NAY1CULAR-JQINT LAMENESS. 



437 



weight so much upon the opposite foot to relieve the lame one in 

 standing or walking, there is liability to bring on the same trouble 

 in the well one, — a not uncommon occurrence,— when the lameness 

 will be equally marked in both fore feet. The horse will grow worse 

 when the heel is lowered by putting on a thin shoe, or by losing the 



shoe, and will go better when the 

 heel is raised, and especially so if 

 the toe is rounded so as to aid mo- 

 bility. 



Causes. — The coffin joint is com- 

 posed of three bones ; viz., the 

 lower or pedal bone, and the na- 

 vicular and' pastern bones. (See 

 Fig. 772.) 



It will be seen that the navicular 

 bone extends across the back edge 

 of the coffin joint ; that the flexor 

 tendon passes down under it, and 

 inserts itself into the lower surface 

 of the pedal bone. This supports 

 the navicular bone when weight is 

 thrown upon the limb, as the back 

 part of the small pastern rests upon 

 the navicular bone. Now, if from 

 any cause irritation is set up in the 

 synovial membrane of this small 

 bone, or of the sheath of the tendon 

 which supports it, or of the sur- 

 rounding parts, whether by sprain, 

 concussion, injury, contraction, im- 

 proper shoeing, changing the ob*- 

 liquity of the foot, that is, raising or lowering the heel too much, 

 allowing the toe to grow too long, or any cause of changing the 

 proper adjustment of the foot, etc., the effect is practically the same 

 in causing inflammation and lameness! ' 



The best authorities agree that the most common indirect causes 

 of this lameness are raising the frog from the ground and contrac- 

 tion. An old author of high standing says:— 



When the foot is in its natural condition, the frog is its strong point of support; 

 and if this support is removed by paring, or by the use of thick-heeled shoes, which 

 raise the frog from all possible contact with the ground, the support is weakened, 

 and there is necessarily great. strain thrown upon the tendon. This is caused by 

 pushing the coronary against the navicular bone, which, being "repeated at every 



-Attachment of Perforans Ten- 



Fig. 752, 



don to Bottom of Pedal Bone 

 Manikin of the Foot. 



From 



