300 THE SENSIBLE SOLE FROG NAVICULAR BONE. 



and the superior portion of the crust, gradually lengthen, and 

 suffer the coffin-bone to press on 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 complicated apparatus 

 oi^ the foot remains uninjured. 



THE SENSIBLE SOLE. 



Between the coffin-bone and the horny sole is situated the sen- 

 sible sole, (Fig", 37,) formed above of a substance of a ligamentous 

 or tendinous nature, and below of a cuticular or skin-like sub 

 stance, 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 293, 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 Avill evince. The lameness which ensues from tlie pres- 

 sure of a stone, or of the shoe, on the sole is caused by inilamma- 

 tion of the sensible sole. Corns result from bruise and inflamma- 

 tion 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 ligament- 

 ous, and partly tendinous (o. Fig. 37). Its shape below corres- 

 ponds with the cavities of the horny frog ; in front it is attached 

 to the inferior part of the coffin-bone ; and farther back, it ad- 

 heres to the lower part of the cartilages of the heels, where they 

 begin to form the rounded protuberances that constitute the heei 

 of the foot. It occupies the whole of the back part of the foot 

 above the horny frog and between the cartilages. Running im- 

 mediately above the frog, and along the greater part of it, we 

 find the perforans flexor tendon, which passes over the naviculai^ 

 bone, e, Fig. 37, and is inserted into the heel of the coffin-bone 



THE NAVICULAR-BONE 



Is placed behind and beneath the lower pastern-bone, and behina 

 and above the heel of the coffin-bone, e, Fig. 37, so that it forms 



