Horn is a general term applied to all hard and pointed appendages of the head, as in deer, cattle, etc, but as a term denoting a particular kind of substance nothing should be called horn which is not derived from the epidermis or outer, layer of the integument, whether on the trunk, hoofs, or head.
Horn is a tough, flexible, semi-transparent substance, most liberally developed in the horns of bovine animals, but also found in connection with the 'shell' of the tortoise, the nails, claws, and hoofs of animals, the beak of bird and turtle, etc
Horn is softened very completely by heat, so as to become readily flexible, and to adhere to other pieces similarly softened. True horn consists principally of an albuminoid principle, keratin, with a small portion of gelatine and a little phosphate of lime. In some species of animals the males only have horns, as for instance the stag. In cattle both male and female have horns, though there are also hornless cattle.
Horns differ widely in the case of different animals. Thus the horns of deer consist of bone, and are deciduous; those of the giraffe are independent bones, with a covering of hairy skin; those of oxen, sheep, and antelopes consist of a bony core covered by a horny sheath. The horns of the rhinoceros alone consist exclusively of horny matter. The horns of oxen, sheep, goats, and antelopes are never shed, except in the case of the prong-horned antelope. The number never normally exceeds four, and in the case of deer the horns are branched.
The various kinds of horns were formerly employed for many purposes. The principal formerly used in the arts are those of the ox, buffalo, sheep, and goat. Deer horns were almost exclusively employed for the handles of knives and of sticks and umbrellas. Those which furnish true horn can be softened by heat (usually in boiling water), cut into sheets of various thickness, which sheets may be soldered or welded together at the edges so as to form plates of large dimensions, and were formerly polished and dyed so as to imitate the much more expensive tortoise-shell. The clippings of horn may be welded together in the same manner, and were formerly made into snuff-boxes, powder horns, handles for umbrellas, knives, forks, etc. As horn has the valuable property of taking on and retaining a sharp impression from a die, many highly ornamental articles were also turned out. Combs for the hair were made from the flattened sheets, and out of the solid parts of buffalo horns beautiful carvings were made. Research Horn
A hoof is the horny casing of the foot of a ruminant, horse, swine or similar animals. Hooves may be regarded as homologues of the toe-nails of other animals. They are composed of epithelium cells, agglutinated and dried, and of intercellular substance and cell contents. Chemically they consist of keratin. Research Hoof
In humans the nails are flattened, horny, protective coverings on the upper surface of the outer segments of the fingers and toes comprised of dead cells containing the fibrous proteinkeratin. Each nail consists of a root concealed within a fold of the skin; an exposed body attached to the surface of the skin; and a free anterior extremity called the edge. The skin below the root and body of the nail is termed the matrix. The matrix is thick and covered with highly vascular papillae, and its colour is seen through the transparent horny tissue. Near the root the papillae are smaller and less vascular making this portion of the nail appear whiter. From its crescent form this portion is termed the lunula or moon. The nail advances forward by the successive growth of new cells at the root and under the body of the nail. Homologous structures in other animals include the hooves of horses and the claws of birds. Research Nails
The sebaceous glands lie just below the skin adjacent to the hair follicles and connected by a short duct. They secretes sebum into the hair follicles, providing a lubricant for the hair and skin. Sebum is a semifluid substance composed of waxes, fatty acids, cholesterol, and debris from skin cells. By coating the hair and the dead keratin cells of the stratum corneum, sebum sequesters moisture, keeping hair glossy and skin pliable. Sebum is important for many other reasons. It contains a precursor to vitamin D that produces the mature vitamin when struck by the ultraviolet rays of the sun. It also kills certain forms of harmful bacteria. Research Sebaceous glands
The stratum basale is the deepest layer of the epidermis, consisting of a single row of columnar or cuboidal cells. The epidermal cells originate from this layer and new cells are continually being produced. Some of these cells make the proteinkeratin, which toughens them. Others produce melanin, the substance that gives skin colour. As the cells in this layer increase in number, they are pushed outward and become part of the stratum granulosum. Research Stratum Basale
The stratum corneum is the outer layer of the epidermis. It is composed of flat, dead cells which have lost their nuclei. It is constantly being sloughed off as dandruff. These cells are rubbed off as you move, wear clothes, and wash. Keratin, a horny protein found in hair and fingernails, is also found in the cells of the stratum corneum and prevents evaporation. It also helps to ward off injury because of its toughness. Research Stratum Corneum
The stratum granulosum is the thin layer of epidermis, composed of only a few layers of cells just above the stratum spinosum. The cells of the stratum granulosum fill with keratin and die as they continue upward to reach the top layer, the stratum corneum. The entire process takes about a month and the cells are worn away with friction. Research Stratum Granulosum
The albuminoids are organic nitrogenous compounds chemically allied to the proteins, but differing from them and from one another in various ways. The chief recognised albuminoids are collagen, gelatin, keratin, elastin, ossein and chitin. Research Albuminoids
Keratins are fibrous proteins occurring in hair, feathers, hooves, and horns.
Keratins have coiled polypeptide chains that combine to form supercoils of several polypeptides linked by disulphide bonds between adjacent cysteine amino acids. Aggregates of these supercoils form microfibrils, which are embedded in a protein matrix. This produces a strong but elastic structure. Research Keratin
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Horn
