378 THE SENSIBLE FROG. 



it is sloped for articulation with the navicular bone, and more underneath, is a 

 depression for the reception of the perforating flexor tendon, m, continued down 

 the leg, passing over the navicular bone at n, and at length inserted into this 

 bone. On either side, as seen p. 350, are projections called the wings, or heels 

 of the coffin-bone, and at the bottom it is hollowed to answer to the convexity 

 of the internal part of the sole. 



That which deserves most attention in the coffin-bone is the production of 

 the numerous lamina round its front and sides. They are prolongations of the 

 thick and elastic membrane covering it, and consist of cartilaginous, fleshy 

 plates, proceeding from it, running down the coffin-bone, and corresponding 

 with and received between the horny leaves that line the inside of the hoof- 

 bone — each horny plate being received between two sensitive plates, and vice 

 versa. These laminae are exceedingly sensitive and vascular, and elastic, and, 

 as first simply and beautifully explained by Mr. Percivall, their elasticity is 

 not inherent in the laminae, but in the substance which connects these laminae 

 with the coffin-bone, and which, while it contains highly elastic properties, 

 affords a convenient bed for the numerous vessels that secrete the laminae. 

 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 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 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 com- 

 plicated apparatus of the foot remains uninjured. When the foot is again 

 lifted, and the weight which pressed upon it is removed, the principle of elasti- 

 city 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 leaves 

 regain their former length, and every thing is prepared for a repetition of action. 



THE SENSIBLE SOLE. 

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

 p. 345, formed above of a substance of a ligamentous or tendinous nature, 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 

 structure 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 all under the frog. 

 Leaving a space for the frog, it proceeds over the bars, and there is covered by 

 some laminae, to unite with those that have been described, page 372, 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 ihe 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 pos- 

 terior part is filled by a soft mass, partly ligamentous, and partly tendinous 

 (o, page 345). Its shape below corresponds with the cavities of the horny 

 frog ; in front it is attached tc the inferior part of the coffin-bone ; and farther 



