JN"AVICULAE-J01NT LxVMENESS. 785 



causes of this lameness ai-e i-aisiug the frog- from the ground and 

 contraction. I copy the remarks of an old author of high stand- 

 ing on this cause, who says :- — 



•• When the foot is iu its natural condition, the frog is its strong 

 jDoint of support; and if this support is removed by paring, or b}^ 

 the use of thick- heeled shoes, which raise the frog from all pos- 

 sible contact with the ground, the support is weakened, and there 

 is necessarily great straiji thrown u[»on the tendon. This is caused 

 by pushing the coronary against the navicular bone, and which, 

 being repeated at every step or jump the horse takes, strains the 

 tendons, or causes inflammation. By contraction, because in pi'o- 

 portion to the drawing together of the heels, there will be a com- 

 pressing or forcing upward of the arches of the commissures and 

 horny frog against the tendon and navicular joint, impeding the 

 action of the joint generally, and liable to cause inflammation of the 

 synovial membrane, ulceration, and change of structure; it also 

 destroys the natural position of the limb by making the pastern 

 joint more perpendicular, which, as has been mentioned, increases 

 the jar of the corona on the pedal bone. So that we have involved 

 the lower surface of the navicular bone, its synovial membrane, the 

 flexor tendon which i)lays over it, and sometimes the upper sur- 

 face, when it is called coffin or navicular-joint lameness." 



Another author says: — 



"Disease of the navicular joint is the chief danger to be appre- 

 hended from a good-looking strong foot, just as the open, flat one is 

 ])rone to laminitis, and is rarely subject to disease of the navicular 

 joint. The reason of this immunity on the one hand, and the con- 

 trary on the other, is this: The open foot, with a large spongy frog, 

 exposes the navicular bone and the parts in contact with it to con- 

 stant pressure in the stable, so that these parts are always prepared 

 for work. On the other hand, the concave sole and well-formed 

 fi'og are raised from the ground by our unfortunate mode of shoe- 

 ing, and when the whole foot is exposed to injury from battering, 

 and iu addition to the tendon which plays over the navicular bone 

 presses it against the os corona), the unprepared state in which this 

 part is allowed to remain, is sure to ])roduce inflammation, if the 

 work is carried far enough." 



In 1816 an English veterinary surgeon, James Turner, was 



the first, after careful observations and numerous dissections, to 



call attention to the causes of this lameness and its treatment. 



His explanation is so good that I will include it also here, though 



experience has since proved, as explained, that -contraction is only 



one of its causes: — 



"The next deviation from nature is the passive state to which 

 tho foot is submitted, at Uasl iwenly two or twenty-three hours 



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