8o THE SURGICAL ANATOMY OF THE HORSE 



the size of half a walnut, palpation will reveal the fact that in these cases 

 the grooves are even more distinct. Plate XV. represents a good 

 example of a case of this kind. The bones represented are those of 

 the hocks of Ambush II., which skeleton is in the Museum of 

 Veterinary Anatomy of the University of Liverpool. In the Plate it will 

 be seen that the ridge on the cuneiform magnum of the off hock is 

 very much larger than that on the corresponding bone of the near, 

 and it is reasonable to assume that this abnormally large ridge would 

 cause a marked difference in the conformation of the two hocks in the 

 living animal. Yet the bones are perfectly healthy, and the articular 

 surfaces quite normal. 



This method of comparison, and also the palpation of the affected 

 hock, must therefore be taken in conjunction with evidences deduced 

 from the action of the animal, and from all the premises thus obtained 

 our conclusion must be drawn. 



Regarding the cause of lameness in spavin, there is little doubt but 

 that, as Macqueen maintains, it is due to the pain experienced as a 

 symptom of the active inflammatory process which is proceeding. That 

 it is not due to mechanical interference with the action of the joint is 

 conclusively proved by the fact that the tibio-astragaloid or true hock 

 joint is only affected in cases which are extremely rare, and it is in 

 this joint that almost the whole of the flexion and extension of 

 the hock takes place. Further contributory evidence in support of this 

 view is found in the fact that cases are frequently met with in which 

 lameness has disappeared and yet a prominent exostosis is present. 

 In such cases a post-mortem examination will reveal the fact that 

 the small bones concerned are firmly united with one another ; i.e.^ 

 anchylosis is complete, with the result that the active inflammatory 

 process has subsided and the animal is not subjected to pain. The small 

 bones now perform the function of a single bone, and the hock may be 

 flexed and extended with freedom. 



We are thus led to a rational method of treating the disease ; for 



