CHANGES IN FORM OF COXTKACTED FOOT. 343 



where the coronary band is reflected forwards to become con- 

 tinuous with the corresponding part of the bars. 



The strain on the coronary margin often causes sandcrack, 

 and as the bars become distorted from the continued approach 

 of the heels they may also exhibit fissures. 



Contracted feet expand to a much less extent than do normal 

 feet, and experiments on the living animal show that in well- 

 marked cases this movement is diminished, sometimes even 

 entirely absent or replaced at the most anterior portion of the 

 bearing surface of the heel by contraction. The coronary 

 margin of the heels, on the other hand, dilates, and whilst, in 

 the healthy foot, contact of the frog with the ground produces 

 dilatation both at the coronary and bearing margins, in con- 

 tracted feet this is always diminished if not inhibited. The 

 symptoms seem due to the position of the heels relatively to the 

 ground, because the more the heels converge, from above down- 

 wards, the less does the bearing margin expand. Under tha 

 body- weight the portions comprised between the two heels, 

 that is, the plantar cushion, lateral cartilages and sensitive 

 wall, are strongly compressed by the inner surfaces of the heel 

 walls, especially when the shoe is fitted ' too fine ' at the 

 heels. Tliis pressure (caused by the body-weight) is rendered 

 more injurious by the shoe preventing any yielding at the heel — 

 a condition comparable to that produced in man by too narrow 

 a boot. 



This contraction at the heels leads to bruising of sensitive 

 structures, rupture of small blood-vessels, and extravasation of 

 blood, which stains the new horn red, while the increased strain 

 at the coronary margin favours splitting and formation of sand- 

 cracks. 



Though usually easy to detect, the condition may be 

 mistaken for shoulder lameness, chronic navicular disease, or 

 strain of the pastern joint. Tlie corns which occur as a sequel 

 are sometimes regarded as the principal disease. 



The causes are numerous, but may be divided into two groups, 

 namely, predisposing and exciting. 



(a) The predisposing causes include faulty conformation of 

 the limb and defective shape of the hoof, but they seldom 

 come into play before the hoof is shod. The greatest tendency 

 to contraction is seen in weak feet, wliich naturally possess long 



