SENSIBLE SOLE AND FROG. 287 



bone, and corresponding with, and 'received between the horny leaveb ihat 

 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 in num. 

 I)er, 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 sup- 

 ported by them, and not by the sole. This extraordinary fact has been put 

 to the 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 

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

 fleshy, gradually lengthen, and suffer the bones to press upon the sole 

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

 admirable mechanism, the violent sliock which would be produced by tne 

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

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

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

 weight wliich 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; tiie quarters return to their former situation; the little 

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

 tion o{ action. 



HE SENSIBLE-SOLE. 



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

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

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

 blood-vessels. It was placed between the coffin-bone and the sole, by its 

 yielding nature to assist in preventing concussion, and also to form a supply 

 of horn for the sole. It extends beyond the coffin-bone, but not at a'l under 

 the frog; leaving a space for the frog, it proceeds over the bars, and there 

 is covered with some laminae, to unite with those we have described, page 

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

 and by its elastieity is evidently assisting in obviating concussion. It is 

 supplied with nervous fibres, and is highly sensible, as the slightt-st experi- 

 ence in horses will evince. The lameness which ensues from the pressure 

 of a stone or of the shoe on the sole is caused by inflammation 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 coffm-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 the 

 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 

 ♦he frog, and along tlie greater part of it, we find the perforans flexor ten- 

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

 the heel of the coffin-bone. 



