HORSES, JACKS, JENNETS, AND MULES 215 



slight or possibly no external development at all. In this 

 form of spavin there may be diseases of the bones in the 

 deeper parts; particularly erosions of the articular cartilages. 

 Animals with bone spavins have a tendency to recover with- 

 out treatment, although in many cases the period required for 

 natural recovery is very long, extending through a period of 

 years. In other cases recovery can never occur. Recovery, 

 , when brought about by natural or artificial conditions, implies 

 that certain of the tarsal bones have united in the process 

 called technically,, anchylosis, and the inflamed surfaces are 

 no longer rubbing together as the limb moves. 



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. A 

 spavined horse steps on the toe, and carries the hock-joint 

 with as httle 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. The horse 

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

 are very lame. Old horses not affected by spavin may respond 

 to this test and lead to error in judgment. 



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. 



Wind puffs usually indicate considerable amount of hard 

 road work. 



Bog Spavins. — These are enlargements of the synovial 

 sac of the hock-joint, and appear at the inner and front 

 part of the hock. They are often hereditary. 



Thoroughpins are very similar to bog spavins and wind 

 puffs, except in location. Thoroughpins appear at the 

 upper and back part of the hock. They may or may not 

 connect with the synovial sac of the hock-joint. 



Open Joint. — Lameness from open joint is quite common 

 among city horses. This usually results from punctures of 



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