294 



THE HORSE. 



their surface of a plasma, in which roun led cells develop them- 

 selves, in correspondence with the villi from which the secretion is 

 poured out. These cells are arranged in layers, corresponding 

 with the secretory surface. In the crust this growth takes place 

 from the superior border to the inferior, but in the sole and frog, 

 from the internal surface to the external. This growth is constant 

 through the life of the animal, and it would give the hoof an 

 excessive development if it were not either for the wear of the soil 

 in the unshod horse, or of the action of the smith's knife in the 

 shod one ; but the increase of the wall being solely from above 

 downwards, it does not require any reduction on its external sur- 

 face. The coronary substance, sometimes called the coronary liga- 

 ment, is a fibro-cartilaginous band intervening between the skin of 



the leg and the hoof, covered 

 with cuticle externally, and with 

 villi, which form a secretory sur- 

 face on the edge towards the 

 hoof. It is most liberally sup- 

 plied with blood, as we shall 

 presently see, and is attached to 

 the upper part of the coffin bone 

 and extensor tendon by cellular 

 tissue. It gradually becomes 

 thinner as it descends upon the 

 pedal bone, and ends in puckers 

 or folds, which are continuous 

 with those of the laminae, and 

 are not even separable from them 

 by maceration. The laminse 

 thus continuing upon the pedal 

 bone, consist of about five hun- 

 dred parallel folds or plaits, 

 plentifully supplied with blood, 

 and forming a secretory surface, 

 which aids the coronary sub- 

 stance to form the horn. They 

 lie upon an elastic substratum 

 of fibrous periosteum, which is 

 of great service in taking off the 

 jar from the foot in its batter- 

 ing upon hard roads, for it ap- 

 pears that the weight of the 

 body is suspended from these 

 plates, and not carried upon the 

 sole. The laminae are continu- 

 ous at the toe with the sensible 



FlO. 16. VIEW OP VESSELS OF THE FOOT, IN- 

 JECTED. 



1. Plantar vein. 



2. Plantar artery. 



3. Branches to the coronary substance and 



laminae. 



4. Posterior division of plantar artery. 



5. Perpendicular branch. 



6. Anastomosis with opposite plantar artery. 



