298 THE FROG. 



the weight was. thrown upon it. It is not so brittle as the crust, 

 and it is more elastic than it. It is thickest at the toe.(see t, Fig 

 37), because the first and principal stress is thrown on that part 

 The coffin-bone, /, is driven forward and downward in that direc- 

 tion. It is likewise thicker where it unites with the crust than it 

 is towards the centre, for a similar and evident reason, because 

 there the weight is first and principally thrown. 



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 mi^st 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 lamuiEe, and the shoe will not permit its descent, the sen- 

 sible 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 produces so much lameness. Of the too great 

 concavity of the sole, or the want of concavity in it, we shaU 

 treat when we arrive at diseases of the foot. 



THE FROG. 



In the space between the bars, and accurately filling it, is tno 

 FROG. It is a triangular portion of horn, projecting from the so^e, 

 almost on a level with the crust, and covering and defending a 

 soft and elastic substance called the sensible frog. Its shape all 

 are familia,r with. It is firmly united to the sole, but is perfectly 

 distinct from it. It is softer and far more elastic. It discharges 

 various duties besides the one above named. It comes in contacl 

 with the ground and prevents the horse from slipping, especially 

 when the heel comes first to the ground, as in galloping. It as- 

 sists materially in the expansion of the foot. To discharge these 

 various duties, it must come in contact with the around, and in 



