Blaine further describes the construction of the hoof thus:—
“The hoof itself is conical, or rather, as Clark observes, slightly truncated, and is a secretion as well from the vascular parts of the foot as from the skin, as our nails are formed from the portion of skin called quick. The structure of the hoof is firm and fibrous. Externally it is plane and convex, but internally concave and laminated. The quarters are the lateral parts. As the horn approaches the heels it becomes soft and is reflected inwards. The heels are parted by the horny frog (b, fig. 3); and without, the frog on each side the hoof inflects its fibres to form the bars which are seen on the under surface (c, fig. 4). In a healthy foot, fig. 4, the heels are round, wide, and smooth (a, a), the frog fully expanded, the bars or binders distinct (c, c), no corns in the usual angle (d), the sole broad and concave (d). In a diseased foot, fig. 3, the heels are high, and drawn together by contraction (a, a), the frog narrow, and filled with fissures from contraction and thrush (b), corn frequently present (d), the sole greatly shortened in its transverse diameter, which is morbidly counterbalanced by the increased heights in the truncated form (c). When the hoof is removed, the sensible or fleshy sole (h, section of foot), above which it immediately lies, presents itself, covering the whole of the horny sole, except so much as is taken up by the sensible frog (h). This part is exquisitely sensible and vascular, and thus we learn why injuries to it from puncture produce such serious effect, and why very slight pressure from contraction of the hoof gives so much pain. The sensible frog and the sensible sole form the insensible frog and sole; but when from pressure, too much moisture, or other causes, the sensible frog, instead of forming horn, secretes pus or matter as in thrush, the structure of the whole becomes injured, and the frog, thus losing its support, gradually wastes and decays. It is therefore evident that no thrush can be entirely harmless, as is erroneously supposed.
“Above the sensible frog is the great flexor tendon, or back sinew, inserting itself into the vaulted arch of the coffin (a, section of foot). This important tendon, arising from its parent muscle above the knee, whose origin is taken from the humerus and ulna, in its passage unites with an assistant flexor, but which latter is principally distributed to the pastern bones, while the perforans, so called because it is perforated by the assistant flexor tendon, is inserted into the vault of the coffin; in the posterior extremities the attachments of these two leading flexors and a smaller lateral one are from the femur and tibia.
“The Sensible Laminæ.—Around the surface of the coffin-bone, it has been noticed that there are linear indentations to which about five hundred fibro-cartilaginous leaves are attached. Each of these is received between two of the horny lamellæ, which line the interior of the horny hoof; and when it is considered what a vast surface of attachment is formed by these means, the strength of the union will not be wondered at. No common violence can separate these parts, and their use as a spring (for they are extensile) to support the action of an animal at once weighty, strong, and extremely agile, must be apparent.
“The vessels and nerves of the foot are derived from the metacarpal arteries, veins, and nerves, which pass behind the pastern, when the main trunks divide to proceed to each side of the foot, and are ramified from thence throughout. It is a division of the metacarpal nerve on each side of the lesser pastern, or on each side of the larger, as occasion suits, which forms the nerve operation now in vogue as a remedy (?) for navicular disease.”
Laminitis, or Fever of the Feet, although generally the result of too long a journey, or any exercise where excessive and continuous concussion has been occasioned to the feet, frequently arises from other causes. It is often what is termed secondary, as one of the sequelæ of inflammatory diseases of a more constitutional character.—([See “Metastasis,” page 155.]) The laminæ are plates (technically, semi-cartilaginous leaves received between the horny lamellæ which line the interior of the hoof) resting on the inside of the horny hoof, and giving an elastic support, whereby the whole weight of the horse’s structure is thrown against the wall of the hoof and kept off the side. It is not surprising, therefore, that these causes should produce derangement here.
As laminitis generally attacks the fore feet, the poor beast in his anguish endeavours to throw his weight off them by resting on his hind quarters, which are tucked under him, with the fore legs and feet pushed out before him merely to keep him from falling; he can barely hobble if he attempts to move. If the fever be only slight and in one foot, he will point it, while extreme lameness and unnatural heat in the foot mark the disease. The shoe should (in this as in all cases of foot-lameness) be instantly removed by a smith brought to the stable instead of giving the poor creature the pain of limping to the forge.
The foot should be put into cold water, constantly renewed, and kept in it all day; at night a bran poultice or water-dressing should be left on ([see “Water-dressing” and “Poultices,” page 160]). Also administer a purge.
In acute cases, bleeding at the toe is sometimes practised by paring away there till the veins appear. This is a very questionable remedy, and there is little doubt that the use of the knife only aggravates the inflammation.
The fact is, that beyond its incipient stage none but the veterinary surgeon is competent to deal with this disease.