THE FOOT 



503 



fibrous, but not nearly so much so as the wall ; and the fibres are not 

 arranged in so parallel a manner, taking rather an oblique direction from 

 behind forwards, and being more easily sepai'ated into scales. The fro"- 

 differs from both, in possessing finer fibres and in smaller quantity, in 

 comparison with the gelatine, which formation renders it more soft and 

 elastic and also more prone to decomposition. The horny matter is some- 

 times coloured a greyish brown, sometimes white, and sometimes marbled 

 by a mixture of the two colours. (These parts are shown more clearly in 

 the article treating of Shoeing in Chapter xxxii.) 



The hoof is developed by secretion, which has its seat in the coronary 

 substance and laminre. It consists in 

 a pouring out on their surface of a 

 plasma, in which rounded cells develop 

 themselves, in correspondence with 

 the villi from which the secretion is 

 poured out. These cells are arranged 

 in layers, corresponding with the se- 

 cretory 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 de- 

 velopment if it were not either for 

 the wear of the soil in the unshod 

 horse, or the action of the smith's 

 knife in the shod one ; but the in- 

 crease of the wall being solely from 

 above downwards, it does not I'equire 

 any reduction on its external surface. 

 The coronary substance, sometimes 

 called the coronary ligament, is a fibro- 

 cartilaginous band intervening between 

 the skin of the leg and the hoof, 

 covered with cuticle externall}^, and 

 with villi, which form a secretory sur- 

 face on the edge towards the hoof. It 

 is most liberally supplied with blood, 

 as we shall presently see, and is at- 

 tached to the upper part of the 



coffin-bone and extensor tendon by cellular tissue. It gradually becomes 

 thinner as it descends \\])on the pedal-bone, and ends in jDuckers or folds, 

 which are continuous with those of the laminae, and are not even separable 

 from them by maceration. The lamijice thus continuing upon the pedal- 

 bone, consist of about five hundred pai-allel folds or plaits, plentifully 

 supplied with blood, and forming a secretory surface, which aids the coro- 

 nary substance 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 battering upon hard roads, for it appears that the weight of the 



L L 



Fio. S9.— View of Vessels of the Foot, injected. 



1. Plantar vein. 



2. Plantar artery. 



3. Branches to the coror.arv substance and laminae. 



4. Posterior division of plantar arterj'. 



5. Pcriiendicular branch. 



6. Anastomosis with opposite plantar artery. 



