DIGITAL CORNIFICATIONS – Claw Nail Hoof this the best and interesting topic for exams so read it carefully. it can arrive in papers in 7 marks or any one of it part can come in 3 mark
DIGITAL CORNIFICATIONS – Claw Nail Hoof
• Digital cornification is the conversion of the epithelial tissue at the end of the digits into a hard structure (keratin).
• Claws, nails, and hoofs are homologous organs and are built on the same plan.
• These are hard structures on the distal end of the digits.
• The stratum lucidium is best developed at the base of these structures.
• Nails and hoofs are the modification of claws, which are present only in amniotes.
• But few amphibians (eg Xenopus) have claw-like tips on the first three digits of hind feet.
• All three structures are only present in mammals.
DIGITAL CORNIFICATIONS – Claw Nail Hoof : Structure and Function of Nails:
• Nails protect fingers and toes
• Made of dead cells packed with keratin
• Metabolic disorders can change their structure
• Occurs in deep epidermal fold near the bone called nail root.
• Onychology: Study of nail
• Well-developed hooves are found among extant mammals only in ungulates (Artiodactyla and Perissodactyla). Hoofs are present in ungulates (hoofed mammals).
• The unguis in hoof is present around the end of digit and encloses subunguis within it.
• The softer sub-unguis wears away more quickly than the unguis, thus forming a sharp edge.
• A pad lies just behind the hoof and is called the frog. •In ungulates normally only the hoof, not the frog, is in contact with the ground.
• The torus lies just behind the hoof and it is called frog.
• The ungulates walk on unguis, which is very hard wears off slowly.
• True horns are made of keratin and are found in sheep, goats and cattle.
• They are never branched and, once grown, are never shed.
• They consist of a core of bone arising in the dermis of the skin and are fused with the skull.
• The horn itself forms as a hollow cone-shaped sheath around the bone
• Keratin-fibre horn is found only in the Rhinoceros
• It is a hard conical structure located on the frontonasal region of the skull.
• It is composed of a cluster of long fibres cemented together by a mass of hard and keratinized cells growing from the epidermis.
• Each fibre resembles a very thick hair and emerges from a dermal papilla.
• The fibres are not true hairs since their bases lack follicles.
• In Indian rhinoceros there is a single horn.
• In African rhinoceros there are two horns.
• The two horns are located on the same median line along the frontonasal bone and the larger one lies in front.
• Cattle, sheep, goats and buffaloes possess hollow horns
• In certain species they are present only in males but in most both the males and females possess horns.
• There is a pair of horns, one each on the frontal bone.
• The horn consists of a bony projection from the frontal bone of the skull.
• The projection is covered over by a cornified layer of the epidermis. •A cavity extends into the bony projection.
• The horny layer is never shed.
• In very young animals the first indication of the future development of horn is seen in the formation of the os cornu.
• Os cornu is a loose button-like mass of bone cells which can be felt under the skin on the frontal bone.
• The os cornu later on becomes fused with the frontal bone.
• If the os cornu is destroyed by applying chemicals the horn fails to develop.
• This is a unique type of horn found only in the antelope, Antelocapra americana of the Western America.
• It consists of a conical projection on the frontal bone.
• A horny epidermal sheath covers the projection.
• The sheath usually bears one side projection or Prong , but as many as three have been encountered.
• The epidermal sheath is shed with annual periodicity and a new epidermal sheath again covers the bony projection.
• Antlers are present only in the male members of the deer family
• In reindeer (called caribou in North America) both the sexes bear antlers.
• When fully developed the antler is nothing but a solid bone and, as such, entirely mesodermal in origin.
• During the early phase of growth of the antler, an outgrowth on the frontal bone appears one on each side.
• It remains covered with soft skin.
• The blood vessels on the overlying dermis bring minerals and other elements necessary for the growth of the structure.
• At this stage the antler is said to be ‘in velvet’.