STRUCTURE AND EC0N03IY OF THE FOOT. 30 



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secreting surface of the frog, and communicating with those of 

 the skin of the sole, or sensible sole : so that the frog and sole 

 form one continued surface of skin, of great vascularity and sen- 

 sibility ; but greatly inferior in both respects to the laminated 

 substance, which is more richly organised, both as to blood- 

 vessels and nerves, than any other part of the body. From this 

 view of the foot it will appear that, when the horse stands in 

 the stable, without exercise, the veins of the fore leg do not 

 return the blood freely, from want of the pressure which exercise 

 occasions. The blood therefore accumulates in the foot. The 

 vessels of the laminated substance, from the pressure of the hoof, 

 admit only of a determinate quantity, especially at that part 

 where the horn is remarkably thick, and where elasticity is 

 not so essential. The lateral cartllao;es are two elastic bodies 

 attached to the coffin bone, at its upper part, and proceeding- 

 backward, like expanded wings, terminate at the extremity of 

 the heel : they assist, as I have before observed, in expanding 

 the heels and quarters. The navicular, or nut bone, is placed 

 behind the coffin bone, and is attached to it as well as to the 

 small pastern bone, and affi)rds a synovial or slippery surface for 

 the flexor tendon to move upon. This bone with the coffin 

 and small pastern forms the coffin joint, and is represented in 

 the perpendicular section of the hoof. See Frontispiece. 



The small pastern thus articulates with the coffin bone and 

 the nut bone below, and with the great pastern above : these arc 

 all the bones comprehended in a descri|)tion of the foot. The 

 coffin bone is completely cellular throughout, and has more 

 blood within it than any one bone in the body, though not far 

 from being the smallest of the whole. The o-reat flexor tendon 

 is inserted into the bottom of the coffin bone, and the extensor 

 tendon on its front and upper part. Thus the sensible foot is 

 composed of the pastern, the navicular, and the coffin bone; the 

 lateral cartilages, the sensible frog and sole, and the laminated 

 substance ; at the upj)er part of which there is a kind of car- 

 tilaginous ring, which has been named by Mr. Coleman the 

 coronary ligament. This coronary substance, instead of termi- 

 nating at the heels, is continued into the sensible frosT) and from 

 this connection, and its situation over the lateral cartilages, it 

 nnist be subject to the same motion which these parts have. 

 When the frog, then, is exposed to that pressure for which it 

 was evidently designed, it expands and contracts, and in so 

 doinjz: communicates a similar motion to the cartila2;es, the co- 

 ronary ring, and the heels and quarters of the hoof.* 



* The followinpr experiment serves to show the expansive properties of the 

 foot. After tlie shoe of a moderate-sized foot was removed, and the sole part 

 pared out, a smooth sheet of paper was a2:>plied to it -while off the ground, and 

 being pressed against the foot, the edges of (he crust were carefully marked, so 

 as to give the exact size of the foot This being done, the foot was then placed 

 on a smooth deal board, with another sheet of paper placed upon the board; 



