INTERNAL STRUCTURE OF THE HOOF IN HORSES.

Otago Witness, Issue 2840, 19 August 1908, Page 8

INTERNAL STRUCTURE OF THE HOOF IN HORSES.

Although the hoof is a firm, strong, protecting covering to the sensitive foot within it, very serious injury to the horse results from defects in its structure which are often overlooked. These will be appreciated mow Teadily when it is known that within the hoof is a particularly delicate and complex arrangement. Wihen a hoof is removed with care, a beautiful, sensitive struoture is exposed, having a contour exactly matching the inner surface of the hoof (figs. 626, 627). The inner surface of

the- wall is covered with rows of thin, horny plates running from above downwards parallel to each other, all sloping forwards like the fibres of the wall. The corresponding portion of the sensitive foot presents hundreds of similar parallel projecting leaves of soft, velvety, fibrous tissue. These are called the sensitive laminae, and in the living foot Are dove-tailed between the horny lamina oi the wall so as to afforcf a firm, secure attach.Tnen.t between the two. The sensitive frog and sole are firmly attached to the corresponding horny parts, but instead of plates the connecting medium here is a mass of little papillae, so closely arranged ac to give a velvety appearance and feel to the exposed surface. This sensitive layer, known to farriers as " the quick," is bountifullysupplied with nerves and! blood vessels. Just where the hair meets the horn — the part called by horsemen the coronet — is a very important struoture, seen when the hoof is detached. This is a prominent ring or band extending round the foot and covered with very large papillae. From it the wall grows, and. injuries to it are fol- x lowed by serious defects in the horn. Not only do such easily-recognised conditions aa " sand-crack " and 1 " false-quarter " follow injuries to the coronet, but all the defective qualities of horn, such as are found in dry, brittle hoofs, proceed from the coronet. So also do the rings and irregularities i often noticed on the front of the hoof.

Growth of Hcof. — The wall grows downward from the coronet at the rate of about an inoh in three months. It is constantly growing, and when protected from wear by a shoe, soon causes a disproportionate hoof. If allowed to grow it may even produce deformity. Remembering this, horseowners will understand how necessary it is that no shoos^ehould be worn more than about a month without the euperfluous growth of horn being removed from the hoof. Farm horses in idle seaeons are often grossly neglected by being forced to stand m shoes attached to hoofs so overgrown as to place the foot quite out of its proper relative position to the limb. Young horses that have never been ohod Are often injured by being allowed to run in yards or small soft pastures where the ihoof is not naturally worn down. Their feet become so overgrown and disproportionate that the limbs arc injured and joints twisted permanently. Even foals should be attended 1 to by the farrior when their hoofs become overgrown. No pairing is necessary. All that is wented is the removal of the excess of wall with a raep. This necessary attention would frequently make all the difference between good feet and limbs and bad once.

Cartilage. — It is unnecessary to enter more into detail as to tho anatomy of the foot. Within the sensitive layer just noticed are tii& Horc-e-s, aJbd at fcztch-ec! to tii^m the fcorj<3oris which move the limb in progression. There are two structures, however, which must bo mentioTned. The chief bone of the foot — the coffin bone — which gives tho general form to the hoof, does nor extend throughout it 6 whole interior. It forms the basis of the front and' sides of the hoof, but towards the heels is replaced on each side by plates of gristle or cartilage (fig. b2B).

A, os pedis. B, lateral oartilag«. C, j>eripole. D, penpohc" band. E, cororiiry cushion. F, sensitive Hminaa, or flealiy loaves G, section, of akm H, fleshy frog. I, horny frog. J, horny sole.

[ This elastic material can be felt at the inner and outer sides of the coronet through } the skin of the living horae. When diseased and converted into bone it forms the socalled sido-bones, which sometimes cause lameness, a^d always destroy the natural elasticity of' the foot. These cartilages, replacing bone at the back parts of the foot, give resiliency to the hoof, and so prevent concussion. The Frog. — If we examine the under sur- ' face of the foot, to find another provision | against jar, for whilst the sole rests upon I & bony basis, the frog does not (fig. 629).

i The body of the coffin bone only extends backwards to about an inch past the point of the frog. It there divides into two pro- ! cesses which extend nearly to the heels, but j leaving between them a large space, which i ie filled by a. pad of elastic material, over which the frog rests. This arrangement I permits tho frog great freedom of move- I ment, and gives to the back portion of the ! hoof the special feature of elasticity so ' necessary to its function of breaking con- ' ou&sion when the foot cornea to the ground j during progression. The front parb of the , foot, by the thickness and hardness of the wall, and by the rigid basis of bone within, is specially fitted to sustain the strain, which is placed upon it when the toe takes the weight of the hor3e, ac it does in all for- i ward movements. The back part of the ; foot, by its thinner and more elastic horn, ; by its prominent and eoft frog, and by the ' partial substitution of cartilage for bone as its inner basis, is specially endowed for , receiving its first impact with the ground ' during progression. That the foot may pre- . serve its funotions intact the hoof must be I maintained in jte best form. No parts must be defective, and all must bs proportionate. A foot denuded of horn may have its sensitive portions injured, and a foot covered • by an excessive or disproportionate hoof may so destroy tihe balance of the limb as to cause grave lesions, resulting in lameiees. j