376 THfc fliOG. 



In a state of nature it is, to a certain degree, hollow. The reason of this is 

 plain. It is intended to descend or yield with the weight of the horse, and by 

 that gradual descent or yielding most materially lessen the 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 given 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 discharged ; nor would the foot have so secure a 

 hold. Then if the sole is naturally hollow, and hollow because it must descend, 

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

 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 to admit of this descent. If the sole is pressed upon by 

 the coffin-bone during the lengthening of the elastic laminae, and the shoe will 

 not permit its descent, the sensible part between the coffin-bone and the horn will 

 necessarily be bruised, and inflammation and lameness will ensue. It is from 

 this cause, that if a stone insinuates itself between the shoe and the sole, it pro- 

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

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



THE FEOG. 



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 sensible 

 frog. It is wide at the heels, and there extending beyond a portioa of the crust ; 

 narrowing rapidly when it begins to be confined between the bars, and terminat- 

 ing 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 from 

 a different surface, for it is thrown out from the substance which it covers. It 

 very much resembles a wedge with the sharp point forwards ; 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 consi- 

 derable 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 would 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, discharges 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. 372), and a 

 cleft in the centre, presenting two concavities 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 thrown on it? 

 How easily will these irregular surfaces yield and spread out, and how readily 

 return again to their natural state ? In this view, therefore, the horny frog is 

 a powerful agent in opening the foot ; and the diminution of the substance of 



