DOMESTIC ANIMALS. 65 



back of the joint. Professor Williams says : "We can 

 now understand why the external deposit is not the 

 cause, but the result of the disease. So long as the 

 ulcerated surfaces of the bones are unrepaired, the 

 lameness will remain, but when the bones are united 

 together (anchylosed) so as to form one bone and per- 

 forming the functions of one bone, the lameness disap- 

 pears, and the new material becomes as one of the es- 

 sential structures of the body. " 



Causes. Inheritance is perhaps the greatest cause. 

 Hard work at an early age is also a frequent cause. In 

 young horses, where the growth is not yet completed, 

 the natural condition of the structures of the body is 

 very easily upset, and diseased cl^aracters arise. It is 

 also found that horses with small hocks are more fre- 

 quently the subject of spavin lameness than those that 

 are known as coarse hocked. Sprain of the fibrous 

 ligaments, situated between the bones of the hock, and 

 concussion of the bones setting up an inflammation in 

 the bones themselves are the most frequent active 

 causes. External violence may also be a cause. In 

 many cases animals are foaled with one hock formed 

 somewhat different from the other, and it will remain 

 larger than the other, and no disease will be present, 

 so that a horse is not necessarily spavined because one 

 hock is larger than the other. A remark of Percivall 

 may be quoted here: "Spavin, like splint and other 

 transformations of soft, elastic tissues into bone, may be 

 regarded as nature's means of fortification against more 

 serious failures." 



Symptoms. Perhaps the most constant symptom is 

 the tendency to stand on the toe with the heel elevated 

 5 



