300 THE FOOT. 



THE COFFIN-BONE. 



The interior part of the foot must now be considered. The lower pastern, a small 

 portion of which (see d, page 272) is contained in the horny box, has been already 

 described, p. 276. — Beneath it, and altogether inclosed in the hoof, is the colhn-bone, 

 or proper bone of the foot, (see /, page 272, and d, fig. 1, page 270). It is htted to, 

 and fills the fore part of the hoof, occupying about half of it. It is of a light and 

 spongy structure (see d, fig. 1, page 276), and filled with numerous minute foramina. 

 Through these pass the blood-vessels and nerves of the fjot, which are necessarily 

 numerous, considering the important and various secretions there carrying on, and 

 the circulation through the foot which could not possibly be kept up if these ves- 

 sels did not run through the substance of the bone. Considering the manner in 

 which this bone is inclosed in the horny box, and yet the im])ortant surfaces around 

 and below it that are to be nourished with blood, the circulation which is thus carried 

 on within the very body of the bone is one of the most beautiful provisions of nature 

 that is to be found in the whole frame. No inconvenience can arise from occasional 

 or constant pressure, but the bone allows free passage to the blood, and protects it 

 from every possible obstruction. 



The fore part of the coffin-bone is not only thus perforated, but it is curiously rough- 

 ened for the attachment of the numerous minute lanunee about to be described. On 

 its upper surface it presents a concavity for the head of the lower pastern, p. 276. 

 In front, immediately above d, is a striking prominence, into which is inserted the 

 extensor tendon of the foot. At the back, e, p. 272, it is sloped for articulation with 

 the navicular bone, and more underneath, is a depression for the reception of the per- 

 forating flexor tendon, m, continued down the leg, passing over the navicular bone at 

 «, and at length inserted into this bone. On either side, as seen p. 276, are projec- 

 tions 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 nu- 

 merous laminae 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 re- 

 ceived between two sensitive plates, and vice versa. These lamina? are exceedingly 

 sensitive and vascular, and elastic, and, as first simply and beautifully explained by 

 Mr. Percivall, their elasticity is not inherent in the lamina, but in the substance 

 which connects these lamina? with the cotlin-bone, and which, while it contains highly 

 elastic properties, affords a convenient bed for the numerous vessels that secrete the 

 lamina;. 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 expe- 

 riment. 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 sutler the bones to press 

 upon the sole. The sole then descends, and in descending, expands; and so, b}^ an 

 admirable mechanism, the vioh>nt shock which would be produced by the pressure 

 of such a weight as that of tlie horse, and the velocity with which it descends, is 

 lessoned or destroyed, and tlie cfnni)licated apparatus of the foot remains uninjured. 

 When the foot is aijain lifted, and the weight which pressed upon it is removed, 

 the principle of elasticity is calli d into exercise, and b}' it the sole resumes its con- 

 cavity, and the horny frog its folded state; — the quarters return to their former situ- 

 ation, — the leaves regiiin their former length, and everytliing is jirepared for a rejjeti- 

 tion of action. 



THE SENSIBLE SOLE. 



Between the coffin-bone and the horny sole is situated the sensible sole, p. 272, 

 formed above of a substance of a ligamentous or tendinous nature, and below cf a 

 cuticular or skin-like substance, ))lentifullj' supplied with blood-vessels. It was 

 placed between the coffin-ttone and the sole, by its yielding structvire to assist in pre- 

 venting concussion, and also to form a supply of horn for the sole. It extends be- 

 «rond the coffin-bone, but not at all under the frog. Leaving a space for the frog, it 



