THE FROn. 399 



horpe, and by tliat gradual descent or yielding most materially lessen tlie 

 shock which would result from the sudden action of the weight of the 

 animal in rapid and violent exercise ; and this descent can only be gi^-en 

 by a hollow sole. A flat sole, already pressing upon the ground, could 

 not be brought lower ; nor could the functions of the frog be then dis- 

 charged ; nor would the foot have so secure a hold. Then if the sole is 

 naturally hollow — and hollow it should be because it miTst descend — the 

 smith should not interfere with this important action. When the foot 

 ■nWII bear it, he must pare out sufficient of the horn to preserve the proper 

 concavity ; also a small portion at the toe and near the crust, and cutting 

 deeper towards the centre. He must put on a shoe which shall not 

 prevent the descent of the sole, and which not only shall not-press upon 

 it, but shall leave sufficient room between it and the sole lo admit of this 

 descent. If the sole is pressed upon by the coffin-bone during the length- 

 ening of the elastic laminte, and the shoe will not permit its descent, the 

 sensitive part between the coffin-bone and the horn will necessarily be 

 bruised, and inflammation and lameness will ensue. It is from this cause, 

 (hat if a stone insinuates itself between the shoe and the sole, it produces 

 so much lameness. Of the too great concavity of the sole, or the want 

 of concavity in it, we shall treat when we arrive at diseases of the foot. 



THE FROG. 



In the space between the bars, and accurately filling it, is the frog. It 

 is a triangular portion of horn, projecting from the sole, almost on a level 

 with the crust, and covering and defending a soft and elastic substance 

 called the sensitive frog. It is wide at the heels, and there extending 

 beyond a portion of the crust ; narro^^^ng rapidly when it begins to be 

 confined between the bars, and terminating in a point at somewhat more 

 than half the distance from the heel to the toe. It consists of two rounded 

 or projecting surfaces, with a fissure or cleft between them reaching half 

 way down the frog, and the two portions again uniting to form the point 

 or toe of the frog. 



The frog is firmly united to the sole, but it is perfectly distinct from it. 

 It is of a different nature, being softer, and far more elastic ; and it is 

 secreted fi'om a different surface, for it is throAvn out from the substance 

 Avhich it covers. It is very analogous in texture to a piece of india-rubber, 

 being neither so fibrous as the crust, nor as scaly as the sole. It very 

 much resembles a wedge with a sharp point foi-wards : and it is placed 

 towards the back part of the foot. The foot is seldom put flush and flat 

 upon the ground, but in a direction downwards, yet somewhat forwards ; 

 then the frog evidently gives safety to the tread of the animal, for it 

 occasionally ploughs itself into the ground, and prevents the horse from 

 slipping. This is of considerable consequence, when some of the paces 

 of the horse are recollected, in which his heels evidently come first to the 

 ground, and in which the danger from slipping Avould be very great. 

 Reference needs only be made to the gallop as illustrative of this. 



The frog being placed at, and filling, the hinder part of the foot, dis- 

 charges a portion of the duty sustained by the crust ; for it supports the 

 weight of the animal. It assists, likewise, and that to a material degree, 

 in the expansion of the foot. It is formed internally of two prominences 

 on the sides (see a, p. 395), and a cleft in the centre, presenting two con- 

 cavities with a sharp projection in the middle, and a gradually rounded 

 one on each side. It is also composed of a substance 'peculiarly flexible 

 and elastic. What can be so well adapted for the expansion of the foot 

 when a portion of the weight of the body is thro^vn on it ? IIow easily 

 will these irregular surfaces yield and spread out, and how readily return 



