SENSIBLE SOLE AND FROG. 287 



bone, and corresponding with, and received between the horny leaves that 

 line the inside of the crust. The horny little leaves are secreted from", or 

 produced by the fleshy, and being-, as we have stated, five hundred m num- 

 ber, their union with each other is so strong, that no violence can separate 

 them While the animal is at rest, the whole weight of the horse is supported 

 by them, and not by the sole. This extraordinary fact has been put to th^ 

 test of experiment. The sole, bars, and frog were removed from the foot 

 of a horse, and yet as he stood, the coffin-bone did not protrude, or in the 

 slightest degree descend ; but when the rapidity with which the foot de- 

 scends is added to the weight of the horse, these little leaves, horny and 

 fleshy, gradually lengthen, and suff"er the bones to press upon the sole. 

 The sole then descends, and, in descending, expands; and so, by an 

 admirable mechanism, the violent shock which would be produced by 

 the pressure of such a weight as that of the horse, and the velocity with 

 which it descends, is lessened or destroyed, and the compHcated apparatus 

 of the foot remains uninjured. When the foot is again lifted, and the weight 

 which pressed upon it is removed, the principle of elasticity is called into 

 exercise, and by it the sole resumes its concavity, and the horny frog its 

 folded state ;— the quarters return to their former situation ,— the little 

 leaves regain their former length, and every thing is prepared for a repeti- 

 tion of action. 



THE SENSIBLE SOLE. 



^Between the coffin-bone and the horny sole is situated the sensible sole s, 

 p. 249, formed above of a substance of a ligamentous or tendinous nature, 

 and below of a cuticular or skin-like substance, plentifully supplied with 

 blood-vesselsTSIt was placed between the coffin-bone and the sole, by its 

 yielding nat«¥€rto assist in preventing concussion, and also to form a supply 

 of horn for the so'^It extends beyond the coffin-bone, but not at all under 

 the frog; leaving-a^pace for the frog, it proceeds over the bars, and there is 

 covered with some laminae, to unite with those which we have described, 

 page 283, as found in the bars. It is here likewise thicker, and more 

 elastic, and by its elasticity is evidently assisting in obviating concussion. 

 It is supplied with nervous fibres, and is highly sensible, as the slightest 

 experience in horses will evince. The lameness which ensues from the 

 pressure of a*elene or of the shoe on the sole is caused by inflamma- 

 tion of the sensible sole. Corns result from bruise and inflammation of 

 the sensible sole, between the crust and the bar. 



THE SENSIBLE FROG. 



The coffin-bone does not occupy more than one half of the hoof. The 

 posterior part is filled by a soft mass, partly ligamentous, and partly ten- 

 dinous (o, page 249). Its shape below corresponds with the cavities of 

 the horny frog ; in front it is attached to the inferior part of the coffin-bone ; 

 and farther back it adheres to the lower part of the cartilages of the heels, 

 where they begin to form the rounded protuberances which constitute tlie 

 heel of the foot It occupies the whole of the back part of the foot, above 

 the horny frog, and between the cartilages. Running immediately above 

 the frog,' and along the greater part of it, we find the perforans flexor 

 tendon, which passes over the navicular bone, e, p. 249, and is inserted into 

 the heel of the coffin-bone. 



