THE FOOT 661 



time the horny are gliding between the sensitive leaves, the vascular 

 lamellae furnish them with horny lamellae ; when the wall reaches 

 the sole the horn lamellae are left behind, while the primary laminae 

 emerge with the wall destitute of these structures. This statement 

 does not explain away all the difficulties which could be raised, but 

 suffices for practical purposes. 



The Wall-secreting or Coronary Body is a thick, half-round, cornice- 

 shaped welt of material situated above the laminae (Figs. 223, 2\ 224, 

 2, j) ; it has received several names, the most rational being that based 

 on its function as the structure which secretes the hoof wall. Ex- 

 ternally this body is covered by a highly vascular membrane pos- 

 sessing long papillae, which are readily seen by immersing the foot 

 in water, while on section it is fibro-fatty in appearance, and consists 

 of a coarse network of elastic and fibrous tissue. It is this latter 

 which forms the main substance of the welt, which projects like a 

 big rim from the sensitive foot. The basement substance takes no 

 part in the secretion of horn ; the papillated membrane which covers 

 it alone carries out this function, while the use of the welt is to 

 provide the secreting membrane with a sufficiently firm and extensive 

 surface. The wall-secreting substance extends all round the coronet 

 from heel to heel, and here joins the plantar cushion. On its superior 

 margin is a narrow groove (Fig. 223, /), which is the dividing-line 

 between skin and hoof, and from which a peculiar horn known as 

 the periople is secreted . This horn cements over the j unction between 

 hair and hoof (Fig. 227, X). On its lower margin the coronary 

 substance fuses with fibres from the vascular laminae. The entire 

 body fits into a half-round groove in the wall, and the papillae on 

 its surface are lodged in canals formed in the horn. Beneath the 

 coronary welt is a well-developed subcutis, which unites it to the 

 tissues covering the corona and lateral cartilages. The vascular 

 papillated membrane covering the coronary substance is fre- 

 quently irregularly pigmented, corresponding to the colour of the 

 horn wall. 



The Vascular Sole (Fig. 221, 5) is scarlet in colour, and covered by 

 long papillae which are lodged in the depressions in the horn sole. In 

 each papilla an artery and one or more veins may be found. The 

 corium covering the plantar cushion is similarly arranged, the papillae 

 being lodged in canals in the foot-pad, or horn frog. 



The Blood-Supply to the foot is exceedingly rich. With the excep- 

 tion of the internal organs, there is no part of the body so vascular, 

 and the horse has more blood in his feet than in his brain. Mention 

 has already been made of the scarlet appearance presented by the 

 laminae, the vascular sole, and the tissue covering the plantar cushion. 

 The pumice-stone-like appearance presented by the pedal bone is 

 for the purpose of affording passage to the innumerable vessels 

 which are passing from the interior of the bone in an outward 

 direction to reach the vascular tissues ; in fact, no description or 

 drawing can adequately convey an idea of the appearance presented 

 by this vascular body. The veins are large and numerous (Fig. 226), 

 and are not provided with valves ; some pass through the substance 

 of the lateral cartilage, and a large plexus exists both outside and 

 inside the cartilage. The relation of these vessels to the lateral 

 cartilages and the absence of valves are matters which will be 

 considered later. 



The Hoof, or insensitive foot, is moulded over the sensitive struc- 

 tures in such a way as to cover them completely, and form in horn 



