THE SENSITIVE SOLE. 401 



about to be described. On its upper surface it presents a concavity for 

 the Lead of tlie lower pastern. In front is a striking prominence, into 

 wliich is inserted tlie extensor tendon of the foot. At the back it is sloped 

 for articulation with the navicular bone, and more luiderneath is a depres- 

 sion for the reception of the perforans tendon, continued down the leg, 

 joassing over the navicular bone, and at leng-th inserted into this bone. 

 On either side are projections, called thewdngs, 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 laminae round its front and sides. They are prolongations 

 of the thick and elastic membrane covering it, and consist of fleshy plates, 

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

 and received between the homy leaves that line the inside of the hoof — 

 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 elas- 

 ticity is not inherent in the lamina, but in the substance which connects 

 these laminae with the coffiji-bone, and w^hich, while it contains highly 

 elastic properties, affiDrds 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 fi'og were 

 removed fi'om 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 

 httle leaves, horny and fleshy, gradually lengthen, and suffer the bones to 

 press upon the sole. The sole then descends, and, in descending, ex|Dands ; 

 and so, by an admirable mechanism, the violent shock which would be 

 produced by the pressui'e of such a weight as that of the horse, and the 

 velocity with which it descends, is lessened or destroyed, and the compK- 

 cated apparatus of the foot remains uninjured. "When the foot is again 

 lifted, and the weight which pressed upon it is removed, the princij)le 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 theii* former 

 situation, — the leaves regain their former length, and every thing is pre 

 pared for a repetition of action. 



THE SENSITIVE SOLE. 



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

 formed above of a substance of a fibrous 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 structiu'e 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 397, as found in the bars. It is here likewise thicker, and ruore 

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

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

 experience 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 sensitive sole. 



