The Foot. 363 



extensive layer of elastic tissue found at this part ; as the 

 weight comes on the foot, the pedal bone slightly descends, 

 to rise again when the weight is taken off it. As the pedal 

 bone descends, the sole on which it is resting also slightly 

 descends and comes nearer to the ground, which is the 

 reason why the sole is concave instead of flat. The descent 

 avoids concussion, in the same way that it is easier to 

 catch a cricket-ball with a retreating movement of the 

 hand than by rigid opposition. 



Much more might be said of practical importance on this 

 subject, but we have other points which press for our 

 consideration. 



The Frog. — The function of the horny frog and its 

 peculiar physical features we have already alluded to. The 

 manner in which it protects the important navicular bursa 

 is also no insignificant part of its function. The soft and 

 elastic condition of the horn of the frog has been attributed 

 to certain perspiratory glands which are found in that part 

 of the sensitive frog on either side of the frog stay ; how 

 far these actually contribute to the elastic condition of the 

 frog is not clear, especially as the surface over which they 

 are distributed is of very limited area. 



The frog is peculiar, inasmuch as it needs for its perfectly 

 healthy condition contact with the ground. It is strange 

 that in this respect two structures situated side by side, 

 viz., the sole and frog, should be so opposed in function. 

 We know practically, that if the frog be kept off the 

 ground, the part atrophies, the heels contract, viz., the foot 

 is rendered smaller, and the frog becomes diseased. This 

 wasted condition of the frog may be restored by pressure, 

 but that pressure must be ground pressure. It is possible 

 by means of a bar- shoe to throw considerable pressure on 

 the frog and heels, but the foot still contracts ; it is only 

 when the frog is touching the ground that it continues in a 

 healthy condition, and retains its normal size. Frog 

 pressure is therefore one of the golden rules in shoeing if 

 the frog is to exercise its natural functions. 



The Wall. — From what we have previously said, it can 



