



Symptoms. — A spavined horse steps on the toe, and carries 

 the hock joint with as little movement as possible. The lameness 

 usually disappears or at least greatly improves with exercise. 



What is known as the hock test, is made by holding up the 

 limb with the hock sharply bent, for several minutes. Then the 

 horse is started suddenly. In case of spavin the first few steps 

 are very lame. Old horses without spavin may respond to this 

 test and lead to error if one is not careful. 



FROM SYNOVIAL MEMBRANES. 



Synovial sacs. — The ordinary wind puffs of the ankle, and 

 bog spavins and thoroughpins at the hock are typical illustrations 

 of enlarged synovial sacs. They are not usually the cause of 

 lameness, but are to be regarded rather as symptoms^ 



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