76 HORSESHOEING. 



the wall, and presses the perforans tendon down upon the 

 plantar cushion. The plantar cushion being compressed from 

 above, and being unable to expand downward, is correspond- 

 ingly squeezed out towards the sides and crowded against the 

 lateral cartilages, and they, yielding, press against and push be- 

 fore them the wall at the quarters. The resistance of the earth 

 acts upon the plantar surface of the hoof, and especially upon 

 the frog, and it, widening, crowds the bars apart, and in this 

 manner contributes to the expansion of the quarters, especially 

 at their plantar border (see Fig. 73). The horny sole under the 

 descent and pressure of the os pedis sinks a little — that is, the 

 arch of the sole becomes somewhat flattened. All these changes 

 are much more marked upon sound unshod hoofs, because in 

 them the resistance of the earth upon the sole and frog is pro- 

 nounced and complete. These changes in form are more marked 

 in front feet than in hind. In defective and diseased hoofs it 

 may happen that at the moment of greatest weight-bearing, in- 

 stead of an expansion a contraction may occur at the plantar 

 border of the quarters. 



Three highly elastic organs there are which play the chief part 

 in these movements, — namely, the lateral cartilages, the plantar 

 cushion, and the horny frog. "Besides these structures, indeed, 

 all the remaining parts of the horn capsule, especially its coro- 

 nary border, possess more or less elasticity, and contribute to 

 the above-mentioned changes of form. 



In order to maintain the elastic tissues of the foot in their 

 proper activity, regular and abundant exercise, with protection 

 against drying out of the hoof, is absolutely necessary, because 

 the movements of the different structures within the foot and 

 the changes of form that occur at each step are indispensable in 

 preserving the health of the hoof. Long-continued rest in the 

 stable, drying out of the hoof, and shoeing decrease or alter the 

 physiological movements of the foot, and this leads under cer- 

 tain conditions to foot diseases, with which the majority of horse 

 owners are entirely unacquainted. 



