588 DISEASES OF THE HOBSE. 



the short pastern sinks backward and downward between the lateral 

 cartilages and presses the perforans tendon upon the plantar cushion. 

 This cushion being compressed from above and being unable to 

 expand downward by reason of the resistance of the ground acting 

 against the horny frog, acts like any other elastic mass and expands 

 toward the sides, pushing before it the yielding lateral cartilages and 

 the wall of the quarters. This expansion of the heels is assisted and 

 increased by the simultaneous flattening and lateral expansion of the 

 resilient horny frog, which crowds the bars apart. Of course, when 

 the lateral cartilages are ossified, not only is no expansion of the 

 quarters possible, but frog pressure often leads to pa,inful compres- 

 sion of the plantar cushion and to increase of lameness. Frog pres- 

 sure is therefore contraindicated in lameness due to sidebones (ossi- 

 fied cartilages) . Under the descent of the coffin bone the horny sole 

 sinks a little; that is, the arch of the sole around the point of the 

 frog and the wings of the sole become somewhat flattened. All these 

 changes of form are most marked in sound unshod hoofs, because 

 in them ground pressure on the frog and sole is pronounced; they 

 are more marked in fore hoofs than in hind hoofs. 



The movement of the different structures within the foot and the 

 changes of form that occur at eA^ery step are indispensable to the 

 health of the hoof, so that these elastic tissues must be kept active by 

 regular exercise, with protection against drying out of the hoof. 

 Long-continued rest in the stable, drying out of the hoof, and shoeing 

 decrease or alter the physiological movements of the hoof and some- 

 times lead to foot diseases. Since these movements are complete and 

 spontaneous only in unshod feet, shoeing must be regarded as an evil, 

 albeit a necessary one, and indispensable if we wish to keep horses 

 continuously serviceable on hard, artificial roads. However, if in 

 shoeing we bear in mind the structure and functions of the hoof and 

 apply a shoe whose branches have a wide and level bearing surface, 

 so as to interfere as little as may be with the expansion and contrac- 

 tion of the quarters, in so far as this is not hindered by the nails, we 

 need not be apprehensive of trouble, provided the horse has reason- 

 able work and his hoofs proper care. 



GROWTH OF THE HOOF. 



All parts of the hoof grow downward and forward with equal 

 rapidity, the rate of growth being largely dependent upon the 

 amount of blood supplied to the pododerm, or " quick." Abundant 

 and regular exercise, good grooming, moistness and suppleness of the 

 hoof, going barefoot, plenty of good feed, and at proper intervals 

 removing the overgrowth of hoof and regulating the bearing surface, 

 by increasing the volume and improving the quality of the blood 



